Orban 111B No Output Either Channel

Last week I bought a broken Orban 111B. For some reason a previous owner removed the dual input/output attenuation potentiometers . They aren’t jumpered so obviously it doesn’t pass signal.
They are an unusual pot because it has two values...10K and 500K log clockwise.There isn't a readily available modern alternative so I ordered individual pots from Mouser.

Unfortunately I'm not getting any reverberated output. One the left channel, using the "mixed" output I get dry, unaffected signal and the input does turn it up or down, but the output doesn't do anything. If I increase the input, the "limiter" indicator flashes so I believe it's getting that far! Using the balanced, all wet output I get nothing.

On the right channel, again using the "mixed" output I get dry, unaffected signal but it cuts out. However the "limiter" indicator stay solid no matter what so not sure what's going on there. Using the balanced again nothing.

Any thoughts on where to start? I recapped the electrolytic caps.

Here's the schematics: http://www225.pair.com/audio/waltzingbear/Schematics/Orban/111B.htm

You need an oscilloscope to see where the signal gets lost. If you don't have a scope, you could use a sound card with a high-z buffer.

But how are you going to use two pots in place of one?

I don’t have a scope but could I use a multimeter?

The original pots were stacked, so I’m just going to drill a couple extra holes in the face plate

sws2h said:

I don’t have a scope but could I use a multimeter?

The original pots were stacked, so I’m just going to drill a couple extra holes in the face plate

Click to expand...

Eah. That seems a little drastic. You could use a 100K dual concentric (smallbearelec has them) and tweak the circuit a bit. Using 100k vs 10k on the input is no problem. And 100K for the output is no problem either (better actually) but there is a filter network connected to it that would have to be adjusted quite a bit. Or, if what you're plugging into has a level control (mixer fader?), you could just hard-jump the output to maximum and then use the 10K input pot only.

As for using a multimeter probably not. In theory if you put in a sine tone, the meter AC measurement should pick it up ok. But a sound card would be much better. You don't have any kind of audio interface for the computer? Even the builtin computer sound input would be fine if you have the right circuit in front of it. Or perhaps just some kind of amplifier with a speaker and then you could test by ear. You would need a cap coupled high impedance probe in any case. The simplest might just be 100n into two resistors like 470K / 100K. Then take signal from across the 100K and feed that into the puter. It will be noisy but that doesn't really matter for debugging. An active circuit could be very quiet (maybe even use the voltage coming out of the computer to power a simple buffer).

Cool piece of gear to have (I have one)!

I agree with square wave on using a different value dual pot. Input could be higher. I think you could put a dual 1M in and it would probably work fine.

I repaired one of these a few years ago and it was tough to troubleshoot.  The limiter module is all encased and not serviceable so hopefully that is fine. Be careful while testing around it.  I think I have a better schematic - the link you posted is hard to read.

First test is to have the output all the way up and physically lightly shake it. If you hear the springs on the output (fully wet), then the recovery is OK. If you don't hear anything than there is a problem with either the spring tank or the recovery stage.

Assuming you don't get any sound, then take the output plug going into the reverb tank and try plugging it into a different reverb tank. Try tapping the 'good' reverb tank and see if you hear it. That will tell you if it's the tank or the recovery circuit.
Hopefully the reverb tank isn't the problem.
Replacing a IC in these isn't easy but it possible. You'll need a good desoldering gun and then put a socket in.
On mine it was a bad IC.

I tried to upload the manual in the tech docs section but it was too large. PM me your email if you want a copy.

A better schematic is in the tech docs section already if you want a version you can read.

if you want, send the manual to Ethan who. can convert it and make it all fit.

sws2h said:

Any thoughts on where to start?

Click to expand...

You need to check if you have signal at pin 1 of IC101; that's the drive signal for the tank. You then need to check the tank itself. Start by checking continuity of the input and output coils.

BTW, you could use 2x50k Log pots, at the cost of modifying the Twin-T filter C125,127 & 129 and R135,137 & 139. The original  load is 333k, so you would need to multiply cap by a factor6.6 and divide the resistors by a factor 6.6.

sws2h said:

The original pots were stacked, so I’m just going to drill a couple extra holes in the face plate

Click to expand...

Before you do that, contact Orban. They do have some spares for old kit

Nick Froome