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Old 31st October 2005, 03:56 PM   #1
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Default Transformer based phono stage

Dear All,

I am thinking about putting together a phono stage based around the S&B stepup and riaa transformers. To go with this I will need some sort of buffer amp preferably discrete. I am considering the Welbourne labs miniamp, the borbely super buffer and the lcaudio zapfilter2, along with their corresponding PSUs. I am not a electronics wizard so a third party unit is the only option. Is anyone aware of any other transistor based options? Gain needs to be about 2500 overall but this could be achieved in two stages. The riaa and stepup seem to cancel each other out at a gain and loss of 20db respectively but the stepup could go up to a gain of 26 dB.

The unit would then feed my existing preamp or perhaps I would switch to the S&B attenuation transformer so the buffer would need to be able to drive difficult loads.

Regards,

Nick.
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Old 31st October 2005, 04:17 PM   #2
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Or peranders discrete diamond buffer...

http://home.swipnet.se/~w-50719/hifi/qrv05/index.html

Can this type of approach be reconfigured for gain?
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Old 31st October 2005, 04:41 PM   #3
bocka is offline bocka  Germany
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Hi bovizier,

which source do you thinking of? MC?

Do you mean this configuration:

stepup transformer -> buffer -> riaa transformer

If so, I don't think it works. A gain of 2500 by simply using a transformer is impossible. A transformer can do 1 : 10, maybe 1 : 100 with a reduced bandwidth. If you want to do a 1 : 2500 stepup you also do a 1 : (2500)^2 = 1:6.250.000 impedance transformation. If your buffer has a 10meg input impedance your input impedance of the transformer is less than 2 ohms which loads your cartridge. The same with capacitors: A buffer input capacitance of 10pF (typical) gives a 62.5µF load of your cartridge.
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Old 31st October 2005, 05:00 PM   #4
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Default Re: Addition

Quote:
Originally posted by biovizier
Or peranders discrete diamond buffer...

http://home.swipnet.se/~w-50719/hifi/qrv05/index.html

Can this type of approach be reconfigured for gain?
A buffer can't normally have nothing else than gain slightly less than 1. May I ask what you mean by "RIAA transformer"? Do you mean a normal RIAA amp?
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Old 31st October 2005, 07:19 PM   #5
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Default phono

Thats right the transformer cant provide all that gain of course. Given that the transfomrer and RIAA virtually cancel out in terms of gain all of the gain of 2500 will need to be provided using active gain stages. At least one and possibly two. Which is why I was looking at the borbely super buffer or the zap filter. The borbely has 66 db OLG so that might do it at a pinch.

I am referring to the two units produced by Stevens and Billington. One is a step up transformer and the other provides the RIAA EQ.

Its an MC cartridge - brinkmann EMT.

From what you have said of the diamond buffer it is just a buffer and cant provide gain.
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Old 31st October 2005, 08:18 PM   #6
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Haven't you missed something? A transformer can't amplify anything, just transform. You must amplify the outcoming power from the cartridge, how do you do that?
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Old 31st October 2005, 08:57 PM   #7
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Default phono

With an active gain stage - something like the super buffer that I believe can even be used open loop.
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Old 31st October 2005, 09:12 PM   #8
moamps is offline moamps  Croatia
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The idea is shown here:
http://www.stevens-billington.co.uk/riaapage.htm

Quote:
Originally posted by peranders
...You must amplify the outcoming power from the cartridge... [/B]
Power or voltage in the first place?

Regards,
Milan
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