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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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6th Apr 2021, 8:38 pm | #41 |
Pentode
Join Date: Nov 2013
Location: Essex, UK.
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Re: Dansette Prince
Correct, the loudness of the hum is proportional to how much the volume is turned up. Will eagerly get on with those tests tomorrow PM and report back.
Thank you. |
7th Apr 2021, 8:57 am | #42 |
Hexode
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Re: Dansette Prince
I had the valve version of this player a while back which had the same issue, hum that increased with the advancement of the volume control. The only way I got it to be quiet was by shorting the input to the amplifier, thus proving it was being picked up by the cartridge wiring rather than being amplifier generated. I tried lots of different things to minimize the hum with little success. Make sure that the leads going from the tagstrip to the amplifier are routed away from the motor, transformer and mains cable. It may be worth experimenting with the outer screen of the cables from tagstrip to amp/sockets, lifting one end may make a difference.Also check if the arm wiring has an extra cable in it for earthing the arm (if arm is of metal construction). It may well be though as I found with mine, it just hums.
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7th Apr 2021, 10:23 am | #43 |
Pentode
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Re: Dansette Prince
Thank you.
Checked tag bar mounting screw and tightened.No effect on the hum. Shorted red and green and absolute silence Shorted black and white and absolute silence. Jiggled all wires around and has no effect. So it is some sort of cartridge problem? Regards Gary |
7th Apr 2021, 10:36 am | #44 |
Dekatron
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Re: Dansette Prince
Well cartridges per se do not create Hum. The fault will lay in the connections to the amp or within the amp itself.
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Edward. |
7th Apr 2021, 11:09 am | #45 |
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Re: Dansette Prince
What's the problem within the amp itself likely to be Edward?
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7th Apr 2021, 12:33 pm | #46 |
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Re: Dansette Prince
Has someone put a magnetic cartridge in the player, albeit a higher output one. It would pickup hum from the motor.
Unlikely I know but do we know what cartridge it is?
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Frank |
7th Apr 2021, 2:38 pm | #47 |
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Re: Dansette Prince
As Graham has set me up for the challenge, I would be measuring the high value cap C10 from the PSU and also the low value cap C2 feeding VT1. I would also check the screening/braiding around the pick-up leads to the volume control and (less likely) around the tone controls situated between VT1 and VT2. I take that the OP has checked the routing of the mains lead to clip it away from the input area.
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7th Apr 2021, 2:49 pm | #48 | |
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Re: Dansette Prince
Quote:
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7th Apr 2021, 2:53 pm | #49 |
Pentode
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Re: Dansette Prince
Cartridge is Acos GP 91-3sc
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7th Apr 2021, 3:37 pm | #50 |
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Re: Dansette Prince
Fair enough,
Is that a mono stereo compatible cartridge? I don’t have circuit for the record player but should it have a stereo cartridge fitted.
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Frank |
7th Apr 2021, 4:12 pm | #51 |
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Re: Dansette Prince
I think it’s stereo, fairly sure it is and it has four pins. Gary
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7th Apr 2021, 4:24 pm | #52 |
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Re: Dansette Prince
Parts list for Bush SRP52 says Acos GP93/1.
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7th Apr 2021, 4:30 pm | #53 |
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Re: Dansette Prince
Ahhhhh - now this has come to light, that is the wrong cartridge for your record player.
It is a high-output, 2 pin Mono, Stereo-Compatible type. It is liable to overload/distort the 1st stage of the amplifier. It may also emphasise any residual hum within the circuit. You may find that when fitted with the correct, medium-output cartridge, the hum level may drop and you will get a much cleaner sound from the record player. The good news is that (if you want to) you can sell that very rare Acos cartridge for quite a lot of money. These are as scarce as Hen's Teeth! A suitable Chinese LPS/78 flip-under type can be bought for around £14-00.
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Edward. |
7th Apr 2021, 4:43 pm | #54 |
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Re: Dansette Prince
Sorry again.it is 93-1 as Graham states. The images were on my iPhone and I looked at the wrong image
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7th Apr 2021, 4:51 pm | #55 | |
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Re: Dansette Prince
Quote:
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7th Apr 2021, 4:55 pm | #56 |
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Re: Dansette Prince
Check the continuity between the deck chassis and the amplifier chassis. It should measure zero ohms, if it doesn't either connect another wire between the two or connect the screens of the audio cables which go to the amp to the deck.
This can usually be done by connecting all of the three middle terminals on the pick up tag strip under the deck together. |
7th Apr 2021, 5:34 pm | #57 |
Octode
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Re: Dansette Prince
Oh. So it's a Garrard 1000 turntable or similar not the 2025 fitted to the Bush version.
This makes it easier for you as the 2025 has a very small socket in which the cartridge is fitted. Shorting out the pins on the tag strip and checking the screw connection tells you that the earth connection to the amplifier is making contact. It also confirms that there is nothing wrong with the amplifier, as far as capacitors used in the power supply. The record player deck is steel and so the task is to track down where the hum is being picked up. It really will be either obvious or more elusive. The first thing to note is that the hum is AC mains and being radiated to the pick up leads somewhere between the amplifier and the pick up cartridge and leads to the amplifier. This, for turntables using a magnetic cartridge could be from the motor. Your cartridge is not magnetic, so this shouldn't apply. Any wires carrying AC mains should be as far away from the pick up cartridge as possible. However, remember that it is only when the turntable motor is switched. This is done on your record player by a switch on the deck and from pictures of the underside of the turntable is far away from the pick- up leads and their connection to the amplifier. Make sure any leads from the pick up onwards are away from the switched supply to the motor. If that didn't work, my next action would, working back from the cartridge, I'd disconnect the wires at each soldered point until the hum stopped and then concentrated on the disconnected section. It's a difficult fault to find because there are no voltage measurements to read which illustrate a problem and without the record player "in front of those giving advice," it's a little harder to see what is what. Chris |
7th Apr 2021, 5:39 pm | #58 | ||
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Re: Dansette Prince
Quote:
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7th Apr 2021, 5:53 pm | #59 |
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Re: Dansette Prince
It would help if you quoted from the post you are responding to.
In post #51 (which precedes your reply) the OP says that the cartridge has 4 pins yet your reply in post #53 refers to a 2 pin cartridge??
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7th Apr 2021, 6:40 pm | #60 |
Pentode
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Re: Dansette Prince
Thank you all. I have done some of the things suggested but will go over things again. I don’t think the mains cable can go any farther away. It was neatly moved by the manufacturer with a cable tie which I had to remove to get the deck out.
With respect to redoing the soldering the four coloured wires are attached with spade connectors so I assume I can pull one spade out at a time. Earthing the tag bar to the earthed amp case didn’t improve matters. Also shall I try disconnecting the leads to the cartridge one by one to see if I can eliminate the hum which actually seemed a bit louder this afternoon for some reason. Is this mains hum being transmitted directly through the wiring or is it an electromagnetic signal. If it is the latter should I try selectively screening various areas. I have a Faraday pouch which is used for car keys. Sorry if I am talking nonsense. Gary |