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SOHA II Builders Thread - Page 14

post #196 of 1688
Thread Starter 
C4P (the one you put in for C12P) is certainly toasted since it was running 70V or so over its rating. You'll have to replace it before the negative supply will come up properly. You shouldn't power up with the old C4P in place and it won't be good for the regulator to power up with C4P removed so . . .

After C4P is replaced with a good cap . . .

This still could be hard to troubleshoot because other components in the HV supply could also be damaged. This would be C8P, C9P, C10P, and C11P along with all of the multiplier diodes.

Try removing C12 to see if there is any voltage at its positive terminal. There will be a lot of AC here, but you should still get a DC reading. If this DC voltage is mV then I've got to think about what to do.

Can you do some probing around with the power applied? If so:

1. What is the TH voltage?
2. What is TL+ voltage?
3. What is the voltage at the + terminal of C8P
4. What is it at the + terminal of C9P

This will make a start.
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 #197 of 1688
Quote:
Originally Posted by runeight View Post
Uncle Bob I forgot to ask you what the voltage is at C12P?
Slightly over 124V dc
post #198 of 1688
Thread Starter 
Thanks. It looks like all of your pre-regulator voltages are on target.

When do your new regs arrive?
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 #199 of 1688
Quote:
Originally Posted by runeight View Post
Thanks. It looks like all of your pre-regulator voltages are on target.

When do your new regs arrive?
Still haven't placed an order. I rashly decided to build a PPA at the same time and I'm having a real headache with that at the moment, so I'm holding off until I know if I need any parts to fix the PPA.
post #200 of 1688
I put the caps in correct and now read proper voltages. I am going to replace all the caps but know for now that they do work. Will continue testing tomorrow.
post #201 of 1688
Is there any news on the perforated case tops?

This seems to be just what we need:
post #202 of 1688
Any idea where those can be sourced from?
post #203 of 1688
Thread Starter 
Quote:
Originally Posted by rds View Post
Is there any news on the perforated case tops?

This seems to be just what we need:
I don't know gents. I haven't heard from Jeff R in a while now so I don't know what the status of the kits is and whether or not he's making the various metal panels.

I'll email him again . . .
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 #204 of 1688
Quote:
Any idea where those can be sourced from?
Unfortunately no. I got that picture from the M3 section of AMB's website. The builder is darkisz.
post #205 of 1688
I've seen a bunch of those at case-mod stores.
500mm
post #206 of 1688
Earlier in the prototype process I thought about supplying these pre-cut (I have a bunch of perforated stock lying about).

Cutting with the precision necessary for an exact fit and alignment of tube holes is beyond my resources at this time.

However, I could easily do a rough cut - If anyone is interested in a blank that they could cut to exact fit, PM me..
post #207 of 1688
Sorry for such a long delay in posting HV supply photos, had this project benched for a week while I was getting other things together. I shortened and untwisted the HV wires after the photo was taken, they are now simply straight wires and about as short as they can be.

I checked without tubes installed, the hiss is present here as well, so it's from the "front end".

Here are photos of the HV board.



I let the amp warm up a bit, the hiss is barely noticeable in anything except these blasted Denon D5000, but it's there, very persistent and quite loud with no music playing.

For the top of the case, I actually got this RF shielded screen
http://www.surplussales.com/Cab-Rack...nclosures.html

Quite easy to cut and work with, costs $15 and enough to make a few amp covers.
Looks like this:
post #208 of 1688
Jeff should be getting the boards this week and he has the kits pretty much ready for ordering, so check your inbox, or email him if you have not received the info. Or, if you want me to email you the info (I can forward his email to you), pm me.
post #209 of 1688
Thread Starter 
[QUOTE=FallenAngel;5069257]Sorry for such a long delay in posting HV supply photos, had this project benched for a week while I was getting other things together. I shortened and untwisted the HV wires after the photo was taken, they are now simply straight wires and about as short as they can be.

I checked without tubes installed, the hiss is present here as well, so it's from the "front end".

I let the amp warm up a bit, the hiss is barely noticeable in anything except these blasted Denon D5000, but it's there, very persistent and quite loud with no music playing.

QUOTE]

FallenAngel, I've been thinking about this problem with not much success. It's hard to isolate hiss like this because it may not be coming from a single source. Ferrari has told us that he's tested the noise in the buffer stage and it seems to not be the cause of this problem.

This leaves only three possibilities:

1. The HV PS
2. The tubes
3. The Plate load current mirrors

I'm assuming that the hiss is equally as large in both channels? Or is it asymmetrical?

If it's the same in both channels then it's most probably the PS. Now why your HV PS would be different from the others is very hard to tell. Are you feeding the regulated HV into the cap multipliers on the board? Have you left them out of the circuit?

Do you happen to have a scope available?

As you can see I'm a bit stumped, but perhaps we can find the cause.
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 #210 of 1688
I have hiss also. It's barely audible with my high sensitivity headphones, but very much so with 16-ohm IEMs.

I haven't had a chance to do much of anything about it. I was just thinking, as well, that it's possible the HV is just a red herring.

I am using all 3 cap multipliers on the original board.

I probably won't have much time to look at it till after the holidays.
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