Re: op amp-based effects loop circuit for guitar amplifier

On Sun, 17 Jul 2005 19:51:51 +0200, in sci.electronics.design martin
griffith <martingriffith@xxxxxxxxxxxxx> wrote:

>On 17 Jul 2005 10:20:56 -0700, in sci.electronics.design
>eerickson_1@xxxxxxxxx wrote:
>
>>I need help with a circuit design for an effects loop in my tube guitar
>>amp. Because I don't have space for another tube, I'd like to use an
>>op amp based circuit. However, my knowledge re: op amp circuit design
>>is limited - I'm a tube guy....
>>
>>After poking around I found this schematic:
>>
>>http://www.drtube.com/schematics/marshall/pcbp-00119-60-02.pdf
>>
>>Is this a reasonably decent design to clone?
>>
>>I think it would work well for me since it was designed for an
>>amplifier very similar to mine and doesn't require an additional power
>>transformer; just step down the 380VDC rail (B+) voltage with a power
>>resistor and let the regulators do the rest.
>>
>>Are there any easy improvements that could be made to this design? Am
>>I right to think it would be improved by using 7815 regulators over
>>Zener diodes and, by using an improved op amp (Analog Devices OP249)?
>>Any help is appreciated!
>>
>>Eric
>>
>>FWIW, an effects loop allows one to insert a low impedance signal
>>processor into an optimal section of the amp's high impedance signal
>>path.
>
>Yep, looks reasonable at first sight.
>But you are totally wrong in replacing the zeners. These are here to
>prevent high voltage signals from zapping the opamps.
>
>I'd just use 8 pin ic sockets on a homebrew, so you can easily change
>the opamp. you may blow up a few prototyping. Stick with the TL072
>until you have it working.
>
>What the circuit doesn't show is the power supply. what are you going
>to use?
>
Oops misread your post about the power supply.

I would personally not use 380V dropped down. This circuit needs
split rail supplies, say +12V and -12V. Also there is a safety factor
while testing to be considered. try www.epanorama.net for suggestions
or
http://sound.westhost.com/project05.htm


martin
.

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