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BAF 2015 Coverage
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Old 22nd October 2015, 08:58 PM   #141
Nelson Pass is offline Nelson Pass  United States
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Quote:
Originally Posted by famousmockingbird View Post
Is there any stability issues due to phase shift with the transformer in the feedback loop? Maybe I should rephrase my question. If there was no stability issues with the current Jensen transformer used and if another was used in it's place could there be stability issues due to the resonance placed differently by the manufacturer? Will there be a need for possible compensation components?
I had that discussion yesterday with 6L6, as he's ready to start laying out
pcb's, and I noted that I need to check for the possibility of low frequency
motor-boating if the signal source has a capacitor in series. This could be
addressed by using a buffer with a DC output value, but possibly as easily by
adjustment of feedback impedance. No high frequency issues are anticipated.

Anyway, I'll report back after I fire one up and check.

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Old 22nd October 2015, 09:00 PM   #142
Nelson Pass is offline Nelson Pass  United States
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Originally Posted by drjbf1 View Post
Interesting. I don't recall Papa using an optocoupler in his current sources before. Is there some particular reason he does so in these circuits? I wasn't at BAF to ask the question.
I've come to appreciate the better temperature coefficients and sharper
corner to the LED used in the opto. Otherwise it's no big deal.

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Old 22nd October 2015, 09:01 PM   #143
Nelson Pass is offline Nelson Pass  United States
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Originally Posted by generg View Post
isnīt there a fault around the optocoupler in the slide about the Mosfet XFN circuit?
Yes, you're much smarter than my computer.

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Old 22nd October 2015, 09:08 PM   #144
ci11 is offline ci11  United States
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For a regulated +60V PS, what would be the minimum recommended capacitance per rail that can keep the 3.2A draw nice and happy? I know many would splurge but I have some potential real estate issues.
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Old 22nd October 2015, 09:25 PM   #145
Nelson Pass is offline Nelson Pass  United States
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Regulated is nice, but not particularly essential. The PSRR is on the order of
40 dB, so if you want 100 uV of noise at the output, the supply needs less
than about 10 mV ripple. A quick sim shows that two 47000 uF separated
by .5 ohms for the RC filter will get you about 7 mV rms.

You can do more capacitance or resistance if you want.

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Old 22nd October 2015, 09:29 PM   #146
ci11 is offline ci11  United States
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Quote:
Originally Posted by Nelson Pass View Post
Regulated is nice, but not particularly essential. The PSRR is on the order of
40 dB, so if you want 100 uV of noise at the output, the supply needs less
than about 10 mV ripple. A quick sim shows that two 47000 uF separated
by .5 ohms for the RC filter will get you about 7 mV rms.

You can do more capacitance or resistance if you want.

Thanks, papa. Exactly what I needed. The other parts are on the UPS truck today...;-)
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Old 22nd October 2015, 10:10 PM   #147
famousmockingbird is offline famousmockingbird  United States
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Quote:
Originally Posted by Nelson Pass View Post
I had that discussion yesterday with 6L6, as he's ready to start laying out
pcb's, and I noted that I need to check for the possibility of low frequency
motor-boating if the signal source has a capacitor in series. This could be
addressed by using a buffer with a DC output value, but possibly as easily by
adjustment of feedback impedance. No high frequency issues are anticipated.

Anyway, I'll report back after I fire one up and check.

Ahhh yes LFO.........the chance of a capacitor in series with the input is probably pretty high since most sources and preamps will have an output capacitor.

The talk of PCB's being laid out is exciting!!

Thank you for all your work, there are some exciting things in the near future
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Old 22nd October 2015, 11:26 PM   #148
2 picoDumbs is offline 2 picoDumbs  Australia
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Quote:
Originally Posted by Nelson Pass View Post
I need to check for the possibility of low frequency
motor-boating if the signal source has a capacitor in series. This could be
addressed by using a buffer with a DC output value, but possibly as easily by
adjustment of feedback impedance. No high frequency issues are anticipated.

Anyway, I'll report back after I fire one up and check.

Quite a few of us do not have source equipment with the output impedance you mentioned (eg B1 is 1k output impedance), will there be the option for a cascoded jfet buffer at the input on this amp for us poor souls (sought of like F6)?
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Last edited by 2 picoDumbs; 22nd October 2015 at 11:42 PM.
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Old 23rd October 2015, 12:19 AM   #149
Zen Mod is offline Zen Mod  Serbia
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use F4 , F6 -like buffer

so , JFet complementary one

pretty low output impedance

you can double them , if you wish , for more ooomph

or you can use superduper diamond buffer , but tweaked for nice 2nd
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Old 23rd October 2015, 05:19 AM   #150
generg is offline generg  Germany
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It was used in J2 and in M2.....:-)
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