I found the schematic for the Ampeg VH-140c which uses the Crate patent for the distortion. I drew it up in Eagle, and wondering if anyone would look at it to see if it looks like it might work?

I know Jack Orman drew one up on AMZ, but it look a little different. The patent uses a inverting stage, and the one that Jack did is a non-inverting stage. Would this make a big difference in the distortion sound?

Thanks
Rob

I'd like to see it.

Quote from: caspercody on March 10, 2010, 06:43:22 PMWould this make a big difference in the distortion sound?

Yes.

Yes. The diodes will clip differently depending on whether the gain stage is inverting or non-inverting. At mild levels of overdrive there is not much difference but when the amp is driven harder the non-inverting stage will have softer clipping characteristics.

In essence, the different characteristcs spawn from the clipping Zener diodes being configured very differently in inverting vs non-inverting amp: In inverting amp they are an open circuit and turn to a shunt to virtual ground once Vzener is exceeded. In a non-inverting amp they are open circuit and turn short circuit once Vzener is exceeded. When you calculate the effect on gain on both scenarios you see why the behavior is very different.

This is a plot from simulation comparing two gain stages (inverting and non-inverting) that use the SLM's patented distortion. Gain and frequency response of both circuits is matched. Gain is 40 dB and zener diodes are 4V7. Input signal is 100mV, 500mV, 1V and 2V. You can notice how the overdriving characteristics turn completely different with higher amounts of overdrive.



Oh, if you wonder how the SLM's circuit works it's explained in the patent. In nutshell, extended overdrive will gradually charge the capacitor in between those two resistors and this will consequently introduce a DC offset voltage to the signal. Signal's "zero crossing point" biases to this offset voltage and as a result the zener diodes will clip one of the half waves more than the other. This asymmetry naturally introduces even order harmonics.

The process does not show up in the attached plot because it captures only a very short time frame. In the actual circuit the process of fully full charging the capacitor takes about a few hundred milliseconds.

Oh... In the SLM's circuits they kinda do this process "backwards": The Zener diodes are selected to have different Zener voltages (and hence clipping levels) so that the initial clipping is asymmetric. The introduced DC offset shift will then "correct" this asymmetry.

Thanks everyone!

Aron, how d I attach a file here? I have Jacks schematic, the one I did up (actually three), and the one for the Ampeg amplifier.

I added the designs, and the Ampeg VH140c schematics onto the Layouts Gallery. Just do a search for Ampeg, there are three files I uploaded. Ampeg VH140c, Crate distortion, and Crate pre gain tone shaping.

The Crate distortion is just the two stages of the Ampeg distortion. Added some components at input and output. Not sure if these values would work or not (took from a distortion article I read). The power supply is directly from the Ampeg schematic, and not sure if need all the parts? I was thinking of using two 9 volt batteries to get 18 volts for this project. Looks like it is around 13 volts at the IC.

The pre gain tone shaping circuit is directly from the Ampeg. The out put would connect at the pin 2 on the distortion (and remove R2, R12, C13, and C14 on the distortion circuit).

Please look over and let me know of any errors.

Thanks
Rob

Just hopping someone can look at my design based off the Ampeg VH140c? I am still wondering about the power supply for this (the distortion circuit)? The original calls for a +15 and -15 volts. I am guessing this is a bi-polar supply. Will two 9 volts wired in series work? Would you connect where the two batteries connect (the positive and negative leads) be the ground reference?

Thanks
Rob

Please anyone? I want to start building this, but want to make sure of the power supply before I start. The distortion side and the pre gain stage take two different voltages. Looks to be a bi polar source. Want to try to do this with batteries if possible.

Quote from: teemuk on March 11, 2010, 01:59:41 PM

That is a great picture and explanation!  I wonder how it would work out to make both the inverting and non inverting versions, invert the inverted version, and make a knob to pan between them?

i gave up with tube emulation long time ago... ive seen the peavey transtube technology and it seems to be very complicated with lots of power supply biasing with odd voltages...
the "easiest" one would be to use FETs or build the LXH2 Marshall which i really love...

http://home3.netcarrier.com/~lxh2/marsh.html

I was thinking of making the LXH2, either the Marshall or Fender. What is the voltage supply for these? Is it bipolar? Did you make the cab sims, or just the amp sims? I play thru a amp, and thought one should not use cab sims thru amps?

My amp is a Peavey with the transtube, but I am to addicted to building these pedals. I want to get this Crate going because it is my first one from schematic to pcb to build. All the pedals I have built are from others designs. And I have not seen anyone else convert this amp. I liked the sound I heard on Youtube, and thought this would be a good one to try. I know it is patent, and this is only for me to use.

I have found a bi polar voltage doubler circuit, so now I am not worried about thepower supply.

But, can someone still look at the layouts I uploaded to the gallery (just enter Ampeg in the search)? I think the distortion part is good to go, but curious of the pre gain stage? I had to remove the transistor switchers and hope I left in the correct resistors and caps to get this to work.

Please note: If you combine the two circuits, must delete some of the components at the front of the distortion circuit. These were added as a stand alone distortion pedal.