|
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. -- Thanks, Fred. |
A better mic preamp
On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
"Jim Thompson" wrote in message ... On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Your gain is 57.69K or 95dB That gain also multiplies any offset mismatches :-( You dig ?:-) ...Jim Thompson -- Well.... Ignoring the NPNs. Since I was in the realms of Av = gmRL and thinking gm is 1/re and, in the circuit what I drew has 10K resistors for the op-amps then 10K/re is close enough for me. Then since the PNPs are forced to run at 1mA by the NPNs and gm is Ic/26E-3 then re is 26E-3/1E-3 so re(PNP) is 26..... And then since that is reduced by the BETA of the NPNs of 150 then...... 10K*BETA(NPN)/re(PNP) So, sort of....... apart from I still think you have your PNP/NPN swapped and your sum has part of it in the wrong place. Or was I meant to say. Thanks for clarifying my mistake ;-) ;-) ? Or am I still wrong because I haven't included extra stuff? I sort of know about the offset stuff and things what involve other sums I'd have to guess at. Ta DNA |
A better mic preamp
Fred Bartoli wrote: Jim Thompson a écrit : "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Is idiocy your stock in trade ? Graham |
A better mic preamp
On Wed, 14 Mar 2007 19:35:53 GMT, "Genome"
wrote: "Jim Thompson" wrote in message ... On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Your gain is 57.69K or 95dB That gain also multiplies any offset mismatches :-( You dig ?:-) ...Jim Thompson -- Well.... Ignoring the NPNs. Since I was in the realms of Av = gmRL and thinking gm is 1/re and, in the circuit what I drew has 10K resistors for the op-amps then 10K/re is close enough for me. Then since the PNPs are forced to run at 1mA by the NPNs and gm is Ic/26E-3 then re is 26E-3/1E-3 so re(PNP) is 26..... And then since that is reduced by the BETA of the NPNs of 150 then...... 10K*BETA(NPN)/re(PNP) So, sort of....... apart from I still think you have your PNP/NPN swapped and your sum has part of it in the wrong place. Or was I meant to say. Thanks for clarifying my mistake ;-) ;-) ? Or am I still wrong because I haven't included extra stuff? I sort of know about the offset stuff and things what involve other sums I'd have to guess at. Ta DNA I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
1 Attachment(s)
Jim Thompson wrote: I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( I thought that's what you meant. The beta of those NPNs is somewhat higher than 150 though. 420 minimum from the data sheet. BC850 is the SMT version of a BC550 btw. Graham |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Jim Thompson a écrit : "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Is idiocy your stock in trade ? I surely wasn't expecting you to be able to understand that. -- Thanks, Fred. |
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) -- Thanks, Fred. |
A better mic preamp
Eeyore a écrit :
Jim Thompson wrote: I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. Nope. Not the NPN vs PNP swap, which I overlooked too. I think NPN diff pairs too much :-( I thought that's what you meant. The beta of those NPNs is somewhat higher than 150 though. 420 minimum from the data sheet. BC850 is the SMT version of a BC550 btw. Even with a 10K beta it won't change a dime. -- Thanks, Fred. |
A better mic preamp
"Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. DNA |
A better mic preamp
Genome a écrit :
"Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. -- Thanks, Fred. |
A better mic preamp
On Wed, 14 Mar 2007 21:46:28 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
On Wed, 14 Mar 2007 22:19:32 +0100, Fred Bartoli
r_AndThisToo wrote: Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. Huh? A drinking Eyetalian ?:-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 21:46:28 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. What's the 680R doing on the NPN _stage_ current gain? -- Thanks, Fred. |
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 22:19:32 +0100, Fred Bartoli r_AndThisToo wrote: Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. Huh? A drinking Eyetalian ?:-) Maybe you didn't enough? :-) -- Thanks, Fred. |
A better mic preamp
On Wed, 14 Mar 2007 22:29:55 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 21:46:28 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. What's the 680R doing on the NPN _stage_ current gain? Aha! An amateur. You tell _me_ what it's doing ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
"Fred Bartoli" r_AndThisToo wrote in message ... Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. -- Thanks, Fred. Is the correct answer..... Oh Right? Or is it I should be looking at the re for both transistors? 'Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand.' Well there you go! I said I was wrong and I knew that thing I was doing for ratio mirrors instead of Q3/Q4 and setting the gain with I1 was the right way to go! Um, if I reference U1 and U2 to the emitters of Q1 and Q2 don't they force no volts across...... Never mind. DNA |
A better mic preamp
On Wed, 14 Mar 2007 22:31:16 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 22:19:32 +0100, Fred Bartoli r_AndThisToo wrote: Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. Huh? A drinking Eyetalian ?:-) Maybe you didn't enough? :-) I guarantee that I drink more than you. Ask Spehro about my famous "grow hair in your throat" martinis. Spehro, now improved... 5 parts Sake 2 parts Frangelico 7 parts Vodka 2 parts R/O water ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 22:29:55 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 21:46:28 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. What's the 680R doing on the NPN _stage_ current gain? Aha! An amateur. You tell _me_ what it's doing ;-) Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. -- Thanks, Fred. |
A better mic preamp
Genome a écrit :
"Fred Bartoli" r_AndThisToo wrote in message ... Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. -- Thanks, Fred. Is the correct answer..... Oh Right? Not at all. I certainly don't want anybody to take anybody else words, including me, for granted. Or is it I should be looking at the re for both transistors? 'Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand.' Just trying to not give the full answer upfront. Well there you go! That wasn't directed towards you, but to Jim, given the tone of some of his recent posts. It's a pretty basic mistake for an IC designer, thus my laugh. The NPN stage current gain is at best gm(NPN)*680R = 38 Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. I said I was wrong and I knew that thing I was doing for ratio mirrors instead of Q3/Q4 and setting the gain with I1 was the right way to go! You were almost right. U1/U2 output bias might be worth a look WRT current mirrors Vbe and degeneration resistors mismatch. Um, if I reference U1 and U2 to the emitters of Q1 and Q2 don't they force no volts across...... Never mind. Well, sorry I was a bit fast. I should have said AC reference the opamps inputs to the emitters. Obviously you'll have to keep some bias there :-) Say 3V. The point is: force no AC voltage across the diff pair instead of across the Q9/Q10 current sources will improve CMRR. Q1/Q2 output conductances aren't matched and neither are R14-R15 or R8-R9. -- Thanks, Fred. |
A better mic preamp
Fred Bartoli wrote: Genome a écrit : "Jim Thompson wrote I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) Jim said it was that actually. I was simply correcting his assumption of a beta of 150. I can see there's more going on there but I haven't analysed it to my satisfaction yet. Obviously you have to take into account delta Vbe of Q3 and Q4 which adds to the delta Ic of Q1 and Q2. So the effective current gain is less than beta. By a decent margin I suspect. Low Rbb would help here too btw. Graham |
A better mic preamp
Jim Thompson wrote: Fred Bartoli wrote: Jim Thompson a écrit : Fred Bartoli wrote: Jim Thompson a écrit : "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. I see no problem either. Incidentally, the effective re works out in practice to be about an ohm or so. Graham |
A better mic preamp
Jim Thompson wrote: Fred Bartoliwrote: Jim Thompson a écrit : I don't see a problem. Maybe I'm overlooking one?? Point me to it. What's the 680R doing on the NPN _stage_ current gain? Aha! An amateur. You tell _me_ what it's doing ;-) He's pointing out that there isn't a perfect constant current flowing through them. Graham |
A better mic preamp
"Fred Bartoli" r_AndThisToo wrote in message ... Genome a écrit : "Fred Bartoli" r_AndThisToo wrote in message ... Genome a écrit : "Jim Thompson" wrote in message ... I got it backwards... that must be why Bartoli is laughing... swap NPN-PNP and it's correct. The value is correct though, just the naming was wrong. I think NPN diff pairs too much :-( ...Jim Thompson I still don't think you are spilling the full tin of beans but since all those circuits like wot you learned them in the old days were upside down before someone else discovered the NPN transistor it's probably an easy mistake to make. That Bartoli bloke sounds a bit Eyetalian to me so he probably has no problem making the adjustment..... you know, tanks and gears and stuff. One thing you could do to improve CMRR is to reference your U1 & U2 positive inputs to the Q1/Q2 emitters. (the output conductance of Q1/Q2 is multiplied by the Q3/Q4 stage current gain (eh Graham, it's not Q3/Q4 beta) and will thus be much lower than the common bases Q9/Q10 output conductance. -- Thanks, Fred. Is the correct answer..... Oh Right? Not at all. I certainly don't want anybody to take anybody else words, including me, for granted. Or is it I should be looking at the re for both transistors? 'Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand.' Just trying to not give the full answer upfront. Well there you go! That wasn't directed towards you, but to Jim, given the tone of some of his recent posts. It's a pretty basic mistake for an IC designer, thus my laugh. The NPN stage current gain is at best gm(NPN)*680R = 38 Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. I said I was wrong and I knew that thing I was doing for ratio mirrors instead of Q3/Q4 and setting the gain with I1 was the right way to go! You were almost right. U1/U2 output bias might be worth a look WRT current mirrors Vbe and degeneration resistors mismatch. Um, if I reference U1 and U2 to the emitters of Q1 and Q2 don't they force no volts across...... Never mind. Well, sorry I was a bit fast. I should have said AC reference the opamps inputs to the emitters. Obviously you'll have to keep some bias there :-) Say 3V. The point is: force no AC voltage across the diff pair instead of across the Q9/Q10 current sources will improve CMRR. Q1/Q2 output conductances aren't matched and neither are R14-R15 or R8-R9. -- Thanks, Fred. Sure.... but I know you are really French and therefore working with Jim to confuse us British people to score the Trident contract. Win did all this stuff in AoE and he is a well known Canadian. And you still haven't scored the recipe for the right gravy to go with tripe. See, not so clever now are you. DNA |
A better mic preamp
"Eeyore" wrote in message ... Genome wrote: "Eeyore" wrote . In response to various posts please find attached a mic amp which has seen volume production in commercial equipment. Feel free to ask any questions / criticise whatever. Here you go...... Listening to the criticism that others are giving you I'd do something like this. As to wether I've got it right is another matter. I'd also claim that U1 and U2 also cascode the input stage improving bandwidth. That's an interesting design. Graham No it isn't. You think you look sexy in Y-fronts because you've seen Charlie Sheen in them. DNA |
A better mic preamp
On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 22:29:55 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 21:46:28 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 20:28:59 +0100, Fred Bartoli r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 18:59:59 GMT, "Genome" wrote: Genome, Your differential gain is.... 10K/re(equivalent) Or... 10K/re(NPN)*BETA(PNP) Take re(NPN) = 26 Take BETA(PNP) = 150 Bwaaaahahahahah.... Sorry but you deserved that one. Ehhh? Did you look at Genome's schematic? Yep. But there's a 680R somewhere and only 1.5mA of collector current for the 3904s. I won't tell more, I know you understand. But just ask Eeyore to explain this new idiocy of mine :-) Hmmm? I see Q5 sourcing 5mA. I see Q10 and Q9 sinking 2.5mA each. Yes? Q1 and Q2 nominally get 1mA each, due to the 680 ohm resistors. So there 1.5mA available for Q3 and Q4 each. I don't see a problem. Maybe I'm overlooking one?? Point me to it. What's the 680R doing on the NPN _stage_ current gain? Aha! An amateur. You tell _me_ what it's doing ;-) Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. Graham |
A better mic preamp - CompoundTransistor.pdf
1 Attachment(s)
On Wed, 14 Mar 2007 16:20:56 -0700, Jim Thompson
wrote: On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli fred._canxxxel_this_bartoli@RemoveThatAlso_free. fr_AndThisToo wrote: [snip] Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson Attached. Another glass of wine will do it every time. Optimization left to the student ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp - CompoundTransistor.pdf
"Jim Thompson" wrote in message ... On Wed, 14 Mar 2007 16:20:56 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli fred._canxxxel_this_bartoli@RemoveThatAlso_free .fr_AndThisToo wrote: [snip] Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson Attached. Another glass of wine will do it every time. Optimization left to the student ;-) ...Jim Thompson Do yourself a flavo(u)r Tadpole Technology. Software is **** but now we have to stream our **** so you may as well stream your **** efficiently. Winky Winky. DYOR Up and down stuff and whatever. DNA |
A better mic preamp
On Wed, 14 Mar 2007 10:38:22 +0000, Eeyore
wrote: In response to various posts please find attached a mic amp which has seen volume production in commercial equipment. Feel free to ask any questions / criticise whatever. Graham Love those 1N4148 Reference Noise Generators. John |
A better mic preamp - CompoundTransistor.pdf
Jim Thompson a écrit :
On Wed, 14 Mar 2007 16:20:56 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli r_AndThisToo wrote: [snip] Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson Attached. Another glass of wine will do it every time. Optimization left to the student ;-) Yes but: *** the process you use is very nice to you since it kindly make identical NPN and PNP betas; (going to the trouble of such a calculation supposes you pretend to some accuracy(significance of beta/(beta+1)), at any rate more than any possible beta matching) I tend to prefer simpler equations which don't obscur the physical meaning: Zin = reP /(RB.gmN+1) *** then you can get a deeper by noticing that gm(PNP) is linked to RB, i.e. to the NPN apparent beta, giving: Zin = kT/q * RB/VBE /(RB.gmN+1) or Zin = kT/(q.VBE) 1/(gmN+1/RB) which, with reasonable RB values give Zin almost not depending on RB Zin = kT/(q.VBE.gmN) With the usual values that is Zin = 40/gmN (with gm in mA/V) Since gm is linked to Ic (gm=Ic.q/kT), Zin expresses in a very simple manner: Zin = (kT/q)^2/(VBE.Ic) but (kT/q)^2/VBE is remarkably close to 1mV (1.028mV for VBE=0.65V). Then Zin = 1/Ic(NPN) (with Ic in mA) -- Thanks, Fred. |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. With beta = 400 that is: apparent beta = 35.9 with beta = 800 that is: apparent beta = 37.6 QED. -- Thanks, Fred. |
A better mic preamp
John Larkin wrote: Eeyore wrote: In response to various posts please find attached a mic amp which has seen volume production in commercial equipment. Feel free to ask any questions / criticise whatever Love those 1N4148 Reference Noise Generators. How much do you think they leak ?They're shunted by the source Z of course. The reason they're there is to deal with 'hot plugging' microphones when phantom power is on. Without them you take out the input devices instead. What do you reckon the 4R7s are for ? Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. With beta = 400 that is: apparent beta = 35.9 with beta = 800 that is: apparent beta = 37.6 Exactly, not as low as 30-35. Graham |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. With beta = 400 that is: apparent beta = 35.9 with beta = 800 that is: apparent beta = 37.6 Exactly, not as low as 30-35. That was for the 100-300 range that the 2n3904 Genome used give. -- Thanks, Fred. |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote Eeyore a écrit : Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. With beta = 400 that is: apparent beta = 35.9 with beta = 800 that is: apparent beta = 37.6 Exactly, not as low as 30-35. That was for the 100-300 range that the 2n3904 Genome used give. Understood. Graham |
A better mic preamp - CompoundTransistor.pdf
On Thu, 15 Mar 2007 09:09:01 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 16:20:56 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli r_AndThisToo wrote: [snip] Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson Attached. Another glass of wine will do it every time. Optimization left to the student ;-) Yes but: *** the process you use is very nice to you since it kindly make identical NPN and PNP betas; (going to the trouble of such a calculation supposes you pretend to some accuracy(significance of beta/(beta+1)), at any rate more than any possible beta matching) I tend to prefer simpler equations which don't obscur the physical meaning: Zin = reP /(RB.gmN+1) Wasn't sure what I'd find that would be of significance. *** then you can get a deeper by noticing that gm(PNP) is linked to RB, i.e. to the NPN apparent beta, giving: Zin = kT/q * RB/VBE /(RB.gmN+1) or Zin = kT/(q.VBE) 1/(gmN+1/RB) which, with reasonable RB values give Zin almost not depending on RB Zin = kT/(q.VBE.gmN) With the usual values that is Zin = 40/gmN (with gm in mA/V) Since gm is linked to Ic (gm=Ic.q/kT), Zin expresses in a very simple manner: Zin = (kT/q)^2/(VBE.Ic) but (kT/q)^2/VBE is remarkably close to 1mV (1.028mV for VBE=0.65V). Then Zin = 1/Ic(NPN) (with Ic in mA) I don't follow your slang, "you can get a deeper", nor your equations. I'll take a look after I drop a granddaughter at the airport. She's off to the hinterlands for a college interview. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
On Thu, 15 Mar 2007 09:17:27 +0100, Fred Bartoli
r_AndThisToo wrote: Eeyore a écrit : Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 gm*R is a CURRENT gain?? Ah you're using 1.5mA for Ic ! Accounting for the NPNs finite beta (parallel beta(NPN)/gm(NPN) with the 680R) this is rather 30-35. To be honest with a beta of 400 min I don't see a reduction as large as that. With beta = 400 that is: apparent beta = 35.9 with beta = 800 that is: apparent beta = 37.6 QED. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
A better mic preamp
Jim Thompson wrote: Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: The NPN stage current gain is at best gm(NPN)*680R = 38 gm*R is a CURRENT gain?? Current gain is unitless (amps/amps). gm is amps/volts and R is volts/amps. So the result is unitless. So yes. Graham |
A better mic preamp - CompoundTransistor.pdf
On Thu, 15 Mar 2007 09:09:01 +0100, Fred Bartoli
r_AndThisToo wrote: Jim Thompson a écrit : On Wed, 14 Mar 2007 16:20:56 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 22:47:56 +0100, Fred Bartoli r_AndThisToo wrote: [snip] Aha! Finally speeding up :-) Yep, max effective current gain is only 38, down to 30-35 with realistic betas. Aha! An anomaly! In simulation, I get an "Alpha" of 0.997 (Iout/Iin), which is equivalent to a composite Beta of 332. But simulation of Zout looks like around 3 ohms. That certainly is not what I expected. I tried to do an exact solution, but it's nastily transcendental :-( Time for a glass of wine ;-) (It would appear to be the shunting input impedance on the NPN stage, yet replacing the 680 ohm with an ideal current source still has an error I can't account for.) Time for another glass of wine... BURP ;-) ...Jim Thompson Attached. Another glass of wine will do it every time. Optimization left to the student ;-) Yes but: *** the process you use is very nice to you since it kindly make identical NPN and PNP betas; (going to the trouble of such a calculation supposes you pretend to some accuracy(significance of beta/(beta+1)), at any rate more than any possible beta matching) I tend to prefer simpler equations which don't obscur the physical meaning: Zin = reP /(RB.gmN+1) *** then you can get a deeper by noticing that gm(PNP) is linked to RB, i.e. to the NPN apparent beta, giving: Zin = kT/q * RB/VBE /(RB.gmN+1) or Zin = kT/(q.VBE) 1/(gmN+1/RB) which, with reasonable RB values give Zin almost not depending on RB Zin = kT/(q.VBE.gmN) With the usual values that is Zin = 40/gmN (with gm in mA/V) Since gm is linked to Ic (gm=Ic.q/kT), Zin expresses in a very simple manner: Zin = (kT/q)^2/(VBE.Ic) but (kT/q)^2/VBE is remarkably close to 1mV (1.028mV for VBE=0.65V). Then Zin = 1/Ic(NPN) (with Ic in mA) So you presumed Beta(PNP) is infinite? Back in a few hours. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
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