BTDR-3 reverb module

[JazzGuitarGimp]

At the very minimum, you will need two resistors for the second opamp stage to work: one from the output (pin 7) to the inverting input (pin 6), and one between the brick output and the inverting inout. Let's call them Rf (feedback resistor) and Ri (input resistor), respectively. The gain is set by Rf/Ri. I would start with a gain of two, so make Rf 100K and Ri 51K. Connect the non-inverting input (pin 5) to "common". You will need an AC coupling capacitor between the output of the opamp and the input of your amp, something in the neighborhood of 1uF. If you use an electrolytic cap here, connect its posative lead to the opamp output. Don't use a tantalum cap here.

[martin manning]

For the breadboard experiment, why not wire it up exactly as shown in the Belton app notes? The only things you need to add are the Vcc/2 voltage supply (I would use 2x 10k to reduce current drain) and DC blocking caps at the input and output (anything for now to get it working, 100n would be fine).

[Theashe]

Here's a datasheet that I found: http://amptone.pl/templates/images/file ... btdr-3.pdf

The datasheet says that the inputs and outputs are already AC coupled.

[martin manning]

The device itself is AC coupled, but if the op-amps in the circuits shown are powered by a single supply voltage there will be DC on their inputs and outputs because the "common" points are connected to Vcc/2.

[John_P_WI]

Man at 60 to 100 ma that is a power hog for a ss device!

[xtian]

Man at 60 to 100 ma that is a power hog for a ss device!

Yes, I have observed it draining my 9v batteries quickly!

[xtian]

Whelp, after my fourth or fifth attempt at the Belton schematic for the recovery stage, I gave up. Couldn't get it to pass signal. Instead I radically simplified, using Lou's recovery stage (opamp's + tied to common, - to signal from BTDR, and output AC coupled. Set gain to 2. Works great.

Next I need a create a mix control. Want to stuff this in a pedal.

[JazzGuitarGimp]

Do you want the mix control to be completely dry at one end and completely wet at the other end? Or do you want the guitar's signal (dry) to always pass from input to output at unity gain, with the "mix" control adding no reverb at one end and maximum reverb at the other end, maintaining the same, unity gain dry signal throughout the mix pots' rotation?

[xtian]

Do you want the mix control to be completely dry at one end and completely wet at the other end?

This. I've been experimenting with various pots. 20k to 50k seems like a good compromise. Anything larger causes the signal to drop too much when the control is at 50%.

What's your recommendation?

[John_P_WI]

Xtian do a search on the reverb pedal rub a dub for inspiration.

[xtian]

Xtian do a search on the reverb pedal rub a dub for inspiration.

I love it. Where was this a week ago?!?

[xtian]

The Rub-a-Dub Deluxe uses the BTDR-3h module:

http://1776effects.com/wp-content/uploa ... xe-BOM.pdf

[John_P_WI]

Xtian do a search on the reverb pedal rub a dub for inspiration.

I love it. Where was this a week ago?!?

Hey i can't give up all my secrets right away lol... truly i had meant to but work and Easter interfered. Just think of it as a forced learning period...

[JazzGuitarGimp]

I was going to suggest a 25K pot, but since you already have a 20K, that will work just fine. I am going to assume you're using U1A (output pin 1) as the input buffer, and U1B (output pin 7) as the recovery stage. If you have it the other way around, then swap the CCW and CW ends of the mix pot in the following paragraph.

First, remove the AC coupling capacitor from the output of U1B for later use.
Then, connect the CCW end of the pot to U1, pin 1, and the CW end of the pot to U1, pin 7. Connect the wiper of the pot to the plus side of the cap you put aside (assuming it is polarized), and connect the other end of the cap to your output jack tip. Though it isn't necessary, I would add a 1M resistor from the output tip to GND - this will prevent a pop when plugging the reverb pedal into the input of a live amp.

The DC voltage at each end of the pot will be the same: (Vcc/2), meaning there is no net DC voltage across the pot, so there won't be any scratchiness when making mix adjustments.

You may find that you get too much of a volume increase when you engage the pedal (I am assuming you still have the recovery stage gain set to 2). If that is the case, then you will need to adjust the gain of the recovery stage to something closer to 1.

If you find the dry signal is too thin, increase the value of the output AC coupling cap. 10uF will give you an Xc of 200R at 80Hz, which, for all intents and purposes with give you full-bandwidth into a 1M load. 1uF will give you an Xc of 2K, and you might notice a slight bass roll-off.

HTH
Lou

[xtian]

Using the Rub-a-Dub values now, working better and better.

Lou, you were a step ahead of me--I noticed a bass rolloff, and it is fixed by using 10uF on the output.

Testing by pumping an 808 drum beat thru the circuit (http://www.html5drummachine.com/) -- it's very wide bandwidth, so easy to hear what's up. Also great because the 808 samples have very sharp decay, so easy to hear when I'm adding reverb or not.


Question about FLAT EQ amplification using opamps. At this point, I have no feedback snubbers (the 47pf and 100pf caps in the schematic). Are they required to get a linear response?