DeadAstronaut's Chasm Reverb

[MAO]

There's already a verified smaller layout with fewer cuts and links  posted here.

I designed this layout so the brick would mount to the underside of the board, lined up the off-board wiring, have all the components laying down and holes to route the wires through the board.

Unfortunately, these obsessions resulted in a larger layout with a ton of cuts and links. But rotated clockwise, it still fits in a 125B. I did have to file down the side edges just a little.

The build doc is here

Note: bottom IC is upside down

Update - 06-12-2016: Cut (or omit) the link between Pins 2 & 4 of the brick, It's not needed as pins 2 & 4 are connected internally on the brick itself. Also, consider socketing the 47k resistor as this controls how fast the oscillation kicks in when the switch is engaged.

VERIFIED 04-28-2016
(I found a 2v drop across the 33R on mine, I lowered the value to 10R for a 0.64v drop)


(with temporary brick harness - recommended in case troubleshooting is needed!)


(and the payoff for all the extra cuts and links - tidy wiring)

[Mark SL]

Built it.  Doesn't work and 33R starts smoking.

[MAO]

Ouch, let me check it over again.

In fact, I'll build it myself tonight and we can compare notes.

[MAO]

Shoot, did you catch that the bottom IC is upside down?

[Mark SL]

I didn't catch that but it doesn't explain the fried resistor.

[Mark SL]

Right off the bat, the first thing I checked,you have the 33r before the 1n5817 and it should be reversed.  I'll keep looking for other mistakes.

[Mark SL]

I switched them around and it is working to a degree.  Doesn't seem to get very wet at max and the Oscillation switch doesn't do anything.

[Mark SL]

The Decay pot has no effect on the reverb either.  It just has a kind of mid level decay no matter where the pot is set.

[Mark SL]

Switch the 10u and 100r on the output.

[MAO]

Thanks Mark,

I just finished mine and it worked as is.

I did notice there was a 2v voltage drop across the 33R though, I lowered mine to 10R. Now I have a 0.64v drop across the 10R.  

Let me now if I'm wrong about this - I don't think it matters which comes 1st with a resistor and diode in series.  Same with a resistor and capacitor in series, shouldn't matter which comes 1st.

If you don't mind, check the voltage drop across the 33R, curious what you see. I had 9.14V before the 33R and 7.14 after the 33R.  Now I have 9.14 before the 10R and 8.5 after.

 

 

[MAO]

You'll need the Decay knob turned up for the oscillation to kick in.

Mine seems to be working just like this video, but without all the background hiss :0)

https://www.youtube.com/watch?v=_qDYDs661ts

Here are my voltages for reference

9.14v supply

Top TL072
1. 4.08
2. 4.08
3. 3.68
4. 0
5. 4.08
6. 4.08
7. 4.08
8. 8.18

Bottom TL072
1. 4.08
2. 4.08
3. 4.08
4. 0
5. 4.08
6. 4.08
7. 4.08
8. 8.18

2n5457 (both)
D. 4.08
S. 4.08
G. 0

2n7000
D. 8.18
G. 4.08
S. 4.65

78L05
I. 8.18
G. 0
O. 5.03

[dan.schumaker]

I just want to say I got this one working too.  I burned out a 10R resistor, but replaced it with a 1W 10R resistor, and everything sounds good now.  I would think you can verify this :)

Thanks for the layout!

[MAO]

Thanks Dan!

If it's easy enough to do, would you check and post the voltage drop across the 10R?

The Wampler Faux Spring Reverb draws 78ma, I would think the Chasm is around the same.  I believe that calculates to .06 watts dissipated by the 10R.

That should mean a 1/4 watt resistor would be fine.

I seem to recall Madbean eliminated a similar resistor from the Moodring Reverb as it too would burn out. I think he went with just the 1N5817 in the 2015 release and eliminated this power supply resistor all together.

Curious, how long did it take for the resistor to burn?  

[dan.schumaker]

I'll try to measure the voltage when I get home.

It was pretty quick for it to burn out.  When I first built it up, there was no sound, and I could feel the 10R getting hot.  A few days later I revisited it, taking voltages.  That is when I noticed the resistor burned out.  It hadn't been plugged into 9V very long at all.

But now that I got that sorted, it sounds really good, and is super clean for a Vero

[traktop]

This kind of layouts are great, so build friendly...
I was late to this one, so I built the other one around:

It fired up first time, but the damp knob works in reverse, so I guess I wired it wrong...

Used 2n5458´s and seemed to carry a certain amount of white noise when the damp knob is fully open... Is not that the effect is noisy all the time with a backround noise like the video, is more like when you hit an staccato chord you hear a blow sound that quickly fades out. Maybe a certain faulty cap?

Both 2N5458s drains read 4.08v from a source power supply of 8.97v.
The 2n7000 reads 8.20v at the drain.
I get a solid 4.99v going to the brick.

The TL074 reads at follows:

1 -4.09v
2 -4.09v
3 -3.67v
4 -8.19v (Vcc+)
5 -4.09v
6 -4.09v
7 -4.09v
8 -4.09v
9-4.09v
10-4.09v
11-0v (ground)
12-4.08v
13-4.09v
14-4.09v

It sounds great anyway. With the decay at full and the tone at 12 o´clock it feels like a tape echo washed on reverb.

I´m sure this would be great with a short brick too. I only tried long and medium ones, and always felt that it has too long of a decay time to start with.
That linear vol pot is smart, (I used a log one), as it seems that is going to be dialed always on the last quarter of the run, so you get more precission.

[MAO]

Update 06-12-2016 I was looking over the datasheet for the Belton Bricks and noticed pins 2 & 4 of the brick 2 are connected internally. They show the 5v regulator's ground connected to pin 2, and the rest of the circuit's ground connected to pin 4.

Can't easily replicate that setup with this vero, but cutting (or omitting) the link connected to Pins 2 & 4 of the brick should be good enough. (cut and verified by me)

Also, consider socketing the 47k resistor as this controls how fast the oscillation kicks in. Lower = faster

[MAO]

Finally boxed it, and slightly modified.

I removed the 33R power resistor altogether to make room for an additional oscillation resistor.  

I replaced the standard OSC switch with a SPDT on/off/on giving a 3rd setting for 'maximum trails without self oscillation' (w/Damp and Decay on full)

[traktop]

MAO Pedals wrote

I replaced the standard OSC switch with a SPDT on/off/on giving a 3rd setting for 'maximum trails without self oscillation' (w/Damp and Decay on full)

Very nice.
So what does the "off" position is doing here? No resistor at all...?

[MAO]

Thanks traktop,
 
The off position leaves the stock 100k resistor in the signal path, switch up parallel's in an 82k (100k might be better if oscillation is to much), switch down parallel's in a 56k (62k or 68k may be better if oscillation is over the top - distorted)

In the up position, with both Decay and Damp full CW, I get long trails just on the verge of self oscillation, the down position crazy self oscillation comes on quickly.

[traktop]

I´m trying to make the volume pot more usable. It always seems to remain on the last quarter of the pot run, what makes quite hard achieving unity gain,(tried with 100k log/linear pots with same results).
Looking at the schematics, maybe reducing the 5k6 resistor before the output buffer will do...? (or lowering the volume pot value...?)
Cheers, Gilberto.