BTDR-3 reverb module

[xtian]

Phil, I'm starting my own thread so I don't clutter yours.

I have had limited success. I am able to get the TL072 dual-op amp working by itself as a buffer/amp, and the BTDR-3 by itself as a reverb, but I cannot get them both working in concert on the breadboard.

But, the BTDR-3 by itself sounds very good. I just plugged a guitar in, thru a 33nF cap into pin 3 of the BTDR-3. The outputs 5 and 6 are simply jumpered together, and sent out to my Smokey battery-powered amp. The rig is powered by 5vDC from an LM7805, supplied by a 9v battery. As simple as possible with as few components as possible.

This configuration is WET only, no dry signal. The reverb sounds good! The first thing I experimented with was the Depth control. First, I disconnected the two 10K pots, and noticed that the reverb time got VERY long, and began to self-oscillate. Then I put 39K resistors in place of the 10K pots, and found I had a nice long decay, but no oscillation. So, forget about having 10K pots there! Much higher values allow longer decay times--possibly 50K will be a good top value, but need more experimentation.

I'll hack more on it later. Can't understand what I'm doing wrong with the TL072.

[JazzGuitarGimp]

Aaron,

Can you post the schematic you're working from, with the opamps and reverb brick? Are you powering the opamps with a single supply, or a bipolar supply?

Cheers,
Lou

[bluesfendermanblues]

Aaron,

Can you post the schematic you're working from, with the opamps and reverb brick? Are you powering the opamps with a single supply, or a bipolar supply?

Cheers,
Lou

It's in the top left corner of the pic.

[xtian]

I'm using the schem from the application data sheet. I've notated it with pin numbers.

Note that the BTDR's power and signal grounds are internally connected, so there's no way to run separate busses for the grounds. I'm connecting together all points marked "common," the TL072 ground (pin 4) and the negative pole of my battery.

I was getting zero signal out of the BTDR when I had it wired up like this.

[martin manning]

"Common" points go to Vcc/2 when using a single (non-bipolar) supply.

[JazzGuitarGimp]

Martin is right. You'll need to create a 1/2Vcc supply. But you should also be running the opamp at +9V directly from the battery, not +5V as you have indicated. Use two 1K resistors in series from +9V to ground to get +4.5V for the "common" connections. You should add a small electrolytic (100 to 220uF) from +4.5V to ground (across the lower of the two 1K resistors).

I'm curious about what you've discovered with the Decay Time set resistors. When you leave these two terminals open, is the oscillation you're hearing more like infinite feedback from a delay pedal?

Cheers,
Lou

[xtian]

+4.5V for the "common" connections.

Confused because the "common" points on the schem are where I had the sleeve of input and output 1/4" jacks connected. Instead I will connect the sleeve to 0vDC, same as battery negative terminal?


I will make a video later of the sounds I'm getting.

[JazzGuitarGimp]

Correct, all points with the ground symbol go to battery negative, and all points labeled common go to +4.5V.

[Phil_S]

Separate thread is a good idea.

I got up early today to solder the prototyping board for the brick. I came up with at least one missed solder. I've got to go over it with a magnifying glass to be sure the other joints are good. Provided it can pass my lackluster QC process, I'm inclined to put it into the amp and see if it is "on." I've discarded some of the good advice Lou gave on the pots. I did not have the space on the board and I've got holes in the front panel of the chassis. This combination of circumstances gave me a path of least resistance. Given the elapsed time on the project, I took that path! This means I've got to make a wiring harness to get from the pots on the front to the board on the back. Yeah, a great layout special. I've got a short length of 6 conductor shielded and I've got yards of shielded single pair 22 AWG (that I like better) that I might shove inside of some heatshrink. I'm not sure I'll get it done tonight and I'll be traveling over the weekend, so this might get delayed yet again.

Then I have to figure out where to connect everything ;-}, and see if I can get the soldering iron to actually solder it. Not joking. This, for me, on those tiny boards, is a challenge.

I won't post a progress note again in my thread until there is something to tell, pass or fail. This sort of thing...making a harness, soldering it, tightening screws...it is like watching the grass grow, so I'll skip that minutae.

I'm very happy to have a partner in crime on this. The brick is out there already working for others, so, it is just a matter of getting the circuit right. "Just..." that's more that one might imagine.

Between Martin and Lou, you are getting the best advice on the planet. Stick with this and you'll get it working!

Good luck.

[Theashe]

For my own interest, Xtian (or anyone else who knows), can you tell me what the differences are between the BTDR-2 and BTDR-3 as far as reverb tone and functionality go? I'm about to start a 12W build using one of the two, and NE5532 op-amps (I prefer them to TL072).

As far as protoboard choices go, I'm not a fan of the single-dot or long-strip styles. I just finished a solid state headphone amplifier, and I found it a lot easier to go from breadboard testing to this type of board because of the similar layout:

http://www.ebay.ca/itm/10x-PCB-8-5x20cm ... Sw2s1UrlVx

If I'm not allowed to post links to ebay, I'll replace that with a picture.

[xtian]

^^ If you read the BTDR-2 and -3 spec sheets, you'll know as much as I do!

Made a demo:

https://youtu.be/t_0Xc-1WugM

At 0.45 I pull out the Depth pots, making the depth resistance value very high, and inciting self-oscillation or feedback. It's a pretty cool feedback, too...

You can also hear at the end of the video when I replace the pots and turn the value down to 0 ohms, the noise floor also decreases with the Depth.

[Phil_S]

The 3 module let's you adjust the "spring length" or time factor decay. The real spring tanks come in short, medium, and long decay. This is controlled by a depth pot. The 2 module has no adjustment. I think they offer the 2 in short, medium and long as a fixed factor. For an extra buck you get a more complicated build and another adjustment.

That demo sounds great! Congratulation on getting it done so quick. I am slow as molasses on this. Part of the problem is trying to shoehorn it into an amp build.

[xtian]

Congratulation on getting it done so quick. I am slow as molasses on this. Part of the problem is trying to shoehorn it into an amp build.

Mine isn't done. I still can't get the recovery stage running properly. In the demo, I'm going directly out from the BTDR's pins 5+6.

[JazzGuitarGimp]

It sounds like the decay time is continuously adjustable? I was thinking there may be three presets for short, medium and long decay, and the first third of the pots' rotation would give you short, the middle third would give you medium and and the last third would give you long decay times...

As for the recovery amp, did you move pin 8 of the opamp to +9V? Pin 4 of the opamp should be at ground, and all points labeled common should be at +4.5V.

I am going to order one of these in the next day or two. At this point, it sounds like the decay pot might actually want to be 50K, or even 100K.

I've finished a pcb layout for this. It is 1.8" x 3.5", and has trim pots for:
- Input Level Trim
- Channel 1 Decay
- Channel 2 Decay
- Mix or Blend (pans between the two channels for an infinite mix of the two)
- Tone (a tilt style tone control)

Any of the trimpot solder pads can be wired to panel-mounted pots.

No power supply circuits on the board, it will need +5V and +15V from an external source. But I will also do a power supply board that will provide these two voltages from an unused 5VAC filament tap.

I plan to make these unstuffed PCB's available for sale if there is enough interest.

[xtian]

It sounds like the decay time is continuously adjustable? I was thinking there may be three presets for short, medium and long decay, and the first third of the pots' rotation would give you short, the middle third would give you medium and and the last third would give you long decay times...

It is a continuous, analog adjustment, not stepped.

As for the recovery amp, did you move pin 8 of the opamp to +9V? Pin 4 of the opamp should be at ground, and all points labeled common should be at +4.5V.

Yes. The first stage works great.

I totally simplified the second stage: input signal, Vcc/2, output. Tried isolating input and output with caps to block DC. Voltages measure fine. No output. Tried swapping pins 5/6, no change. Tried no NFB, yes NFB.

I am going to order one of these in the next day or two. At this point, it sounds like the decay pot might actually want to be 50K, or even 100K.

Yes! I searched for a ready-made PCB. Look at the attached schematic and PCB, which I found at http://uk-electronic.de/onlineshop/prod ... ts_id=3758

I plan to make these unstuffed PCB's available for sale if there is enough interest.

Very intersted! Maybe 6 units.

I don't think separate Depth pots has much value...unless in stereo operation. It doesn't make much tonal diff. in mono mode.