6th Jun 2016, 12:14 pm | #121 |
Octode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Indigo girl, nice to see you're trying to make use of the old kit and learning along the way. I think its important we help people learn their way with audio like this.
I've attached a simple circuit, which may or may not be of use to you. It will enable you to send the ceramic cartridge output into a modern magnetic phono preamp with good results. So if you wanted an easier path to using the deck on its own with modern equipment, this might work well for you while you learn how to repair the rest of it Obviously you will need 2 of these networks for stereo, very simple with 1 capacitor and 2 resistors per channel. I used this myself a while back as I wanted to run an auto changer through my hifi rig. I understand such networks used to be in amplifiers that featured a "ceramic / magnetic" switch on the phono input. (excuse the poor diagram, should do the job though!) |
6th Jun 2016, 12:30 pm | #122 |
Dekatron
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Re: Hum when old BSR connected to new op-amp/speaker circuit
If you only have one speaker in your Sobell cabinet, how are you going to connect up your new IC Stereo amplifer? Are you going to connect a second speaker somewhere else, say, in a seperate cabinet? Edward
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6th Jun 2016, 12:34 pm | #123 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Quote:
I'm not sure what I'll end up making out of this project but I feel like I've learnt so much and have so many options to try out and compare. I'm an ex-scientist so love all this kind of stuff! Nicola |
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6th Jun 2016, 12:48 pm | #124 |
Octode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Its both attenuation and equalisation. The resistors form a voltage divider to attenuate the signal down to the level of a magnetic cartridge (or thereabouts), and the capacitor provides a rising high frequency response so that when the RIAA curve is applied you get the results you'd expect. You're essentially making the signal similar enough to that of a magnetic cartridge
It worked well for me, but then I started using a Garrard SL65b with magnetic cartridge so it became redundant. You can experiment with different resistor values if that combo doesn't work. Ceramics can vary in output, from what I recall the circuit posted worked well with a BSR SC5H high output cartridge. |
6th Jun 2016, 9:19 pm | #125 |
Hexode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Can this amplifier be modified so the channels are bridged, as this should give more output (mono) to a single speaker?
I think it was suggested above but in light of the OP using the original speaker it might be worth revisiting. Ignore this comment if it's too complicated. |
6th Jun 2016, 10:47 pm | #126 |
Dekatron
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Ohh - not a good idea! Edward
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6th Jun 2016, 11:41 pm | #127 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
With only one speaker in the cabinet I only need mono from by stereo cart so I've bridged the cart outputs so there's just one ground and one signal wire coming from the pick up arm. This gets amplified through one channel of the amp and then into one speaker.
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6th Jun 2016, 11:47 pm | #128 |
Hexode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
By bridging, I didn't mean joining the outputs together. I was thinking along the lines of a car amplifier, where it can be configured in bridged mode to power a subwoofer, or used as 2 channels for normal stereo. In bridged mode generally the output power in increased.
Actually doing it would involve careful study of the i.c datasheet to see if it's possible. I certainly wouldn't suggest parallelling the outputs as this would very likely destroy the i.c. |
7th Jun 2016, 6:48 am | #129 |
Octode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
It can be bridged as per the data but lets see how the single channel goes first.
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7th Jun 2016, 7:29 am | #130 |
Dekatron
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Re: Hum when old BSR connected to new op-amp/speaker circuit
What about the loading on the other IC channel where no speaker is planned to be connected? Edward
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7th Jun 2016, 7:36 am | #131 |
Dekatron
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Re: Hum when old BSR connected to new op-amp/speaker circuit
IC amplifiers are as near as possible ideal voltage sources, and don't mind running an into open circuit.
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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
7th Jun 2016, 4:46 pm | #132 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Bit confused here then - so what is the best way to connect a stereo cart to a stereo amp with only one speaker? I get good audio when just one channel from the stereo cart goes through the amp with only one speaker connected. I can't really notice the difference by ear when both cart channels are joined so that a mixture of the two channels gets played through one speaker. I'd prefer to have both channels from the cart playing through the speaker ideally. Is this a problem? Alternatively, why is it not a good idea to have both channels from the amp playing through one speaker?
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7th Jun 2016, 5:03 pm | #133 | |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Quote:
Nicola |
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7th Jun 2016, 5:05 pm | #134 |
Hexode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
You shouldn't join the outputs together as this will probably damage the i.c
The suggestion that seems the best is to connect the outputs of the cartridge together in parallel (+ to + and - to -) then feed this into one channel of the amplifier. Perhaps the reason you've not been able to notice any difference when connected this way is that you are maybe playing a mono record? A mono record will provide the same information to both channels of a stereo cartridge. |
7th Jun 2016, 5:07 pm | #135 |
Hexode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
I wouldn't worry too much about the impedence matching, it's not going to do any harm to either the cartridge or the amp, and the best suggestion with what you've done is to leave it they way it sounds best to you.
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7th Jun 2016, 6:06 pm | #136 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Thanks Clyde
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7th Jun 2016, 6:11 pm | #137 |
Octode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
You say 100 to 200 ohms Did you mean K ohms?
I would parallel the cart for single amp use. |
7th Jun 2016, 6:57 pm | #138 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Yes, sorry, I meant to say 100 K ohms. I've paralleled the cart and compared it to just a single channel (but this time using a stereo record - thanks Clyde). Much better with both channels mixed
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7th Jun 2016, 7:01 pm | #139 |
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Re: Hum when old BSR connected to new op-amp/speaker circuit
Just wired up your Bardwell amplifer Nick - wow what an improvement! The 5W output per channel is powerful. I can get away with turning the 1M ohm pot up all the way because it doesn't matter that the input signal drops - I still get more than enough volume
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7th Jun 2016, 7:29 pm | #140 |
Octode
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Re: Hum when old BSR connected to new op-amp/speaker circuit
You have still learnt a great deal first hand and hopefully although frustrating at times, I hope,had fun as well.
Those carts are best, if possible, to play into between 500 K and 1 meg. as you have found out. |