Bipolar version of Marshall speaker simulator

[Yazoo]

I built the Marshall speaker simulator a while ago but I wasn't that impressed by the sounds I was getting. I then built the Celestion V30 speaker simulator recently and like the results. The Celestion simulator uses a 15v bipolar power supply. I then thought why not try using a bipolar power supply on the Marshall simulator to give it more headroom, so I connected it up to a 9v bipolar supply. In my version, I had used a TL074 so I only needed to make one change to the circuit, connecting pin 11 of the TL074 to the 9v- output of the power supply rather than ground.  The simulator did work but it was distorted.

Is it possible to simply change the power supply in a circuit like this to a bipolar supply or would you need to redesign the whole circuit. Needless to say, redesigning the circuit would be beyond me.

There is a layout for the Marshall speaker simulator on Jim Radmer's site http://www.radmer.dk/

[DougH]

Do you have a link to the schematic?

[frequencycentral]

Is this the schematic you used?

http://www.diystompboxes.com/pedals/schems/msim.jpg

You have missed something - see the VB on the +ve input of the first opamp? That needs to be connected to your bipolar power supply's earth. You should also remove the two 10K resistors and the 22uf cap from your PCB that connect to pin 3 of the left TL072. Why use a VB when you have a real one available?



EDIT: ......and you should also connect your socket's earths to the bipolar power supply's earth too.

[MetalGuy]

This simulator comes from Marshall JTM30 and JTM60 series of combos and originally it's powered by a bipolar supply. The changes that need to be made are simple:

1/ Connect VB to ground. Connect (-) and (+) rails to their respective IC pins.
2/ Decrease the input signal at least by a factor of 7 (the amplification of this circuit) otherwise it will clip like crazy. 

[DougH]

I remember when Ed first posted this, many years ago. IIRC there may have been some discussion about bumping the gain up. As mentioned, it was originally part of an amp which may have supplied it with a hotter signal. Try reducing the gain of the first stage to get rid of the distortion. Otherwise, tie Vb to ground, as others have mentioned.

[Yazoo]

Thanks for pointing out the Vb changes. I originally built the circuit from the Radmer layout and I have to be honest, there are a lot of things I don't understand. Looking at the schematic was useful.

I made the changes, supplying Vb from the bipolar ground. It worked but was very distorted, so I removed the 47k resistor and replaced it with a 250k pot as suggested. I think it now sounds much better. I had to "tune" it with the 250k pot and I found that when I had got a good sound the pot resistance was around 5k.

I built the V30 simulator in an old 1U rack box I was given. There's loads of room inside, so I'm going to put the Marshall simulator in as well and so that I can switch between them.