DBA Reverberation Machine

[guidoilieff]

Hi. I taught a friend to make pedals and he went with the reverberation machine.
http://effectslayouts.blogspot.com/2015/12/death-by-audio-reverberation-machine.html

Video
https://flic.kr/p/29TKYZf

Image
(In this picture I removed the ground connection to the jacks)


After debugging it I can't make it sound right.

I replaced the 100uf capacitor that goes to the 1st leg of the accutronics with a 470uf to reduce noise and also added a 1000uf on the 9v plug.
I Also replaced the 470pf caps with 680pf and the TLC27M4 with a TLC2274.


Input
9v

TLC2274

4,50
4,50
4,30
9
4,23
4,45
4,45


4,50
4,50
4,30
0
0
0
0



Accutronics BTDR-2H

5
0
Starts draining*
0
Starts draining*
0

*When I check the voltage with the dmm the voltage starts to drop



Any ideas or more info needed?

[guidoilieff]

Schematic:

[guidoilieff]

Just wondering if anyone knows the voltages of the accutronics....

[samhay]

Your posted voltages are as expected*
The reverb bricks have internal capacitors on the input and outputs, so these will sit at whatever voltage you connect them to. V+ should be 5V and the 2 grounds at 0V.

*For what it's worth, the circuit in the schematic would benefit from a number of major tweaks and/or a significant redesign. Unless it is supposed to sound like sh1t, there should be a capacitor on the output of U1, which is probably why you are having problems. As drawn, it should pass dry signal, but reverb will be quiet and/or distorted.

*assuming you have a cheap DMM.

[guidoilieff]

Your posted voltages are as expected*
The reverb bricks have internal capacitors on the input and outputs, so these will sit at whatever voltage you connect them to. V+ should be 5V and the 2 grounds at 0V.

*For what it's worth, the circuit in the schematic would benefit from a number of major tweaks and/or a significant redesign. Unless it is supposed to sound like sh1t, there should be a capacitor on the output of U1, which is probably why you are having problems. As drawn, it should pass dry signal, but reverb will be quiet and/or distorted.

*assuming you have a cheap DMM.

Thanks a lot

Cheap dmm indeed


The output capacitor in U1 should be before or after R10?

[iefes]

@guidoilieff: After R10. R10 serves as feedback resistor of the opamp stage.

@samhay: Why is the missing capacitor a problem? Is it because of R11 (100k to gnd)? After R11 there's the RC-network and hence there is a capacitor decoupling the stages. No offense, I'm just trying to learn some stuff :-)

[samhay]

>@samhay: Why is the missing capacitor a problem? Is it because of R11 (100k to gnd)? After R11 there's the RC-network and hence there is a capacitor decoupling the stages. No offense, I'm just trying to learn some stuff :-)

No offense taken. Always better to ask a quesiton than wonder why.
The output of the op-amp is biased to about 4.5V, so R11k will be fighting this. Some hi fi designs use this trick to bias the op-amp output into class A, but there is no advantage here and may be causing the op-amp to misbehave (I can't read the op-amp stencil in the photo).
See: https://tangentsoft.net/audio/opamp-bias.html

@guidoilieff: this may not be the only problem. What does the circuit sound/behave like.

[iefes]

The output of the op-amp is biased to about 4.5V, so R11k will be fighting this. Some hi fi designs use this trick to bias the op-amp output into class A, but there is no advantage here and may be causing the op-amp to misbehave (I can't read the op-amp stencil in the photo).
See: https://tangentsoft.net/audio/opamp-bias.html

Thanks for the explanation. Then the same applies for the output opamp U2 right? Good to know. I wanted to build the Reverberation machine myself soon and knowing some ways to improve it are always welcome.
cheers

[guidoilieff]

>@samhay: Why is the missing capacitor a problem? Is it because of R11 (100k to gnd)? After R11 there's the RC-network and hence there is a capacitor decoupling the stages. No offense, I'm just trying to learn some stuff :-)

No offense taken. Always better to ask a quesiton than wonder why.
The output of the op-amp is biased to about 4.5V, so R11k will be fighting this. Some hi fi designs use this trick to bias the op-amp output into class A, but there is no advantage here and may be causing the op-amp to misbehave (I can't read the op-amp stencil in the photo).
See: https://tangentsoft.net/audio/opamp-bias.html

@guidoilieff: this may not be the only problem. What does the circuit sound/behave like.

I posted a video, I hope you can watch it. Heres the link https://flic.kr/p/29TKYZf

[samhay]

 @iefes. yes, good spot. U2 is the same. Perhaps easiest thing would be to remove the 2 resistors. They are not doing anything essential.

@guidoilieff. It sounds like the reverb is working, but there is quite high distortion. I assume this is what the circuit is supposed to sound like - it certainly isn't designed to be clean.
If the blend pot is only giving reverb in the middle of its rotation, then you have a bad pot or wiring problem.

[guidoilieff]

@iefes. yes, good spot. U2 is the same. Perhaps easiest thing would be to remove the 2 resistors. They are not doing anything essential.

@guidoilieff. It sounds like the reverb is working, but there is quite high distortion. I assume this is what the circuit is supposed to sound like - it certainly isn't designed to be clean.
If the blend pot is only giving reverb in the middle of its rotation, then you have a bad pot or wiring problem.

It doesn't distort anything like the original... maybe try another ic?


How would you recommend to add this capacitor at the outputs given the layout made by effectslayouts?

[samhay]

Rather than adding capacitors, you could try removing R11 and R22.
However, this is not going to increase the distortion.

You should have plenty of distortion. Are you sure you are using a 1Meg gain pot? If so, check part values, particularly resistors.

You could try changing the op-amp, but I doubt this will make much difference.

[guidoilieff]

Rather than adding capacitors, you could try removing R11 and R22.
However, this is not going to increase the distortion.

You should have plenty of distortion. Are you sure you are using a 1Meg gain pot? If so, check part values, particularly resistors.

You could try changing the op-amp, but I doubt this will make much difference.

Hi. I've removed those resistors and had little to no effect on the audio. Maybe some volume drop.

Resistor values are ok. I check em all with a dmm, even pots. I can't remember if i did the same with the caps.


Since this layout is verified I think it's time to move on and convince my friend to star over or find another pedal with the same accutronics brick don't you think? or maybe you have another trick under your sleeve....? (is that an expression?)

[samhay]

Yes, that's an expression.
There are fairly easy mods that you can make. What do you want it to do?

[guidoilieff]

Yes, that's an expression.
There are fairly easy mods that you can make. What do you want it to do?

I think what my friends pedal is lacking is some distortion and a good amount of reverb on the bright mode.

I read somewhere that swapping R1 from 100k to 10k should improve something but I don't know what they were referring to

[iefes]

I think the bright mode is active when the switch is set so that C6, C7, R12, R13 are used. There's this 100k / 1k voltage divider which dumps a lot of signal. Try a higher value for R13, maybe 10k or higher. This should give you a lot more signal entering the belton brick and thus should result in more reverb.
I just saw that this mod is also mentioned in the comments section over at the effectslayouts blogspot page of the Reverberation Machine.

If you decrease R1 to 10k you'll get more dry signal, so less reverb. However, this could increase the distortion with high input signals. I've read about upping the gain of the first opamp stage to increase the overdriven sound on higher gain settings.

[guidoilieff]

I think the bright mode is active when the switch is set so that C6, C7, R12, R13 are used. There's this 100k / 1k voltage divider which dumps a lot of signal. Try a higher value for R13, maybe 10k or higher. This should give you a lot more signal entering the belton brick and thus should result in more reverb.
I just saw that this mod is also mentioned in the comments section over at the effectslayouts blogspot page of the Reverberation Machine.

If you decrease R1 to 10k you'll get more dry signal, so less reverb. However, this could increase the distortion with high input signals. I've read about upping the gain of the first opamp stage to increase the overdriven sound on higher gain settings.

That worked. Made R13 10k.


Next I'm gonna try R1 because it has no distortion at all.

or swapping R6 to a higher value to increase gain? maybe?