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Groove Tubes MD-2a - strange noise
Old 31st July 2020
Lives for gear
Saudade's Avatar

Groove Tubes MD-2a - strange noise

Hi there,

I have had this mic for maybe 20 yrs. Recently it started having this noise (click links to hear). There is still signal and it still works. Just a very loud and changing hum-like noise in the background which reminds me of dial-up modems.

I have changed the tube, I have switched to my back-up of the proprietary cable connecting to the PSU (PS2m), I have connected to the other channel on the PS2m, I have changed preamps, mic cables - all to no avail.

I have tried emailing Mr Aspen Pittman (who had very kindly corresponded with me many years ago) but there was no response.

Anyone has any clue which component may be faulty - the mic or the PSU? I am not based in the US so I need to know how difficult it is to repair so I can weigh my options.

Thanks for any help
Old 1st August 2020
Gear Nut

Sadly, Aspen Pittman passed away, I believe it was in 2019.
Old 2nd August 2020
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Saudade's Avatar

:( May he rest in peace
Old 2nd August 2020
Lives for gear
gyraf's Avatar

Perhaps try to borrow another power supply, or try your supply with another mic - this will tell you if it's supply or mic

If it is mic, find someone in the knows that can clean the capsule and high-z part of the electronics

Last - are you sure the exact tube you put in is suitable for a microphone front end? When using tubes not made for the purpose (AC701, VF14) you NEED to select tube to ensure it's suitability, as any standard grade tube won't always (or even just often) do despite being 100% within specs. This because parameters needed for mics are very different from what tubes are designed for (above exceptions apply)

/Jakob E.
Old 4th August 2020
Lives for gear
Saudade's Avatar

Thanks Jakob for your suggestions. I know I should probably send it to a mic tech but I live in South East Asia and I don't know anyone qualified that I would trust enough to handle it.

I ordered the replacement tube from Tube Rules which says the tubes there are used in their Reference Gold Mics.
Old 5th August 2020
Lives for gear
gyraf's Avatar

Yes, if Manley selected and graded the tube, there's very little chance that your problem lies there.

Which leaves 1) dirt that has contaminated high-impedance part of microphone electronics or capsule and 2) power supply

/Jakob E.
Old 17th August 2020
Lives for gear
Saudade's Avatar

Thanks Jakob. I'm contacting Aspen Pittman designs to see if they could point me to a tech whom I can trust.
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