Add diode clipping?

[Lonzo]

This might sound far fetched, but could it be possible to add diode cliping to an amp? I know what you're saying....WHY? Well, it's an experiment to see if I can smooth out the dirty channel of an amp on the bench. The results are probably going to be horrible, but I'd like to hear the results pending it could be done.

Thanks for reading.

Lonzo

[Arthur B.]

You can certainly add diode clipping, but I highly doubt it would smooth out the sound. What is the amp in question?

[Enzo]

I can't think of a good example of clipping smoothing anything out.

All you need do is parallel a couple diodes - one facing each way - and wire it from signal path to ground. Or some equivalent. But watch the signal levels. Since the typical diode drop is about a half volt, anything over a half volt of signal would be lopped off. SO if you add this at a spot in the circuit where the signal is only a volt or so, voila. If you wire it in where the signal level is oh 30 volts, you will lose most of your level.

You could also run a couple diodes in series and them parallel them back to back. That would net you twice the voltage drop. SOme amps use LEDs. They have a higher voltage drop than vanilla diodes. Depending upon color it varies.

Answer Arthur's question.

[Lonzo]

The amp in question....

It's a Bedrock 600 series. 4 EL84s, 3 12AX7, ch. switcher. It has plenty of gain but the breakup is none too smooth. I've tried 12AT7s, 12AU7s, and numerous brands of 12AX7s. It's a really good sounding amp, I'd just like to get it to sound a bit smoother...maybe fluid would be a better adjective.

Thanks for your time & advice,
lonzo

[Ray Ivers]

Lonzo,

Do you have a schematic, or know of one on the Web?

In the "AB2 .5hr..." thread BobW mentioned having success using the 'Paul Ruby Zener mod' on preamp stages, and I'll be trying this out on a Marshall 2000 either today or tomorrow. Bob ended up using a 6.3V Zener (along with a conventional diode) from a 12AX7 grid to ground, which is what I'll be starting out with as well. This should sound much more 'tube-y' than back-to-back clipping diodes.

Ray

[Lonzo]

Schemo below...

http://bedrock27.tripod.com/sitebuil...aschematic.jpg

Ray - HTH, it's kind of grainy but hopefully you'll get what you need. I have a hard copy if you need clarification on a value or ???

Thanks,
lonzo

[Ray Ivers]

Lonzo,

Thanks for that print... I see what you mean about the values... Cool reverb driver!

Wow... early reverb, series LDR's, paralleled gain controls; pretty much how I would not design a medium/high-gain preamp (my $.02, YMMV, etc.). You could try removing C17 for starters, and adding small-value caps (maybe 220pF to begin with) across all plate resistors and perhaps the cathode follower's Rk; unfortunately, this will affect your clean sound's treble response as well. Would you describe your problem as "fuzzy distortion"?

Ray

[Lonzo]

Fuzzy? Not Really...

The distortion is not really fuzzy, it's almost farty, uneven. It's not a saturated, smooth breakup. I'm sure I'm not doing the description justice - let's try this:
My idea of smooth distortion would be a straight line, horizontally. My amp's disto sounds like it has a lotof little peaks. Wow...that's probably a horrible description...

What about increasing the gain? Would that be a step closer to my goal?

Thanks so much for your time and knowledge.

lonzo

[Ray Ivers]

Lonzo,

OK, sounds similar to the situation I have with the Marshall's channel B...

I think we're both candidates for the 'Zener mod'. In this circuit, I'd think the best placement would be directly at V1b's grid; a 1N4003 to 1N4007 or 1N914 diode (a zillion different types would work, but these are the most commonly found in guitar-amp-workshop parts bins IME) with cathode to grid, in series with a 500mW or 1W 6.3V Zener, cathode to ground. The Zener value can be adjusted to taste.

Hopefully this will sidestep the whole adjusting-coupling/bypass-caps issue, which is just as well since I can barely read any of them.

Ray

[Lonzo]

Thank You So Much!

Ray
Thanks for your assistance. I didn't know I'd spark such a response. Actually, I was expecting some flames to come shooting back at me...add diode clipping? are you crazy?

If I read correctly, I'll place the first two diodes (1N4003 to 1N4007) in series with each other and then follow-up with the Zener (series with the first two) to ground? The 1N4003 cathode will be connected to the grid of V1b.

Thanks again for your assistance.

Lonzo

[Ray Ivers]

Lonzo,

Oops, sorry - a picture's worth a thousand words:



Just replace "-ve grid bias" with ground (i.e., leave your present grid resistor in place).

Ray

[Lonzo]

Pic link not working

Ray

I can't view the pic.

Thanks,
'zo

[Ray Ivers]

Lonzo,

Here's the link:

http://music-electronics-forum.com/a...1&d=1156955633

The thumbnail is also available back in one of my posts in the "AB2: $5..." thread.

Ray

[Amp Kat]

Heres a pretty cool article on soft clipping and I've done a few myself but had more sucess using a reference voltage for top and bottom to keep it from dropping out at any frequency. Some do and some don't. I've also wired a 12AX7 as a diode with reference voltages for compliance and the wave was very round at clipping as I think you'll get more of a square wave with the zener diodes and I've heard of using a resistor at the bottom to simulate more of a tube soft clip than SS. enjoy

http://sound.westhost.com/articles/soft-clip.htm#2

[Satamax]

Lonzo,

Do you have a schematic, or know of one on the Web?

In the "AB2 .5hr..." thread BobW mentioned having success using the 'Paul Ruby Zener mod' on preamp stages, and I'll be trying this out on a Marshall 2000 either today or tomorrow. Bob ended up using a 6.3V Zener (along with a conventional diode) from a 12AX7 grid to ground, which is what I'll be starting out with as well. This should sound much more 'tube-y' than back-to-back clipping diodes.

Ray

Ray, would that work for clipping in a non tube pedal? As back to back diodes do? And in tube environement, would back to back diodes above a zener do anything intresting?

By the way, your atachement above doesn't seem to work!