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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 9

post #121 of 1816
check voltages around Q5 and Q6 ..dB
post #122 of 1816
What values do you have for R19, R20, and R21?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #123 of 1816
I take it back..adjusting R21 seemed to do the trick..didn't think that trimpot had so many turns on it.

Am now reading 0.2 volts across R32 and R33.

Voltages around Q7 check out as well..they are slightly higher than 3.2 volts..more closer to 4 Volts all around.

Going to bring up the second board and check if that works too with changing R21.

Alex, R20 and R19 are 220 and 3.3k respectively. R21 is a 1k trimpot
post #124 of 1816
Those are the correct resistors and I see that you have dialed up the right idle current.

There some other measurements to take that I'd be interested to know, but these are not important now. Just follow the website instructions.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #125 of 1816
Quote:
Originally Posted by sachu View Post
I take it back..adjusting R21 seemed to do the trick..didn't think that trimpot had so many turns on it.
post #126 of 1816
Success!...both boards are now up and running fine..

Thanks Alex, Don.

Next up, connect inputs and outputs and have a listen
post #127 of 1816
Quote:
Originally Posted by runeight View Post
Those are the correct resistors and I see that you have dialed up the right idle current.

There some other measurements to take that I'd be interested to know, but these are not important now. Just follow the website instructions.
Sure thing ALex..Let me know as I have a board connected now. Will only be testing one board. Will have to disasemble everything on the chassis as I have some work left to do on it. SO now is the best time.

I have followed everything listed on the website and everything checks out.
post #128 of 1816
great news sachu, i had forgotten about the first time I fired it up and it took forever to adjust those trimmers. This is a good reminder for the folk who follow in your footsteps, especially as everything else seemed to check out and make sense ..dB
post #129 of 1816
Sachu, I would like to know the voltage at the output of the opamp (pin 6 I think).

Then I would like to know if you can zero this voltage by carefully adjusting R6 (at the cathodes of the tube).

Then I would like to know what this did to your idle current.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #130 of 1816
Woohoo!!We have music ..one channel at least..

Am excited now!! Can't wait to get the case work all done.. Planning on getting this for the heater supply +S22 delay.

A pic of my amp under testing..

post #131 of 1816
Quote:
Originally Posted by runeight View Post
Sachu, I would like to know the voltage at the output of the opamp (pin 6 I think).

Then I would like to know if you can zero this voltage by carefully adjusting R6 (at the cathodes of the tube).

Then I would like to know what this did to your idle current.
Alex, I didn't check to see the idle current but the voltages across R32, R33 dropped from 0.2Volts to 0.128 volts as I zeroed the output on the opamp.

On a side note, there is a hiss in the channel but I think its mainly becuase I am running really long wires from the RCA input to the Pot and then to the amp. Minor things that can be dealt with later.
post #132 of 1816
Congrats sachu! Really looking forward to your listening impressions *thumbs up, I've ordered boards and tubes from Jeff*
Wish I could keep my work area that tidy.
post #133 of 1816
Quote:
Originally Posted by digger945 View Post
Congrats sachu! Really looking forward to your listening impressions *thumbs up, I've ordered boards and tubes from Jeff*
Wish I could keep my work area that tidy.
Awesome Scott! Be prepared to be amazed at what was hidden away in the shadows all this while cause this amp is amazing I tell you. I take full credit for dusting off the cobwebs
Even with one channel going I can tell you this is going to be one sweet sounding amp. I have Don's EHHA hooked up to my computer as I type this. After having listened to this amp almost two years ago (and ever since have I been trying to acquire one) and on many other occasions since then I can't wait to finally have one that would be mine and mine alone.

This to me is one of the best headphone amps out there.

Quote:
Originally Posted by digger945 View Post
Wish I could keep my work area that tidy.
heheh..believe me that is neat by my standards..I had just finished 2 other amps yesterday and the day before..that's why its so dirty and haphazard.
post #134 of 1816
Quote:
Originally Posted by sachu View Post
Alex, I didn't check to see the idle current but the voltages across R32, R33 dropped from 0.2Volts to 0.128 volts as I zeroed the output on the opamp.

On a side note, there is a hiss in the channel but I think its mainly becuase I am running really long wires from the RCA input to the Pot and then to the amp. Minor things that can be dealt with later.
Thanks. Can you adjust the idle current back up to 100mA now?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #135 of 1816
Quote:
Originally Posted by runeight View Post
Thanks. Can you adjust the idle current back up to 100mA now?
Can I bias it higher? Like 150mA? Would there be a problem in doing so? Unless there is no advantage to be gained from biasing it so high.
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