john12ax7

Re: Help with adding diode distortion to a tube preamp
« Reply #20 on: May 09, 2020, 04:48:29 PM »
The diode schematic is ok, it will work and distort.  But you will need to build and adjust according to taste.  Most likely you will need to roll off some high end so it's not really fizzy sounding. Notice how the jubilee has a cap across the diodes.


sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #21 on: May 09, 2020, 05:08:29 PM »
The diode schematic is ok, it will work and distort.  But you will need to build and adjust according to taste.  Most likely you will need to roll off some high end so it's not really fizzy sounding. Notice how the jubilee has a cap across the diodes.

Thanks for your reply John :)
I'll look into what you say, do some testing and report back.

I find both options (opamp/diodes) very interesting.

Thanks Volker for the circuit suggestion. This afternoon I've been digging into the original Marshall Blues Breaker since it's the starting point for most overdrive pedals. I'll take a look at ZVex SHO and Jack Orman's Mini Boost and try to sketch something up. I'll report back soon.

Thanks again to all for your time and help.
Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #22 on: May 10, 2020, 02:28:39 PM »
Notice how the jubilee has a cap across the diodes.

Would this be more like it?
I'm not sure the switching is correct. The Jubilee is a bit complicated with all the switching options :)

Why sleep when you can mix?
M.P.Stavrou

john12ax7

Re: Help with adding diode distortion to a tube preamp
« Reply #23 on: May 11, 2020, 01:24:57 AM »
Yes that's fine.

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #24 on: May 11, 2020, 05:42:54 AM »
Excellent. Thanks John :)

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #25 on: May 11, 2020, 02:05:25 PM »
Sorry if this is a dumb question in but just to be sure, the 47k resistor is there to avoid frying the LEDs right?

If so, shouldn't it be placed AFTER the switch, between the LEDs and the switch?


Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

john12ax7

Re: Help with adding diode distortion to a tube preamp
« Reply #26 on: May 12, 2020, 02:45:43 AM »
The first way is better.  You could put it after the switch too,   but it would need to be between pin 3/6 of the switch and pin 2 of D4.

It would be a good idea to put a resistor in the thru part as well,  pin 4 to pin 4 of the switch. As you might need to compensate for the level drop when you switch the diodes in.

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #27 on: May 12, 2020, 07:22:22 AM »
Excellent John! Hopefully I'll tweak it tomorrow 😉

Thanks!
Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #28 on: May 13, 2020, 09:59:18 AM »
Ok, so I built the diodes option with the first switching solution and the result is simply GREAT!!! It even works in front of the amp (not only the loop return).
The guitar responds nicely with dynamics and the palette goes from Creamy Clean to really angry metal :)
I will try the opamp option further down the road. I want to try implementing a balanced DI Out and a Speaker Simulator to be able to record/gig with it without carrying an amp.
I've found a couple of speaker sim circuits that look good.


Any suggestion for the balanced Out?


Thanks again a lot for all the time and help :)
Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #29 on: May 14, 2020, 09:51:57 AM »
Would this work as a Balanced Out for the pedal? Could I use 9v for the TLs?

Thanks
Sono
Why sleep when you can mix?
M.P.Stavrou


mhelin

Re: Help with adding diode distortion to a tube preamp
« Reply #30 on: May 19, 2020, 11:39:04 AM »
High gain tube amps typically have two conventionally biased gain stages followed by a cold biased follower stage made to be overdriven. That stage would have something like a 100k anode resistor and 39k cathode resistor like on EVH 5150 mk3 but sometimes also the anode resistor has more ohms and/or cathdode less, and then there might be two other gain stages followed by yet another  "clipper" stage. It varies.

There was though the JCM600, propably one of the worst sounding Marshals built ever, which used diode clippers:
https://www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-JCM600-60W-Revch-Schematic.pdf
« Last Edit: May 19, 2020, 11:44:26 AM by mhelin »

sonolink

Re: Help with adding diode distortion to a tube preamp
« Reply #31 on: May 21, 2020, 08:49:28 PM »
Thanks for your input mhelin. The thing here is that the JTM45 PREAMP circuit I built sounds great in front of a clean amp (or even not so clean), as a preamp/overdrive/distortion/call it what you like/ pedal. The idea of this project is not to substitute a real tube amp but to create something that allows a guitar player to use it in front of his amp, in its fx loop return (so bypassing his amp's preamp), or even to avoid using/carrying an amp at all and being able to plug into a soundcard/mixer through something that although not totally, does essentially behave like a tube amp (from the player's POV). I hope this makes sense :)

So far, the unit sounds great in front of an amp and in its fx loop return, but in this position, if the player wants some more gain/distortion/overdrive/you name it/ the nature of the circuit doesn't provide that in that position. So I thought of using diodes distortion (like using a pedal in front of an amp) to provide that, to add to it, basically. Diodes work great for that using the Marshall Jubilee topology. Still I have to test the opamp option suggested by Volker, which I will soon.

Maybe the JCM600 really did sound horrible (I have never tried one) but the diode config of the Jubilee is excellent because it does not "alien" ("denature", sorry for my language barrier) the essence of organic tube dynamic response to playing.

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou


 

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