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#1
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Yucky diode recovery. Advice ?
I'm helping to sort out a piece of alleged studio recording gear that was
somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Graham |
#2
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Yucky diode recovery. Advice ?
On Wed, 18 Apr 2007 05:21:44 +0100, Eeyore
wrote: I'm helping to sort out a piece of alleged studio recording gear that was somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Graham Try either fast-recovery or soft-recovery diodes. Or lower voltage rectifiers. The higher-voltage 1N4004+ and 1N5404+ series parts are actually p-i-n structures that like to behave like step-recovery diodes. The bitch is that they will make a wafer of, say, 1N4007's and sell them as 4001's, 4002's, and so on, so they may all be pin's. Or use schottkies; they don't snap at all. John |
#3
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Yucky diode recovery. Advice ?
John Larkin wrote: Eeyore wrote: I'm helping to sort out a piece of alleged studio recording gear that was somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Try either fast-recovery or soft-recovery diodes. Or lower voltage rectifiers. The higher-voltage 1N4004+ and 1N5404+ series parts are actually p-i-n structures that like to behave like step-recovery diodes. The bitch is that they will make a wafer of, say, 1N4007's and sell them as 4001's, 4002's, and so on, so they may all be pin's. I see. But it's the higher voltage process that's to blame ? Or use schottkies; they don't snap at all. Yes I found the 11DQ10 and MBR1100 which could do the job. Vrrm needs to be ~70V. Would schottkies still benefit from snubbing ? Graham |
#4
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Yucky diode recovery. Advice ?
On Wed, 18 Apr 2007 06:09:30 +0100, Eeyore
wrote: John Larkin wrote: Eeyore wrote: I'm helping to sort out a piece of alleged studio recording gear that was somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Try either fast-recovery or soft-recovery diodes. Or lower voltage rectifiers. The higher-voltage 1N4004+ and 1N5404+ series parts are actually p-i-n structures that like to behave like step-recovery diodes. The bitch is that they will make a wafer of, say, 1N4007's and sell them as 4001's, 4002's, and so on, so they may all be pin's. I see. But it's the higher voltage process that's to blame ? Or use schottkies; they don't snap at all. Yes I found the 11DQ10 and MBR1100 which could do the job. Vrrm needs to be ~70V. Would schottkies still benefit from snubbing ? Graham It wouldn't hurt. It wouldn't make much difference to emi, but some schottkies are fragile in the reverse direction, so some 0.1 uF or so caps could help protect them from line transients. People are making silicon schottkies up to about 150 volts (IR for example), and up to about 600 volts in SiC (Infineon and Cree.) There are soft-recovery rectifiers, too, designed to not snap. John |
#5
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Yucky diode recovery. Advice ?
"Eeyore" wrote in message ... Or use schottkies; they don't snap at all. Yes I found the 11DQ10 and MBR1100 which could do the job. Vrrm needs to be ~70V. Would schottkies still benefit from snubbing ? Graham Some of my experiences with SB diodes from my monitor repairing days might be informative. First you should note the ESD warnings most manufacturers put on SB diodes, they are very sensitive to excessive reverse voltage. Some monitor manufacturers used SB diodes to protect the gate in the SMPSU MOSFET as it doesn't suffer junction storage delay if ringing drives it into forward conduction and they reliably fail S/C if the PIV is exceeded, on some blown PSUs in which the MOSFET channel had been destroyed the 1N5817 had successfully protected the O/P of the UC3842 long enough for the fuse to break. My experience with snubbing SB diodes is probably not all that relevant, some monitors were badly designed with underrun heaters - the cure was to upgrade the heater rectifier to an SB type, as the SMPSU was invariably a flyback type the peak reverse voltage was often many times the rectified voltage, which made it harder to find SB diodes with adequate PIV. The cure was to snub the flyback peak with a diode, capacitor and resistor, the diode and capacitor forming an extra O/P with opposite polarity to the heater supply and the resistor to load it and pull down the flyback peak. As SB diodes seem somewhat less robust against excessive reverse voltage, and fail S/C more reliably. It is important to consider carefully before replacing regular diodes with SBs, what are the chances of spikes exceeding the PIV? And what other damage will happen if the rectifiers fail S/C? |
#6
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Yucky diode recovery. Advice ?
On Tue, 17 Apr 2007 21:50:43 -0700, John Larkin
Gave us: use schottkies; they don't snap at all. Proper response. |
#7
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Yucky diode recovery. Advice ?
On Wed, 18 Apr 2007 00:08:58 -0700, MassiveProng
wrote: On Tue, 17 Apr 2007 21:50:43 -0700, John Larkin Gave us: use schottkies; they don't snap at all. Proper response. Thank you kindly. John |
#8
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Yucky diode recovery. Advice ?
"Eeyore" wrote in message ... I'm helping to sort out a piece of alleged studio recording gear that was somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Graham Hard to see with the picture quality but do you have full wave? (Xfrmr secondaries may be out of balance.) Try 1nf across the Xfrmr secondaries as well. John Larkins suggestions as to rectifier selection is on the money. |
#9
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Yucky diode recovery. Advice ?
"Daniel A. Thomas" wrote in message ... "Eeyore" wrote in message ... I'm helping to sort out a piece of alleged studio recording gear that was somewhat thrown together by a bunch of useless idiots whose company has now ceased trading. It's a quasi 'replica' of some historic equipment that once belonged to Air Studios in Monserrat. The latest joy (of many!) is pickup from the PSU. I was concerned about these spikes (see pics) that the mic amp delights in reproducing. I've never seen anything as bad as this before but I don't use mic transformers myself and this unit does, which appears to be a problem. The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across them to see if it helped at all but it didn't. I have some UF4004s I could use instead of them (their 1 A rating is fine in this application) but I'm open to other advice. The top trace is the output of the mic amp on max gain (70dB). The bottom trace is the ripple voltage on the (half wave) rectified positive supply (only on 2nd pic). I can't figure why the spikes seem to be displaced but it's that rotten TDS210 again and I have next to zero faith in it. Sorry about the pic quality btw, I didn't take them. Graham Hard to see with the picture quality but do you have full wave? (Xfrmr secondaries may be out of balance.) Try 1nf across the Xfrmr secondaries as well. John Larkins suggestions as to rectifier selection is on the money. That should have been 10nf! Dan |
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