Two-Rock TS1 / ELI Ground Loop Hum nightmare

[ocianic]

IMG_5357.jpeg

Hi Guys,

Interested if any Dumble style ODS users who use FX loop buffers can help?

Going through troubleshooting hell to try to solve this ground loop hum issue. I have a TS1 and Two-Rock recently sent me their ELI (FX Loop buffer interface) to add Reverb.

The factory ELI (Effects Loop Interface) is causing an obnoxious 60 Cycle Hum when connected to the TS1. I have checked and exhaustedly tried to troubleshoot what's is causing this with the following:

1) Placed the Surfybear and ELI on the ground and away from the amp transformers.
2) Tested cables, and tried multiple good cables.
3) Sent the ELI back to Two-Rock for repair _ Was returned by them saying it had been fixed.
4)Purchased multiple hum eliminators and adaptors that remove the ground pin on receptacle plugs


None of these solved the problem.

The amp is dead quiet when a place any FX unit in the TS1 loop direct without a buffer. (Strymon, Surfybear etc)

It is only the ELI that is causing the hum and it is specifically on the return side of the ELI.

I took the setup to the Guitar Sanctuary in Dallas a couple of days ago to get another opinion that I wasn't just making some simple mistake. They verified that my setup was correct and the ELI was the cause.
We cross-referenced it in the loop of a Bloomfield and the problem was the same. Here is a short showing both amps...

https://youtube.com/shorts/XB0Z9q74PNs? ... r9ubOYnAWz

Let me state that Eli and Mac at Two-Rock have been amazing, super kind and generous and have helped me a lot. I just can't understand how this unit could be designed specifically for my amp but be causing this hum.
They don't have any answers either.

The combo of the TS1 and Surfybear sounds amazing, if only I could get rid of the hum somehow.

Any ideas would be greatly appreciated!

Cheers

[R.G.]

First, good job of elimination. Going through cables and connections and substituting units until you can eliminate down to one chunk is the right first step.

Do you have the tech skills to work inside the units, soldering and de-soldering, using meters and such? I'm guessing not, from the description. That limits your actual fixing options to finding the right tech.

But I do have guesses and tech approaches. My first guess is ground routing and connections having a ground discontinuity; second is an issue with power supply leakages; third and is an issue with AC power "polarity" if any of the units have two-wire AC cords. These are really generic, but they're where I would start. This is going to sound simplistic, but I don't have the schematics of the units to consult.

1. How are the units powered? The amp has a wall plug; do the ELI and Surfybear have their own AC line cords or power adapters? Is the ELI installed inside the amp? There are a number of quirks in AC power or wall-wart power that can cause ground hum. These need schematics of the power supply details to debug in detail. There is a fairly well-known issue in separately powered pedals where the power supplies interact to cause ground hum.
2. Guessing at separate AC cords or adapters, are any of these two-wire devices? If they are, have you tried plugging in the two-wire cords and/or adapters in both directions?
3. When Two-rock fixed the ELI, did they tell you exactly what they fixed?

[ocianic]

R.G. - Thank you very much for your reply and ideas! Really appreciate it.

I have built one amp so I am reasonably familiar with the general concepts. My amp build below...

IMG_0948.jpg

Both the TS1 and ELI have 3 prong (grounded) IEC cables - the ELI has an internal power transformer. (The Surfybear has a wall wart adapter and DC connector to the unit. But this is not causing the hum, I have eliminated this.)
The hum exists with simply the ELI connected to the TS1 loop.. and nothing else. No guitar connected.
The hum disappears when the TS1 is on and I remove the cable connecting the ELI and amp loop return jack, and also the hum disappears when I turn the master power to the ELI unit off.
The hum seems to be directly related to the ELI return pot. When this is turned down to zero, the hum fades to zero... inversely, the hum increases as this pot is turned upon to max.

The hum is present regardless of TS1 amp master level as well.... so min or max volume, the hum is the same.

The ELI init is separate and the hum is the same whether sitting on top of the TS1 head (as designed) or on the ground away from the head... anywhere, its the same hum.

I asked Two-Rock about what they identified as a problem when it was returned under warranty... this was their reply:

some of the internal wiring was a bit longer compared to some of the quieter units that were made previously. It was causing some interference.

This ELI is unit number #134. I asked whether they had come across this GL Hum issue with other customers, but didn't get a reply.
Doesn't make sense.... again, they are awesome and have helped me greatly in the past so I have nothing but love for TR. The TS1 is amazing... it all should work.
Very perplexing!

If it is a power supply design problem (AC) then the problem is shared with their Bloomfield drive as well.


Again, thank you!

[Stevem]

When you have multiple ac powered things plugged in there’s always a chance for a ground loop to take place.

Your guitar cable and the interconnecting cables carry the ground potential from all your gear on the jacks sleeve so if one units chassis has a noise producing voltage on it that voltage gets shared with all the gear.

Wha you need to try is having only the amps power cable having a connection to ground which means the first two units before the amp need to have a ground lift adapter put on them.

I have had this procedure cure 99% of problems assuming that your hum issue is 60 hz and not 120 hz.

The other 1% of the time when a item in the signal chain was powered by a wall wart I have had to trim down the wide tab so that wall wart could be plugged in the other way around in the ac outlet.

I hope this info might help you out.

[ocianic]

Hi Stevem, thanks for your reply.

The hum is happening when there is nothing but the ELI in the loop. i.e. no guitar connected at all - and no effects connected to the loop insert on the ELI.

((If I put a pedal in the passive loop of the TS1 (strymon etc) its dead quiet))
Everything is quiet except for this FX Loop buffer unit designed by Two-Rock.

I have exhaustively tried every type of ground loop lifting method and purchased hum eliminators to use before the 3 prong AC connectors. None of these worked or made any difference.

I am pretty deep into the weeds on this one and have thoroughly worked through all of the obvious causes.

There must be some inherent design problem with the ELI that is leaking voltage to the signal.

It's definatly a low smooth hum and not a buzz, so pretty sure its 60hz not 120hz... I may try to put a frequency analyzer on next to verify this.

I have searched YouTube and found multiple Dumble clones using various Dumbleator's or C-Lators with no hum.

There must be an answer, its frustrating because the boost that the ELI gives the loop with FX is really amazing. I have been used to the sound of FX in the passive loop... still sounds good but gain is def lost.

[ocianic]

I found this post re. a Ceriatone C-Lator with the same problem. Changing the PT was the fix... I think the internal ELI PT is what might be causing the hum.

https://ampgarage.com/forum/viewtopic.p ... &start=195

[ocianic]

Edited

[sluckey]

Here's a gut shot of the ELI... to me it must the proximity of the internal PT that is causing the hum. IMG_5702.jpeg

So, disconnect the PT and remove from chassis. Now reconnect the PT leads inside the chassis using 12" jumpers. Does this temporary arrangement cure the hum?

[Stevem]

What does that tube use for filament supply, ac or dc?

If it uses ac does the PT have a center tap or does it use an artificial tap made up of two 100 ohm resistors?

Does it hum as soon as your turn it on or only once the tube warms up?

[R.G.]

An interesting test would be to plug in and turn on both the amp and ELI, but not connect them with a guitar cord. You could then measure the voltage difference between the signal ground on the amp versus the signal ground on the ELI.

Especially if they're both plugged into the same duplex outlet, this voltage should be so near zero that it's less than the meter's sensitivity and offset on its lowest range. If it isn't, and you read many millivolts of difference, then either the amp or the ELI does not have signal ground solidly connected to AC safety ground. If this is the case, connecting a signal cable will flow current in the shield, trying to equalize the voltages, and this gets impressed on one or both signal grounds as a hum voltage.

It's a guess, but t would produce similar symptoms.

I'm a little perplexed at the description of the "fix". Sure, wire routing is a possible source of hum, but didn't they try it before shipping it back? The only reason I can think of for not fixing on it until is is for sure fixed is that they could not replicate the problem as you see it, and tried something based on earlier situations.

[ocianic]

Thanks so much for your help and ideas R.G. and SteveM!

I reached out to Two-Rock just to get their OK to move the PT outside the chassis, will try that this week.

R.G. - I love Two-Rock but I'm having trouble understanding how this unit that is specially designed for this purpose with my amp would have any ground problems at all!
And yes, wouldn't they test it before sending at back to me? Strange....

I will try measuring the signal grounds to see if there is any difference.

Steve, the filament supply is AC and looks like uses an artificial center tap using 2 x 50 ohm resistors. (at least I think this is what is happening) Should be able to see it in the photo.
The hum only starts as the tube warms up.

[R.G.]

As a caution, it may be that there is some issue inside your amp that interacts with the ELI. A flaw in the amp wiring >>could<< interact with the ELI itself. Without the schematics to see where the possibilities are, I can't tell much. The pictures help, but I haven's spotted anything definitive yet.

There are a huge number of ways hum can get in. I tried to write up some quick hints and tips on the topic. 50+ pages later, I was finis... er, tired of typing and drawing pictures. You can find that here:
https://www.dropbox.com/scl/fi/vpijj3al ... cmrs5&dl=0
Or the much shorter "cartoons" version:
https://www.dropbox.com/scl/fi/soyg9csg ... 3asd0&dl=0

[R.G.]

Had another thought. Are you placing the ELI in the same physical position relative to the amp every time? Some power transformer emit magnetic fields that can couple into other units sitting nearby.

[ocianic]

Hi R.G.-

The hum exists no matter where I place it in relation to the amp... leads me to think that th PT so close to the components and wiring inside the ELI unit is the cause.

I chopsticked the board and components inside the ELI and at least one cap, and one of the jacks that connects the FX unit to the ELI were quite microphonic. These must have been picking of the EMI from the transformer 1-2 inches away.

Also, trying this ELI unit in another Two Rock amp with a passive loop (Bloomfield) made me confident to rule out my amp as the culprit. The hum was the same in both.

I think relocating the PT outside of the unit as a test is the next step.

Thanks again for all your ideas!

[Stevem]

What happened to the photo of the guts of the ELI that was in this string?

The microphonics from the jack should cease once a cable is connected to both units.

The cap if a tubular type may just need to be spun around end for end to make it less susceptible to picking up magnetic fields, or just rotating the PT 90 to 180 degrees might solve the issue also .

You might also find some .003” thick brass sheet at a hobby shop or order such on line and you could fold up and solder a shield case around the PT and then ground that to the units main grounding point.