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Old 18th May 2013, 10:23 PM   #451
shaan is offline shaan  India
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Quote:
Originally Posted by PMI View Post
Some of my best insights into sound have come from musicians...
Yes, only a musician can teach what to listen for in the music...

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Originally Posted by ivanlukic View Post
...people in India have superior hearing compared to us westerners...
I'v never heard that. But appreciate the complement very much.

Pete and Ivan, thank you guys for your encouragement and support. You are genuinely good people.

Quote:
Originally Posted by JOHN BALI View Post
At no load at output or open output my DMM can't read the DC offset...
What does the meter show then? The number '1' on the left sidd of the screen? If so, then try setting the range to 'volts' instead of 'millivolts' and see if it shows some reading.

High or unstable offset without load isn't normal and indicates oscillation; most probably in the FETs. Replace 100R gate stoppers with 330R or 470R and see if it helps. All the best.
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Old 19th May 2013, 01:09 AM   #452
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@John Bali:Thanks for the tip, but.... naaah, I'll skip that test .

I tested my boards without zobel installed, with 44pF compensation caps, and with the six elcos as shown in the pics. Even with the 44 pF, I measured a maximum slew rate of around 100V/usec. Plenty for me, and I will try 22pF when I compare to the boards from the VSSA GB.
I got some clue have some 22-33-47 pF for compensation caps,
I will wait when that comparison is
Quote:
Originally Posted by shaan View Post
What does the meter show then? The number '1' on the left sidd of the screen? If so, then try setting the range to 'volts' instead of 'millivolts' and see if it shows some reading.

High or unstable offset without load isn't normal and indicates oscillation; most probably in the FETs. Replace 100R gate stoppers with 330R or 470R and see if it helps. All the best.
Yes, 1. after change to range volts it is can read some voltage & not stable.
So I will try to change gate stopper resistor
btw this is my first time using FET OPS
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Old 20th May 2013, 03:25 AM   #453
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Default Now it is warm :)

Today I add zobel & let it warm...
Stable 1 mV when cold max 4 mV when warm (when I pause the music),
it more than an hours now

Quote:
Originally Posted by PMI View Post
@John Bali:Thanks for the tip, but.... naaah, I'll skip that test .

I tested my boards without zobel installed, with 44pF compensation caps, and with the six elcos as shown in the pics. Even with the 44 pF, I measured a maximum slew rate of around 100V/usec. Plenty for me, and I will try 22pF when I compare to the boards from the VSSA GB.

The DC offset does drift a bit with time and temperature, but only a few mV. No sign of any instability or oscillation, at least not so far.

I will repeat some of the tests when I build a second set of boards, but I consider the design as "tested" by LC and by Shaan. So, my goal is to make sure I did not "break" their circuit through some oversight on my part.
Hi Pete,
try without that caps & only with zobel ...
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Old 20th May 2013, 03:34 AM   #454
naf is offline naf  Indonesia
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nice, Bli John...
mine only with zobel + output inductor and it stable, no comp. cap (offset in range of 0.1 - 0.4 mv difference)
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Old 20th May 2013, 05:14 AM   #455
PMI is offline PMI  United States
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Hmmm, interesting. So, the conclusion would be that all you need is the small cap in the Zobel for stability... (?)
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Old 20th May 2013, 05:27 AM   #456
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Originally Posted by naf View Post
nice, Bli John...
mine only with zobel + output inductor and it stable, no comp. cap (offset in range of 0.1 - 0.4 mv difference)
I am very careless... shorted 10 ohm series with diode & sparks
but I am lucky only changed that 10 ohm & everything just better...

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Originally Posted by PMI View Post
Hmmm, interesting. So, the conclusion would be that all you need is the small cap in the Zobel for stability... (?)
I'm not sure, but because of the little accident I remove the zobel & put on the compensation caps
I use 33pF.
Also I put more parts
Now it is stable at 1mV without zobel...

@Naf try to install compensation caps & see if yours is more stable with it, no need zobel or inductor

Now I need to choose take an enclosure or just leave it naked for a while
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Last edited by JOHN BALI; 20th May 2013 at 05:35 AM. Reason: trry this mas Naf
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Old 20th May 2013, 05:44 AM   #457
PMI is offline PMI  United States
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Originally Posted by JOHN BALI View Post
Not right, because of the little accident I remove the zobel & put on the compensation caps
I use 33pF.
Also I put more parts
Now it is stable at 1mV without zobel...
Ok, that makes a lot more sense now. I admit I may have gone too far with 47pF, but in my defense, I already had those on hand... hmmm, maybe not a good defense after all...

Seriously, if you find the smallest value that appears to make the circuit stable, the CORRECT value, allowing for things like component tolerance, supply voltage swings, and temperature, is probably 50% bigger.

@John Bali: you know what they say, "if you never break anything, it just means you are not trying hard enough"
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Old 20th May 2013, 06:48 AM   #458
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@PMI I just do what I can at the moment even a little accident
I have some 10pF & 22pF but because you use 47pF I use a bit lower 33pF
you inspired me I think

Quote:
Originally Posted by shaan View Post
Congrats naf.
Remove that 470ohm parallel to the diodes and you'll get ~170mA.

Yes. Removing it will set the bias to that with the two diodes, i.e. about 170mA.

happy listening
shaan
Hi Shaan,
I'm re-read again and found my total current is around 200mA
(200mV on 1R resistor you suggest)
I Vas 16mA
Fet Current almost 180mA with that 470 ohm resistor
Rail is +/- 33VDC before 1R safety resistor
This is normal right, one more question do you put zobel on output?
If yes is that 100nF + 10R

Regards
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Old 20th May 2013, 07:35 AM   #459
shaan is offline shaan  India
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Quote:
Originally Posted by JOHN BALI View Post
Hi Shaan,
I'm re-read again and found my total current is around 200mA
(200mV on 1R resistor you suggest)
I Vas 16mA
Fet Current almost 180mA with that 470 ohm resistor
Rail is +/- 33VDC before 1R safety resistor.
This is normal right?
Absolutely normal. Perfect bias.

Quote:
One more question, do you put zobel on output?
If yes is that 100nF + 10R?
My peeceebee has no Zobel and no Compensation. But 2K2/100R feedback node setup and medium gain BJTs for input and VAS. I think these together do the trick. It's a pair of stable, offset steady(with or without load), high bandwidth, transparent sounding(you may say 'ethereal' sounding) amplifiers. My holy grail. I can die now.

Okay ignore my fanboy words. Yes the standard values for a zobel is 100nF + 10R. However, certain applications might require different values, e.g. the LM1875 chipamp needs 220nF + 1R.

Last edited by shaan; 20th May 2013 at 07:48 AM.
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Old 20th May 2013, 09:49 AM   #460
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Quote:
Originally Posted by shaan View Post
Absolutely normal. Perfect bias.

My peeceebee has no Zobel and no Compensation. But 2K2/100R feedback node setup and medium gain BJTs for input and VAS. I think these together do the trick. It's a pair of stable, offset steady(with or without load), high bandwidth, transparent sounding(you may say 'ethereal' sounding) amplifiers. My holy grail. I can die now.

Okay ignore my fanboy words. Yes the standard values for a zobel is 100nF + 10R. However, certain applications might require different values, e.g. the LM1875 chipamp needs 220nF + 1R.
Thank you Shaan, very nice tricks you've shared...
maybe I must try it in another time.

BTW second channel has passed the test too, 6mV DC offset a little bit lower bias and I feel this one has nicer sound

I will share my PeeCeeBee layout soon
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