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SOHA II Builders Thread - Page 7

post #91 of 1669
Thread Starter 
Looking good gewa. Are you going to come in last in the EU race? Can you let that happen?
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 #92 of 1669
Quote:
Originally Posted by runeight View Post
what kind of noise is it? hum? buzz? static? white noise?
Hmm... I'm not very good with describing noise, I would say it's white noise / hiss. Not static and not distinct hum of transformer and doesn't sound like a ground loop.
post #93 of 1669
Thread Starter 
Hiss. Hmmm. Can be hard to find.

Does it go away when the headphones are unplugged?

Does it go away if you pull out the tubes and just listen to the buffers?
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 #94 of 1669
I think I'm going to come in last on the European side as i have had to put my project on hold due to financial matters..bloody recession...
post #95 of 1669
Thread Starter 
Quote:
Originally Posted by FallenAngel View Post
Hmm... I'm not very good with describing noise, I would say it's white noise / hiss. Not static and not distinct hum of transformer and doesn't sound like a ground loop.
Say, FallenAngel, I just reread my response above. I think it sounds a little flip, but I didn't mean it to be. I think I'd better start including more smilies.

The source of hiss can be very difficult to locate and sometimes it comes from several different places.

I asked about unplugged phones because I was wondering whether the hiss might be partly due to the clamshell effect. But, I know that this is a long shot.

It will be helpful if we can isolate the hiss to either the front end or the back end of the system. Which is why I asked about pulling the tubes.
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 #96 of 1669
Thread Starter 
Quote:
Originally Posted by onform View Post
I think I'm going to come in last on the European side as i have had to put my project on hold due to financial matters..bloody recession...
Sorry to hear that onform. But I can tell you that things are getting pretty rough here in the US too.
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 #97 of 1669
Quote:
Originally Posted by runeight View Post
Say, FallenAngel, I just reread my response above. I think it sounds a little flip, but I didn't mean it to be. I think I'd better start including more smilies.

The source of hiss can be very difficult to locate and sometimes it comes from several different places.

I asked about unplugged phones because I was wondering whether the hiss might be partly due to the clamshell effect. But, I know that this is a long shot.

It will be helpful if we can isolate the hiss to either the front end or the back end of the system. Which is why I asked about pulling the tubes.
I don't know what "flip" is, not to stretch to being able to identify it.

It's not from the headphones "effect" because when I have the headphones on, I know just when the muting relay clicks and then the noise comes.

I also checked without tubes, the hiss is still there and at the same volume, so I'm assuming it is the buffers.
post #98 of 1669
Thread Starter 
Is there any way that you can remove the lead of C1 where it connects to the base of Q5 on both channels? This will disconnect the buffers from the B+. One source of the noise in the buffers could be the B+, although not likely.

If it is not the B+ then something in the buffers is just noisy. Is the noise the same on both channels?

One thing about the buffers is that they are pretty simple, not much to go wrong. So I'm not yet sure what can be causing this.

Do you happen to have a scope available?
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 #99 of 1669
That might be kind of difficult, but I'll try.

The noise is the same on both channels as far as I can tell.

Nope, no scope around and I wouldn't know the first thing to do with it if I get one (or considering how often I've wanted to measure something, it might be a "when I get one").
post #100 of 1669
Don't have my ultrasensative M-Audio Q40 around to test with higher impedence, but I plugged in one of my 16-ohm IEMs (Crossroads MylarOne X3) which are quite sensitive as well and I have a hiss too. I don't notice it with my other sensitive cans, like the ATH-ANC7 and the K81DJ.

I recall checking this with the old B+ (pre-HV) config, and I recall not noticing this, but that was also before casing when it was sitting out on my desk.

I'll see what I can find out tomorrow, if I have time. I will try to isolate the buffers first.

I have a scope, but my 200MHz probes are broken. I think I have some 400MHz probes around somewhere, but I haven't used my 400MHz unit plugin so I'm not sure if it's functional.

If I can measure, I will. What would you like done?

With the protoboards we have, we should just be able to disconnect the external HV perfboard as well, if you don't want to desolder C1/C2 and you put terminals on. At least, I think that'll work.

Edit: I hear it with my DT660, but it's slight.
post #101 of 1669
I have looked at the instrinsic noise of the output buffer (more than once) during the prototyping phase and it is very low, so I’m quite sure that it’s not likely that the noise is coming from there.

Take a closer look at the wiring of the input => volume pot => PCB, all these wires are unshielded and the distance is quite long. Pure from technical point of view, this can’t be healthy for the very sensitive input signal.
post #102 of 1669
Quote:
Originally Posted by Uncle Bob View Post
It's progressing, pretty much all of the passives are mounted and I'm hoping to get a few hours work on the board this weekend.

GeWa has been pretty quiet, wonder how he's getting along?
Normally… the Belgians way is a bit slow, mostly (comparing to the Dutch way).
Hope that he’s not going to give it up.
post #103 of 1669
Taraaaaaa!!!!!



Regards
post #104 of 1669
excellent ..dB
post #105 of 1669
Quote:
Originally Posted by GeWa View Post
Taraaaaaa!!!!!



Regards

Well done GeWa. Looks like you are not going to come in as last.
Now testing and listening. Enjoy!
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