Diode clipper in a tube amp, what do you think of it?

[teemuk]

Try this setup vs. 3 series diodes in the normal configuration (just side by side strings) & you'll see what I mean. The harmonic content is at a higher frequency.

Are you suggesting there is a difference between the JCM900's "bridge rectifier"-style clipping circuit and the ordinary clipping circuit that uses 2 x 3 anti-parallel diodes? If so, I must disagree. As you say, if you follow through both circuits you will see that both of them do exactly the same thing: At each half wave signal amplitude is limited by shunting the signal to ground through three series diodes. With the help of SPICE simulation you can even verify that the two clipping circuits behave exactly identically. However, if in real-life you truly hear differences in tone or see differences in signal shape on the scope?s screen then the only thing I can think of is that they must be due to different characteristics of integrated diodes in a bridge rectifier versus discrete diodes (or whatever diodes you used in your experiment). Sort of like the Silicon versus Germanium thing. But as is I see no "higher frequency" thing happening in the JCM900 circuit.

If someone is able to give me a technical explanation of what I have overlooked in this issue I will gladly admit I've been wrong, though.

The cunning thing of the JCM900 setup, though, is that the "bridge rectifier" allows getting rid of one diode, or, even better, more of them if you want to add more diodes into the string (anyone remember those LXH2 circuits). Say, a string of five series diodes will require only 7 diodes in bridge in oppose to 10 of the conventional configuration. I'm quite sure it saves some board space as well. However, at the point where I would find myself using more than five clipping diodes in a string I would likely start thinking about using some other methods of getting soft clipping.

[Leroy]

Anyone try out the bridge rectifier yet? I was thinking it might sound good in a big muff clone

[Steve Conner]

The high voltage, high current diodes in the JCM900 bridge rectifier circuit give remarkably soft clipping compared to signal diodes. It's easy enough to try if you don't believe me, just grab some 1N4007s and give it a go.

[Leroy]

The high voltage, high current diodes in the JCM900 bridge rectifier circuit give remarkably soft clipping compared to signal diodes. It's easy enough to try if you don't believe me, just grab some 1N4007s and give it a go.

I'll for sure give it a try, I'm just confused about one thing is the diode bridge in the Marshall jcm 900 an integrated piece or made up of discrete diodes. If it's a integrated piece what is the part number?

Thanks

[Steve Conner]

Yes, it's an integrated piece. The part number is right there on the schematic that 10 seconds' googling would have found:

http://www.drtube.com/schematics/mar...d0109-iss9.gif

W005, which is seemingly a 1.5 amp 50V bridge rectifier. The diode inside it is a 1N4007.

[rexindigo]

z-drive diode clipping

this thread seems to start again so i just want to contribute.
after completely rebuilding the el34 amp that started this thread , i added a diode clipping stage again.
but this time i used the type of diode clipping that i found in a schematic of a stompbox called z-drive
its the input diodes of some fet transistors that are used there,
this is very smooth sounding and i like it very much.
This is of course no integrated bridge rectifier......

[tedmich]

cascode ideas from Ted Weber (RIP)


C Ted Weber