Diezel Herbert Mk2 very loud noise with Multi-FX in the loop

Jacky Thrilla

Jacky Thrilla

New member
Hi all,

I am quite new in this board and I am not a native speaker.

I've recently bought a used Herbert Mk2 (I guess it's from 2010 or 2011). It's a versatile and great sounding amp, very well designed, which was the reason I decided to buy one.
Played only with my guitar plugged in, everything is working well. Massive sounding amp, I love it.

Now that I want to use my gear with which I am recording at home together with the Herbert I ran into the following issue:
As soon as I hook up my Fractal AX8 with recommended humbuster cables (4CM) into any of the three FX-Loops of the Herbert the amp begins to produce a very loud noise, I mean it's not just a loud hiss or something it's a really loud hum. It's so loud you can't play the amp anymore. Even on bedroom level the hum is way too much.

Doing some tests:
1. Unplug the Input cable: the noise is gone
2. Unplug any of the cable from the FX-Loop: noise is still there
3. Connecting the AX8 in the same fashion with another amp (Marshall DSL f.ex.) no noise at all, so it seems not the pedal is the source for that

What I did to resolve the issue:
First thing that came into my mind: V1 preamp tube is faulty! So I decided to replace the whole tube set, the preowner told me he never changed the tubes. That wasn't quite correct, he at least changed the V1 preamp tube, because all other tube were Ruby Tubes except the V1 it was a TAD 12AX7. I replaced preamp and powertubes with a matched set from TAD (their shop is located just a few miles away from my home!). But nothing changes with the noise, still the same amount of noise is going on.

Reason?
So, did anybody experience a similar issue with his Diezel? In the service manual from Diezel there is on page 34 an issue with the hum trim pot of a VH4 described which sounds to me pretty much as if this was the reason for my problem. But I didn't check for the trim pot when I replaced my tubes, so currently I just don't know if there even is one inside the Herbert!

@Peter Diezel:
Maybe you can point me to the right direction? Is this an issue a local amp doctor can fix? Or should I ship the amp over to you? I am not a technician, I have no technical background, I can replace tubes and due to your excellent decription and the superb design of your amps biasing the Herbert was quite simple. So even a n00b like myself was able to bias the new power tubes to 60mA for each pair!

I am eager to play the amp with my band, so I can't wait to have this issue fixed!

Greetings
Jacky
 
Synthoms may suggests that there is no direct reference path from Amp to FX unit and earth is then being used as reference.

Obvious check: Make sure both of "stereo TIP" of the Humbuster cables are on the AxeFX side.

Then I would suggest trying to place a standard mono cable from Amp FX Send to Amp FX Return (so bypassing it externally) and check for the HUM, if no HUM:
- Swap one of the "humbuster" cable with a standard cable
- Swap both of the "humbuster" cable with two standard cables
 
Leo Diezel":2suw0ddj said:
Synthoms may suggests that there is no direct reference path from Amp to FX unit and earth is then being used as reference.

Obvious check: Make sure both of "stereo TIP" of the Humbuster cables are on the AxeFX side.

Then I would suggest trying to place a standard mono cable from Amp FX Send to Amp FX Return (so bypassing it externally) and check for the HUM, if no HUM:
- Swap one of the "humbuster" cable with a standard cable
- Swap both of the "humbuster" cable with two standard cables
Click to expand...

Hi Leo,

many thanks fpr your suggestions.
Basically I think I already did many of your suggested tests with the amp except bypassing the FX-Loop with a mono cable.
I already used standard mono cables to connect the AX8 to the amp, which was the reason I ordered humbuster cables.

Yesterday I hooked up my AX8 on another amp (Marshall DSL) and theere was no noise at all. But I will go and get my analogue Pedalboard from the rehearsal room today and will test, if this board is also producing the same or an similar amount of noise. And of course I will repeat my tests analogue to your suggestions! Just to make sure, the mistake isn't mine. Thank you!

And as I said, it's not just a tiny amount of annoying hiss which is bothering me a bit, no, it's nearly as loud as the guitar signal and increases together with the master volume to earpiercing noise. Ch1 Volume @9 o'clock and Master 1 @ 12 o'clock and the noise is earsplittingly loud and doesn't change it's sound character with channel switching to Ch2 or Ch3.

Greetings
Jacky
 
You are experiencing a ground loop. That's a common issue with the 4-cable-method. Even humbuster cables will not solve that problem in all cases. Put a Lehle P-Split between one of the connections from the amp to the AX8 or even between both.
 
MourningEngine":1t02xrq8 said:
You are experiencing a ground loop. That's a common issue with the 4-cable-method. Even humbuster cables will not solve that problem in all cases. Put a Lehle P-Split between one of the connections from the amp to the AX8 or even between both.
Click to expand...
Yep.
 
Hi guys,

after a couple of tests with humbuster cables, Lehle isolation box (P-split), my analog pedalboard and a couple of other amps I found that the Herberts FX-loop design doesn't work well with the AX8s outputs in particular. Or let's say, that the AX8 design is not usable for all ampdesigns.

However, currently I am building a new rig around the Herbert and a Boss GT-1000. I use only the effects of the GT-1000 and MIDI functionality for amp switching. I connect the GT with 4CM to the switchable loop. I looped in the Lehle P-split into the amp return and all noise is gone, I mean really there is no noise at all now, except a little interspersal noise coming from the guitars pickups.

This setup seems to be working great for me. Next friday I'll haul the Herbert to the rehearsal room, and then we'll see ... but in my home even with super low volume it's sounding great.

Channelswitching via MIDI is super fast. GT-1000 (I owned GT-8 and GT-100 years ago) is a great sounding and easy to program FX-device.

Greetings
JT
 
The threads title should be edited:
It's not "multi-FX" in general, it's the "AX8" which doesn't fit to the Herberts FX-loops in particular.

That's my conclusion.

Greetings
JT
 
MourningEngine":2kxe1a47 said:
You are experiencing a ground loop. That's a common issue with the 4-cable-method. Even humbuster cables will not solve that problem in all cases. Put a Lehle P-Split between one of the connections from the amp to the AX8 or even between both.
Click to expand...

Using the GT-1000 I can hear a slight groundloop hum. Looping a Lehle P-Split (or any isolation box/ground lift) into the amp return eliminates this small amount of ground hum, yes. But even without the Lehle P-Split the setup with GT-1000 and Herbert would be usable quite good imho.

The noise with the AX8 was way more! Maybe it's also ground hum, but in this case a brutally loud hum, totally unusable for me, and the ground lift didn't change anything.

But now I'm happy with the GT-1000 connected via P-Split to the Herbert, it's a very silent setup.

Greetings
JT
 
The reason is that the AX8 has a build-in power supply and therefore needs to ground its chassis and jacks to PE whereas the GT-1000 has an external power supply. So the Boss's chassis and jacks are not grounded to PE hence no or only minimal ground loop.

Also, the ground lift switch on the AX8 is only for the XLR jacks.

But anyway, I'm happy to hear that you found a solution for you with the GT-1000.
 
To bring this story to an end:



Now I built a new pedalboard with a BOSS GT-1000 as a Multi-FX for the DIezel Herbert (not using the preamps of course!) and as a MIDI-controller to switch amp channels and functions on the Herbert. Since the pitch shifting on the BOSS sounds poor, I decided to use the Digitech "The Drop" to do this job for me. I've played this pedalboard now for the first few hours in the rehearsal room and it works as a charm. The Herbert is a monster and sounds so good. It's not just a metal amp.

The Lehle P-Split makes the low noise setup here even less noisier! Made my own multicore cable to connect the pedalboard with 4CM to the amp. Now the AX8 stays at home as my recording device for which it is the perfect tool.

Greetings
JT
 

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Spending that amount for an amp that can’t handle an AX8 on the loop is weird.

No other amp does that noise issue?
 
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