Box of Hall Reverb build Troubleshooting

[vigilante397]

I know how much everyone loves helping moderately inexperienced pedal-builders troubleshoot pedals   but I really don't know where to go with this one.

I'm building the Box of Hall Reverb using the lovely Belton reverb brick, and I can't seem to get it to work. I made one attempt to build it a couple months ago but I had my voltage regulator flipped around which I am 80% sure fried my reverb brick. However, I'm willing to admit that I may be mistaken and there is just something wrong with my build. When I plug in I get clean tone through it, no distortion or anything, which is why I think it's the reverb brick.

I haven't been in this forum a long time, but I know that if I ask for help and post DETAILED information I'm more likely to get help

So this is the schematic I'm using: https://www.dropbox.com/s/96lmumkk3rj2b5r/Box%20of%20Hall%20-%20Heavenwithin%20mods.png

This is a picture of the front of my board: https://www.dropbox.com/s/0kc13vvutgilb0g/boxOfHallFront.jpg

This is a picture of the back of my board: https://www.dropbox.com/s/krj92zhcclt93aq/boxOfHallBack.jpg

This is a picture of the board with the brick: https://www.dropbox.com/s/dhyl7u85u2oon2q/boxOfHallBrick.jpg

And these are the voltages I'm getting:

78L05:
In - 12.34 (I'm using a 12v power supply)
Ground - 0.0
Out - 4.89 (that's why I think a 12v power supply should still be okay)

TL074CN
Pin 1 - 6.17
Pin 2 - 6.17
Pin 3 - 6.16
Pin 4 - 12.36
Pin 5 - 5.60
Pin 6 - 6.17
Pin 7 - 6.17
Pin 8 - 6.17
Pin 9 - 6.17
Pin 10 - 6.17
Pin 11 - 0.0
Pin 12 - 6.16
Pin 13 - 6.17
Pin 14 - 6.17

BT DR-2H
Pin 1 - 4.89
Pin 2 - 0
Pin 3 - 6.17
Pin 4 - 0
Pin 5 - 6.15
Pin 6 - 6.16

Other useful information: I followed the schematic EXACTLY. I was REALLY careful in cutting the board, I used thin diameter solder and a fine tip to avoid bridges, I didn't make any substitutions, I used the exact values noted in the schematic.

Do these look right? If not, what should they be and where should I start looking for problems?

If these do look right then I can conclude that the problem is in fact that the brick is fried and shell out the $18.50 (+shipping) Small Bear charges for a new one.

Thank you

[PRR]

Truly odd that you power the Brick with 4.89V but find 6.16V on a lot of pins. Also inneresting that a similar 6.17V is on many TL074 pins, where it may be expected (half-ref from 12.36V supply).

The "schematic" you cite is a LayOut, and is incomplete (pots jacks etc not shown). Deciphering what-connects-to-what (supposedly) is tougher on stripboard than on a Chevy Truck--- need a conceptual map.

A link to Brick documentation would be useful. (I could Google it but: so many moderately inexperienced pedal-builders troubleshooting pedals, so little time.)

[vigilante397]

Sorry about that. I suppose I don't actually have a schematic then. The hookups for the pots are at the bottom of the layout page, and I guess jack hookup is artistic license

This is the manufacturer's datasheet for the Reverb Brick http://www.smallbearelec.com/Projects/BTDR-1H.pdf

The datasheet includes an actual schematic (not layout) of an example application for the brick.

"Truly odd that you power the Brick with 4.89V but find 6.16V on a lot of pins."

I did find that rather odd, but that's definitely what I've got  

Any thoughts?

[induction]

This is the manufacturer's datasheet for the Reverb Brick http://www.smallbearelec.com/Projects/BTDR-1H.pdf

Careful. That's the datasheet for BTDR-1H. You claim to be using BTDR-2H. The pinouts are different.
Which are you using?

[vigilante397]

This is the manufacturer's datasheet for the Reverb Brick http://www.smallbearelec.com/Projects/BTDR-1H.pdf

Careful. That's the datasheet for BTDR-1H. You claim to be using BTDR-2H. The pinouts are different.
Which are you using?

Yikes, you're absolutely right. My apologies. I'm definitely using the BTDR-2H. I guess Small Bear thought they were similar enough to put that link on the page to the 2H.

[samhay]

^Truly odd that you power the Brick with 4.89V but find 6.16V on a lot of pins.

I don't think this is a problem if those are the input and two output pins of the brick - the brick claims to AC couples these pins.

I would suggest you cobble together an audio probe and see if you are getting audio into the brick.

[vigilante397]

^Truly odd that you power the Brick with 4.89V but find 6.16V on a lot of pins.

I don't think this is a problem if those are the input and two output pins of the brick - the brick claims to AC couples these pins.

I would suggest you cobble together an audio probe and see if you are getting audio into the brick.

That sounds like an excellent idea   ... how would I go about doing that?  

And question #2 - if I am getting audio into the brick but still no reverb out of it, would that mean that the problem is in fact that the brick is fried? I'm prepared to accept that outcome and have already ordered another one just in case.

[samhay]

audio probe: http://www.diystompboxes.com/pedals/debug.html

If sound is getting into the brick and you can't hear it coming back out again, then you have probably either fried the the brick, or you have grounded the outputs.

[vigilante397]

audio probe: http://www.diystompboxes.com/pedals/debug.html

If sound is getting into the brick and you can't hear it coming back out again, then you have probably either fried the the brick, or you have grounded the outputs.

Excellent! I shall give this a try when I have a bit of free time, be it this evening after work or tomorrow. The audio probe definitely seems like the kind of thing I should have around. You've been remarkably helpful and I'll keep you posted on progress

[PRR]

> brick claims to AC couples these pins

Ah, yes, you are correct. I have struck-out my comment, and will try to remember this.

We need a map to plan an attack (such as signal tracing). I found a plan with a similar number of opamps doing pretty much what we expect. It isn't the SAME as yours but is probably a useful guide.



Signal comes in (left) and is buffered so we can abuse it without loading the guitar.

Dry signal goes right across to the Mixer and the output (right). This is because the echo-module is ALL echo, sounds like the player is in the bottom of the well, so we need some non-reverb signal to place him at the top of the well.

A tap of the dry signal goes to an EQ stage which cuts bass so it isn't boomy/farty. Then to the Echo Module. This model has two differently-delayed outputs which can be assigned left/right in stereo. For guitar-cord we just mix them together (5K6 resistors) for a twice-phatt sound. We may want a whisp of reverb or or a Topanga Canyon, the Reverb pot gives a little or a lot. The Mix stage blends dry and wet. (There are other ways to mix; this one is unusal but I have seen it on Belton plans before.)

And up top your raw supply (12V is safe for TL07x chip), Vb divider and buffer, and a 5V regulator (4.89V is close-enough for government work).

From symptom and history, I suspect you MAY have burnt the Belton, and you are hearing only the Dry signal. But poke the Belton input and both outputs. Input should be dry signal and output should be sopping wet.

Bogus wiring around the EQ stage or on the Reverb pot could be blocking valid wet signal from the mix stage.

[vigilante397]

Okay, so I have my audio probe up and running and I have the following to report:

TL074CN
Pin 1 - nothing
Pin 2 - nothing
Pin 3 - nothing
Pin 4 - odd distorted squeals (this seems significant, as it is also the only pin receiving ~12v)
Pin 5 - dry guitar signal
Pin 6 - dry guitar signal
Pin 7 - dry guitar signal
Pin 8 - nothing
Pin 9 - nothing
Pin 10 - nothing
Pin 11 - nothing
Pin 12 - dry guitar signal
Pin 13 - dry guitar signal
Pin 14 - dry guitar signal

BT DR-2H
Pin 1 - nothing
Pin 2 - nothing
Pin 3 - nothing (as I understand it this was an important place to have something ) see update below
Pin 4 - nothing
Pin 5 - nothing
Pin 6 - nothing

Any thoughts? PRR I'm looking at your schematic and it's still not really giving me a clear idea where to start with detailed signal tracing  

[vigilante397]

I just looked at the datasheet for the TL074 found here http://www.futurlec.com/Linear/TL074CN.shtml and it looks like pin 4 is supposed to be VCC, not pin 1 Does that mean I'm sending 12 volts into it when I'm supposed to be sending 5? Or is this the wrong datasheet?

This is REALLY embarrassing, but I was just comparing my board to the layout for the millionth time and noticed that I LEFT OFF A CAPACITOR. I AM ONE CAPACITOR SHORT OF A REVERB.

So I'm warming up the soldering iron now and I'll let you all know what happens. 

[vigilante397]

UPDATE

So I kicked myself a few times for being an idiot then went back and added the missing capacitor. I still got the same signal across the same pins of the op-amp, but this time I got dry signal from Pin 3 of my Belton brick On Pins 5 and 6, which I understand to be the outputs, there's nothing. When I turn the Reverb pot ALL THE WAY UP then crank the amplifier on the audio probe ALL THE WAY UP I can hear a TINY bit of the signal, but it's bone dry. This leads me to believe the problem is in fact the Belton brick

I don't know why I put a smiley face on the end of that sentence, that's the priciest part of the pedal 

[samhay]

Bummer, Sounds like the brick is fried.
If you want to be sure, unsolder the connections to the output pins and see if they are still mute.

[vigilante397]

Bummer, Sounds like the brick is fried.
If you want to be sure, unsolder the connections to the output pins and see if they are still mute.

I've already got one ordered, and if this pedal turns out to be as good as people say it is, then it will be worth the money on the extra brick, as will the lesson of thoroughly studying pinouts before soldering transistors and IC's.

And I think I probably will try out unsoldering the connections and probing it again tonight. Thanks for the help

[vigilante397]

Okay, so it turns out the problem was that the brick was fried. I finally got my new brick today (USPS estimated it would be here last Monday ) and got it all wired up and..... worked first try without a problem Great sounding pedal, I highly recommend it for someone looking for that classic spring reverb tone in a smaller package.

[samhay]

Well done getting it going and R.I.P. the brick.