Noise on new build

[rzenc]

Hi forum!

I'm building an amp and came across a trouble  which I have never seem before - or happened before on my buildings - It's located at  V1a pin 2 input grid. I could isolate it by taking first tube out. The rest of the amp is very very quiet, no hiss or hum.
I tried the following:

1- change PS cap;
2- moved ground around;
3- chopsticked the whole thing;
4- running 12Vdc heaters;

Right now V1 has it's own ground point, away from the rest of the amp and close as possible to input jack. I'm using shielded wire from jack to socket.

What I have notices while poking around:

5- eq is inserted between first and second gain stage, James type, even with all controls down there is noise coming out of V1b - I know this because when I take V1 out, noise disapperas completely;
6- gain pot, treble pot and shape pot alters noise characteristics;
7- depending on pot settings, there is more or less noise;
8- connection between turrtes and pins 6,7,8 on V1 makes noises - have already reflowed them;
9- while probing with oscilloscope - I have pics with notes - I found the noise to be on socket pin 2;
10- when I ground pin 2 noise dissapears.

By now my kinda lost here...I will appreciate all insights you guys can give me. It's not the first time I'm building this circuit - Klein Baphomet - there are differences, quad 6V6 instead of EL84 and 8K2@10W between reservoir and screen supply instead of choke.

Many thanks in advance for your kind attention.

Best Regards
R.

[sluckey]

Got a schematic?

[archaos]

Interesting, what kind of noise is it ? Did you record a clip ?

[TIMBO]

I have found that some of my builds have suffered from V1 noises.  They seem to be hard to find.
The last build had a noise when the chassis was tapped the noise would come through the speakers :- cheep chinese  12ax7 
Another, when CHOP STICKING tapped wires around V1 would give micophonic sound :- minute strand of wire on valve pins 
Annoying buzz :- relay circuit,used 51r resistor to elevate 
Also on last build had multiple hums,buzzes,oscilation, thinking that it was layout etc. rebuilt to different amp but with the almost the same layout, so QUIET i wasn't sure it was turned on (thought i blew the fuse) WTF 

So depending the type of noise you will eventually find it.Hope this helps   

[John]

Timbo, if I tap around the preamp tubes I get the "toc" sound through the speaker too.

So I don't do that. 

[Willabe]

Timbo,

I have a great deal of respect for you. You have more patience in your little finger and more stick to it-ness in you than I do in my whole body, at least at this point in my life.         The way I see it you are not afraid to try things and then work them out.    

I really mean that.

The last build had a noise when the chassis was tapped the noise would come through the speakers :- cheep chinese  12ax7  

I've read things on different sites that talked about this, including NOS/new tube sellers. They talked about buyers complaining about buying bad tubes from them. It was especially bad with the dreaded "EF86" small bottle/signal pentodes.  After talking with the buyers, it came to light that the buyers were _NOT_ having problems when the tubes were being used _under normal_ circumstances but where finding "problems" _when_ they where "testing" their tubes by taping them and banging on them with different tools.    

What it boiled down to was as long as the amp was played normally (without banging/taping on the tubes), and had no problems, then the tubes were fine. No tube was made for banging on them while passing audio signal/current.

Yes some tubes were made for high G forces in jets and for mobile boogie action, ie, car/truck radios and military vehicles/backpacks.

But where talking about music amps. To me big differance.

With that said, hope you and John get a laugh out of this?

So I don't do that.  

Old, old, joke;

A man goes to the Dr. and says, " Dr., Dr., when I do this it hurts" Dr. says "It hurts when you do this" Man says "Yes it hurts when I do this".

Dr. says "Well than don't do that".    


                          Brad        

[TIMBO]

Thanks Willabe, I do believe that when a amp is built it can be quiet as a mouse and work to its full potential but every build has related problems.The problem is that lots of things come into play when its is all put together and the guy's like Tubenit and his sidekicks i'm sure have had shear of nonstarters but have learn't from these builds.Anyway this is how i see it.

rzenc, I'm sure you'll find the problem as it is usually something small. Thanks STICKTOITNESS (Timbo)

[Willabe]

I'm sure you'll find the problem as it is usually something small. Thanks STICKTOITNESS (Timbo)

Our good friend rzenc is IMO, cut from the same cloth as you, who, FWIW, I also have a lot of respect for.

He's got the same _STICKTOITNESS_ IMO.


            Brad                              

[rzenc]

Got a schematic?

Yes I do Steve.

Unfortunately, I had a computer crash and need to recover all data.. If I can get to it today, I will upload schem, pics, voltages and notes....

I will also test the amp on my friends house, my wall outlets are noisy and while some amps have no noise at all, orhers scream like crazy...gotta figure a way to get clean AC...

Thanks for the kind words and help guys!!
I will try a Schurter AC line filter and see if things clear...

Best Regards
R.

[sluckey]

That bridge rectifier can't work as it's drawn. And there should not be a bridge there anyhow. The STBY switch can only reduce B+, not switch it totally off. But that's stuff to talk about later.

Does the amp work at all?

I'm interested in the dc filament supply. How much dc voltage do you have across the input cap c18? I would also think you need to ground the CT of the winding feeding the regulator. Can you temporarily wire V1 and V2 filaments to the 6.3VAC winding to see if noise improves?

[Willabe]

That bridge rectifier can't work as it's drawn. And there should not be a bridge there anyhow.

IIRC, someone here wired up their PT B+ that way and killed the PT.

The STBY switch can only reduce B+, not switch it totally off.

Switch is in the wrong place? Should be moved to the junction of DO 3, DO 4 and C13?

The way it is wired now only half of the bridge supply (1 PT leg) is taken out?


                  Brad    

[rzenc]

Guys, sorry for the mess...there is no CT on HT winding..while editing schem I forgot to delete it...my bad...

The amp plays and sounds good...except for the nasty noise on V1...

As soon as I arrive home I will correct and post.

Thanks for the heads up!

Steve: I will take more voltage readings as asked and try AC on preamp heaters.

Best Regards!
R.

[stingray_65]

I will also test the amp on my friends house, my wall outlets are noisy and while some amps have no noise at all, orhers scream like crazy...gotta figure a way to get clean AC...

While no help for your original post, I know you like to build things yourself.
http://mysite.verizon.net/vze22yzp/id11.html

Ray

[rzenc]

I know you like to build things yourself.

Thanks Ray!!! The VTVM project is on and I collecting parts...

Best Regards

R.

[rzenc]

And the oscar goes to.....................................Steve!!

Thanks man! I tried AC heaters again and it cleared the remaining noises. Althought noise on V2 - P.I. - increased a bit, but noise on V1 is gone!!  which is exactly the opposite that happened at first power on. At start, amp was picking a lot of noise from AC heater string, this time I used a smaller gauge which allowed me to tightly twist them together...
The amp is very quiet and sounds great, abyssal bass response, defined chords and crystal clear highs. Easy to push into feedback. Will give last refining touches with owner this weekend..

Tried it with 6 different guitars and 4 speaker cabinets. All sounded very good.

The amp is leaving on monday morning to a recording session.

Schem attached. DELETED WRONG SCHEM - ATTACHED CORRECT SCHEM BELOW

Best Regards
R.