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SOHA II Builders Thread - Page 82

post #1216 of 1688
Hi,

Completed my SOHAII build over the weekend after a few errors (E12 regulators were reversed) it sounds great. Kudos to Alex for the design and making it available to the DIY community.

However, with sensitive earphones (Etymotic) I did get a constant amount of hum despite trying different ground methods. Volume control didn't make any difference to the loudness of it.

Rotating the transformer worked wonders here, I'd consigned myself to moving the transformer out of the case.

To complete it I need to find a suitable top and source some isolation washers for the input jacks.

As the amp runs pretty hot I was thinking of using a perforated top, I found something that might work on Ebay here:
3003 Hex Perforated Aluminum Sheet .032" x 12" x 48" - eBay (item 350270376416 end time Mar-25-10 12:21:42 PDT)

As the holes are pretty big there's potential for dust build up which I know can be a problem for very high voltages (arcing) although I'm not sure if this applies to the soha.

While this gives 79% open area there's also a sheet perforated alu at 40% open area.

Does anyone have an opinion on which would be more suitable, I'm erring on using the 79% to keep things as cool as possible?

For isolation washers I'll try my local hardware store but I anyone has any other suggestions that would be appreciated too.
post #1217 of 1688
I seem to remember reading that it's recommended to have roughly the equivalent of the board surface area vented.
I say cut a hole above the board of the same size and fit it with Al perf mesh.
post #1218 of 1688
Quote:
Originally Posted by Rooford View Post
Does anyone have an opinion on which would be more suitable, I'm erring on using the 79% to keep things as cool as possible?
Do you have holes drilled on the bottom of the chassis? Doing so will create more airflow (bottom to top).
post #1219 of 1688
OK, I'm all done....at least for now. Everything checks out and the Bantam DAC fit nicely in the back with some sweet AmpOhm Copper Foil/PIO caps. Hopefully I can start burn-in tomorrow.

One thing I can't figure out is why access to the B+ trimmer is needed? Why drill the hole to adjust B+?
post #1220 of 1688
Quote:
Originally Posted by tubesmuggler View Post
OK, I'm all done....at least for now. Everything checks out and the Bantam DAC fit nicely in the back with some sweet AmpOhm Copper Foil/PIO caps. Hopefully I can start burn-in tomorrow.

One thing I can't figure out is why access to the B+ trimmer is needed? Why drill the hole to adjust B+?


The hole to adjust B+ is just so folks can hear the differences from low/high voltage, if you know the voltage you like it isn't needed.


How do you like the copper AmpOhm's ? I just ordered a pair.

.
post #1221 of 1688
Quote:
Originally Posted by regal View Post

How do you like the copper AmpOhm's ? I just ordered a pair.

.
I'll let you know. I haven't played music through this puppy yet.
post #1222 of 1688
how hard is this to build? i only built tangets cmoy....is this the next DIY project i should do or is there something else i should be looking at, also roughly what is the cost of this project?
post #1223 of 1688
The step up in parts count alone form a cmoy is quite extreme, not to mention the requirement of AC voltages, casing choices ect.

Something a bit simpler with a fantastic kit (including machined case!) is the millet mini max from beezar.
It will get you used to a higher parts count with out the added complications of straight ac outta the wall (it uses a wallwart which is supplied in the kit)
post #1224 of 1688
Quote:
Originally Posted by igotyofire View Post
how hard is this to build? i only built tangets cmoy....is this the next DIY project i should do or is there something else i should be looking at
I would recommend a MiniĀ³ for your next build. You wont have to work with AC mains and you'll get a bit of experience with smd soldering (if you don't already have it). Plus... it sounds amazing.
post #1225 of 1688
Quote:
Originally Posted by igotyofire View Post
how hard is this to build? i only built tangets cmoy....is this the next DIY project i should do or is there something else i should be looking at, also roughly what is the cost of this project?
I would say if you can understand heatsink mounting and the concept you should be OK. Roughly $200 to build. I don't think it is much more difficult than a minimax.
post #1226 of 1688
I hope you won't mind revisiting some stuff from the past.
I was getting help troubleshooting my sohaII back here, but never really finished.

To recap, every measurement I've taken so far is spot on, except TP (R/L)

108v @ TB
-12.8v @TH
+/-15v @ TL+/-

65v @ TB+ (r/l)
64.7v @ TP (r/l)

41.9v and 42.6v @ pin1 with respect to ground

I replaced Q1 and Q2 on both channels, and all measurements are identical.

I've been eager to listen to this amp for a long time, so I really hope I can get this up and playing music =)
post #1227 of 1688
Thread Starter 
The measurments seem ok to me. Are you having problems?
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 #1228 of 1688
Quote:
Originally Posted by runeight View Post
The measurments seem ok to me. Are you having problems?
I haven't tested the amp, but shouldn't there be approximately 19v drop from TB+ (r/l) to TP(r/l)?

Right now, TP is reading almost the same as TB+.
post #1229 of 1688
Ok so I am in the middle of my SOHA II build - found a few errors but am getting ready to start working on the case. I am planning to use a different enclosure than the hammond and not planning to mount the pot to the board. Does anyone have a good way of soldering wires to the pot? Is there some kind of little connector that I could use? Any recommendations?

Thanks
post #1230 of 1688
Quote:
Originally Posted by capernicus View Post
Ok so I am in the middle of my SOHA II build - found a few errors but am getting ready to start working on the case. I am planning to use a different enclosure than the hammond and not planning to mount the pot to the board. Does anyone have a good way of soldering wires to the pot? Is there some kind of little connector that I could use? Any recommendations?

Thanks
Have you looked at AMB's nifty little e27 boards?
Otherwise, you can solder right onto the pins and heatshrink over it.
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