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Old 7th February 2009, 02:32 PM   #1
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Default Preamp in the headshell?

I was toying with the idea of playing with preamplification in the headshell. Does anyone have a feel for how much mass I could add before things are unmanagable? I have a Grado in an MMT arm at exactly 10Hz resonance now. The setup is in storage so I can't fiddle with it now (I also forgot the brand of the headshell but it is some kind of premium carbon fiber thing).
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Old 7th February 2009, 02:57 PM   #2
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With the right SMT parts it seems like you could do it at under a couple grams. On the down side, you'll have extra wires for power, and the caps I'd want to use for even half the RIAA eq wouldn't be itty bitty SMT ceramics, but larger films. Fortunately there are lots more SMT part options now than even a couple years ago. IMO, it's a good idea to investigate, along with putting the pre in the table itself. I know that's been done commercially.
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Old 7th February 2009, 04:57 PM   #3
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As Conrad says, it should be possible with SMD parts to keep the circuit under a couple of grams. I do think you should leave any RIAA equliziasion out of this circuit, and just make it as a clean buffer with gain of e.g. 20-40dB. Resistors in the receiving end could bring signal down to what normal RIAA circuits accepts.

My thoughts are going more to shielded cables and a piece of mu copper around the shell
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Old 8th February 2009, 04:21 AM   #4
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Quote:
Originally posted by Conrad Hoffman
With the right SMT parts it seems like you could do it at under a couple grams. On the down side, you'll have extra wires for power, and the caps I'd want to use for even half the RIAA eq wouldn't be itty bitty SMT ceramics, but larger films. Fortunately there are lots more SMT part options now than even a couple years ago. IMO, it's a good idea to investigate, along with putting the pre in the table itself. I know that's been done commercially.
SMT caps are problematic, but you can get 1206 NPO now up to .1u and I think I remember higher. I was thinking of a phantom power arrangement similar to the Schoeps transformerless mic circuit. There are several external sound devices with P48 and balanced inputs. You could also try RIAA in software or a hybrid approach.
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Old 8th February 2009, 06:13 AM   #5
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We did this back in the '70s, with some high gm FETs (CM860, if memory serves), drilled some holes in the headshell to mount the FETs, then remote powered it. That didn't add too much mass. Worked very well.
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Old 8th February 2009, 08:42 AM   #6
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Default Re: Preamp in the headshell?

Quote:
Originally posted by scott wurcer
I was toying with the idea

The dream analogue source for the "hear no difference" brigade.

Hey, i have other bright ideas for you. How about making a speaker cable with "network boxes" which in fact hide power amps? Wouldn't that be something to play your headshell riaa through?
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Old 8th February 2009, 09:42 AM   #7
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Certainly one could do that - at least to fit a single gain stage - even if your setup seems not to be perfect for this task (low compliance MC like SPU, Denon DL103 and the likes that benefit from high mass arms).

As I'm currently working on my phono, I would be more sceptical regarding shielding. Even a simple alu-box is probably already too heavy and without shielding it's likely to pickup lots of noise so there's no net benefit.

But being the person you are, you already thought about that

Have fun, Hannes
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Old 8th February 2009, 10:04 AM   #8
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Quote:
As I'm currently working on my phono, I would be more sceptical regarding shielding. Even a simple alu-box is probably already too heavy and without shielding it's likely to pickup lots of noise so there's no net benefit.
my-copper - Not alu
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Old 8th February 2009, 10:17 AM   #9
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Quote:
Ballmann headshell mounted digitizer
This one digitizes at 768/24 at the headshell and sends the digital signal to a receiver at the armbase. Requires arm re-wiring
Regards
James
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Old 8th February 2009, 10:39 AM   #10
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Nice

Sadly using an AD makes the sound compressed like on CDs......
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