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SOHA II Builders Thread - Page 72

post #1066 of 1688
Thread Starter 
Ah. Looking at the bottom of the device the side that goes against the heatsink is the side that the pins are closest to.
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 #1067 of 1688
Thanks Alex.
post #1068 of 1688
Quote:
Originally Posted by runeight View Post
Those numbers on pin 1 are nearly perfect. But you still get 65V at pin 6??

Then it has to be the transistors.

Please let us know how you do. The amp will work when all the parts are right and working.
hey again,
I replaced q1/q2 on both channels and I am getting the exact same measurements as before(which are on posts #1033-#1050)
Do you have any other suspicions on what could be wrong?
post #1069 of 1688
I remember when the SOHA II was in its infancy there was a member that had a higher voltage PS, has that been incorporated in this final design I'm building?

Also is there a thread about tube rolling/sonic impressions or is this the right one?
post #1070 of 1688
Stupid question maybe but... has anyone tried to replace the CCS by the heaters as a load (Starving Student-like) ?

150ma @12.6V seems quite ok for this (with heaters in serie), with sufficient heatsinking for the bd139 of course. Running 12V for the positive supply would give a dissipation of less than 2W. The transistor can cope with that.

I would implement a softstart in the heater supply (easy to do with the lm337).
post #1071 of 1688
The Digikey heatsinks from the BOM have no hole to attach the transistors, just a knob protruding, do we have to drill them out?
post #1072 of 1688
Quote:
Originally Posted by regal View Post
I remember when the SOHA II was in its infancy there was a member that had a higher voltage PS, has that been incorporated in this final design I'm building?

Also is there a thread about tube rolling/sonic impressions or is this the right one?

Pretty much - Ferrari rolled his own HV plate supply, and then the amps plate supply was redesigned for higher voltage.
post #1073 of 1688
Quote:
The Digikey heatsinks from the BOM have no hole to attach the transistors, just a knob protruding, do we have to drill them out?
No. Those heathsinks normally have metal clips to keep the transistor in position.
post #1074 of 1688
Quote:
Originally Posted by 00940 View Post
No. Those heathsinks normally have metal clips to keep the transistor in position.

That's odd - I did the BoM and I don't think we vetted the Digi-key column as throughly as the Mouser - but I'm pretty sure some have used those part numbers.

I'll take a look and update the BoM when I get a chance. Sorry for the mixup...
post #1075 of 1688
Well, I just checked digikey. I don't have one at hand (but plenty of similar heatsinks).

post #1076 of 1688
Those are the ones, they don't come with clips so I had to drill holes. They also made contact to a few resistors and had to be dremelled.
post #1077 of 1688
I am using the 2" aavid thermalloy version of the one that Ti sells except with solder pins.
Fits very well =]
post #1078 of 1688
Anyone else using PIO coupling caps? Wondering if I should ground their cases? I ended up mounting 1uF russian caps, only to find a better sized .22 uF vit C's in the mail box, I doubt a will switch them unless someone thinks they would be better.


Also I really like the templates someone posted, helped the case work significantly.
post #1079 of 1688
Quote:
Originally Posted by 00940 View Post
Stupid question maybe but... has anyone tried to replace the CCS by the heaters as a load (Starving Student-like) ?

150ma @12.6V seems quite ok for this (with heaters in serie), with sufficient heatsinking for the bd139 of course. Running 12V for the positive supply would give a dissipation of less than 2W. The transistor can cope with that.
Anything wrong with the idea ? I'm about to build a p2p version of the soha (found some mullard 12au7 for free and a suitable case) and plan to go that way.

It saves one regulator, two transistors, two heatsinks and a few caps/resistors, all that at the cost of a slightly reduced voltage output swing. And it reduces the current draw on the PS.
post #1080 of 1688
I will not call it stupid but it has nothing to do with the SOHAII design.
If you want to save a couple of components the way you think, just give it a try.
You have nothing to loose with a p-p build.
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