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Old 31st August 2012, 01:07 AM   #571
bcarso is offline bcarso  United States
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Quote:
Originally Posted by dimitri View Post
This is not correct: 2x2SK117=2x2SK209=2SK2145=2SK3320

Brad, 2SK2145 IS 1nV/sqrtHz device. 2SK246 has 10 dB higher noise voltage
Yes, that was a quote about the 246 from EUVL, to which I was taking exception.

The 2145 etc. is about like a half-area SK170, about the same gm/Cin figure-of-merit. 1nV/sqrtHz is also what I got based on gm and the Van der Ziel theory.
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Old 31st August 2012, 01:40 AM   #572
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Quote:
Originally Posted by john curl View Post
Wavebourn, the previous analog record amp design used 30uF polycarbonate caps. I just could not justify them in this design.
It is strange why such big capacitance, because current drive is needed. But Brad was right, power supply transients on on / off could magnetize the head.
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Old 31st August 2012, 02:19 AM   #573
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> It is strange why such big capacitance, because current drive is needed.

Little capacitance passes current just as easily as big capacitance ?
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Old 31st August 2012, 02:27 AM   #574
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Originally Posted by hitsware View Post
> It is strange why such big capacitance, because current drive is needed.

Little capacitance passes current just as easily as big capacitance ?
I mean pretty high dynamic resistance of the output stage. "Easiness" depends on frequency and resistance. The lower is resistance, the higher capacitance is needed for the same frequency response. And vice verse.
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Old 31st August 2012, 03:16 AM   #575
EUVL is offline EUVL  Europe
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> This is not correct: 2x2SK117=2x2SK209=2SK2145=2SK3320

Was a typo from me in a rush. Sorry for my blunder.

2SK117 = 2SK209 = 2SK880 = 1/2*2SK2145 = 1/2*2SK3320
2SK246 = 2SK208 = 2SK879
2SJ103 = 2SJ106


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Old 31st August 2012, 03:19 AM   #576
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Originally Posted by Wavebourn View Post
I mean pretty high dynamic resistance of the output stage. <snip>
Not an easy task, if one uses NFB at the same time to define gain and/or to reduce overall distortion.
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Old 31st August 2012, 03:26 AM   #577
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Quote:
Originally Posted by elektroj View Post
Not an easy task, if one uses NFB at the same time to define gain and/or to reduce overall distortion.
That one should better use NFB by current, not by voltage. To define gain and reduce overall distortion. However, HF bias adds additional requirements for filtering, but it was done.
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Old 31st August 2012, 04:04 AM   #578
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Originally Posted by Wavebourn View Post
That one should better use NFB by current, not by voltage. To define gain and reduce overall distortion. However, HF bias adds additional requirements for filtering, but it was done.
Wavebourn, do you mean by that circuit similar to Widlar Op-Amp Current Source?
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Old 31st August 2012, 04:35 AM   #579
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
I still don't see Vgs matching between N and P channel tracking over temp, diff pairs make this a common mode error.
Id set at the zero temp - they work fairly well.
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Old 31st August 2012, 04:42 AM   #580
RNMarsh is offline RNMarsh  United States
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Default should be better ??

Quote:
Originally Posted by coluke View Post
Quickly breadborded the design in #451, and did a few tests - did find only 10 2N5458s, so the selection was a little bit poor ; BC550/560 in the gain/driver stage, MJE243/253 running at ~70 mA in the output stage. At 10 dB gain BW is in the MHz range out of the box, and THD @ 1Vrms, 1 kHz into 30 ohm (~30 mW) is about 0.004% (only 2nd and 3rd harmonics), quite load insensitive (THD drops to 0.0038% into ~300 ohm). No compensation needed; DC drift good (for audio, at least) while not spectacular: output stage Iq rock stable, output offset in the +/- 5 mV range en plein air over a couple of hours. Well, it needs some more work, but seems promising - going to get plenty of J113s, do a better selection and see what happens

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L.
With the large amount of nfb used in Scott's circuit the distortion should be lower -- lower than .001%.
but your numbers are comparable to the little circuit I put up when it also has not well matched devices. When well matched, the distortion at moderate nfb is measured as under .001% (1v/30 Ohms). -RNM

Last edited by RNMarsh; 31st August 2012 at 04:44 AM.
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