Questions about Zener Diodes and JCM 800's

[endofall]

Hey guys! I have another question. I keep reading about the use of zener diodes for adding additional gain to amps. I think this would be a cool mod to make switchable kind of like a boost, or possibly make it a 3 way switch with no diodes, 12v, and 20v diodes. My question is there seems to be a lot of suggestion about where to place it (before eq, after eq etc). I was wondering how does this work, is there any suggestions regarding this, have any of you tried it, also could anyone give any information on how to perform this in a horizontal input 2204! Thanks

 

[wakjob]

Hey guys! I have another question. I keep reading about the use of zener diodes for adding additional gain to amps. I think this would be a cool mod to make switchable kind of like a boost, or possibly make it a 3 way switch with no diodes, 12v, and 20v diodes. My question is there seems to be a lot of suggestion about where to place it (before eq, after eq etc). I was wondering how does this work, is there any suggestions regarding this, have any of you tried it, also could anyone give any information on how to perform this in a horizontal input 2204! Thanks

Quite tough on that amp because the pots are PCB mounted.

The popular place to put them is between the CF and the tone stack, but also moving the Master Volume just before the tone stack also. To hard for a horizontal 2204.

Try this, take two zener's, 12-20v and solder them back to back, or anode to anode. The lines facing out/away from each other. Now, put them through holes 1 & 3 of the Master Volume pot and solder.

Two 20v are very gainy btw. But it'll give you an idea of what it sounds like.

 

[endofall]

Thanks so much! Yeah I just want to play with it and see how it makes the amps sound/feel.

 

[Tüßermensch]

Hello again,

If you hased done this to a jcm800 MV model you hased just made a peevey VTM model

Regard,

Heinrich

 

[Tüßermensch]

if you will place it before eq all coming before eq will be clipped, and will bring harmonics if such, maybe good maybe not so good. after you can filter more out of a composite clipping much like interstage shaping. Agian maybe good maybe not so good

-Heinrich

 

[Thiez]

The most common diode clipping thing in older marshalls is the jose master.
It's a pre EQ master volume with diode clipping. In this schematic it's made switchable.

You can also just add clipping resistors back to back on the signal chain.

On this site is a lot of fun clipping schematics. AMZ Saturation Controls and Diode Clipping
This is based on fx pedals but you can also put this in your amp with zeners.

Here's a bit of info from an other amp forum about the voltages:
The Jose Master Volume mod is the addition of a) a clipping circuit just after the cathode follower and b) the placement of a master volume before the tone stack in addition to the standard master volume post tone stack which is the normal configuration on a 2203 master volume amp. The clipping circuit is composed of a 10k resistor and a 0.22uF (to keep DC) off the pair of zener diodes (which face opposite direction for symmetrical clipping). The zeners can be 12V, 14V, 16V, 18V or 20V. The lower the zener value, the greater the compression, but there is also a significant volume drop in the overall volume (which is not a bad thing with a 100W amp) with low values. 20V zeners for instance result in a classic plexi sound (very loud), 16V (a little volume drop) a more 80s tone and 12V (significant drop in volume...compensate by opening up the master volume) is quite "modern" and smooth, in my experience.

Besides the voltage amount you can put in assymetric clipping. Try some variation with different values. On the negative curve aswel as on the positive curve of the signal.

 

[clutch71]

Hello again,

If you hased done this to a jcm800 MV model you hased just made a peevey VTM model

Regard,

Heinrich

The diodes you are refering to effect the compression dip switch. There are no other diodes in the signal path of the vtm.

 

[chadjwil]

OK, diodes do not add gain, they distort (clip actually). I realize that's what you meant, but I feel like it's important to know the difference.

Gain refers to the ratio of output/input of an amplifier device. Diodes, in the simplest sense, turn a sine wave into a semi-square wave...and actually results in a reduction of gain (the waveform is reduced in amplitude by the amount of clipping on both sides of the cycle) but much more distorted sound.

Increasing the gain of an amplifier until the output is saturated also accomlishes a very similar thing, but of course the sound is a bit different than diode distortion circuits.

Sorry to jump your post with technical stuff endofall...everyone knew what you meant...I may have some sort of disorder!

 

[Kunnz]

What type are the best or preferred as I would like to give this a go too, Germanium or silicone? and what about zeners,

More detail would be good as I'm into semiconductors these days and fed up with shitty valve amps.

 

[endofall]

Chadjwil thanks for the post! Yes I was talking about the distortion level present but it is always good to get a clear technical answer when talking about things like this, so thank you for the post! Also everyone else thank you very much, I still haven't tried this because I really do have the amp sounding very nice now and I am not sure if I really want to try it yet, it just seems like a cool idea, but I suppose I could always just use my SD-1 or TS-9!

 

[Tüßermensch]

The diodes you are refering to effect the compression dip switch. There are no other diodes in the signal path of the vtm.

completely aware. But please take another look at this plan and you will see they are just clipping diodes on a MV plan precisely as the poster hased suggested. Just a MV circuit plan with the clipping diodes like Jose

-Heinrich

 

[Tüßermensch]

The most common diode clipping thing in older marshalls is the jose master.
It's a pre EQ master volume with diode clipping. In this schematic it's made switchable.

You can also just add clipping resistors back to back on the signal chain.

On this site is a lot of fun clipping schematics. AMZ Saturation Controls and Diode Clipping
This is based on fx pedals but you can also put this in your amp with zeners.

Here's a bit of info from an other amp forum about the voltages:
The Jose Master Volume mod is the addition of a) a clipping circuit just after the cathode follower and b) the placement of a master volume before the tone stack in addition to the standard master volume post tone stack which is the normal configuration on a 2203 master volume amp. The clipping circuit is composed of a 10k resistor and a 0.22uF (to keep DC) off the pair of zener diodes (which face opposite direction for symmetrical clipping). The zeners can be 12V, 14V, 16V, 18V or 20V. The lower the zener value, the greater the compression, but there is also a significant volume drop in the overall volume (which is not a bad thing with a 100W amp) with low values. 20V zeners for instance result in a classic plexi sound (very loud), 16V (a little volume drop) a more 80s tone and 12V (significant drop in volume...compensate by opening up the master volume) is quite "modern" and smooth, in my experience.

Besides the voltage amount you can put in assymetric clipping. Try some variation with different values. On the negative curve aswel as on the positive curve of the signal.

The MV that becomes before the tonestack greatly alters the tonestack workings, as source z varies greatly this way

-Heinrich

 

[wakjob]

What type are the best or preferred as I would like to give this a go too, Germanium or silicone? and what about zeners,

More detail would be good as I'm into semiconductors these days and fed up with shitty valve amps.

Best I've personally tried was a 1N968B zener diode.

Another great one is a certain 3mm green LED that I can't find anymore.

And don't quote me on this but, I've played a 20 watt amp that had some sort of Friedman type mod done to it. And I saw what I think were UF5408 rectifier diodes for added clipping. Sounded nuts.

 

[Tüßermensch]

Best I've personally tried was a 1N968B zener diode.

Another great one is a certain 3mm green LED that I can't find anymore.

And don't quote me on this but, I've played a 20 watt amp that had some sort of Friedman type mod done to it. And I saw what I think were UF5408 rectifier diodes for added clipping. Sounded nuts.

Hello again,

They were cheap npn transistor connected for internal 4v Avalanche characteristic. Friedman usually has this one in a heatshrink tube, with glue. And I hased mention on the other thread the other ones are usually cheap pnp Conected to do the same. It is just solid state clipping and not much so different from a mxr dist+ by mechanism

-Heinrich

 

[diesect20022000]

not to seem counter productive but one other idea. you could sell or trade it for a 2205 (which already is pretty much this setup) and end up with some extra cash.

may not be your route or taste etc but i thought i'd throw that one out there just in case it IS a good idea and you just hadn't thought of it

either way i hope you get what you're seeking my friend!

 

[endofall]

not to seem counter productive but one other idea. you could sell or trade it for a 2205 (which already is pretty much this setup) and end up with some extra cash.

may not be your route or taste etc but i thought i'd throw that one out there just in case it IS a good idea and you just hadn't thought of it

either way i hope you get what you're seeking my friend!

I love my 2204, and having it really sounding great. Out of my Mesa Rectoverb and Splawn Nitro it is currently my favorite amp. My problem is that I just always like messing with things to see what it does! I had a 2205 in the past and just couldn't really get along with it for some reason.