TC Electronic Echobrain Signal Loss in Bypass

[Big Monk]

Just a shot in the dark here while I wait to see if TC will send me a service schematic and before I build a True Bypass loop box.

I recently acquired an Echobrain. I used to own an Ibanez AD9 and I have a real soft spot for these types of analog delay pedal. The good news is that the pedal sounds really great. Nice and lush with a good range of very slight accent type of echo that works well with distortion, as well as really nice slapback.

I do notice, however, a significant drop in signal level when the pedal is bypassed. At first I didn't notice because I was just using the pedal on all the time (very short time, low repeats to thicken up the sound) but when running through the chain the other day, I noticed it. I did some basic tests and verified equivalent levels plugged straight into amp and with pedal enagaged, but in bypass mode (it claims to be True Bypass) there is a significant drop in volume and high frequency content.

Just thought i'd poll the regulars to see if anyone had any insights. I asked TC for the schematic to see the signal path in bypass and worst case i'll just build a loop box.

[duck_arse]

put a blank plug into both in jack and out jack, switch to bypass, measure resistance from tip in to tip out, and from each tip to ground. might reveal something.

[Big Monk]

put a blank plug into both in jack and out jack, switch to bypass, measure resistance from tip in to tip out, and from each tip to ground. might reveal something.

Great idea Duck! Should have thought of that.

Frankly, I think even if I diagnose it and/or TC gives me the schematic, a loop box might be best anyway. There are surface mount components all over this thing and i'd prefer to just use a bypass box so i don't smoke a good pedal goofing around.

[Big Monk]

put a blank plug into both in jack and out jack, switch to bypass, measure resistance from tip in to tip out, and from each tip to ground. might reveal something.

Measured about 500k ohms when I check it out this evening. Something ain't right!

[antonis]

500k between tips (IN-OUT) smells an "open" switching FET..
(either defective or not properly biased..)

[Big Monk]

500k between tips (IN-OUT) smells an "open" switching FET..
(either defective or not properly biased..)

Unfortunately, I have not gotten a response back from TC to my request for the service schematic. For the time being I have the spare parts for a true bypass loop box. That should do the trick.

[duck_arse]

500k between tips (IN-OUT) smells an "open" switching FET..
(either defective or not properly biased..)

an open fet in a true bypass pedal, when bypassed, measures how many ohms?


[there's coffee here if needed.]

[antonis]

I might lead you down the garden path, Stephen...
(and I can ensure you I don't wish for it..)

[duck_arse]

are we off to smell the roses, then?

[antonis]

I presume local moderator should feel a sudden impulse for violent ban so let's stay on topic..

In case of true bypass pedal only means a DPDT mechanical switch (neither IN/OUT buffering nor JFET switching arrangement) 500k resistance between IN-OUT tips calls for a defective DPDT switch, period..

In case of IN/OUT buffering & JFET switching, it calls for defective JFET (500k R_DSON) or some bias issue, period again..
(as far as effect ON works fine, both buffers & series JFET switch should be OK..)

P.S.
In any of the above periods case, due to local time, cider is much appreciated..

[Big Monk]

I presume local moderator should feel a sudden impulse for violent ban so let's stay on topic..

In case of true bypass pedal only means a DPDT mechanical switch (neither IN/OUT buffering nor JFET switching arrangement) 500k resistance between IN-OUT tips calls for a defective DPDT switch, period..

In case of IN/OUT buffering & JFET switching, it calls for defective JFET (500k R_DSON) or some bias issue, period again..
(as far as effect ON works fine, both buffers & series JFET switch should be OK..)

P.S.
In any of the above periods case, due to local time, cider is much appreciated..

The TC switches are notoriously bad. I'm not complaining too bad because they are a budget pedal but they have these sturdy cases and are otherwise well built. Why would you throw a plastic switch on these things?

[Big Monk]

Ok.

TC Electronic got back to me with the schem:



I know at this point it is stating the obvious but looks like a switch issue for sure. It's a 4PDT but it looks like replacement wirth a 3PDT will be suitable because SW1-A and SW1-B are essentially a single switch.

[Big Monk]

Just want to bump this with some recent developments to see if someone can get me my pedal back to normal.

I had this in storage awaiting a switch replacement and in addition to the volume loss in bypass I was experiencing, I now have extremely low volume in general, even with the pedal on.

[willienillie]

Maybe the switch has had beer or soda spilled in it?  Did you get the pedal used?  The SW1A + SW1B redundancy should have prevented the original issue you were having.

Edit:  Oops.

[Big Monk]

Maybe the switch has had beer or soda spilled in it?  Did you get the pedal used?  The SW1A + SW1B redundancy should have prevented the original issue you were having.  It's not true bypass, which would have been at least as simple as what they did.

I did purchase it used. It's a plastic box switch. It has what appears to be a sturdy stomp switch on the exterior but it's really a spring loaded cover that pushes an itty bitty plastic switch.

I'll have to get in there and replace the switch I guess. It's finding the time to do it that's troubling!

[willienillie]

I edited as you were quoting me.  It IS true bypass, I was looking at it wrong.

[willienillie]

I'll have to get in there and replace the switch I guess.

Is there any way to clean it out?  Maybe it's all sealed up, but some switches have holes.

[Big Monk]

I'll have to get in there and replace the switch I guess.

Is there any way to clean it out?  Maybe it's all sealed up, but some switches have holes.

I'll check tomorrow. I'm pretty sure it's fully sealed but there may be hope for a quick fix. I have some spare 3PDT switches in my parts organizer so it would simply just be getting the old switch out cleanly and rigging a mini 9 wire harness to attach it.

I have some wiring to do on a Ge Rangemaster and Tonebender plus a modified Valve Junior board so I'll get in there soon enough.

[Big Monk]

I edited as you were quoting me.  It IS true bypass, I was looking at it wrong.

Coming at it from a more practical direction, I may just jumped out the switch first to ensure it is actually the culprit. Frankly, I'm not sure I want to spend the time troubleshooting this thing if it isn't the switch, even though I love the sound when it's working.