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Pioneer A400.  Headphone output fine speakers distorted
Pioneer A400.  Headphone output fine speakers distorted
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Old 5th December 2017, 04:55 PM   #11
RJM1 is offline RJM1  United States
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This probably wont help you with this but about 5yrs ago when I rebuilt my HK CIT I pre-amp and had a problem with signal breakthrough ( Before and after it had been rebuilt) from the tuner to phono. The HK shorted the non-selected inputs and ran the shielded cables from the back to the selector switch all tied together. This probably worked very well with a tube tuner with an output impedance of about 30K ohms but with a solid state tuner with an output impedance of <1K ohms it caused enough current to flow to bleed through to the phono wires. I ended up rerouting the phono wires from the back to the switch which eliminated the problem. If your inputs are shorted when they are not selected ( You can check this with a meter) you could try adding a 1 to 10K resistor between the input connector and the PC board and see if that helps.

Last edited by RJM1; 5th December 2017 at 05:02 PM.
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Old 6th December 2017, 02:56 PM   #12
bigshuggy is offline bigshuggy
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I guess we'll never know...

It's going back. I offered the going rate for a broken unit and got no response.

I have, however, just got another one AND a Pioneer PD-S904 CD Player. Like I need another CD player!

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Old 6th December 2017, 05:33 PM   #13
Mooly is offline Mooly  United Kingdom
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Pioneer A400.  Headphone output fine speakers distorted
Sounds like you have plenty to keep you busy.
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Old 6th December 2017, 08:47 PM   #14
bigshuggy is offline bigshuggy
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Just a quicky. Fired up the new A400 tonight - there's a bit of a hum from the transformer - at least this one works though! No hum through audio.

Any ideas on a cure? The first broken amp was totally silent....
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Old 6th December 2017, 09:06 PM   #15
Hamish119 is offline Hamish119  Europe
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Default Shame on me!

Quote:
Originally Posted by bigshuggy View Post
Any ideas on a cure?
I'll state the obvious: swap transformers between machines.
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Differential input (instrumentation) amplifiers - the correct method of amplifying the output from a phono cartridge!
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Old 6th December 2017, 09:28 PM   #16
bigshuggy is offline bigshuggy
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Unlike the first seller - I'm too honest to do that. Bloody well feel like doing it though!!
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Old 7th December 2017, 07:36 AM   #17
Mooly is offline Mooly  United Kingdom
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Pioneer A400.  Headphone output fine speakers distorted
Mechanical hum can be very very hard to stop. Although the problem seems trivial, the windings/laminations are noisy, the reasons and 'fix' are not.

There is so much localised magnetic energy within the core that simply dipping or soaking the transformer in suitable varnish (for example) doesn't always work.

Other reasons can be that the transformer is saturating (mains voltage a bit to high) and that the mains isn't a pure sine but slightly asymmetric which gives the equivalent effect of a slight DC offset which again can cause core saturation. The last is more applicable to toroids).

If you are lucky you might find something like a rubber bung placed on top of the transformer to exert a bit of pressure when the case is fitted might help any rattling chassis panels that vibrate in sympathy.
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Old 8th December 2017, 09:40 AM   #18
AndrewT is offline AndrewT  Scotland
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Originally Posted by bigshuggy View Post
I guess we'll never know...

It's going back. I offered the going rate for a broken unit and got no response.

I have, however, just got another one AND a Pioneer PD-S904 CD Player. Like I need another CD player!

Ebay.co.uk's policy on refunds for faulty/not as described has changed.
Now the Buyer gets a full refund of purchase plus postage costs.
As a result the Seller has to pay for the two postage costs, because they were not honest.
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Last edited by AndrewT; 8th December 2017 at 09:43 AM.
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Old 8th December 2017, 09:47 AM   #19
AndrewT is offline AndrewT  Scotland
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as Mooly states:
mechanical noise from the transformer can be loose wire/laminations vibrating in sympathy with the current pulses through the transformer and/or near saturation due to distorted sinewave of the mains.

The near saturation can be significantly reduced by adding a DC block in the primary circuit. It can even be an external box and work just as well.
The wire/lamination vibration is much more difficult to cure/attenuate.
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Old 8th December 2017, 06:32 PM   #20
bigshuggy is offline bigshuggy
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Doesn't sound as bad now for whatever reason. Maybe it was just settling in to it's new home

Pleased (at last) with both amp and CD player - seems to be good combo.
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