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Utterly baffled by speaker hum..

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John C View Drop Down
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Post Options Post Options   Thanks (2) Thanks(2)   Quote John C Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 6:04pm
Hi Steve,

Please give me a call on either of the first two numbers shown at the bottom of every page on the website. Anytime from 10:00 to 19:00, 7 days a week and you should get me and I'll be happy to help.
Alternatively, PM me your number and a convenient time and I'll call you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 6:36pm
Same happens with the Era Gold V?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote frimmers3 Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 6:37pm
John.. thank you very much for that kind and considerate reply...this thing is driving me nuts! Will try a call tomorrow at a sensible time...and p.s....those Spatia cables are bloody marvelous!
Best regards,
Steve H.

Rega P8, Exact m.m, Accession m. phono stage, Graham Slee /Chord interconnects, Dali Oberon floor standers.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 6:54pm
Can you try connecting the Accession to the AV or HDD inputs please?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote frimmers3 Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 7:03pm
At work(again)...will  try that as soon as I get home in the morning....Yet to experiment with those inputs....Thank you so much for the help to date....I am sure it is not the Accession that is at "fault" as it works perfectly with the other amplifier thing by hooking it up to s I have available...just seems that the P8/Accession is being halted from doing its renowned thing by hooking it up to the Naim. Again, thanks for your time and trouble....
Steve H.
Rega P8, Exact m.m, Accession m. phono stage, Graham Slee /Chord interconnects, Dali Oberon floor standers.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 8:39pm
Unfortunately, there doesn't seem to be a Hi-Fi industry standard for circuit grounding within a product's casing. There is in other branches of electronics! I have learned not to accuse others, but you have to start questioning grounding compatibility when hum rears its ugly head. The ground potential should be zero, source to speaker, and the moment it isn't, hum happens. Every product should have its input common grounded to the case. In a preamp, the output common should run via the circuit to the input common. By making the ground paths short and hefty, both input and output commons in a preamp can be classed as zero ground potential, so the only variable is the signal itself. Interconnects must also ensure this zero impedance or hum will develop. We use a coaxial cable having both copper foil and copper braid to keep the impedance as close to zero as is physically possible. Some designers ground common at some other point in the circuit, and therefore, some amps don't have their input commons grounded to the case. That pushes the ground common to the source equipment, and to be precise, the input terminals where the cartridge signal connects and a 'floating ground' there will add noise (hum). If the arm maker commoned the interconnect screens at the arm end and made that the arm ground, then there'd be no need for a separate 'turntable earth wire'.
However, some arm bases use the SME 5-pin plug socket arrangement, which doesn't make the best grounding contact in the world - it usually gives rise to some hum. Using just one of the screens isn't wise, but an Essex manufacturer seems to do so. Using the mono switch, the ground from one channel might supply the ground of the other. Then again, a lost ground to one channel's '-' cartridge pin might have the same effect (good idea to try a different turntable if available). The turntable manufacturer who also makes a partnering phono stage might have a fix, I as an independent, don't know about. Once a costly phono stage never suffered hum and caused us a lot of head-scratching until we put one on test, and sweeping through the frequencies, suddenly the signal disappeared. The phono stage had a steep notch filter at 50Hz (I guess the US version must have been modded for 60Hz). I wouldn't do that because it screws the bass/mid-phase, but some people liked the (non-high-fidelity) effect.

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2021 at 10:44pm
Usually, power amps use output inductors to prevent a capacitive load from forming a filter pole, pushing the amplifier output so far out of phase that its negative feedback becomes positive. Positive feedback makes an amplifier oscillate and can destroy all the transistors in the circuit.
Naim doesn't use output inductors and warns not to use highly capacitive speaker cables, and the Spatia is suitably low capacitance.
Instead of an output inductor, a resistor of 0.22 ohms is used, preventing a filter pole before the amplifier runs out of current gain and prevents it from oscillating. However, the longer the cables, the higher the capacitance, and the closer the filter pole approaches the frequencies where there is sufficient beta for the onset of oscillation.
Naim also uses a filter on the driver transistor bases to counter negative resistance, without which a small momentary oscillation can occur. It might be sufficient to send the amplifier into instability, and that's why the filter is there.
I design our phono stages to be stable by a conservative amount, but at the same time, to have a reasonable slew rate to reduce slewing induced distortion (SID). Output filtering is a passive 6dB per octave to correct the RIAA (or other EQ) response up into the frequencies beyond our hearing range. Although the stage will not rectify airborne radio frequencies, it does not hard-filter.
This would generally be OK if a properly shielded interconnect were to be used between the phono stage and amp input. Still, if not 100% screened against radio frequency interference, it can be picked up as the phono stage source impedance doesn't drop to zero.
For those who remember being able to tune an ITV 405 line transmission on an FM radio, as it went off-tune, a loud hum was heard - it being the screen refresh or raster frequency, which is synched to the screen frequency (50, 75 or 100 Hz these days).
An emitter follower - which, by the way, is what makes up the output stage of the amp - can often tune to the strongest, most constant airborne interference frequency, even where the transmission frequency is way beyond the transition frequency of a device. The negative resistance filter is there to counter that occurrence, but nothing is perfect.
It's not only TV transmissions that can give rise to hum. Off tune short wave using single-sideband can sometimes modulate with its power supply frequency.
Knowing about all the communications interference that has grown considerably over recent years makes sense for amplifier manufacturers to use output inductors. The use of sensible, fully screened interconnects will help an inductor-less amplifier stay stable.
Radio frequencies can enter the output of an amplifier (preamp or power) and go straight to the input via the negative feedback loop, and that is why many of the boutique interconnects, which might be OK with unity-gain devices such as CD, cause so many problems when a vinyl source is added.

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