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HD150 Reverb-on-both-channels-mod


Peter Maziar (mosfet)
Username: mosfet

Registered: 11-2006
Posted on Sunday, November 12, 2006 - 08:45 pm:   

Does anyone know exactly what needs to be done to get reverb and phaser on both channels of my 410-HD-150 musicman amp? Many thanks.
Steve Kennedy (admin)
Username: admin

Registered: 03-2002
Posted on Saturday, November 18, 2006 - 06:40 pm:   

Well, it isn't exactly straightforward but it could be simple. The way I would approach is to remove the 56k at R64. Take a smaller resistor value (probably between 10k & 30k... too small and you'll get channel loading/interaction, too large and Channel 1 will be much quieter than Channel 2) and install one end into the connection of R64 that also connects to the 10k at R62 (right-hand side of R64 on the schematic).

Than take the other end of this new resistor and connect it to the end of the 56k at R65 that also connects to the 10k at R63 (right-hand side of R65 on the schematic). This in effect will "mix" the outputs of the two channels onto the Reverb/phasor input buss that was previously only connected to the output of Channel 2.

Alternatively you could try connecting a 50k or 25k trimpot as a variable resistor in place of the new resistor I just talked about above to make it easier to find a value that gives you what you want.

Anything else would get more complicated. Channel 1 might always be quieter when compared to Channel 2 but this should work otherwise if the resistance value is chosen by ear.

Peter Maziar (mosfet)
Username: mosfet

Registered: 11-2006
Posted on Monday, November 27, 2006 - 06:13 am:   

I assume you would leave in R65, as you made no mention of removing it? I will post the results when I get around to doing this mod. I currently have some other equipment on the bench. Thank you very much, Steve.
Mike Kaus (mm210)
Username: mm210

Registered: 05-2006
Posted on Monday, November 27, 2006 - 04:50 pm:   

Yup-leave in the 56k and use that as a anchoring point. that's your "input".
Peter Maziar (mosfet)
Username: mosfet

Registered: 11-2006
Posted on Sunday, April 29, 2007 - 02:12 pm:   

Hey Steve, I have come up with an alternate plan: make it into a channel switching amp. I have already put assymetrical LEDs into channel 2, and the distortion is really cool. Now I want to put a pair of optocouplers at the inputs to switch channels, and a pair of optos at the effect input to simultaneously switch that. I am not sure if I can leave a channel input floating (ungrounded). I am also not sure where to get the power supply for the optos - in my Fender Concert II, it is a -6.2v rectified supply. Any ideas?