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SOHA II Builders Thread - Page 5

post #61 of 1676
Quote:
Originally Posted by holland View Post
Did you personally get to compare to the SSMH? I have my own opinion, owning both, but am interested in hearing others.
I compared the SOAH II to the SSMH, no comparison. The SSMH is a great little amp, probably best you can do <100 but... The Soha II is a superb amp. Simply in a different league.
post #62 of 1676
The amps were setup in groups of two:

EF-1 and Singlepower Squarewave XL, Woo WA6's and GS/Starving Student (!) The Melos remote was left behind, we never got it out of mute My Soha I and II...

There were SOOO many phones and cables that I couldn't keep track of what was what (I had about $10K worth of phones and cables on my head over the course of a couple of hours - Overwhelming for my not -so - experienced ears.

The D7Ks and Senns sounded very good on both the EF-1 and Singlepower. The EF-1 had quite a bit in common with the SS sq wave (a family resemblance to my SOHAS, solid bass, but without quite the definition on the bottom. )

I didn't pay enough attention to the WA6s.

The Starving Student sounded quite good, noiseless and clean, without the full sound stage of the SOHA II but quite good, and with less bass but still respectable.

Gentlemen, there wasn't one stinker in the room, as you can see form the pics!

I look forward to some mini-er meets in the near future, heck I may host one!
post #63 of 1676
Quote:
Originally Posted by holland View Post
wiatrob,
Which tube and transistors are you using? I do know the sonics differ drastically with tubes and slightly with transistors, so you can definitely dial down or up certain areas.
Looks like a fun meet.
Stock transistors, closely matched RCA black plate 5963's, B+ @ 90V
post #64 of 1676
Quote:
Originally Posted by wiatrob View Post
Stock transistors, closely matched RCA black plate 5963's, B+ @ 90V
Have you tried the RCA grey plates? I was wondering if the black plates were worth it. The grey plates aren't really my thing (think thin and shrill).
post #65 of 1676
Quote:
Originally Posted by holland View Post
Have you tried the RCA grey plates? I was wondering if the black plates were worth it. The grey plates aren't really my thing (think thin and shrill).
I like the BPs, I have a set of grey plates as well, but they are very microphonic and do accentuate the highs. I also have some RCA clear tops which I've been swapping in, as they look so freaking cool...

-Bill
post #66 of 1676
waitrob,

That SSMH isn't completely noiseless.
Throw in a set of CD3000 and turn the volume up all the way. If the room is dead silent, you should hear a VERY faint noise (My friend said no noise, but YMMV)
I tried adding more capacitance to the power section to get silence and 100uf more was just a bit too much, changing the sound sig to be a bit wonky (~470uf should do the trick without changing sound too much). Pitch black came with a price, so overall SQ had to be chosen.

However, you really need to meet those conditions to hear it (something not likely in a room full of people).
post #67 of 1676
I was listening to my SOHA II, and noticed a bit of hum. I thought It was coming from the transformer or AC wires, but it turns out that touching the shaft of the pot induces a small amount of hum. I can make sure that the metal front of the pot is grounded and solve the problem, but am surprised to see this behavior with an decent pot. Is it normal to have to ground these to prevent hum?

Grendel23

Update,
I found the problem, the ground wire was not solid, nevermind.
post #68 of 1676
Quote:
Originally Posted by grendel23 View Post
Is it normal to have to ground these to prevent hum?
Yes, I believe the casing of the pot should be connected to ground in some way. Normally just contact with a metallic case is enough, but connecting one of the screws to ground is also a good way to do it.
post #69 of 1676
Thread Starter 
grendel, this hasn't come up yet, but there is a grounding pad between the pot and the input terminal block for just this purpose.

The way I grounded my pot was to remove the screw at the top right looking from the front. You can unscrew this screw out of the back and run a short wire from the grounding pad and wrap it around the screw and then tighten it back in. Depending on the type of wire, you won't be able to tighten if fully, but you'll get close. If you use something like 24awg stranded wire you'll be able to put the screw all the way back in.

Update: Never mind.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #70 of 1676
Quote:
Originally Posted by runeight View Post
grendel, this hasn't come up yet, but there is a grounding pad between the pot and the input terminal block for just this purpose.

Update: Never mind.
I was heartbroken when I first touched the pot shaft of my proto build upon firing it up BZZZZZZ

Groundining with a thin strand from the upper rear screw to the G pad cured it.

(all of my builds with ungrounded RCAs have had this issue, not just the II...)

Grounding: an Art and a Science!
post #71 of 1676
I am glad this is a known and curable ill. I still had a bit of noise after fixing my loose main ground wire. I will ground pot and see if that takes care of it.
Thanks,
post #72 of 1676
Quote:
Originally Posted by grendel23 View Post
...I still had a bit of noise after fixing my loose main ground wire. I will ground pot and see if that takes care of it.
Thanks,
Are you housing the transformer in the same case as the amp?
post #73 of 1676
Quote:
Originally Posted by wiatrob View Post
Are you housing the transformer in the same case as the amp?
Yes I am, but moving the AC wires does not affect the noise. I will ground pot tomorrow and see if that helps.
post #74 of 1676
Quote:
Originally Posted by grendel23 View Post
Yes I am, but moving the AC wires does not affect the noise. I will ground pot tomorrow and see if that helps.
If the case is the stock hammond, some builders have found that rotating the transformer can alleviate hum, if it' snot the pot...
post #75 of 1676
Grounding the pot eliminated the noise. Now it is dead silent even at full gain.
Thanks for the tip Runeight!
I ran into one other small issue. I had the holes for the tubes in the top plate very tight to the tubes. this worked fine until I tried to remove the tubes, the sockets are tight and it was almost impossible to remove the tubes because I couldn't rock them slightly. I am changing to larger openings.
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