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]

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]

http://bedrock27.tripod.com/sitebuildercontent/sitebuilderpictures/600aschematic.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]

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]

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:

http://music-electronics-forum.com/attachment.php?attachmentid=137&stc=1&d=1156955633

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

Ray

[Lonzo]

Ray

I can't view the pic.

Thanks,
'zo

[Ray Ivers]

Lonzo,

Here's the link:

http://music-electronics-forum.com/attachment.php?attachmentid=137&stc=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!

http://music-electronics-forum.com/attachment.php?attachmentid=117&stc=1&thumb=1&d=1153927785 (http://music-electronics-forum.com/attachment.php?attachmentid=117&d=1153927785)

[Ray Ivers]

Max

Ray, would that work for clipping in a non tube pedal? As back to back diodes do?

The "non-tube" category is pretty large, and I'd have to be a lot fresher than I am now to figure out the differences in behavior between NPN/PNP/enh. MOSFET/dep. MOSFET/P-JFET/N-JFET/etc. ;) My gut feeling tells me it won't work exactly the same in any of them, but I could be wrong.

And in tube environement, would back to back diodes above a zener do anything intresting?

Yes, they sure would - the grid would diode-clip between roughly 1.2V positive, and approximately the Zener voltage in the negative direction. The diode above the Zener isolates it from the grid during the positive signal swing; back-to-back diodes would remove this isolation.

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

I don't know what to tell you - I uploaded it fresh from my hard drive to the 'Manage Attachments' section just liked I did before, then cut & pasted the shortcut using the 'Insert Image' button just like I did before, and it displays properly on my screen in both the text body and thumbnail footer, just like before - I'm looking at it right now, as I type. There's not even a thumbnail?

Ray

http://music-electronics-forum.com/attachment.php?attachmentid=117&stc=1&thumb=1&d=1153927785 (http://music-electronics-forum.com/attachment.php?attachmentid=117&d=1153927785)

[Steve Conner]

You can't see attachments unless you're logged in dudes :p

[Ray Ivers]

Steve,

I think something's wrong, though - the pic's gone now, the thumbnails won't open, and the link is invalid. I'll try posting it again.

Ray

[Ray Ivers]

Lonzo,

If at first you don't succeed...

http://music-electronics-forum.com/attachment.php?attachmentid=138&stc=1&d=1157030357

It looks fine here, which means nothing, I guess.

Here's the picture link:

http://music-electronics-forum.com/attachment.php?attachmentid=138&stc=1&d=1157030357

Ray

[Steve Conner]

The new board software seems to automatically log you out after a while too.

[Matt T.]

Regarding the smoothing effect, that's exactly what I would expect (so I was surprised everyone else expected otherwise). Example: Fuzz into clean amp...harsh; Fuzz into overdrive pedal (diode clipping)...smooth.

[Ray Ivers]

Matt,

IMO the key word is "fuzz" - smoothness gained at the expense of a fuzzy tone is a Pyrrhic victory, at least in my book - but YMMV, and FWIW I have heard diode-clipping circuits I thought sounded OK.

Ray

[Lonzo]

The only Zener I could find (on short notice) has a volt rating of 12 volts & 1watt.

Will this work?

Thanks,
'zo

[Ray Ivers]

Lonzo,

The only Zener I could find (on short notice) has a volt rating of 12 volts & 1 watt. Will this work?

Probably not - but try it and see.

Ray

[Carl / Zwengel Amps]

Another option along similar lines as Enzo mentioned is to parallel up a series string of diodes. This will give you more signal swing before they clip. Two diodes gives you 1.2 volts before clipping, 3 gives you 1.8v, etc. Then add a small value ceramic cap across the whole wad to take the hard edges off the signal when the diodes clip.

-Carl

[stevesamps]

I have tried clipping circuits with tube amps, You can use what KOC calls compliance to get around the more harsh clipping and massive signal
loss of diodes strapped to ground, I think the last time I tried about 82k in series
with the clippers to ground this resistor value you can vary to taste for more
or less clipping and signal.. basically it helps dump less signal to ground ans softens the effect

[Lonzo]

Thanks everyone for all the suggestions and advice.

I tried the Zener diode ckt Ray detailed but found that my 1W 12V Zener must not be effective. Another experiment found a quad of parallel (reverse polarity) diodes from the cathode to ground. This effort was to no avail as well.

I think I'll go with a 12AT7 in the phase inverter spot and sub 12A_ into the first gain stage; probably should have started here first....:confused:

Again, thanks for all the advice. I really expected to get flamed for such a strange request.

lonzo