Groove Tubes ViPRE Problem - Repair?

[ripple_fx1]

Hi Dusty - I've got schematics if you need them...IIRC, the power supply filters are barely sufficient - too much ripple on the rails. If you go to a tech, you can try moving the power transformer outboard to see if that's your hum source, or power the unit from a bench supply to see if ripple is the problem.

[Matt Syson]

Hi
Which country are you in?
I spent a while sorting out the hum on one of these, mainly because I couldn't believe one fact, as it is such a high profile expensive unit but all 'fault finding' techniques led me to the same conclusion (eventually proved to be correct).
I did resolve the problem satisfactorily, but it required considerable work.
A 470 Ohm resistor (IIRC) and a 220uF cap on the main HT rail helped clear the remains of the noise but it is not the main culprit.
PM me if you wish.
Matt S

[Dusty Records]

Hello, Matt and ripple_fx1 -

Thanks for your replies! I'm located in the United States, near Chicago - an unfortunately long walk from the UK.

It's very encouraging to hear that you have both been able to isolate the source of this problem. And strange that such an issue would be so common with such an expensive and widely-distributed preamp! I have PMed you both.

Also, I forgot to mention that while the hum is present in both of the microphone input modes, it's pretty much overwhelming with the balanced bridge (transformer bypass) setting.

[Meriphew]

I've never had any humming issues (or any other issues) with mine.

[technut]

Sounds like I'm having the same problem with mine. So I'm bumping the thread to see if something good comes of it.

Phil

[Matt Syson]

Hi
I would not expect someone using their unit in USA (anywhere with 60Hz mains) having the particular humming issue as it is / was 50 Hz with high mains voltage which causes the mains transformer 'core' to saturate on SOME of the units. If you do not have the 'problem' now it will not deteriorate in the future.
Assuming this is not the issue there is some residual 'ripple' that could be removed by another resistor plus capacitor stage on the HT supply reducing the mains ripple by a few dB.
Matt S

[keyboardkungfu]

Originally Posted by Dusty Records

I recently purchased a used Groove Tubes ViPRE preamp. It is in pristine condition, but initially appeared to have been damaged in shipment due to the fact that the microphone channels were passing virtually no signal (the instrument channel works flawlessly). The seller took the unit back and had his technician fix what turned out to be a disconnected soldering joint on the microphone input. The microphone channels are functional now, with the exception of an electronic humming/buzzing noise that becomes immediately apparent with the gain cranked, for example, to the level required by a dynamic microphone on a rock vocalist.

This doesn't sound like any tube issue I've ever come across, as the noise is a steady "buzz" instead of a violent "spitty" kind of thing. I've also eliminated the possibility of it being a grounding issue.

The seller's technician gave the unit a clean bill of health after the soldering fix, and speaking to Fender customer service has gotten me nowhere. So I took the ViPRE to a local repair shop, whose technician has also been in touch with Fender. They tell me that Fender's stance on the issue is that the unit is, in fact, exhibiting normal, healthy behavior - and that this hum is an inherent problem in the ViPRE design.

I find that very hard to believe, and an easy theory to dismiss, as the ViPRE wouldn't have lasted long on the market - especially at its original retail price - if its noise floor was really this high. Not to mention that I've gotten the distinct impression that Fender's knowledge of the unit is very limited.

The seller has offered to take the unit back, but I'd really like to exhaust all of my repair options before giving up. So he's given me the name of a repair center that was originally recommended by Aspen Pittman, and I'm trying (so far without success) to get in touch with them.

Can anyone here recommend a repair facility or technician that has had experience withe the ViPRE? Or has anybody had a similar problem with the unit? I would greatly appreciate any sort of ideas or recommendations to help me sort this out. Thanks very much!

I know this thread is a couple years old now, but, I find myself in a similar situation... I am looking at buying a used ViPRE but, was told they are fairly high maintenance... some what of a formula 1 car of preamps. That being said, I want to find a technician that can service/repair my ViPRE as the need arises.

So, did you ever find a technician capable of working on your ViPRE?
I'm in Toronto and would love to find a tech that can work on these that's not too far... Somewhere local would be ideal, but if not, definitely in North America. Can anyone recommend a capable repair tech?

[Matt Syson]

Hi
Ike Kimbel should be a good candidate. I think he is in Toronto.
The mains transformer 'issue' should not be too serious for you as you are 60Hz mains frequency.
The original units were probably excellent, I have not seen any from the initial batches only later examples.
Matt S

[Ike Zimbel]

I'm in Toronto. I have had a run of sorting out hum issues in high-end devices lately so I'd be happy to look at it.
Best,
Ike