BeoGram4000 solenoid thumping noise

7 replies
AL
Offline
alf
Bronze
Posted July 17, 2025 at 04:54 GMT
#1644873
Hi

i just finished the restoration of my BG4000 but one annoying issue remains:

a thumping noise from the solenoid when activated ?

the coil resistance shows 8.7ohm, which is ok

the emitter voltage at OTR4 shows 2.7V

the associated resistor on board 7 has been replaced with a 8.2ohm, 1W resistor to be safe.

the current limiting switch has been adjusted to specification but……

I can’t get rid of that thumping noise from the solenoid.

sure, one could live with it by turning the amp’s volume right down for a sec but there has to be a reason.

can anyone shed some light on that problem ?

thank you

ALF

 
HC
Offline
hcraig244
Silver
Posted July 22, 2025 at 08:12 GMT
#1670473
Alf

Sounds to me if the thumping noise disappears when you turn down the volume check the muting circuit contacts that close when the solenoid damper closes fully and allows the signal from the stylus to pass into the output cable, this is designed to eliminate the thump noise when the tone arm drops onto the disc.....if the contacts are closed all the time or are closing too soon you will get the thump......take a look

Craig
ET
Offline
etype76
Bronze
Posted July 24, 2025 at 09:50 GMT
#1670488
How loud is the 'thump'? I may be crazy but my stylus creates a slight thump in warmer months, I reckon the heat (even in air con environments) must slightly expand metals, alter the properties of greases etc hence my tonearm seems to lower a touch faster. Earlier this year I wasn't getting any sound. But it's not loud enough for me to actually turn the volume down. Obviously, a purely anecdotal non-technical response.
Mark-sf
Offline
Mark-sf
Bronze
Posted July 24, 2025 at 22:50 GMT
#1670497
While there is no muting delay adjustment as on the later models, you should be able to eliminate the thump by adjusting the damper cylinder set screw. The are should lower in between 1 and 1.5secs.
HC
Offline
hcraig244
Silver
Posted July 25, 2025 at 08:59 GMT
Edited July 25, 2025 at 09:26 GMT
#1670498
I didn't know that earlier versions of the BG4000 came without this adjustment......this is yet another example that everyday is a school day ;¬) However....should your version have been supplied complete with this adjustment the attached gives an explanation how to achieve the correct setting via adjustments contacts D&E.....however it should be noted that the author has confused the contacts  F and its adjustment screws G with contacts D&E in his opening description
Attachments (2)
Mark-sf
Offline
Mark-sf
Bronze
Posted July 25, 2025 at 18:19 GMT
#1670501
I was not referring to to the solenoid screw adjustments you referenced. The correct one to address the OP’s issue is the adjacent damper cylinder screw that regulates the air flow as its piston prevents the arm from dropping with a thump.
HC
Offline
hcraig244
Silver
Posted July 26, 2025 at 06:14 GMT
#1670514

Sorry Alf

in my response I have stated that the contacts should close when the tone arm drops, this should read open. The contacts ground the signal from the stylus until the tone arm is on the disc then open to allow the signal to pass into your amp thus eliminating any noise from the initial contact with said disc, in my view should the noise your hearing be generated by any other way turning down your volume would not eliminate it…..hope this helps craig
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