Blues Junior Conversion Build: "Smooth" Out Distortion?

[jonyoungyi]

Hey all, just finished a Blues Junior Conversion build and it sounds great clean, but when I push the preamp, it just doesn't sound good to my ear. A bit harsh and too much "hard rock" sound? Not sure if this makes sense, but anything I can do to "smooth" out the distortion a bit?

I haven't made any mods to the schematic and judging by the sound demo (humbucker sound demo), that's the way this amp is supposed to sound, but was curious if there was anything I can change or modify to get a more pleasing overdrive sound.

Any and all comments are appreciated!

[tubenit]

This is what I would try to smooth the amp out.  I would lower the value of the cathode caps and then add smoothing caps.

With respect, Tubenit

[jonyoungyi]

This is what I would try to smooth the amp out.  I would lower the value of the cathode caps and then add smoothing caps.

With respect, Tubenit

Thanks for the suggestion Tubenit! I'll give it a shot!

[tubenit]

FWIW,  I would definitely add the "enhance cap" (smoothing cap) on the LTPI plate resistor and lower the cathode cap values.  That is a standard "must have" mod on all the amps I build with LTPI.   Next I would try a smoothing cap from plate to cathode just prior to the LTPI.  Then if more is needed try a smoothing cap on the 2nd gain stage plate to cathode.

In other words,  I'd try smoothing caps further down the signal chain and work backwards toward the preamp on this amp.  You can add them one at a time using insulated alligator clipped wiring being careful with it.  Be sure to drain the voltages prior to clipping and unclipping the smoothing caps.

With respect, Tubenit

[jonyoungyi]

FWIW,  I would definitely add the "enhance cap" (smoothing cap) on the LTPI plate resistor and lower the cathode cap values.  That is a standard "must have" mod on all the amps I build with LTPI.   Next I would try a smoothing cap from plate to cathode just prior to the LTPI.  Then if more is needed try a smoothing cap on the 2nd gain stage plate to cathode.

In other words,  I'd try smoothing caps further down the signal chain and work backwards toward the preamp on this amp.  You can add them one at a time using insulated alligator clipped wiring being careful with it.  Be sure to drain the voltages prior to clipping and unclipping the smoothing caps.

With respect, Tubenit

Hey Tubenit,

Just found your post about the "enhance caps"! (http://el34world.com/Forum/index.php?topic=12723.0;nowap)

I'll probably do all 5 revisions at the same time because, to my ear, it's THAT bad haha

If you could take a look at the attached, revised, schematic with your mods, that would be great!

[Willabe]

No, don't do them all at 1 time, do like Tubenit suggested in reply #3.

   

[jonyoungyi]

No, don't do them all at 1 time, do like Tubenit suggested in reply #3.

 

Yes, sir! Going to go to my local electronics store today and solder tonight. I'll post the results, thanks!

[MakerDP]

Going to go to my local electronics store today...

Where do you live to be lucky enough to have one of those? I thought the Internet pretty much killed-off most of them!

Closest one to me recently closed-up shop and it was 90 miles away...

[pompeiisneaks]

I have one really close, here in the PNW, near Seattle, Vetco Electronics.  They probably sell online as much as they do locally, but audio level stuff can be in weird supply.  Some of their stuff looks like NOS they found anywhere they could get it.  Old resistors, caps, etc.  Just very few high voltage electrolytics in ranges I'm used to (8uF, 10, 20, 47, etc).

Other than that, any 1/4,1/2,1,2 watt resistor I could want, and a lot of selection in higher wattage ones, as well.  Project boxes, etc.  Great selection of 'some' things ;)

Basically if I want specific, good stuff for tube guitar building,  I get exact stuff from Doug, or if he doesn't have it, maybe Mouser/digikey.  Otherwise I try to support the local guys :)

~Phil

[jonyoungyi]

Going to go to my local electronics store today...

Where do you live to be lucky enough to have one of those? I thought the Internet pretty much killed-off most of them!

Closest one to me recently closed-up shop and it was 90 miles away...

Man, I hear ya! Radioshack used to be the go-to, but only in dire circumstances haha Torrance, CA! Torrance Electronics. I've seen a lot of NOS parts here and a lot of capacitor cans. I think it's been here a while and hope it doesn't close down or anything. It's pretty busy whenever I get there, so.... *crossing fingers!*

[MakerDP]

When I go through San Jose on rare occasions I will stop by a pretty big electronics surplus store there but now my only choice is online.

[jonyoungyi]

FWIW,  I would definitely add the "enhance cap" (smoothing cap) on the LTPI plate resistor and lower the cathode cap values.  That is a standard "must have" mod on all the amps I build with LTPI.   Next I would try a smoothing cap from plate to cathode just prior to the LTPI.  Then if more is needed try a smoothing cap on the 2nd gain stage plate to cathode.

In other words,  I'd try smoothing caps further down the signal chain and work backwards toward the preamp on this amp.  You can add them one at a time using insulated alligator clipped wiring being careful with it.  Be sure to drain the voltages prior to clipping and unclipping the smoothing caps.

With respect, Tubenit

Just finished modding! I did each mod one by one from the phase to the 1st preamp tube. I didn't notice too much change with the 220pf or the 390pfs, but as soon as I lowered the 47uf to 4.7uf I noticed an immediate change.

Now the amp sounds a lot "smoother"! It isn't the best, but man, is it a lot better!

Thanks, Tubenit!

[tubenit]

You can replace the .02 coupling caps between the LTPI and EL84's with .01.   And replace the 1.5k grid resistors with 22k (or anything between 10k to 68k).

I think those will also help with the smoothing of this amp.

With respect,  Tubenit

[jonyoungyi]

You can replace the .02 coupling caps between the LTPI and EL84's with .01.   And replace the 1.5k grid resistors with 22k (or anything between 10k to 68k).

I think those will also help with the smoothing of this amp.

With respect,  Tubenit

Tried this last night and seemed to add more of that unwanted "hair" to the amp. I should have played it before the mod though... sorry :( I didn't use 22k resistors, instead went for 33k because that's what I had on hand. I ALSO DIDN'T RE-BIAS... so that might be it!

BUT! Doing this mod led me to read more about the grid resistor from: http://www.aikenamps.com/index.php/grid-resistors-why-are-they-used

What a great resource!

So, I'm curious if increasing the preamp's two grid resistors will help and if that will allow the preamp tubes to breakup later. (My preamp breaks up with the level barely at 9 o'clock!)

OR

Does that mean, since I'm increasing resistance, I'm decreasing current, so my tube amp will break up earlier than expect?

Anyone's thoughts or input is appreciated, greatly!

[jonyoungyi]

Suppose I should try some of these mods and play it by ear:

http://www.premierguitar.com/articles/8_Guitar-Amp_Mods_for_Newbies?page=2

[MakerDP]

Screen grid resistors, when they get large, like in the 100,000's range, will bleed off highs as they interact with the capacitance of the tube. It's another way to get rid of some "hair." The tried-and-true 10k to 60k value doesn't really affect the frequency response at all which is why they are the typical values people use. Try a 220k and a 330k grid stopper and see what you think. It may even things out too. Remember they need to be right at the tube socket for them to do their RF filtering job. Try it at V2a first (the final gain stage.)

By the way, do you have this?

https://smile.amazon.com/Designing-Tube-Preamps-Guitar-Bass/dp/0956154522/ref=sr_1_3?s=books&ie=UTF8&qid=1472592695&sr=1-3&keywords=merlin+blencowe

Required reading for those of us involved in this hobby, IMHO.

[jonyoungyi]

Screen grid resistors, when they get large, like in the 100,000's range, will bleed off highs as they interact with the capacitance of the tube. It's another way to get rid of some "hair." The tried-and-true 10k to 60k value doesn't really affect the frequency response at all which is why they are the typical values people use. Try a 220k and a 330k grid stopper and see what you think. It may even things out too. Remember they need to be right at the tube socket for them to do their RF filtering job. Try it at V2a first (the final gain stage.)

By the way, do you have this?

https://smile.amazon.com/Designing-Tube-Preamps-Guitar-Bass/dp/0956154522/ref=sr_1_3?s=books&ie=UTF8&qid=1472592695&sr=1-3&keywords=merlin+blencowe

Required reading for those of us involved in this hobby, IMHO.

Ah, you're talking about that MILLER CAPACITANCE and how a resistor will affect it's capacitance, right? Yes, yes haha

I'll increase to 220k or so and see if that does the trick.

I don't have that book! I'll buy it soon, as I plan to make a few other amps because I am addicted :D Thanks!

[Tone Junkie]

Sadly the addiction only gets worse. I have 3 amp stands. Somethings always in them. LOL
Bill

[jonyoungyi]

Sadly the addiction only gets worse. I have 3 amp stands. Somethings always in them. LOL
Bill

hahaha I'm at 2 amps and plan on a princeton reverb or AB763! I'll join you soon!

[jonyoungyi]

So just replaced the grid resistors for my two el84 tubes from 33k to 220k and THAT really did the trick, it really helped smooth out the overdrive sound! Although, there is a lot more bass, so I'll either lower the values or switch back to the .022 coupling caps.

I'm currently working on integrating a "Box of Hall" reverb circuit built into the effects loop that can be switched with a true bypass DPDT toggle, but that's giving me some hum.

I'm so close! Thanks so much for everyone that helped and all other comments for their humor!

[tubenit]

Although, there is a lot more bass, so I'll either lower the values or switch back to the .022 coupling caps.

Not sure what you are saying here?   IF the coupling caps have been lowered from .022 to .01, that will lower the bass response.  IF you increase caps from .01 to .022, that will increase the bass.

Increasing the grid resistors from 33k to 220k probably eliminated some higher frequencies?  So, that could give the impression of increasing bass even though in reality it may just be the treble was decreased?

With respect, Tubenit

[jonyoungyi]

Although, there is a lot more bass, so I'll either lower the values or switch back to the .022 coupling caps.

Not sure what you are saying here?   IF the coupling caps have been lowered from .022 to .01, that will lower the bass response.  IF you increase caps from .01 to .022, that will increase the bass.

Increasing the grid resistors from 33k to 220k probably eliminated some higher frequencies?  So, that could give the impression of increasing bass even though in reality it may just be the treble was decreased?

With respect, Tubenit

Hey Tubenit!

I must've misread and reversed what changing the coupling capacitors do. The "bass response" from 33k to 220k you suggested sounds more likely. I'll be sure to mess with the grid resistor values instead! Thanks for the correction!

I'll post some pics and a sound demo soon, hopefully!