3rd Jun 2016, 10:07 am | #101 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
This is becoming rather a long thread Edward but I can assure you that I'm learning so much in this discussion. The desired outcome for me is to salvage as much as possible from an old 1950's radiogram. The receiver is beyond repair for me at my current skill level so instead of discarding the lot I'm trying to utilise the deck in some way. I may put it back in the old cabinet and use the original speakers or I may fashion a smaller case for it with some different speakers. Either way I needed to learn how to match this old deck with a modern IC amp and stumble across all the problems with buzz, impedance matching, attenuation and small speaker size along the way. I feel I've got a much better understanding of the issues now and really appreciate everyones help and advice
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3rd Jun 2016, 10:10 am | #102 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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3rd Jun 2016, 10:17 am | #103 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Yes. You'll hear everything that's on the record instead of only part of it. It will be in mono of course, you can't have stereo without two separate signal paths and speakers.
If you put the deck back into the Sobell cabinet along with the Bardwell amplifier and some passable speakers, you'd have a record player that would blow the socks off the original Sobell setup. 10 watts per channel from a domestic player is serious noise
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3rd Jun 2016, 10:30 am | #104 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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I also need to sort out the issue of combining the two mains supply power sources. I have one mains supply plug running straight to the motor at 240V and also a mains adaptor plug supplying 12V to the amplifier. I'm presuming there's just a simple transformer inside the casing of the adaptor plug that I can get out and connected it to the other mains supply one I only have one power lead trailing from the machine? |
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3rd Jun 2016, 10:43 am | #105 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
I would leave the 12v adaptor alone (it may be a transformer type or maybe a switch mode type) and just use a 2 way mains socket. using a 1M pot instead of the 10K one will still leave you with 100K input impedance but it is on the way, and yes the pot to vary the resistance and see what happens is a good idea.
Last edited by peter_sol; 3rd Jun 2016 at 10:57 am. |
3rd Jun 2016, 11:25 am | #106 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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3rd Jun 2016, 12:13 pm | #107 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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3rd Jun 2016, 12:35 pm | #108 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
That mini amp you have is capable of about 1 wpc so wet finger in the air, say 40% efficient that's 5 watts from the psu. So yes, 500mA should be OK at 12V.
My take to tidy it up would be to build or obtain a small open chassis type psu and mount that under the deck somewhere so you only need one mains lead from the plinth to the wall. If there's room the psu could be a wallwart in a mains socket.
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3rd Jun 2016, 12:48 pm | #109 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Ah, you just said "speakers", whereas earlier you said 9" speaker. Are there 2 speakers in the old Sobell radiogram cabinet then? Be aware 9" is an odd size. They are either 8" or 10" and will be 3 ohms impedence. I am getting more confused and this thread continues......Edward
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3rd Jun 2016, 1:07 pm | #110 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Philips 654A #90 (353A chassis) is that also a scrap radiogram?
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5th Jun 2016, 3:28 pm | #111 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
My plans is to now put the deck back into the original sobell radiogram cabinet and use the exiisting speaker thats inside. (I'm effectively just swapping the valve amplifier and receiver for my own solid state amplifer that I will impedance match to the cart). If the speaker inside is only a 3ohm can I boost this up to the necessary 6-8ohms but putting a resistor in line with it?
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5th Jun 2016, 3:33 pm | #112 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
If you connect a resistor in series with a loudspeaker the power to the loudspeaker will be reduced.
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5th Jun 2016, 3:35 pm | #113 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
the 3 Ohm one should do fine.
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5th Jun 2016, 3:44 pm | #114 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Personally I think the amplifier you're using is a bit feeble for the job you want it to do. It will work but I don't think you'll get much volume at a decent quality. Whether what you get is sufficient only you will be able to determine by trying it.
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5th Jun 2016, 3:50 pm | #115 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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5th Jun 2016, 3:58 pm | #116 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
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Lawrence. |
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5th Jun 2016, 4:00 pm | #117 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
In principle you could, but most modern ic amps should be idiot proof to a first approximation. Just don't run it flat out.
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5th Jun 2016, 4:10 pm | #118 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
The IC is OK for 4 ohms and 3 ohms is the old 4 ohms
A speakers impedance varies across the audio frequency band so its quoted impedance is nominal. Should not do damage but if it does it does Nobody can be sure I should just try it and see how it goes. |
6th Jun 2016, 8:03 am | #119 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
In my post #109 I asked about the Sobell's speaker or speakers. In your post #111, you said "speaker". Do you mean there is only one speaker in the old Sobell cabinet? Edward
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6th Jun 2016, 11:40 am | #120 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Yes. Just one speaker
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