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A better mic preamp
1 Attachment(s)
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 |
A better mic preamp
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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win |
A better mic preamp
"Winfield Hill" wrote in message
... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= |
A better mic preamp
Winfield Hill a écrit :
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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. -- Thanks, Fred. |
A better mic preamp
Winfield Hill 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. Graham Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Graham |
A better mic preamp
colin wrote: "Winfield Hill" wrote in message 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. It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? Now theres no resistors, the diff voltage input to the op amp is always zero, Damn small at least ! so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. You got it. Graham |
A better mic preamp
Fred Bartoli wrote: Winfield Hill a écrit : 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Graham |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Winfield Hill a écrit : 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. -- Thanks, Fred. |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Winfield Hill a écrit : 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. If you will insist on saying silly things ! Graham |
A better mic preamp
Eeyore a écrit :
Winfield Hill 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. Graham Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. You don't even understand the simplest implications of what you... hem, well... design, even when someone point his finger at it, and then call others name? Who's the idiot? (I was about to put a smiley there, but finally I won't) -- Thanks, Fred. |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Winfield Hill a écrit : 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. If you will insist on saying silly things ! It wasn't silly at all. See my other response below. -- Thanks, Fred. |
A better mic preamp
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. The user manual for the product it's used in can be found here btw with some basic performance specs. http://www.studiomaster.com/userg/c1u.pdf The likes of Fred Bloggs can buy one here to test so he can discover how wrong he is about the performance. http://cgi.ebay.co.uk/STUDIOMASTER-C...QQcmdZViewItem Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Winfield Hill wrote: It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. Come on then. Let's see your explanation. Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Winfield Hill a écrit : 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. If you will insist on saying silly things ! It wasn't silly at all. See my other response below. Like the other Fred you're all hot air and no substance. If you want to criticise it you'll need to offer your analysis. Graham |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Winfield Hill a écrit : 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. If you will insist on saying silly things ! It wasn't silly at all. See my other response below. Like the other Fred you're all hot air and no substance. If you want to criticise it you'll need to offer your analysis. I wasn't criticizing. I certainly wouldn't for people of so much substance and so dense. BTW, such an 'analysis' requires at least, maybe half a second, including time to look at the schematics. What's amazing is that it wasn't blindingly obvious to You, not even counting that you still don't understand it. You might try some appnote at TI. They do have some tutorials about opamps and feedback and such advanced concepts. -- Thanks, Fred. |
A better mic preamp
Eeyore a écrit :
Fred Bartoli wrote: Eeyore a écrit : Winfield Hill wrote: It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. Come on then. Let's see your explanation. And you need more explanation than what Win and I said for such an elementary matter? ROFL! Ok, if we really have to spell it. What's the opamp feedback loop made with? -- Thanks, Fred. |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Winfield Hill a écrit : 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? The opamp has not enough distorsion to his taste maybe. IDIOT. Wasn't expecting anything else than that splendid remark. If you will insist on saying silly things ! It wasn't silly at all. See my other response below. Like the other Fred you're all hot air and no substance. If you want to criticise it you'll need to offer your analysis. I wasn't criticizing. I certainly wouldn't for people of so much substance and so dense. BTW, such an 'analysis' requires at least, maybe half a second, including time to look at the schematics. What's amazing is that it wasn't blindingly obvious to You, not even counting that you still don't understand it. You might try some appnote at TI. They do have some tutorials about opamps and feedback and such advanced concepts. I'm still waiting for your answer. I read what TI and National had to say on these matters around 30 years ago btw. So, are you going to elaborate or just continue to post a bunch of whiny crap ? Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote Eeyore a écrit : Winfield Hill wrote: It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. Come on then. Let's see your explanation. And you need more explanation than what Win and I said for such an elementary matter? ROFL! Ok, if we really have to spell it. What's the opamp feedback loop made with? I'm not playing any silly guessing game with you. Explain yourself or shut up. Graham |
A better mic preamp
On 14 Mar 2007 04:34:10 -0700, Winfield Hill
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. Graham Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? That troubled me on the original version which throws away 90% of the signal CURRENT. With my misunderstood gain of 15dB, that loss is an additional NF booster. With the capacitively coupled version, trying to raise that ratio moves a high frequency pole inward, rolling off the high end. Direct coupled, I'd replace the 680's with current sources. ...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 11:53:54 GMT, "colin"
wrote: "Winfield Hill" wrote in message ... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= Sno-o-o-orkle! Does not! ...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
Eeyore a écrit :
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote Eeyore a écrit : Winfield Hill wrote: It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. Come on then. Let's see your explanation. And you need more explanation than what Win and I said for such an elementary matter? ROFL! Ok, if we really have to spell it. What's the opamp feedback loop made with? I'm not playing any silly guessing game with you. Explain yourself or shut up. There's no guessing at all there and that you still don't see it is quite eloquent about your abilities. I just can hear what 'the other Fred' would have to say about this :-) -- Thanks, Fred. |
A better mic preamp
Jim Thompson wrote: wrote: "Winfield Hill" wrote in message 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Sno-o-o-orkle! Does not! ...Jim Thompson Do you have some bizarre new theory of op-amp operation ? For a TL07x family device Avol @ 1 kHz for example is 4000. For a 1 volt rms output the differential input voltage at the op-amp inputs will be 1/4000 volts = 250uV. That means 250uV/2x680R of signal current is 'wasted' = 184nA. Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote: Eeyore a écrit : Fred Bartoli wrote Eeyore a écrit : Winfield Hill wrote: It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? It doesn't. The + and - op-amp input nodes see almost no differential ac signal voltage due to feedback action. Hence no-need for active loading either. The 680Rs simply set the DC condition. Win wasn't speaking about this. Well, you've splendidly succeeded in reducing the loop gain by a 1:11 factor. Come on then. Let's see your explanation. And you need more explanation than what Win and I said for such an elementary matter? ROFL! Ok, if we really have to spell it. What's the opamp feedback loop made with? I'm not playing any silly guessing game with you. Explain yourself or shut up. There's no guessing at all there and that you still don't see it is quite eloquent about your abilities. I just can hear what 'the other Fred' would have to say about this :-) Your posturing is getting boring. If you haven't got anything to offer just shut up. Graham |
A better mic preamp
On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson
wrote: On Wed, 14 Mar 2007 11:53:54 GMT, "colin" wrote: "Winfield Hill" wrote in message ... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= Sno-o-o-orkle! Does not! ...Jim Thompson Not clear speech... Does not have any effect. ...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 08:12:04 -0700, Jim Thompson
wrote: On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 11:53:54 GMT, "colin" wrote: "Winfield Hill" wrote in message ... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= Sno-o-o-orkle! Does not! ...Jim Thompson Not clear speech... Does not have any effect. ...Jim Thompson Damn. I still can't say it right. The 680 ohm resistors don't affect gain to the output (from the input), but they do affect the OpAmp loop-gain operating point. I wonder what stability, and possibly distortion effects, result? ...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 08:16:48 -0700, Jim Thompson
wrote: On Wed, 14 Mar 2007 08:12:04 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 11:53:54 GMT, "colin" wrote: "Winfield Hill" wrote in message ... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= Sno-o-o-orkle! Does not! ...Jim Thompson Not clear speech... Does not have any effect. ...Jim Thompson Damn. I still can't say it right. The 680 ohm resistors don't affect gain to the output (from the input), but they do affect the OpAmp loop-gain operating point. I wonder what stability, and possibly distortion effects, result? ...Jim Thompson One more comment. Noise gain? ...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
Eeyore a écrit :
Jim Thompson wrote: wrote: "Winfield Hill" wrote in message 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. Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Sno-o-o-orkle! Does not! ...Jim Thompson Do you have some bizarre new theory of op-amp operation ? Your feedback theory is bizarre. For a TL07x family device Avol @ 1 kHz for example is 4000. Yep. For a 1 volt rms output the differential input voltage at the op-amp inputs will be 1/4000 volts = 250uV. Yes, and don't forget that this make your output error 250uV*11=2.75mV, which is 11 times worse than necessary and that you'll obtain with a current source load. I said you that was simple. But you'll probably find this difficult as well. Oh yes, I know. Just posturing. Maybe you should reread about loop gain, and the difference between CFB and VFB. That means 250uV/2x680R of signal current is 'wasted' = 184nA. Graham -- Thanks, Fred. |
A better mic preamp
Jim Thompson a écrit :
On Wed, 14 Mar 2007 08:16:48 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 08:12:04 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson wrote: On Wed, 14 Mar 2007 11:53:54 GMT, "colin" wrote: "Winfield Hill" wrote in message ... 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 Content-Type: image/jpeg; "mic amp.jpg" It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? -- Thanks, - Win Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Colin =^.^= Sno-o-o-orkle! Does not! ...Jim Thompson Not clear speech... Does not have any effect. ...Jim Thompson Damn. I still can't say it right. The 680 ohm resistors don't affect gain to the output (from the input), but they do affect the OpAmp loop-gain operating point. I wonder what stability, and possibly distortion effects, result? ...Jim Thompson One more comment. Noise gain? Let Eeyore explain you that this has no impact, and on distortion too. -- Thanks, Fred. |
A better mic preamp
Jim Thompson wrote: Jim Thompson wrote: Jim Thompson wrote: "colin" wrote: "Winfield Hill" 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. It's nice to see the diff-pair currents going directly to the output opamp, with it's 6.8k resistors. But why'd ya steal away loop gain so aggressively by choosing 680-ohms? Now theres no resistors, the diff voltage input to the op amp is always zero, so theres no diff voltage accross the 680r so they dont have an effect on diff voltage. Sno-o-o-orkle! Does not! ...Jim Thompson Not clear speech... Does not have any effect. ...Jim Thompson Damn. I still can't say it right. The 680 ohm resistors don't affect gain to the output (from the input), but they do affect the OpAmp loop-gain operating point. How ? I wonder what stability, and possibly distortion effects, result? ...Jim Thompson None. Graham |
A better mic preamp
Jim Thompson wrote: One more comment. Noise gain? Uh ? Would you care to elaborate ? Graham |
A better mic preamp
Fred Bartoli wrote: Eeyore a écrit : Do you have some bizarre new theory of op-amp operation ? Your feedback theory is bizarre. It's entirely conventional. For a TL07x family device Avol @ 1 kHz for example is 4000. Yep. For a 1 volt rms output the differential input voltage at the op-amp inputs will be 1/4000 volts = 250uV. Yes, and don't forget that this make your output error 250uV*11=2.75mV, What 'output error' ? Graham |
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 Operating within 0.7V of the common-mode voltage spec troubles me. I'd bump up those 680 ohm resistors to say 2.2K, making the common-mode operating point approximately -7V. ...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: 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. Operating within 0.7V of the common-mode voltage spec troubles me. 0.7V ? That's loads ! It was thoroughly chjecked. I'd bump up those 680 ohm resistors to say 2.2K, making the common-mode operating point approximately -7V. The 680R is to be honest a carry over from the previous style of design. With that 2k2 you'd get close to cutting off the input devices with a very large input signal. Graham |
A better mic preamp
1 Attachment(s)
"Eeyore" wrote in message ... 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 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. DNA |
A better mic preamp
On Wed, 14 Mar 2007 17:38:02 GMT, "Genome"
wrote: "Eeyore" wrote in message ... 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 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. DNA Oooooey, patoooey! What's the gain ?:-) ...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
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. The constant current source in the 'tail' I've seen before. ISTR one guy I know who did that found it increased the noise unfortunately. You're missing the variable gain bit though. You need 2 current sources in place of Q5 with the gain setting bits connected between Q1 and Q2 emitters. The 'collector loads' are cute too. I'm tempted to try it btw but I'm just about to post another one that's a bit more up to date. Check that one out. Graham |
A better mic preamp
"Jim Thompson" wrote in message ... On Wed, 14 Mar 2007 17:38:02 GMT, "Genome" wrote: "Eeyore" wrote in message ... 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 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. DNA Oooooey, patoooey! What's the gain ?:-) ...Jim Thompson Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I waste my head figuring out the wrong answer....... was I close about the reduction in re (hre?) by the compound connection of the transistors? Am I even close about gm being 1/re. You did have a larf at my analysis in the other place didn't you. I could get worried about coming up with a 'complicated' equation like Fred. I don't know (remember/didn't pay attention to) this stuff so I've got to do it from my own concept of first principles and it'll still end up half arsed. DNA |
A better mic preamp
On Wed, 14 Mar 2007 18:37:35 GMT, "Genome"
wrote: "Jim Thompson" wrote in message ... [snip] Oooooey, patoooey! What's the gain ?:-) ...Jim Thompson Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I waste my head figuring out the wrong answer....... was I close about the reduction in re (hre?) by the compound connection of the transistors? Am I even close about gm being 1/re. You did have a larf at my analysis in the other place didn't you. I could get worried about coming up with a 'complicated' equation like Fred. I don't know (remember/didn't pay attention to) this stuff so I've got to do it from my own concept of first principles and it'll still end up half arsed. DNA The compound device, as you've applied it, has an _effective_ re of approximately.... re(NPN)/beta(PNP) So you need to stick some real R in there. ...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 18:37:35 GMT, "Genome" wrote: "Jim Thompson" wrote in message ... [snip] Oooooey, patoooey! What's the gain ?:-) ...Jim Thompson Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I waste my head figuring out the wrong answer....... was I close about the reduction in re (hre?) by the compound connection of the transistors? Am I even close about gm being 1/re. You did have a larf at my analysis in the other place didn't you. I could get worried about coming up with a 'complicated' equation like Fred. I don't know (remember/didn't pay attention to) this stuff so I've got to do it from my own concept of first principles and it'll still end up half arsed. DNA The compound device, as you've applied it, has an _effective_ re of approximately.... re(NPN)/beta(PNP) So you need to stick some real R in there. ...Jim Thompson That looks upside down to me. What I said... in the other place, was........ quote Best, at the moment that I can guess..... Short circuit the gain setting pot/capacitor and throw away the NPN transistors. It's a differential pair. The gain is gmRC. gm is set by the 'tail' resistor which is R2||R6. Put the NPNs back in again. It's still a differential amplifier but the NPNs 'pin' the PNP currents at Vbe/Rbe which makes gm some different value......, gm' less than before. However the NPNs 'boost' that value by approximately their Beta....Bnpn [1] So Av = BnpnRCgm' = BnpnRCIcpnp/25E-3 = BnpnRCVbe/25E-3Rbe That might be a factor of two out because it's a diferential amplifier. Open circuit the gain setting network and it's just a pair of 'thingy' amplifiers with Av = RC/RE In between........ I couldn't be bothered. /quote DNA |
A better mic preamp
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 -- | 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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