[Tomo]

Ay,

I built myself a new buzzing amp. Did star grounding and all the fun stuff. I even threw in a line filter. I kinda worked down to two possibilities.

One, there is some odd current flow on the chasis. I grounded everything electronically, but I am still getting chasis-touchy-microphonic-like thing. e.g. I can hear the tap on my chasis.

Two, I am using a bare stepping attenuator and that comes ~5cm of AC lines. I wanted to have a neon switch this time on the front and not on back.

I know isolating the PSU out to another chasis is the easiest solution, but I really want it in a single case. (Plus, other than this tiny low hum, the amp sounds pretty good.)

Let me hear ye experiences, Thanks.

Tomo

P.S.

 

[Mazuki]

I think it might be direction in which you mounted the transformer.

 

[Bjornboy81]

Quote:

Originally Posted by Tomo /img/forum/go_quote.gif Ay, I built myself a new buzzing amp. Did star grounding and all the fun stuff. I even threw in a line filter. I kinda worked down to two possibilities. One, there is some odd current flow on the chasis. I grounded everything electronically, but I am still getting chasis-touchy-microphonic-like thing. e.g. I can hear the tap on my chasis.

So everything is grounded to the chassis, but is the chassis grounded to the AC outlet? Is it a 60Hz (or 50Hz???) buzz? If so, it could be the postion of the transformer, but I doubt it.

 

[headphonejunkie]

Are all of your wires properly routed and twisted?This can be a reason for buzz or hum or whatever you want to call it.

 

[tomb]

The AC and signal ground must always be separate. If AC current is in close proximity to the case, and the signal portion of your amp is also grounded to the case, that's a perfect recipe for picking up AC hum and ripple. The AC must not touch the signal ground - either the high end or the low end AC.

 

[Tomo]

Hey, Tomb.

I have all the signal ground tied to the tiny board on the center through which the signal ground is tied to chasis. This board is ground loop breaker that Jan Meier used. (PSU ground is separate from Signal GND. ... per se)

Only thing that really worries me is that the amplifier ground is connected to the PSU ground through the 3-screw terminal. (the center is PSU ground) I should take that amp ground to the signal ground. Can I leave the PSU ground?

Also, the giant stepping attenuator is not really friendly in the sense that its frame is electrically connected to chasis. I can't do anything about that. So I decided to solder the frame to the signal chasis ... This is a doodoo?

Thanks in advance!

T

 

[Tomo]

Tomb, the oh-so-great-one, the defender of soldering, ... you know whatelse!

I just unscrewed the PSU terminal and connected that terminal to the ground loop breaker. AND BAM! It's all quiet. I mean dead quiet.

Now I can pay attention to massively expensive volume control knobs. Thank you, Tomb!

Tomo

 

[tomb]

Glad you fixed it!

 

[Tomo]

" ... oh just one more thing ... " -Colombo

Do you use ground loop breaker, tomb? Or is it better just simply keep the signal ground 100% isolated from PSU GND?

Tomo

 

[tomb]

IMHO, a ground loop breaker is something you use when connecting into an entertainment center whose patch cords you long ago lost abillity to trace.

Again, just MHO, but it's better to keep the PSU ground 100% isolated.

 

[Tomo]

Roger that, Tomb. Proceeding with the pursuit for spiffy volume knobs! OOOOH I can't wait till tomorrow!

Tomo

 

[Tomo]

Hey,

I just found out the exact reason for the instability. I was reading the articles at Elliot Sound and found just what I was looking for.

http://sound.westhost.com/project04.htm

The problem was from having too thin a wire connecting the center tap to the ground of the regulator stage. Also, ground routing was thin all around. Thus, AC bad-ness crept into the amplifier.

Thus, I decided to beef up the grounding. Look what I did.

You can see in the place of thin ground lanes, you see thick copper rods. I had to buy a new iron for this since it's so thick. (70W 700F Temp Controlled!!) I had so much fun doing this too.

Now it's much more stable.

TOmo

P.S. That's a THS4022EVM. But I rewired it for myself.

 

[headphonejunkie]

Did you make that stepped attenuator yourself? That looks nice too.

 

[gjavitt90]

Quote:

Originally Posted by Tomo /img/forum/go_quote.gif ... ...

What do you have wrapped around the caps? shielding material perhaps?

 

[Tomo]

Hey,

I made the stepped attenuator. It doesn't look much, but it was soooo much fun; 46 soldering points. I had a huge "HIGH". No joke.

wrapping around the electrolytics is ... duct tape. You are right, I think I ought to change it to cupper tape or something.

Going back to BUZZ thing. I think all the AC and Ground line has to be FAT wires. Fat wires can keep the AC badness inside more?

T