mixing stereo outputs of an 18v danelectro cool cat chorus. Formula?

[Chris S]

Hello everyone I have an 18v Danelectro Cool Cat Chorus with a stereo output. The mono output mixes the wet and dry outputs at 50% each. I want to use the stereo outputs (one wet one dry) to get a mix of about 1/3 wet 2/3 dry. Rather than build a box I was planning to build a patch lead with resistors hard wired to that.

1) is using the 100kA pots the correct pots to use for the passive mixer?

2) is there a formula I can use to work out what resistors to use (slightly easier approach) or should I just build a temporary box with two pots get it to the mix I like, measure the resistors and go from there?

Thanks!

[R O Tiree]

You only need to play with the wet output. If you mess with the dry output, then any voltage splitter you put in there will always be there, so you'll have a permanent drop in the dry signal, whether bypassed or not. You would achieve the result you're looking for by just putting a voltage splitter into the wet output lead, leaving the dry lead alone. I'm tempted to advise using relatively small resistors, say 2 x 4.7k. The trouble is, you're going to alter the output impedance of that wet channel. Perhaps it doesn't matter much?

A more elegant solution might be to take a close look at the output opamp stage for the wet channel...

You're going to have to do a bit of detective work to trace the circuit, because I can't find a schem on the net. The wet output is almost certainly a unity-gain inverting buffer. Assuming that this is so, then start from the "tip" terminal of the wet output, and you'll find a resistor to ground and a reasonably large cap leading to an opamp ouput pin (there may be a small resistor in series with that cap). If it's a "standard" 8-pin DIL opamp, this will lead you either to pin 7 or pin 1. If it's a SIL package, you're going to have to get the part number off it and then google for the datasheet to find the pinout. It might also be a 4-amp chip (TL074, for example). Let's assume it's a DIL package - if it isn't then what I say here isn't necessarily wrong... you'll just have to transpose pin numbers to make this work. I'm going to assume this process has led you to pin 7, but I'll put pin numbers for the other half of a DIL opamp in brackets, just in case it led you to pin 1.

OK, now you've found the output pin feeding the wet output you should find a resistor connected between pin 7 (1) and pin 6 (2). Just take it out and replace it with one half the value. This will halve the gain of the output buffer of the wet channel without messing with the output impedance at all.

Of course, Dano have been using SMD for some years and this might cause problems if you're not happy with that stuff. If so, then building a little buffer box with a gain of 0.5 to halve the wet signal level externally might be the way forwards. You could put a pot in there to vary the gain from 0.5 to 1, just in case you wanted to be able to vary the wet signal, perhaps?

[R O Tiree]

Oops - I was assuming you were running 2 amps... that's what the stereo option is for, running one amp with the dry signal and the other with the wet signal.

If you're only running one amp, what you're proposing won't work very well. You could try this pan/blend article at RG's site. This would enable you to pan between full dry, full wet and anywhere in between at constant (pretty much) volume with a little external box. The inputs will be connected to the outputs of the Cool Cat and the single output goes to the rest of your pedal chain or to the amp input.

Alternatively, if you really want to permanently mod the pedal with a reduced wet output signal, then you're going to have to do a little more digging inside your pedal. Trace the circuit back from the mono output tip connection. Again, you should find a resistor to ground and a fairly large cap (maybe a small resistor in series with the cap, as before) to the output pin of the mixer opamp. Again, you should find a resistor between this pin and the -ve input (pins 7&6 or 1&2). From pin 6 (2) trace along and you should find 2 more resistors off this track. One will lead you, probably via another cap, to the CD4053 (switching) chip. That's the dry channel. The other should lead you, again via a cap at least, to the delay chip. Take that resistor out and insert one of double the value.

[Chris S]

Hello R O

Thanks for the replies. Yes I'm planning to run only one amp. The pedal is an older big metal housed dano so, no SMD.



I can build a small pan blend box I was kind of hoping for the simple solution of putting a volume knob on each output and hey presto.

Thanks for the tracing guide I'll do some looking tonight.