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SOHA II Builders Thread - Page 55

post #811 of 1686
Quote:
Originally Posted by zkool448 View Post
although I realize only the 12.6v variants can be used on my SOHA II as I didn't opt for a high current transformer.
You can still use 6.3V. The 12.6V configuration parallels the tube heaters, so the current demand of 2 tubes is 2x the heater specs. The 6.3V uses a serial configuration, so the current demand stays the same. The 2 6.3V heaters in serial make 12.6v.

It sounds like you need to rewire the SOHA II and get a higher current transformer.
post #812 of 1686
Yes I do need to get a higher current one!

What I meant to say was the 300mAh max limitation of my current transformer. I got the stock glassar kit for the convenience and less chance of messing up the BOM -- I do regret not opting for the hi-current transformer indeed.

zk
post #813 of 1686
Quote:
Originally Posted by zkool448 View Post
I replaced it with 6 sip sockets, although a dpdt switch would've been the ideal replacement I didn't have one on hand and I was eager to get it setup.

zk
I have a few mini-dpdt's from my SOHA II proto days, PM me if you're interested, I'd be happy to send you one. Haven't checked but they may fit directly into the sips...
post #814 of 1686
wiatrob, thanks for the kind offer -- I placed my mouser order for the jack and switches just yesterday

zk
post #815 of 1686
Quote:
Originally Posted by adamus View Post
...no hiss, no hum, just clean clean sound. And may i say, with the 5963, quite a solid state sound. very very different to the bijou. but its way off being burnt in, the tubes have barely 10 mins on them.
Adamus, you might try 6DJ8/6922 tubes. At least my Amperex 6DJ8 sound more tubey and less sharp than my Sylvania 12AU7/Phillips 5963. I prefer the Amperex while using RS-1.
post #816 of 1686
I tried it with some bugle boys (6dj8). it was a good step up. Its a different presentation to bijou (as expected, its a hybrid). Its definately a quicker amp the the bijou, and slightly dryer. The best tube i tried was.....


Not saying one is better than the other.... just different. For my listening preferences, the bijou is to my liking, but if was listening to a lot of electronic, hiphop, pop, dance... then the soha II would get a lot of play.

The soha is one hot amp.... i assume its normal for the ouput fet sinks to get hot, too hot to keep your fingers on for a while.
post #817 of 1686
8416 is a mutha of a tube in the SOHA 2, IMO. I'm currently digging the 6N6P and the 6CG7. Both too early to really comment on.

6DJ8/6922 are more tube-y, for sure.
post #818 of 1686
Alex, is 50 ohms safe for the R6 value? I can only dial up 600mV across R6 on the default config (using zeners now for testing). I figure with 50 ohms, I should be able to dial up to 8mA-9mA tail current using the 200-ohm trimpot. I can use a larger trimpot to get back to the 2mA tail current, if need be.

Thanks!
post #819 of 1686
Thread Starter 
Yes, that should be fine. Keep your eye on the power dissipation in Q3. It should about 200mW for the currents you want to run. That is ok for this package but the bjt will get toasty.
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 #820 of 1686
Quote:
Originally Posted by holland View Post
... I figure with 50 ohms, I should be able to dial up to 8mA-9mA tail current using the 200-ohm trimpot...
Keep us informed if this higher tail current tweak make any positive difference
post #821 of 1686
Quote:
Originally Posted by holland View Post
8416 is a mutha of a tube in the SOHA 2, IMO. I'm currently digging the 6N6P and the 6CG7. Both too early to really comment on.

6DJ8/6922 are more tube-y, for sure.
6n6p?? you must have a hell of a heatsink on the 12.6v regulator, those tubes consume 800ma of heater current. they do sound superb though.
post #822 of 1686
Quote:
Originally Posted by adamus View Post
6n6p?? you must have a hell of a heatsink on the 12.6v regulator, those tubes consume 800ma of heater current. they do sound superb though.
Not big enough. It gets hot. I'm using the largest heatsink that fits on the PCB. I need to case sink this bad boy, as I'm running open chassis right now, due to the heat. Using a 1.6A transformer and it's not at full load yet, so there's still headroom on that.
post #823 of 1686
Finally the weekend has arrived.. will now have some time for some serious casework

Quick question about grounding. With wood enclosures, is an aluminum/metal bottom plate necessary to mount the board/torroid for "proper" grounding? I wasn't planning on using a metal plate or SG/standoff and was thinking of just using a 22awg wire from G pad on the pcb to the IEC ground -- this is how I have everything setup an mdf plank board right now until I finish the case... so is this setup acceptable? thanks.

zk
post #824 of 1686
Thread Starter 
This setup is ok but it offers more opportunties for noise and hum since the amp won't be grounded to a nice big piece of metal.
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 #825 of 1686
I finished my SOHAII right now. Everything worked fine (besides I forgot to put the OP amps into the sockets before starting the setup) until the last step: Check TPL and TPR. One channel measures 13,8 V the other one 22,6 V, the measurements follows the tubes when swapping them. Since the tube with the lower voltage also glowed a bit darker I changed it, the replacement tube reaches about 16,0 V. So still both tubes are far away from "approx. 19 V" one too high, one too low.
How much tolerance is acceptable?

At first glance audibly it's ok and there doesn't seem to be a big difference between the channels, not to say the amp sounds great! It makes even the stock Archos phones bearable (I still didn't dare to connect my AKGs).

Chris

PS: Tubes are 6N23P (== 6922/6DJ8)
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