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Humming from Maxxed Out Phono Preamp

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Posted on April 13, 2017 at 17:06:41
elg
Audiophile

Posts: 5
Location: California
Joined: April 13, 2017
 Hi all,
I recently discovered that my K&K Maxxed Out Phono Preamp is the source of humming when connected to my newly acquired Pass Labs INT-60 integrated amplifier. I initially thought it was the turntable power supply but the hum persisted even when the turntable power supply was turned off. I am wondering if anyone could provide me with any advice on how I could isolate and eliminate this hum issue. Thanks!

 

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RE: Humming from Maxxed Out Phono Preamp, posted on April 14, 2017 at 06:09:59
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Try switching the small toggle switch between the output XLR jacks and RCA jacks.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 14, 2017 at 08:20:46
elg
Audiophile

Posts: 5
Location: California
Joined: April 13, 2017
 Thanks Kevin, for your feedback. I did that by alternating between XLR and RCA connection via the toggle switch at the rear (though I unplugged the other interconnects when doing that) but the hum persisted. Is there anything else I should try? Thanks again.

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 14, 2017 at 18:44:18
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Since the Maxxed-Out Phono Preamp has an output transformer, and you manipulated the output - grounding status without success, I am not sure what else to suggest. Are you using a balanced or unbalanced interconnect between the two pieces? Have you contacted Pass about the problem and asked them about interface to an output transformer equipped phono preamp to see if they have any recommendation regarding compatibility. Nelson is up with these things, as I am sure are his colleagues.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 15, 2017 at 09:13:53
elg
Audiophile

Posts: 5
Location: California
Joined: April 13, 2017
 Hi Kevin,

Thanks so much once again for taking the time to respond to my issue. Here is a reply quoted verbatim from Pass Labs' technical support team:

Quote:

" With a phono cartridge by the time signal makes it from the cartridge to the speakers we're looking at gain ratios of over 1-million :1
Any electrical field in the vicinity has potential to be picked up and amplified along with the signal of interest. With gains running a million to one some care is necessary.

DISCUSSION:
1) Turntables like Rega with non metallic plinths offer no shielding from magnetic fields, don't put them above any devices with larger transformers.
2) Many tonearm cables are un-shielded, keep them away from AC power cords, and devices with transformers, if you must cross an AC line, do so at 90 degrees.
3) Do not bundle or wrap AC cords into loops, loops focus and intensify fields.
4) Grounding. Typically there are aux ground lugs on the back of phonostages. These typically must connect to some metal on the tone arm. Your INT-60 likewise has a white ground lug on it's rear panel. That may need a wire to the ground terminal of your K&K phono.

The K&K being a transformer coupled device may look like an isolated ground or un-grounded source to the INT-60. Sorry not really sure how the K&K is wired internally, but it does have an external ground connection and potentially both the tonearm and INT-60 would benefit from being star grounded to that point."

Unquote.

I tried exactly as what was suggested by connecting a wire between the ground connection on the rear panel of the phono stage and the ground connection also on the rear panel of the INT-60 but the hum persisted. The Maxxed Out Phono Preamp is connected to the INT-60 via both XLR and RCA cables and I switch between both via the toggle.

BTW, my turntable is a Rega RP10 with Apheta2 cartridge and the integrated amplifier I was using prior to the Pass INT-60 was the Musical Fidelity A1000 feeding into Stirling LS3/5A V2. I had absolutely no hum issue with the Maxxed Out Phono Preamp driving the MF A1000 and the pairing produces magical soundstaging and presence. I totally understand the huge gain challenges pointed out by the technical support person but there is no such issue with my 22 year old MF A1000 which is considered an outdated design compared to the INT-60.

Please let me know if you could think of anything else to resolve the issue and I really appreciate your taking interest in helping me out.

Best regards,
ELG

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 15, 2017 at 09:30:29
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Remove either the XLR or the RCA interconnects between the phono preamp and the Pass, then try both grounding options at the phono output jack switch and see what that does.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 18, 2017 at 16:29:07
elg
Audiophile

Posts: 5
Location: California
Joined: April 13, 2017
 Yes, I tried what you suggested but the hum persisted. Now I am wondering if it could be the interconnects which I am using (Kimber KCAG for the XLR and Silver Streak for the RCA).

 

RE: Humming from Maxxed Out Phono Preamp, posted on April 27, 2017 at 10:37:52
divo
Audiophile

Posts: 80
Location: Ontario
Joined: June 29, 2004
 Suggest you also try different phono stage into Pass to isolate possible contributor of hum: interconnects or phono stage. I have never had any issue with the transformer output topology as it naturally isolates equipment from grounding issues.

 

RE: Humming from Maxxed Out Phono Preamp, posted on May 20, 2017 at 08:31:19
elg
Audiophile

Posts: 5
Location: California
Joined: April 13, 2017
 Thanks for all your inputs and suggestions. I have finally managed to resolve the hum issue courtesy of an audiophile friend who suggested I try this simple audio interface device from ART: http://artproaudio.com/isolators/product/dti/
or Rolls: http://www.rolls.com/product.php?pid=HE18
and both work beautifully. Yes, I know these are non-audiophile but they truly work and I highly recommend this to anyone who has the same issue as me.

 

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