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Old 28th March 2013, 04:14 PM   #101
naf is offline naf  Indonesia
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Quote:
Originally Posted by JOHN BALI View Post
Ok mas Thanks,
I want to make PCB that input pairs can use BC's pair or SA/SC pair so it can swap easily with different transistor. I'm an "orang lambat" so mine maybe not finish soon
Waiting for Shaan if he let my "hand made PCB" can be post here

Regards
Go head Bli John with your own design I am sure Shaan will glad to see it.
Just remember to thermally coupled input pair. Make as short as possible track this is fast amp.
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Old 28th March 2013, 04:28 PM   #102
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Hi Shaan,

What are the FETs that can be used in your PeeCeeBee layout published in the first post ?
I will document it for future build.

Thank you very much.
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Old 28th March 2013, 04:31 PM   #103
shaan is offline shaan  India
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Quote:
Originally Posted by naf View Post
I've replaced trimmer with fixed resistor as close as I could.
Supply +-40vdc (32vac)
Dco 9-10mv
Vas bias ~10mA
Input bias ~2.3mA

And load with 4ohm (parallel 2 bookshelf), I can't believe my ears.. the sound was incredible. Crispy trebles, punchy bass, open mid... and relaxing sound.
Best sounding amp I've ever assembled so far.
Happy listening...

Quote:
Originally Posted by JOHN BALI View Post
Thanks Naf, congratulation.
I must build this one
Please, can you tell me all transistors you use? Are they all matched?
cause I don't have pairs C grade BC's(only BC550C)
to Shaan it is OK if I post my PeeCeeBee design here?
(I want to made my own PCB layout)

Regards
Sure it's okay. It's a peeceebee so nothing to worry about!
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Old 28th March 2013, 04:31 PM   #104
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Quote:
Originally Posted by naf View Post
And load with 4ohm (parallel 2 bookshelf), I can't believe my ears.. the sound was incredible. Crispy trebles, punchy bass, open mid... and relaxing sound.
Best sounding amp I've ever assembled so far.
And yet so simple, it really is a little wonder.

Quote:
Originally Posted by JOHN BALI View Post
Thanks Naf, congratulation.
I must build this one
Please, can you tell me all transistors you use? Are they all matched?
cause I don't have pairs C grade BC's(only BC550C)
I suggest the input NPN/PNP transistor pair are BC550C/BC560C (or equivalents) to have high and equal hFE (beta - current gain) as much as possible. Normally both should have the same hFE=600 or more. Also the input pair must be glued together with their flat sides so they are in thermal contact and their hFE will change proportionally. This is important since symmetrical DC offset tracking for both positive and negative side of the VSSA is assured in that way, resulting in zero DC offset at the output.
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Old 28th March 2013, 04:55 PM   #105
shaan is offline shaan  India
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Also, buiders are suggested to measure and match the feedback resistors in both polarity as close as possible(2K2/100R or 1K/47R), to balance the fb current resulting in highest attenuation of the even harmonics. However, this is not essential.
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Old 28th March 2013, 05:11 PM   #106
shaan is offline shaan  India
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Quote:
Originally Posted by philippeleite View Post
Hi Shaan,

What are the FETs that can be used in your PeeCeeBee layout published in the first post ?
I will document it for future build.

Thank you very much.
2SK1058 and 2SJ162. You can use other power LATFETs in TO247/TO264 packages too if you want, with maybe some mods in the bias setting zone for setting the FET Iq.
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Old 28th March 2013, 05:15 PM   #107
shaan is offline shaan  India
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Originally Posted by Lazy Cat View Post
It really is a little wonder.
Looking at the schema and layout many will just underestimate it, to their own miss.
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Old 28th March 2013, 05:20 PM   #108
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Quote:
Originally Posted by Lazy Cat View Post
And yet so simple, it really is a little wonder.
I suggest the input NPN/PNP transistor pair are BC550C/BC560C (or equivalents) to have high and equal hFE (beta - current gain) as much as possible. Normally both should have the same hFE=600 or more. Also the input pair must be glued together with their flat sides so they are in thermal contact and their hFE will change proportionally. This is important since symmetrical DC offset tracking for both positive and negative side of the VSSA is assured in that way, resulting in zero DC offset at the output.
Hi Lazy Cat thanks for the guidance, I try my best available part here
I hope can made it easy

Quote:
Originally Posted by shaan View Post
Also, buiders are suggested to measure and match the feedback resistors in both polarity as close as possible(2K2/100R or 1K/47R), to balance the fb current resulting in highest attenuation of the even harmonics. However, this is not essential.
Nice suggestion Shaan, for best result why not.
I'm also find how to match the resistor with cheap digital multimeter, we can apply enough voltage to resistor under test (if needed with series resistor to limit the current) & measure voltage on it by 200mV range

Btw what resistor you preferred cheap carbon matched or metal film matched on this fb position.
I have a few dale resistor somewhere

And one more thing, please link how to accurate matching input bjt, VAS, & output LAT FET
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Last edited by JOHN BALI; 28th March 2013 at 05:24 PM. Reason: add more question, thanks
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Old 28th March 2013, 05:45 PM   #109
shaan is offline shaan  India
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Quote:
Originally Posted by JOHN BALI View Post
Btw what resistor you preferred cheap carbon matched or metal film matched on this fb position.
I have a few dale resistor somewhere
I have never used carbon resistors with VSSA, only metal film, 1% tolerance. Good enough.

Quote:
And one more thing, please link how to accurate matching input bjt, VAS, & output LAT FET
I can't tell you that(I don't know any good online links on that). You need to ask LC, better to post your questions about matching and others in the VSSA thread.

Last edited by shaan; 28th March 2013 at 06:06 PM. Reason: correction
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Old 28th March 2013, 08:07 PM   #110
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Well, it looks like I'll have some more things to do.
I removed cap multiplier. Now I have simple power supply with two Graetz bridges and 4x 6.800uF smoothing caps per channel. I can't hear any difference. Without signal, there's only silence: turn on, turn off, no buzz, no hiss, no brum, nothing. DC offset was zero without adding resistors. Perfect.
But...
Now VAS transistors begun to overheat. Again I had only few minutes to enjoy music.
So I removed trafo, put new one 2x 20VAC and got 25VDC per rail. Finally, everything was good, transistors almost cold, no problems except DC offset of 37mV. I'll solve it tomorrow.
Now I'm listening to music. This is very good amp, definitely it's value is greater then invested money. Like LC said "it really is a little wonder".
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