Reverb pedal with keyboard

[ponce]

I have an old Casio from the 80s with a few decent sounds. I thought it would sound even better with reverb so I installed it between internal amp and its single speaker. Now the sound is much quieter. Is it the unmatched impedance or something else?

[vigilante397]

NEVER put effects between an amplifier and a speaker. You're blasting the input of your effect, and the average effect can't put out the power necessary to drive a speaker.

Effects can go after filtering, EQ, preamplification, etc. but ALWAYS ALWAYS ALWAYS needs to come before the power amplifier.

Hope this helps

[mth5044]

^What he said.

You didn't specify what reverb you're using. If you put in something designed for guitar signals, your keyboard signal may be too hot for it (once you find the right place to put the circuit, of course!) and you may need to pad the input and boost the output.

[ponce]

Thank you for all the good points! It's my diy Belton brick based reverb pedal.

[blackieNYC]

Is the pedal working? With guitar. 

[PRR]

There's 3 stages of audio.

1) Make tiny signals reasonably large.

2) Modify reasonable signals to taste (volume, tone, reverb)

3) Boost reasonable signals BIG to smack a loudspeaker.

[ponce]

Is the pedal working? With guitar.

Yes, with vocals too.

[blackieNYC]

You lucked out. It still works, so you can back away and stick to using it with guitar and vocals, or you can try to build an effects loop into the Casio. It would involve finding an appropriate place in the schematic (where the levels are right for the pedal) to insert a send&return jack(s). I would not recommend this, but if you need to it can probably be done.
How about using the headphone amp output thru the reverb to an external amplifier?  If you keep the volume setting low at the Casio this could work.

[ponce]

I kind of wanted to integrate the reverb to play it through the internal speaker. But it's impossible to get a schematic for those and similar models. I'd have to locate the unamplified signal by the common nonsense and some luck.

[anotherjim]

If it has a real analogue volume control knob or slider, the wiper of that will be between its "pre-amp" and "power amp". If it has digital up/down volume buttons, then that's no help.

It probably doesn't harm a pedal to be driven by the speaker or headphone amp of what is probably a low voltage solid state amplifier except it will need the input volume kept on the low side to avoid overdriving it, but you could put a small 9v "pedal" style amp after the reverb and drive the built-in speaker with that. Such as an LM386 mini-amp or similar.

[ponce]

I've been thinking of adding the Ruby style amp after the reverb, but yes, the keyboard has an analog volume slider pot, that's a good idea. I'll definitely try that one. Thanks a lot!

[ponce]

I've managed to do the connection but I get a lot of feedback that goes into self oscillation at increasing volume and wetness. What can be done to buck it?

[anotherjim]

Keep the in and out signal wires separated/screened apart. Don't use a twin & screened wire to carry the signal out and back, use two screened cables.

[ponce]

Does the shield have to be connected (common ground)?

[Kevin Mitchell]

Does the shield have to be connected (common ground)?

I'd recommend it.

[ponce]

Does that mean I should wire it like a guitar cable or use the shielded cable only for the hot signal wire? I know these are highly ignorant questions for the most of members.

[anotherjim]

One end of the volume control should attach to 0v ground. It will help to be sure which end that is. If it isn't obvious in the unit, the ground end is the one the wiper has the lowest resistance to when it should be at lowest volume if measured with a dmm on resistance range (no power on the keyboard).
2 screened cable should be used, just like guitar cable.
Outgoing cable: screen to ground, signal wire to volume wiper. Wiper contact disconnected from existing connection in the keyboard.
Return cable: screen to ground, signal wire to the existing path which the volume control wiper was connected to.

That perhaps isn't ideal since without the reverb or some other device between the 2 cables, there is no signal to the keyboards amplifier. A better choice, if there is room on the case, is to fit 2 jack sockets as an fx send & return just like you have on some amplifiers and mixers. At least one of the sockets is a switched type, so with nothing plugged in, the keyboard amp is connected as normal.

[ponce]

Thanks! My first attempt was to do the connection at the volume control but because of the feedback I thought I didn't do it correctly, so I found a cable from one of the boards leading to the board with the amp and carrying the signal. I interrupted that connection with in and out sockets and unscreened wires. Feedback was the same.

To get the signal come through without the effect I simply bridge it with a patch cable since I didn't have a switching type sockets.

So I guess, when placing the connection here and not at the volume pot I should just replace existing wires with 2 pieces of guitar cable and that should eliminate the noise?

[anotherjim]

What you described of the problem suggested the reverb output was somehow getting back to the reverb input. If the reverb is known to work normally, the obvious cause is it is getting feedback from the output to the input via radiated coupling between the wires due to no or poor screening.
If the reverb is intended for guitar use, it ought to have a sensitive high impedance input which can very easily pickup radiated noise. In the keyboard, Casio probably have a low impedance connection that is less sensitive, a shorter path and doesn't need the expense of screened wires.

What model Casio is it? I remember using one of their early digital wavetable ones with full-size keys which while most tones were totally unrealistic, they had a nice "otherness" about them, particularly the organs.

[ponce]

It's this model. Not bad at all IMO. Does anybody know any other good mod for it, except random circuit bending?

https://www.youtube.com/watch?v=cTfrL4sOBVs