Help with distortion characteristics.

[walkman]

Hi all,

Hoping this will make sense with out a schematic or voltage and current measurements.

Sometimes describing the problem is half the battle.

From what I’ve read the distortion I’m hearing may be from a microphonic tube.
I know a way to test this is to tap gently on the tube and  it should not ping or introduce other noises.

What I’m hearing in the distortion tone of the amp is on the attack of the note there is a sort of bloom of harmonic distortion that fades into ‘normal’ distortion.

I can kind of hide it by playing in certain ways like vibrato on the note as the bloom kicks in.

It’s not excessive night and day and if it could be tuned somehow perhaps (more second harmonic?) then it could be great.

Wondering what I can do to work with this in general. Small cap on the anode of the stage where I think it’s occurring? Mess around with the bias or grid leak of the following stage? Does this sound like something else altogether.?

[thetragichero]

is this a tweed-type build without grid stoppers?

[walkman]

Hi TheTragicHero,

thanks for your reply.

No it’s not based on a tweed and there are grid stoppers on all stages 10k or greater.

Also the interstate coupling caps are in different places 0.01 or 0.0047.

I’m no thinking a small cap from grid to ground may be a way to test where this is occurring.

[tubenit]

I think you would get more help with posting a schematic of the amp.


Respectfully, Tubenit

[walkman]

Hi Tubenit,

Yes I guess that I’m looking for general pointers at this stage things that may apply or help identify issue.

[walkman]

I strapped a 220p cap from the grid to cathode of the on the stage I think may be  causing the issue.

While it did reduce some of the highs it did not solve the issue. I did notice something else though that either was revealed or introduced by the addition of tge cap.

When holding a single note the sound seams to beat as if you were tuning up strings with harmonics. It also sound a bit like it is going through a phaser in a long cycle.

Makes me think that there may be some phase shifts occurring in the high frequencies and that the distortion I am hearing might be the interplay of these modulating higher harmonics.

Could well be due to layout or grounding or even components choice.

Even with a schematic it may not be obvious what the cause is especially as this amp uses fairly non standard tubes.

If anyone has some general troubleshooting tips that could apply to any amp please let me know what may work for what I have described.

Again just looking for pointers, not a diagnosis.

Overall I’m 95% happy with the design and consider this build a rough prototype with the aim of the next build to concentrate on layout rather than design and component values.

Will definitely put up a schematic when I’m happy that who ever happens to come across it in this forum can build something that works well and is not fundamentally flawed

[sluckey]

You really can't expect any help unless you post a schematic and some hi-rez pics.

[Willabe]

Will definitely put up a schematic when I’m happy that who ever happens to come across it in this forum can build something that works well and is not fundamentally flawed

That has already happened many times.

There's over 85 views of this post.

[walkman]

I should have been clearer and I honestly think I’m not very good at phrasing’s questions on forums.

What I should have said is that I have never posted a schematic for anything I’ve built yet.

As I know l have trawled the net far and wide at times for schematics I want to post something that works well and is fit for purpose and that some one else can build.


I know there are very many fine builders on this and other forums that freely share their work and schematics and want to make sure I have done every I can to resolve any issues before posting.

Ok far enough though and I do understand if help is less likely with out a schematic.

I will keep cracking on with it and hopefully can find the issue. Will post again if I work it out.

[sluckey]

good luck

[Willabe]

......I want to post something that works well and is fit for purpose and that some one else can build.


....... and want to make sure I have done every I can to resolve any issues before posting.

Doesn't work that way if you want help to de-bug/fix a problem.

Your just talking in circles. You want help to solve a problem, but you wont post the schematic until the problems solved?   

What guys do is post the amps schematic in it's current state, then when they get it fixed they can post a final schematic with any/all corrections.

[acheld]

There is no reason not to post a schematic.  Even if you believe your circuit is unique, and you want to monetize the design in the future, that isn't how it works.

Being successful as a boutique amp builder is MUCH more about predictable tone, great customer service, good esthetics, marketing and prudent business practices than it is about having a unique circuit. 

[walkman]

There is no reason not to post a schematic.  Even if you believe your circuit is unique, and you want to monetize the design in the future, that isn't how it works.

Being successful as a boutique amp builder is MUCH more about predictable tone, great customer service, good esthetics, marketing and prudent business practices than it is about having a unique circuit. 

This is definitely a hobby build and not a masterpiece of any sort aesthetic or otherwise. No not looking to make money of this in anyway.

And I respect there are a many very many skilled and knowledgeable people on this forum and want to present what I’ve done well and clearly

[walkman]

......I want to post something that works well and is fit for purpose and that some one else can build.


....... and want to make sure I have done every I can to resolve any issues before posting.

Doesn't work that way if you want help to de-bug/fix a problem.

Your just talking in circles. You want help to solve a problem, but you wont post the schematic until the problems solved?   

What guys do is post the amps schematic in it's current state, then when they get it fixed they can post a final schematic with any/all corrections.

Yes I see why it makes no sense if you put it that way.

But back to basics.
If I had asked why doesn’t my amp make a sound would  you have asked “is it plugged in” or did you forget to turn it on or put the tubes in or connect the speaker or make sure the speaker was working? Or would you have asked for a schematic straight up.

I suppose the question I asked was like going to a doctor and saying I have this weird pain or condition that I think may be such and such.

And wanting to talk about that condition in general and things to look for that might indicate that.

 However doctors often will fairly quickly send you for a blood test an ultrasound X-ray or MRI and I have no issue with that if it seem reasonably necessary or something serious could be the issue and preventable If addressed quickly. So yes just an analogy maybe doesn’t even match this situation.

I think my post should have been tell me about when tube are microphonic or how can you tell when you have blocking distortion.

So wanting to talk generally then work out if that makes any sense with what I think I know and can hear or observe with this build

[shooter]

try this, read before writing;


Microsoft Word - Fundamentals.doc (valvewizard.co.uk)

[walkman]

Hi shooter I see I am approaching this the wrong way.

I have a couple of KOC ultimate tone books and Both of Merlins guitar preamp books.
 
So yes perhaps best to drop this topic and I will repost another topic with a schematic when i have updated it

[Willabe]

Yes I see why it makes no sense if you put it that way.

I didn't put it that way, you did. 

You keep trying to change the meaning of what you just wrote.

Pretzel logic, twisted in circles.

[walkman]

Well I did say first up I was looking for assistance without a providing a schematic.

I also realise I have not been clear with what I have asked.

All I really wanted to know was if the description of the distortion I was hearing sounded like a microphonic tube or not.

And if so how could I test that by applying fixes to test if that addressed the symptoms.

So if I post a schematic you can tell me if the tubes I am actually using are microphonic?

Yes you could possibly tell me that microphonic tubes are a common issue with say a 12at7 or ef86.

And some high gain configurations may accentuate this.

You wouldn’t  need a schematic to tell me that.

Either way it time to drop this thread as I feel I’m not getting anywhere with this and will repost at a different time with a schematic and hopefully more clear information about what I’m doing and what assistance I’m after. 


I am appreciative of all the replies and respect the advice to post the schematic if I would like assistance.

Kind Regards
Walkman

[sluckey]

Either way it time to drop this thread as I feel I’m not getting anywhere with this and will repost at a different time with a schematic and hopefully more clear information about what I’m doing and what assistance I’m after. 

I agree. I'll lock the thread.