T-rex Replica; a tale of broken caps

 This pedal came in as it didn't produce any echoes anymore. He got the pedal quite cheap as it had this problem. With all controls cranked you can determine a very low volume echo sound that does respond to the tap tempo and settings of the knobs. Only one faint echo could be produced and the 'repeat' knob didn't alter that.

This pedal was made by T-Rex in the 2010's and became an instant classic. The combination of a very simple design with great warm analog like sound did a lot good. The Tap Tempo option and MIDI capabilities made the picture complete. More recently T-Rex introduced the new version that replaced this older model. One design change were the switches as the older push switches were quite fragile.

(yes, one of them is missing in my pictures). 

Even more recently a stereo version was introduced making the pedal even more complete.

The pedal runs on a 12V power supply although I had some good results with a decent 9V PSU. From the new stereo version the pedal runs on standard 9V.

The circuit

When opened up you can spot that this pedal has three boards:

- One analog board where all controls are located; the board is secured by tightening the bolts on the potmeters

- One digital board where the jacks are located. This board is secured by the jacks and the third board

- One switching board that is connected to the above described board on which the switches are connected to. This board 'glide' into a rail in the enclosure and is secured by bolting the voltage regulator to the enclosure.

The jacks are located on the digital board but are not connected to this digital side. Two shielded cables run from the jacks to the relais on the analog board (the big black chip you can spot on this board). One ribbon cable runs from the analog board to the digital board.

I've traced the analog part of the pedal. 

 

The problem

This pedal came in as the echo it produced was very faint. Only if you crank all controls you could hear an echo. On the pedal (when it came in) one cap was replaced by a 47u cap. On photo's on the internet I could trace that the original value of this cap was 1u.

I used an audio probe to find the location of the problem. This turned out to be all 1u caps in line with the audio signal. All, but one. I replaced all (but one) 1u caps with a newer equivalent and with this action the echo came back!

In the schematic above I marked the broken caps. 

A couple of years after this fix the pedal came back to me as it got the same problem again. In this case, I replaced the last lasting original 1u cap and the problem was again solved.

The sound

I like the pedal. I LOVE delay pedals and this unit just sounds really warm and good. The tap tempo adds a lot of control to your delay (or just use the onboard delay knob). Also the MIDI addition works great for a big setup.

Only think I didn't get was that the max feedback setting just didn't cut it enough for me; I needed just a little bit more feedback from the unit. 

 

A great little delay pedal with a lot of options!