45-style build overdrive distortion character

[bgkyt1]

Hi all.

I just did a Mojotone 45 build, but I only did one input (bright) and tied both triodes of V1.
The amp also has a pre-phase MV (1MA pot, in the usual spot (off the treble pot...)
Negative feedback is on the 16r tap.

The amp's overdrive/distortion characteristic seems hard and choked off to me.
It doesn't have a nice sandy distortion character and nicer transition from clean to dirt like 45 clips I'm used to hearing.
Even my plexi build has a nicer sandier overdrive and better transition from clean to dirt than this (although no MV).

What would you suggest?
Not using both triodes of V1?
Trying the 8r tap for negative feedback? (like a plexi)
??
Thanks for any info you may have.

[Cartman]

It’s personal preference, but blending the bright and normal channels is best for me. One channel is too bright and the other too dark, but blended they work great together.

[bgkyt1]

It’s personal preference, but blending the bright and normal channels is best for me. One channel is too bright and the other too dark, but blended they work great together.

Thanks.
More info: I don't have a bright cap on the volume pot. The mixer resistor + cap is stock.
It's not a frequency/tone issue. Even on the plexi, I just use the bright channel.
It's about how the amp distorts and/or the character of its distortion.

[WiderGates]

Hi, have you halved the value of the anode and kathode resistors and doubled the value of the kathode capacitor at the paralleled V1?

[bgkyt1]

Hi, have you halved the value of the anode and kathode resistors and doubled the value of the kathode capacitor at the paralleled V1?

No, I left them stock.
plate resistor is 100k.
cathode is 820r and 250uf

I did check other amps that tie in the extra cathode
and they didn't have halved values for their circuits (albeit not 45 style circuits).

[pdf64]

…
The amp's overdrive/distortion characteristic seems hard and choked off to me...

As you’ve added a master volume, you need to clarify whether you’re referring to preamp or power amp overdrive.

[Reeltarded]

Peaker over the mixer before stage 2?

I hate shared cathode first stages. You do need a bright cap. You are basically playing a Bass circuit with less highend. 150-220p minimum. If you are running the volume wide open you are missing the goodness.

Seems like you have 270k mixer setup. Guessing. Bypass is 250p?

Way one: Reduce cathode bypass to 1u5-5u range and add a 220p bright cap over preamp volume.

Way two: Are you insane!!? Split the cathode and use common values. Use the later mixer setup. Add at least 150p over bright volume.

Way three: Turn one triode of v1 into a pre-drive stage with a LOT of face but very little gain.

Absolutely you will notice the difference moving the (what I am imagining to be) 27k to the 4R pin on the selector. 27k at 16R is turning your dull bass amp into a hifi amp under a pile of blankets and using flat strings.

[bgkyt1]

…
The amp's overdrive/distortion characteristic seems hard and choked off to me...

As you’ve added a master volume, you need to clarify whether you’re referring to preamp or power amp overdrive.

Hi, I was referring to preamp drive, but just overall the "distortion" sound I get from the amp.
I probably wasn't hit the power section hard enough to get any el34 mojo.

I also tried with -12db attenuation and tried turning up the master as much as I could in a neighborhood...

[bgkyt1]

Peaker over the mixer before stage 2?

I hate shared cathode first stages. You do need a bright cap. You are basically playing a Bass circuit with less highend. 150-220p minimum. If you are running the volume wide open you are missing the goodness.

Seems like you have 270k mixer setup. Guessing. Bypass is 250p?

Way one: Reduce cathode bypass to 1u5-5u range and add a 220p bright cap over preamp volume.

Way two: Are you insane!!? Split the cathode and use common values. Use the later mixer setup. Add at least 150p over bright volume.

Way three: Turn one triode of v1 into a pre-drive stage with a LOT of face but very little gain.

Absolutely you will notice the difference moving the (what I am imagining to be) 27k to the 4R pin on the selector. 27k at 16R is turning your dull bass amp into a hifi amp under a pile of blankets and using flat strings.

The mixer resistor is 270k and the cap is 250p, although I now see that Mojo's MasterVol version shows a 500p there.
Thanks for the info and tips.

[Reeltarded]

I have done everything that can be done very specifically to this circuit 10000 times over.

If you can accurately describe your goal I can probably tell you exactly how to get there. I am a Marshall whisperer.

[xtian]

"not smooth transition into distortion" can be a lead dress issue. Perhaps you should post some photos for us.

[bgkyt1]

I moved the NFB to the 8ohm, added the bright cap on the vol, and made V1 just the one triode.
It's possible that I just can't crank it loud enough to hear what it will do, but it probably all sounds normal.

Thanks for being willing to help, but I think I'm going to having a garage sale.

[Reeltarded]

No! Wait!

You are the first person I am going to suggest ppimv to in 10 years!

The NFB dies at lower settings but what you really want is all there.

[Stevem]

One good thing about having two amps with effects loops in a situation like this is that you audition the preamp section of a amp that's offensive into the output section of a amp you like.