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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 7th Apr 2021, 6:18 pm   #61
simpsons
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Default Re: Dansette Prince

Gary.

Just a moment. Remember the hum is only there when the record deck is switched on to play a record. This is important. It means that the AC hum is NOT being induced by the mains cable.

By all means remove the spade connectors but leave them free. You have already proved that shorting them together stops the hum. Removing them disconnects the pick up wiring, a good start. Let's see what happens then.

Chris
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Old 7th Apr 2021, 7:02 pm   #62
Edward Huggins
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Quote:
Originally Posted by Station X View Post
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??
Yes, that's quite correct. In his Post #49 the OP states it is an Acos GP91-3SC and I confirmed in my reply that this is a 2 pin cartridge. However, we now know that the OP was mistaken and it's actually an Acos GP93-1 which does have 4 pins. I hope that Members will understand why I became mislead by this.
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Old 7th Apr 2021, 8:10 pm   #63
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Default Re: Dansette Prince

The hum can’t be there until it’s switched on as the power to the amplifier is via the motor/transformer.. therefore it can only be diagnosed when the unit is switched on.
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Old 7th Apr 2021, 9:01 pm   #64
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The hum can’t be there until it’s switched on as the power to the amplifier is via the motor/transformer.. therefore it can only be diagnosed when the unit is switched on.
Vidjoman - that’s exactly what I’ve been thinking.

However, in the schematic that Lawrence linked to in Post#12 there is a variant version of the power supply that seems to have a separate mains transformer - which would provide amplifier power when the motor isn’t running. I don’t think we’ve established which PSU version the OP has.

But I still wonder if we’re chasing a non-problem. We don’t know what the level of the hum is, except (I think) that it’s inaudible when there’s a record playing , and as far as I remember, all record-players, tape recorders, etc of this era and this consumer level would have audible hum levels if turned to max volume without any signal input.. We’re not dealing with a Quad II here...

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Old 7th Apr 2021, 10:46 pm   #65
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Default Re: Dansette Prince

Oh dear,

I do hope that we are not chasing a red herring here.

1. The motor must always be running should the design allow the user to playback through the tape socket without the turntable in motion. This is what the schematic shows.

Does this mean that the turntable has a muting switch? OR

2. The amplifier is switched on only when the turntable is in motion, the turntable has a mains switch, operated by a lever, not shown in the schematic

Gary, the only way of finding out is a photo please of the underneath of the record deck.

Chris
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Old 8th Apr 2021, 8:56 am   #66
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Default Re: Dansette Prince

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However, in the schematic that Lawrence linked to in Post#12 there is a variant version of the power supply that seems to have a separate mains transformer - which would provide amplifier power when the motor isnít running. I donít think weíve established which PSU version the OP has.
That's not for the record player it's for the auxillary amplifier the AU52....

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Old 8th Apr 2021, 10:58 am   #67
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Default Re: Dansette Prince

All, a photo, removed all four spade connectors and no diff.
Poor joint of screened wire on stereo socket resoldered. May have helped. Certainly with the volume low it does seem quieter.
I am continuing to squirt switch cleaner down volume control shaft as crackly and looses volume about 2/3 of the way up then comes on again. Wondering if this is not helping matters
Thank you
Gary
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Old 8th Apr 2021, 11:19 am   #68
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Those pickup wires from the cartridge are unscreened and are in effect open circuit at the cartridge end and they feed into a high input impedance at the other end, as a result of that any 50Hz they pick from any other conductor carrying 50Hz in their vicinity is likely to find its way to the loudspeaker when the volume is turned up.

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Old 8th Apr 2021, 12:29 pm   #69
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Am a bit confused. When I disconnected the pick up wires no effect on hum but I disconnected them individually. Shall I disconnect them all and see. As regards lack of screening I assume that is original spec. Not sure how I screen them without making them heavy?

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Old 8th Apr 2021, 1:11 pm   #70
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Default Re: Dansette Prince

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Not sure how I screen them without making them heavy?
You can't, they have to be very light and flexible.

They're lightly twisted together for best possible hum cancelling anyway.

You can't use screened wire in the pickup arm for the simple reason that it's not flexible enough and will cause the tone arm to put more stress on the groove walls of the record causing mistracking and damage.

In high impedance circuits with crystal cartridges, the stray capacitance in screened cable causes attenuation of the high frequencies making the player sound dull, which is another reason not to use it and keep any that is used to a minimum length.

It could possibly be that your cartridge is slightly low on output and you're more aware of any residual hum at the particular volume setting.

Don't try getting switch cleaner into the pot via the shaft - squirt it in via the connecting tags if you can.
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Old 8th Apr 2021, 1:15 pm   #71
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If they are unscreened, then that is likely to be the original specification. Yes, disconnect all the 4 wires but make a careful note of which colour goes to which tag on the tag card. As previously advised, also check the routing of the mains lead away from the amplifier as much as possible using ties or cleats.
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Old 8th Apr 2021, 1:33 pm   #72
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Thank you, more things I’ve learned.
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Old 8th Apr 2021, 4:08 pm   #73
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Gary

The photo of the underneath of the turntable/record deck says a thousand words.

They are:

1. The amplifier is only switched on when the turntable is set to playing a record. You can quite clearly see the switch which is connected to the red wires to the turntable motor. The yellow wires are the low voltage

You can confirm this by looking at the motor and seeing when the rotor spins. If it is all the time, after the record player is turned on, then I'm wrong. If it only spins when a record is played, then I am right. As an aside this means that the tape socket is really only tape out but perhaps in the wisdom of RBM Marketing, the punter wouldn't have a clue if having the turntable running to play back a tape was not exactly good engineering practice, but I digress.

2. The thin pick up leads are just perfect. The screen cables coming from them are to the industry norm.

What you didn't say from the start was the intermittent volume control. Now this doesn't matter too much as when you shorted the wires the hum went away.

As you have confirmed, the loudness of hum didn't change when you disconnected the thin wires, this by using the process of elimination means that the hum MUST be induced BEFORE them. N'cest pas?

You say that the hum was less after you re-soldered the stereo out socket.

One thing I missed was the earth wire from the turntable, coloured green. Just make sure that, as with the terminal strip, the screw is making a good connection.

Keep the mains, red and low voltage yellow "dressed" away from the input to the amplifier and "Report back."

Over and out

Chris
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Old 8th Apr 2021, 6:36 pm   #74
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Chris/All ,sorry if I am replying twice .My post seemed to crash.
When you turn the deck switch to start, the disc under above the motor bracket starts to spin. When you turn off ,the stylus remains responsive for about ten seconds then is silent .I don’t know the reason for doing it this way but you are of course correct.
As the deck is out the wires are probably as far from the amp as possible.
Obviously wires go to the amp but I am assuming that I just have to tuck loose cabling away as far as possible.
Now the deck earth screw. This was very tight but I undid and retightened and I really think that the hum has improved ��.
The volume control is causing noise but not hum. I don’t think they are easily serviceable? I just continue with cleaner
So It may be that the hum may be within normal limits now for this player, I wouldn’t know.
Thank you again. Gary
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Old 8th Apr 2021, 6:38 pm   #75
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Typo error “hum has improved��”
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Old 8th Apr 2021, 6:38 pm   #76
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Looks like it won’t let me put smiley face. Keeps changing to ��
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Old 8th Apr 2021, 6:49 pm   #77
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Smiley test.
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Old 8th Apr 2021, 9:31 pm   #78
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You have to use the smileys from the advanced editor. Emoji won't work; Paul Stenning will be able to confirm but I suspect the forum software is using a database configuration from the days before Emoji were invented (Latin-I character set as opposed to utf-8), and changing it now would require taking the forum offline for awhile and might break archived posts.
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Old 9th Apr 2021, 8:27 am   #79
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Default Re: Dansette Prince

Gary

This is good progress although I must acknowledge Michael Maurice post which also spoke of checking the earth connection to the deck, which when I saw the green wire to the motor gave me food for thought. Team work!

The scratchy volume control does need sorting out as there is always a nagging thought that poor contact between the resistive carbon track and rotating wiper at 1 meg ohm can lead to a merry dance.

Only thing is, the particular control you have has long plastic (nylon) shaft and has a mains switch known as a DPST (double pole single throw) to switch both live and neutral mains. Because it is a volume control, it has a logarithmic carbon track not linear. It is, in my opinion, also a safety component and must be replaced with a similar type viz: 1 meg log dpst potentiometer nylon shaft.

I've had a quick look see and would you believe, Dansette Products have an exact replacement. At £14.95, its a little expensive but available if needed.

I have no interest in the company etc. They are on the web and can be contacted on 08081 33 45 78.

Chris
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Old 9th Apr 2021, 9:27 am   #80
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Default Re: Dansette Prince

Many thanks also to Michael.I did add an additional earth to the deck earlier but it then made no difference.Wonder if the paint or costing on the deck was adding a resistance as I just touched with the wires rather than through a drilled hole.
Will order new volume control
Gary
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