Mesa boogie Prodigy Four 88

[Godixon]

Hello,
does anyone have? Will apreciate if you have some.
Thank you.

All the best
Tom

[vintagekiki]

No schematic, no service manual ...

Prodigy site:http://www.mesaboogie.com

Out of Production Bass Prodigy Four:88

[doctor]

Bass Prodigy schematic:

https://www.dropbox.com/s/skiiez86tp...me%7D.pdf?dl=0

[Godixon]

Thank you doctor

[camjenkins]

I'm really happy that this schematic is up, but I don't think it's correct, which honestly doesn't surprise me. I modeled it in LTSpice and found that the mid control does very little involving mids. Sweeping the mid control in my simulation affects treble and high mid frequencies while leaving the bass frequencies unaltered. I would have thought that the mid control would have a similar topology to that of the MPulse and the Walkabout, which have very powerful mid controls based off of Marshall/Fender tone stacks. For this mid control to actually function as advertised, I would think that R15 and R22 would be bridged with a small (> 1nF) capacitor.

[g1]

I'm really happy that this schematic is up, but I don't think it's correct, which honestly doesn't surprise me.

boogie S.O.P.

[MarkusBass]

I'm really happy that this schematic is up, but I don't think it's correct, which honestly doesn't surprise me. I modeled it in LTSpice and found that the mid control does very little involving mids. Sweeping the mid control in my simulation affects treble and high mid frequencies while leaving the bass frequencies unaltered. I would have thought that the mid control would have a similar topology to that of the MPulse and the Walkabout, which have very powerful mid controls based off of Marshall/Fender tone stacks. For this mid control to actually function as advertised, I would think that R15 and R22 would be bridged with a small (> 1nF) capacitor.

You can alway ask the OP for a photo of R15, R22 and surrounding components in order to check whether there is a missing capacitor not shown on the schematic.
But since this is just a simple high-pass filter it should work exactly as you described. You could also post your simulation to allow other users to verify it.

Mark

[vintagekiki]

... I modeled it in LTSpice and found that the mid control does very little involving mids ...

LTSpice is LTSpice, but sound is sound. Leave simulations through the model, what the measuring instruments say, what the bass guitar says.

When analyzing the amplifier by simulation, the amplifier should be analyzed in the frequency range for which it is designed. Prodigy 488 is designed to play bass tones.

Generally for many vintage amplifiers, mid control is relatively modestly responsive.
Question. How does Prodigy 488 mid control work in combination with Voice control.

As for the schematics, you can not compare Prodigy with Walkabout because their preamps is based on different concepts.
For the beginning of any story, analyze the schematics. Mid control at Walkabout was configured similarly to Aural Enhancer Control at SWR SM400. Next, Walkabout has three-step EQ parameters. All filters affect the final result of the sound
That's the difference in the sound between amplifier and amplifier.

[camjenkins]

Well, the mid control doesn't interact with the voice control at all. Yes, the Prodigy is designed for bass frequencies, but that doesn't change the fact that the mid control should mainly affect mid frequencies. Rather, it means that the mid frequencies should be lower than for a guitar amp. I referenced the Walkabout and the MPulse simply because they are made by the same manufacturer, and thus, probably would share some design elements, which they actually do. As for my simulation, I'm not denying that it could be wrong, but I don't think it would be was wrong as it is simply due to errors with models and calculations.

These bode diagrams were taken in my simulation just prior to where the effects loop is and the voice circuit is essentially bypassed. The bass and treble controls are at 50%, I absentmindedly left the gain on full and the input mode is the normal mode.

Mids at 0%:


Mids at 50%:


Mids at 100%:


What do you guys think? Is the schematic wrong, or am I wrong?

[MarkusBass]

Well, I asked you to post the simulation and you posted the results of the the simulation. This is not the same and we don't know whether you simulation is correct or not .
It would be much clearer if you use a parameter for the Mid control and display everything on one plot pane. Like this:

I don't know whether the schematic is correct but I see that @1kHz the change is 10dB. Why do you think it is incorrect?
I also mentioned that you can ask the OP for a photo of R15, R22 and surrounding components to verify whether there is an additional capacitor used. Did you do it?

Mark

[camjenkins]

I did just find a few problems with my simulation involving one of the boost relays (I had forgotten it) and with the voice switching. I'll attribute the first one to the pace that I was working at when I was modeling the circuit. The second one I'll blame on Mesa's schematic layout. After fixing the problems, the mid control does do something, but I'm still not happy with the way it works. Let's just say that I was wrong and that I hate the mid eq topology, sound good? Also, how do you get multiple traces on one plot pane?

[MarkusBass]

Let's just say that I was wrong and that I hate the mid eq topology, sound good?

The topology is almost the same as used in several Ampeg bass amps (I mean the VOICE part of the circuit). And in those amps it sounds very good. Why would you hate it? I still haven't seen your simulation but I hope you simulated the MID control together with the VOICE circuit, didn't you?

Also, how do you get multiple traces on one plot pane?

This is quite easy. You assign a parameter as a value (e.g. resistance of a pot) and then provide a formula that changes the value of the parameter. The rest is done automatically by LTSpice.

Mark

[camjenkins]

I simulated the entire amp, so yes. I'm just stupid sometimes. When the voice control is in the 4 and 5 positions, the mid control actually does function fairly decently. However, with the voice circuit bypassed, the mid control doesn't do what I'd like it to do, which is cut or boost the mid frequencies only. Maybe I'm too in love with Ampeg's active mid controls...

[MarkusBass]

On the official website they brag of a passive MID control. I'm also not very happy with the way it works. I think that it is possible that they removed some components from the schematic in order to protect their circuit (from copying).

[camjenkins]

I agree with you on that. Mesa is notorious for omitting components from their schematics or changing their circuit topologies just to throw us off. I already know that the schematic has errors because things like the 4N33 optocoupler on the voice circuit aren't hooked up correctly. As it is in the schematic, it doesn't control the voice circuit at all.