Stereo DBA Reverberation Machine

[joeconnor90]

Hi there, hoping for a little bit of insight from this excellent community!

I'm planning to build a DBA Reverberation Machine as part of a simple (but hopefully quite weird) synth. I've built a bunch of stomp boxes in the past, and I have a reverberation machine already - and love it - but I haven't modded anything or added to designs up to this point.

Cutting to the chase - I'd like to use the 2nd output of the Belton BTDR 2h and run this as a basic stereo reverb. I'm surprised this hasn't come up already given the love this pedal has. Unless I just haven't found the right forum threads yet...

Looking at other's pedal designs and the accutronics page for the reverb brick -- http://www.accutronicsreverb.com/main/?skin=sub01_05_1.html -- I don't feel like this should be too complicated. I would love to get some tips though on adapting the DBA circuit in this way.

I'm following the vero layout & schematic on this page -- http://guitar-fx-layouts.238.s1.nabble.com/dba-reverberation-machine-corrected-schematic-td44924.html#a44991

Because the TLC27M4 has an unused op amp (correct?), am I right in thinking I can change the Blend & Volume knobs for dual gang pots, and then use another set of the components on pins 5,6,7 on pins 8,9,10 of the TLC27M4? So essentially just duplicating the part of the circuit AFTER the brick.

Am I missing anything highly important, and would I need to duplicate any parts of the circuit that are BEFORE the reverb brick..?

Would massively appreciate any suggestions. Cheers!

[joeconnor90]

Anybody have any ideas on this...

I'm wondering if it's even worth trying to use the belton verb as stereo as am I right in thinking it's the same signal on both outputs anyway..?

If anyone knows of a good approach for this I'd love to hear it

Thanks

[niektb]

That first link you listed, it does have a schematic with stereo output already!

Shouldn't be too hard Insert some filtering between the input buffer and the reverb brick if you want to alter your reverb sound and I think you should be very close to what you want to achieve
Compared to the DBA, duplicating the output buffer is indeed essentia (and converting the pots to dual-gang) l think also the GAIN pot should be dual gang

[joeconnor90]

Hey, thanks for the reply & the tips!

Would filtering between the input buffer and reverb brick affect BOTH the reverb outputs? Or to make more of the stereo effect would it be possible to put some filtering after only one of the outputs? OR did you just mean if I wanted to alter the tone of the reverb in general... sorry haha.

Ah you're right, forgot about the gain pot too, thanks.

One last question! Referencing the dba schematic, would the duplicated output buffer include R7, R8, R9, +9v & Ground connections too? Or would just duplicating from the capacitor after the blend pot be the start of the output buffer?

Thanks again!

[niektb]

I've been looking at R7 t/m 9 but the biasing scheme is a bit odd. I wonder why R24 and R15 are connected to ground when the signal is revolving around 4.5V... 

I think you should at least duplicate R7, and possibly R8 and R9 as well but you can just try in practice

[...]
Would filtering between the input buffer and reverb brick affect BOTH the reverb outputs? Or to make more of the stereo effect would it be possible to put some filtering after only one of the outputs? OR did you just mean if I wanted to alter the tone of the reverb in general... sorry haha.
[...]

Yes to all three questions 

[joeconnor90]

No idea about R24&15... When I saw them I assumed they were necessary pull down resistors, but that guess wasn't based on much 

Yes to all three questions 

Ok thanks! 

[anotherjim]

I'm not familiar with that opamp, but some types ideally require a load resistance to the negative supply of the chip. 0v ground in this case. The purpose is either to reduce crossover distortion or because the output source & sink currents are unequal - or both. It's done consistently here so ought to be deliberate. Sometimes schematics do have errors like this but if there's no other reason for a resistor there - you wouldn't have it for a TL072 or RC4558 - this is probably correct.