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SOHA II Builders Thread - Page 10

post #136 of 1686
Quote:
Originally Posted by runeight View Post
Arkku, I'm not sure what you did to fix the problem. Did you alter the traces on the board? I'm using the BoM relay and it worked without problems when installed according to the board's pad locations.
For various reasons, I'm building my amp on protoboard, not the official PCB, so this was all my own fault. The PCB shown on the website has the relay with the correct polarity; I should have checked there instead of trusting the drawing on top of it. =)
post #137 of 1686
Thread Starter 
OK. Now I see.

We'll wait for further news from you.
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 #138 of 1686
Whee, first sound. The bloody thing works! =)

I'll report more later.
post #139 of 1686
Post us the pictures, and no one gets hurt...
post #140 of 1686
Quote:
Originally Posted by pabbi1 View Post
Post us the pictures, and no one gets hurt...
I haven't had time to finish the case yet (e.g. drill the holes for the tubes), but here goes…

The extra toggles on the amp are mostly explained by the selectable inputs and outputs, and the optional crossfeed circuitry with some fine-tuning options. The rest are not so explainable, but I happen to like toggles. =)

The other box contains the transformer and the power supply (other than the high voltage regulator + capacitance multipliers following it).
LL
post #141 of 1686
By the way, if I try other types of tubes, will I need to re-do the settings, e.g. the tail current with P1L/R? This is my first tube amp (and first DIY amp of any kind), so I'm not really familiar with the differences. =)
post #142 of 1686
Thread Starter 
Well, first thing, arkku, congratulations on a successful build.

No, you won't need to make any further adjustments. Just make sure that you set the heater jumpers correctly for the tubes you're using, either 12.5V/150mA or 6.3V/300mA heaters.

You can adjust the B+ while listening to see if you find a position where you prefer the sound.
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 #143 of 1686
Just wondering, how hot can the tubes get? I've been running the amp for about 4 hours straight and damn these things heat up. It's unpleasant to keep my finger on the side of the tube for more than a couple of seconds.

UPDATE: Amp has been running for about 8 hours straight. Tubes still around same temperature - hot enough that I don't want to keep my finger on it for more than 1 second (a real second, not a fraction of one).
Also confirmed there is definite hiss with 32-ohm Grado RS-1.
post #144 of 1686
Quote:
Originally Posted by runeight View Post
Well, first thing, arkku, congratulations on a successful build.
Thank you, especially for the excellent work on the amplifier, and also thanks to the entire forum—most of the questions I had about the build were already answered here before I even had to ask them. =)

I've been listening to the amp now for a few hours today with RCA 5963 tubes, which seem very pleasant, but quite microphonic—any touch on the amplifier results in a “ping” sound from the headphones. Actually the sound is quite nice for the toggles, but a bit annoying when turning the volume. I also briefly tried Channel Master 12AU7A tubes, which weren't at all microphonic. Too soon to say about other differences.

I also tried both the zener and resistor input buffers, but couldn't hear any notable difference with the equipment currently at hand. I left the resistors in for now.

Overall, regardless of other parameters, I find the amp's sound very “airy” and pleasant, not at all tiring. Exactly what I was hoping for! =)
post #145 of 1686
Thread Starter 
Quote:
Originally Posted by FallenAngel View Post
Just wondering, how hot can the tubes get? I've been running the amp for about 4 hours straight and damn these things heat up. It's unpleasant to keep my finger on the side of the tube for more than a couple of seconds.

UPDATE: Amp has been running for about 8 hours straight. Tubes still around same temperature - hot enough that I don't want to keep my finger on it for more than 1 second (a real second, not a fraction of one).
Also confirmed there is definite hiss with 32-ohm Grado RS-1.
Tubes will get burning hot. Don't expect ever to be able to touch them. In this amp the heatsinks will also get very hot, which means that the entire amp is very warm in the box.

This hiss is hard to find. What O/P transistors are you using?
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 #146 of 1686
Quote:
Originally Posted by FallenAngel View Post
Also confirmed there is definite hiss with 32-ohm Grado RS-1.
I'm not familiar with SOHA II schematic, but did you try to short the input (L and/or R) to ground to check if the noise goes away? It could be related to the wiring from the RCA jacks to the PCB.

Runeight: Do you still plan (with Jeff) to release FPE panels with the kit? I would be interested. The winter is hitting Canada and I get the itch to build something.
post #147 of 1686
Quote:
Originally Posted by FallenAngel View Post
...
UPDATE: Amp has been running for about 8 hours straight. Tubes still around same temperature - hot enough that I don't want to keep my finger on it for more than 1 second (a real second, not a fraction of one).
Also confirmed there is definite hiss with 32-ohm Grado RS-1.
Can you post some close-up pictures of your perfboard HV B+ PS ?
(both top and bottom including wirings)
post #148 of 1686
I'm using BD139 output transistors.

Thanks for letting me know about the heat. It's now in a Hammond case with a perforated RF-shielded sheet on top.

I'll post photos of the HV supply tonight Ferrari, thanks.
post #149 of 1686
Ferrari, I have found very nice power button in Your SOHA. Where did You buy it?
post #150 of 1686
Quote:
Originally Posted by mdabro View Post
Ferrari, I have found very nice power button in Your SOHA. Where did You buy it?
mdabro, that 18mm solid aluminum power button came from ATI Thailand.
Unfortunately, ATI is out of business a while back.
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