Great Clean Sound But Poor Distortion With OD/Distortion Pedals

[g1]

No coupling cap shown either.

[Helmholtz]

The DC coupling of the 6V6 to the 12AX7 driver plate must be wrong. It would mean HUGE power dissipation of the 470R cathode resistor.

[HR_Puffinblunts]

No coupling cap shown either.

Sorry, it's been about 5 years since I drew a schematic and I mistakenly left off the ground reference 220k grid leak resistor and .02 coupling cap between 2nd gain stage and output.

Anyone listen to the Youtube clip of my amp I posted in reply #13 ?

[olddawg]

Look at an Epiphone Valve Jr schematic...

[Tony Bones]

Listening to the Youtube vid, that doesn't sound like blocking distortion. The 220k resistor at the grid of V2 and the 10K at the grid of V3 means you would need to overdrive the thing severely to get any blocking. In the vid it doesn't sound like the signal level is increasing nearly enough to cause blocking. In truth, I don't think the amp itself is distorting much at all. Most of the OD comes from the pedal (my guess from listening to the vid.)

The fact is some amps just don't like pedals as well as other. I wish I understood why. If anyone here has any clues, please share them.

In the mean time, you might try removing the 0.01 cap across the 220k resistor to see what happens.

[HR_Puffinblunts]

Listening to the Youtube vid, that doesn't sound like blocking distortion. The 220k resistor at the grid of V2 and the 10K at the grid of V3 means you would need to overdrive the thing severely to get any blocking. In the vid it doesn't sound like the signal level is increasing nearly enough to cause blocking. In truth, I don't think the amp itself is distorting much at all. Most of the OD comes from the pedal (my guess from listening to the vid.)

The fact is some amps just don't like pedals as well as other. I wish I understood why. If anyone here has any clues, please share them.

When I initially built this amp I tried several V2 grid-stopper resistor values between 100K-1M and other than dulling tone they didn't do much to smooth distortion. I have a Blackstar ID:Core 10 (solid state) that at first thought one would think doesn't take Kokko OD and Kokko distortion pedals well but, it sounds great with them. Yet, those two pedals sound like ass with this 5w tube amp. I'd like to hear a tube distortion pedal with this amp and see if it makes a difference.

In the mean time, you might try removing the 0.01 cap across the 220k resistor to see what happens.

I did that about an hour before I made that youtube video and didn't effect the distortion + or -

I found the Texas Heat to be honky/tinny sounding when I first installed it years ago so I put it on a transformer overnight to break it in and it still didn't sound good to my ears. I then removed the speaker and used acetone to thin the doping all over the cone and that did "age" the cone and open the sound some.

[Chuck H]

I agree with Tony. It doesn't sound like blocking or too much input gain. In fact, other than a couple of sharp crackles that I took to be the mic or the recording input clipping I really don't hear what's wrong.?. Your description of "bad", "terrible", "too hi fi" and "unnatural speaker breakup" isn't coming through for me in the clip.

I really don't like to default to the ol' "Some amps don't like pedals." type of answer. I do know that players with multiple amps and pedals always have their favorite pairings. Maybe try a different pedal for that amp.

[HR_Puffinblunts]

Thanks everyone for the replies. Unfortunately, the video clip may not pickup the same distortion I am hearing and I'm not sure if my description of the issue is accurate enough. The only other way I can state is that when I was a teenager (1980's) my brother and I used his stereo input to plug guitars into once in a while. That terrible distorted sound the guitars made through that stereo is similar (but not as bad) as what my amp sounds like with pedals. The natural driven distortion (no pedals) is decent but not as good as I hoped and not as good as these two other builds:

AX84 P1 (another): https://youtu.be/fSvxxU0SHn8

Daisycutter: https://youtu.be/GraNcHM5EiQ

Yes, I build shitty looking amps..LOL

[Chuck H]

Well my own experience doing the same thing (plugging into hi fi SS stereo gear as a teenager ) is that you get a clipped waveform that's more symmetrical and flatter across the peaks, but with slightly rounded corners. Which, BTW, perfectly describes diode clipping. As I recall it did sound cold and sterile. If you had a scope you could actually look at the wave form and see this (or not, but you'd see something).

Maybe try just the opposite of what I mentioned before and hit the amps input harder. Turn down the distortion and turn up the drive on the pedal. If that doesn't do something to get a more wonky and peaky waveform then your amp is just way too well behaved and clipping too gracefully. Something the audiophile guys go all gooey for. Maybe due to the relatively low plate voltage. Maybe fussing with the bias could change things in this case.

Another thought is that if you're inserting the NFB at the cathode of V1B then you have a sort of failed circuit there. Feedback would only be applied to the bass and low mids. And then only when the 1uf bypass cap is selected. With the 22uf bypass cap selected there is no feedback at all. You've probably noticed that the feedback switch doesn't do anything when you have the 22uf bypass cap selected there . Anyway... So selecting the 1uf cap with the feedback engaged is sort of like having a wide band presence control stuck on 10. And it's that or no feedback at all. Those are the only two options your circuit gives you. What you could try would be to hang a 47 ohm tail on the "B" cathode (between the existing circuit and ground). Then reduce your feedback resistor to 1k. Insert the feedback at the top of the 47 ohm resistor. This would make it so all your switches work together and you're actually applying feedback to all frequencies when it's selected for use.

[HR_Puffinblunts]

Well my own experience doing the same thing (plugging into hi fi SS stereo gear as a teenager ) is that you get a clipped waveform that's more symmetrical and flatter across the peaks, but with slightly rounded corners. Which, BTW, perfectly describes diode clipping. As I recall it did sound cold and sterile. If you had a scope you could actually look at the wave form and see this (or not, but you'd see something).

Maybe try just the opposite of what I mentioned before and hit the amps input harder. Turn down the distortion and turn up the drive on the pedal. If that doesn't do something to get a more wonky and peaky waveform then your amp is just way too well behaved and clipping too gracefully. Something the audiophile guys go all gooey for. Maybe due to the relatively low plate voltage. Maybe fussing with the bias could change things in this case.

Another thought is that if you're inserting the NFB at the cathode of V1B then you have a sort of failed circuit there. Feedback would only be applied to the bass and low mids. And then only when the 1uf bypass cap is selected. With the 22uf bypass cap selected there is no feedback at all. You've probably noticed that the feedback switch doesn't do anything when you have the 22uf bypass cap selected there . Anyway... So selecting the 1uf cap with the feedback engaged is sort of like having a wide band presence control stuck on 10. And it's that or no feedback at all. Those are the only two options your circuit gives you. What you could try would be to hang a 47 ohm tail on the "B" cathode (between the existing circuit and ground). Then reduce your feedback resistor to 1k. Insert the feedback at the top of the 47 ohm resistor. This would make it so all your switches work together and you're actually applying feedback to all frequencies when it's selected for use.

Thanks Chuck. I will add the changes you suggested and I don't have a scope. I live in a condo (as of 2014) I don't get a chance to crank the amp as much as would like to and hence no video of this amp cranked. I've tried the OD and distortion pedals at all types of settings without satisfaction. I may try re-biasing the output tube and I'm considering paralleling a 9-pin output socket to either use a 6V6 or EL84..which may sound better at the 260 plate voltage? I did that with the daisycutter by paralleling two additional 8-pin sockets and it can accommodate an EL34, 6V6, 6L6. Of course, without being in optimal operating range (max 340 plate voltage).

As a side piece I once built a quarter-watt amp that employed a 6LY8 (pentode-triode) http://www.nj7p.org/Tubes/SQL/Tube_query.php?Type=6LY8 as a preamp and a 6LY8 (triode-pentode) as the output. It had crazy gain but I couldn't keep it from squealing (microphonics) without dulling tone too much using high value grid stoppers and a pF cap to ground on the output cathode pin (IRRC).

[Chuck H]

As a side piece I once built a quarter-watt amp that employed a 6LY8 (pentode-triode) as a preamp and a 6LY8 (triode-pentode) as the output. It had crazy gain but I couldn't keep it from squealing (microphonics) without dulling tone too much using high value grid stoppers and a pF cap to ground on the output cathode pin (IRRC).

That can be a real problem using NOS cheapies. The tubes no one else used so they can be had for peanuts. Very often they tend toward microphony in guitar amps because they were never meant to be driven and blasted like that. I've been often tempted to try the same sort of thing, but resisted the urge. The craziest thing I ever considered was a 30W Champ type single ended amp using something like an 805 tube. I ultimately decided that I like push/pull tone better for higher power and abandoned the idea. It sure would look cool though. I was going to have the power tube sticking out the top of the cabinet with a cage around it.

[Jazz P Bass]

"The craziest thing I ever considered was a 30W Champ type single ended amp using something like an 805 tube"

Yeah.

800 Vdc supply and drive it with a 6L6.

45 watts easy!

[Justin Thomas]

I do have a pair of NOS 807s back home... But I just gutted & restarted my last build so no new projects till I'm satisfied there! & that blasted too-quiet 6C10-filled Jet!

Justin

[HR_Puffinblunts]

The craziest thing I ever considered was a 30W Champ type single ended amp using something like an 805 tube. I ultimately decided that I like push/pull tone better for higher power and abandoned the idea. It sure would look cool though. I was going to have the power tube sticking out the top of the cabinet with a cage around it.

https://www.youtube.com/watch?v=JoqDYcCDOTg

[Chuck H]

Oh, that's about a dozen deep on the back burner now. A smart, dead guy once said that " Life is what happens to you while you're making other plans."

And the reason I said 30W (instead of 45W) is:

1) 30W is plenty. I'd still like to hear it cranked up after all. And,..

B) 800V B+ is more expensive than typical, lower voltage off the shelf stuff.

I did outfit a Champ with an EL34 not long ago. It was one of those silver face models that use the same PT as the Princeton Reverb. And it's a good thing because the thing sit's cooking at idle around 19W.

A 30W (or 45W) single ended amp could be used as a space heater