The Truth Preamp by Horn Shoppe-massive ground hum issue only with some gear: Help?

[RockRolley]

Hi guys,

I have The Truth Preamp by Horn Shoppe. My main system (actually most of my stuff) is very tube heavy and the Truth preamp brings great clarity and detail without impacting the tubey presentation. I introduced it back into my main system recently after having tube preamps for some time and I loved it. Then after around a fortnight, it started making terrible sounds like a massive ground hum and other unpleasant sounds. I thought it was buggered-I tried earthing it (it has an earth terminal) and it didn't help. I reinstated a tube preamp into the system and no problem. I did some reading and saw that someone had reported similar things and that the trouble was with something else in the chain. I tried it in my office system-still otherwise very tube heavy-and no issue!!! I tried it in the main system again-Horror show!! I checked all the power points in the main area and no problems there, and the Power Amp and other gear works fine with other preamps. I'd love to get it back into that system, as it is the preamp I've most enjoyed with my main setup (LP12, ABBAS phono stage, CED CDT, ABBAS DAC, Eversolo streamer, Geiseler DAC, Radfrord STA25 power amp, IMF RSPM MK4 speakers).

I tried joining the Hornshoppe chat group on their website, but I don't believe I ever got a confirmation email with access, so I'm trying the brains trust here.

Can anyone help solve my mystery?

Otherwise, I'm open to other preamp recommendations that may sing with the aforementioned gear. I'm 100% content with everything else in the chain, but in lieu of the Truth preamp, I'm yet to find a preamp combo I'm really committed to. I did have a locally made tube preamp in the system for a couple of years that I've loved, but looking for a different flavour. Tubes still an option though. 

Thanks for considering.

 

NB: These pics are of my 'The Truth' preamp though were taken by previous owner (I'm not home to take pics and found these online...)

[Ihearmusic]

Well, since you mentioned the fact that the problem started some time in, the problem highly likely is inside the unit somewhere.

So get it checked out by a tech or have a go at it yourself.

A photo of the internals might reveal the offending part. (E.G. a bulging capacitor) 

[mbz]

Measure the frequency of the "hum", sure an oscilloscope would be handy but you can use a mobile phone ap like spectroid (and others) or freeware like audacity. 50Hz would typically point to a GND loop/earthing issues, rectified 100Hz points to the pre internals like caps, voltage regulator... As above several hi-res pix of the internals would be helpful as would a schematic,

[RockRolley]

@Ihearmusicand @mbz thanks so much for your input. I’ll take pics under the hood and try spectroid over the weekend. Any idea why it works well in one set up and not the other? 

[xlr8or]

Hi Simon. These photos have been sourced from the internet showing a similar build and a faulty leaking cap being responsible for a noise related problem. I assume your unit doesn't have a ground lift switch does it? The one below does. As suggested above internal photos would help a lot determine if the fault is obvious.

 

 

 

 

[RockRolley]

1 hour ago, xlr8or said:

Hi Simon. These photos have been sourced from the internet showing a similar build and a faulty leaking cap being responsible for a noise related problem. I assume your unit doesn't have a ground lift switch does it? The one below does. As suggested above internal photos would help a lot determine if the fault is obvious.

 

 

 

 

Oh geez-that IS obvious. Yes, I'll take a look and some pix under the hood ASAP!! I'm not sure about the ground lift... 

[surprisetech]

3 hours ago, xlr8or said:

 

 

PLEASE DISCONNECT THE POWER CABLE BEFORE OPENING.

I SEE A LOT OF EXPOSED MAINS WIRING IN THERE.

VERY POOR FORM WHEN THE PROPER CONNECTORS AND HEATSHRINK TUBING ARE READILY AVAILABLE!

[RockRolley]

37 minutes ago, surprisetech said:

 

PLEASE DISCONNECT THE POWER CABLE BEFORE OPENING.

I SEE A LOT OF EXPOSED MAINS WIRING IN THERE.

VERY POOR FORM WHEN THE PROPER CONNECTORS AND HEATSHRINK TUBING ARE READILY AVAILABLE!

Noted, with thanks

[SonicArt]

Switch can be added easily Simon, happy to have a look at it for you once we see pics. When you use it in the second system have you left it running the same amount of time to see if the hum develops?

[andyr]

4 hours ago, xlr8or said:

 

 

 

The 'groundlift switch' in the pic above seems wrongly implemented, to me?

 

What it would appear to do is: disconnect the chassis earth from mains earth - which is surely a safety concern?

 

What I think it should do is:

• disconnect 'signal earth' from mains earth - signal earth being the maess of dark green wires connecting the PSs to the other boards
• so the mains earth remains permanently connected to the chassis?

Me - I never connect signal earth to mains earth ... so have no need of a 'ground lift' switch.

 

[RockRolley]

23 minutes ago, SonicArt said:

Switch can be added easily Simon, happy to have a look at it for you once we see pics. When you use it in the second system have you left it running the same amount of time to see if the hum develops?

Amazing, thanks, Mark. Yes the Truth, is currently running (without being turned off as there's no on/off switch) into Radford MA50 mono blocks, fed with SP-10>Goldenage (DUC) SUT> Croft Phono stage, no issues. Also ran streamer via dac with no issues. This set up is in a different room to the main system.

Pics coming ASAP-hopefully this evening

[RockRolley]

16 minutes ago, andyr said:

 

The 'groundlift switch' in the pic above seems wrongly implemented, to me?

 

What it would appear to do is: disconnect the chassis earth from mains earth - which is surely a safety concern?

 

What I think it should do is:

• disconnect 'signal earth' from mains earth - signal earth being the maess of dark green wires connecting the PSs to the other boards
• so the mains earth remains permanently connected to the chassis?

Me - I never connect signal earth to mains earth ... so have no need of a 'ground lift' switch.

 

That's interesting... More will be revealed once I upload some pics of the internals of my preamp... stay tuned, Andy, and thanks for your input

 

[RockRolley]

Here’s some pics from under the hood. Mine has goop around some caps but I wonder if it’s on purpose as it is the same on both the boards? 
Anyway, if anyone can spot an issue I’d love to hear more. Thanks crew. 

[RockRolley]

Here are some pics of the other caps similar to what you shared, @xlr8or, and there appears to glue around them but not coated in it as much as your ref pic.., 

[andyr]

1 hour ago, RockRolley said:

Here’s some pics from under the hood. Mine has goop around some caps but I wonder if it’s on purpose as it is the same on both the boards? 
Anyway, if anyone can spot an issue I’d love to hear more. Thanks crew. 

 

 

 

 

What is the purpose of that brass bolt to the left of the mains socket?

It is obviously connected to the case ... but where does the black wire go to?

 

Also, where do the 2 wires attached to the IEC earth pin, go to?

 

[SonicArt]

There appears to be one wire from the earth pin on the IEC socket Andy, going to that eyelet screwed to the base plate, the earth post on the back goes to that too, and there is another wire from the pot at the front going to the tag, is that pot a balance pot Simon?

 

I hate when ppl solder wires to socket pins on boards, why not just buy the plug kits and crimp up looms, its only power supply connections, and colour code the positive on the DC side while you're at it Also a boot on the IEC socket, and maybe we remove that and open the hole up, fit one with a built in switch? Or do you like it without power switch?

 

I can see a nice piece of jarrah etc cut for the front panel, with some nice brushed alloy knobs inset into the wood, make the thing look the biz as well!

[andyr]

28 minutes ago, SonicArt said:

There appears to be one wire from the earth pin on the IEC socket Andy, going to that eyelet screwed to the base plate, the earth post on the back goes to that too,

 

Aah, yes - I can see that now, Mark.    So the case is earthed - and the earth terminal on the back panel is, also.  

 

But why not use green wires for these connections (or green/yellow striped)???

 

Edited May 24, 2024 by andyr

[RockRolley]

20 minutes ago, SonicArt said:

is that pot a balance pot Simon?

Yes, that’s balance. 
 

 

21 minutes ago, SonicArt said:

Also a boot on the IEC socket, and maybe we remove that and open the hole up, fit one with a built in switch? Or do you like it without power switch?

Personally I’d prefer a switch. I know some people like to leave things powered on, but I figure if it’s just one component out of all others staying on, I’d prefer to turn all off. 
 

 

23 minutes ago, SonicArt said:

 

I can see a nice piece of jarrah etc cut for the front panel, with some nice brushed alloy knobs inset into the wood, make the thing look the biz as well!

I’m all about thing’s looking the biz! I must say, though, most people think the Truth is an ugly piece of gear, but I don’t mind it. That said, I’m all about timber finishes. If you have a way to add timber finish without too much problem I’m absolutely interested. 

[andyr]

8 minutes ago, RockRolley said:

That said, I’m all about timber finishes. If you have a way to add timber finish without too much problem I’m absolutely interested. 

 

Here's Simon's latest, gorgeous timber case   (with a Paris head amp inside):

 

 

 

(The case is not my work - only what's inside!)

 

Edited May 24, 2024 by andyr

[RockRolley]

12 minutes ago, andyr said:

Here's Simon's latest, gorgeous timber case   (with a Paris head amp inside):

Yes, here she is: I’m looking forward to a good listen over the weekend. AMAZING work by Andy and my woodworker mate, Adam. I’m aiming to share more pics and listening notes once I’ve had a chance to give it a good run

If I can get The Truth up and running as I’d like it, as well as some lovely timber exterior I’d be happy as the proverbial clam

[RockRolley]

Here’s a Truth I saw online with wood casing around the sides… 

 

[SonicArt]

Its the front that looks ugly not the case

[mbz]

10 hours ago, andyr said:

But why not use green wires for these connections (or green/yellow striped)???

Not really impressed with the lack of wiring convention. First example appears to have been a special on green wire, it's used everywhere. Second example it's black everywhere. Tinkering with my yamaha,

red, right channel audio

white, left channel audio

black, signal ground

blue, brown, green/yellow AC supply, transformer "primary"

brown +ve power rails

...

 

While the boards might be ok the interconnect of boards does appear to be a little above garage workshop standard. A little sad...

[RockRolley]

As unconventional and lacking in order as it may appear, or even actually be, he either stumbled across or brilliantly created an amazing sounding preamp. I’d read glowing reviews and also one smashing it and decided to dive in and try it for myself. All I know is it effortlessly revealed layers of music, instruments and details I’d never noticed on tracks I’d been listening to for forty odd years. Works for me-when it’s working:-D

Edited May 24, 2024 by RockRolley
Typo

[xlr8or]

I think the build quality is being questioned here independent of the SQ. It may be pertinent to have the inside layout and dressing reviewed by a competent technician to tidy it up a bit better if it's definitely going to be a keeper.