G'day all, just an enquiry about using a buffer circuit ahead of a standard phono stage. I'm trialling one of my own design, basically a modified FET source follower between my Shure M97xE and my DIY ESP P06 phono stage.
Subjectively, the buffer really seems to help with improved clarity and 'musicality'. Any thoughts on phono stage 'input buffers'? Regards, Felix.
Subjectively, the buffer really seems to help with improved clarity and 'musicality'. Any thoughts on phono stage 'input buffers'? Regards, Felix.
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If it provides gain then it isn't a buffer. If doesn't provide gain then it adds noise and, possibly, distortion. If it adds "musicality" then it almost certainly is adding a little second-order distortion and possibly adjusting the frequency response. You can easily change the sound of a MM cartridge by changing the load impedance.
Tomlinson Holman used an emitter follower buffer when he was studying cartridge and preamp interaction. Here is a link to the paper.
http://www.davidreaton.com/PDFs/Holman_AES_paper.pdf
http://www.davidreaton.com/PDFs/Holman_AES_paper.pdf
Accuphase use input buffers in the MM stage of their new C-27 phono preamplifier (the MM circuit is a completely separate amplifier inside the box - you can actually see a simplified diagram in their brochure). This makes it easier for them to provide the high input impedance required for their MM stage. Maybe you have a similar effect and that is why you prefer the version with the input buffer in your circuit.
Edit: It should be easy to reverse engineer the buffer section that Accuphase use. And no, it does not compromise the noise performance of their MM stage, at least guessing by their published figures, and considering the input levels of MM cartridgs there is no reason to assume that noise would be an issue.
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Felix,
A moving magnet cart typically has an output impedance of about 600 ohms, against a load resistance of normally 47 kohms. Most people also have 1-2 m of phono cable between the cartridge and the phono preamp.
So putting a buffer right up near the tonearm would lower the output impedance and possibly reduce noise and distortion arising from driving the cables directly with the cartridge output.
Obviously it would be better still to move the phono preamp up to near the tonearm, but well, we can't always have the best arrangement. The buffer will add noise to the signal, the question is how much compared to what is generated at the op amp inputs of the phono preamp anyway. This mostly depends on how well-filtered the power supply is used to supply the buffer.
My overall take is : if you like the result, go with it! It's not obviously a good idea, and not obviously a bad one either.
A moving magnet cart typically has an output impedance of about 600 ohms, against a load resistance of normally 47 kohms. Most people also have 1-2 m of phono cable between the cartridge and the phono preamp.
So putting a buffer right up near the tonearm would lower the output impedance and possibly reduce noise and distortion arising from driving the cables directly with the cartridge output.
Obviously it would be better still to move the phono preamp up to near the tonearm, but well, we can't always have the best arrangement. The buffer will add noise to the signal, the question is how much compared to what is generated at the op amp inputs of the phono preamp anyway. This mostly depends on how well-filtered the power supply is used to supply the buffer.
My overall take is : if you like the result, go with it! It's not obviously a good idea, and not obviously a bad one either.
G'day all, that's a quite interesting patent document. One interesting use that I've found for my buffer circuit is as a impedance converter of sorts.
I primarily use the Shure M97xE which is a fine cartridge but with a substantial HF roll off into 47 k resistive loading. I and others have found considerably improved treble extension and general linearity by loading it at a higher impedance. I use 62 k.
By terminating the input buffer at 62 k, the cartridge sees 62 k and the buffer output happily works into the 47 k input (resistive) impedance of the following phono stage. Regards, Felix.
I primarily use the Shure M97xE which is a fine cartridge but with a substantial HF roll off into 47 k resistive loading. I and others have found considerably improved treble extension and general linearity by loading it at a higher impedance. I use 62 k.
By terminating the input buffer at 62 k, the cartridge sees 62 k and the buffer output happily works into the 47 k input (resistive) impedance of the following phono stage. Regards, Felix.
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G'day mate, yes I normally build my DIY phono stages with a specific input impedance in mind and simply install the appropriate loading resistors.
62 K (metal film) resistors are a standard value at my component suppliers locally. 62Kohm 1/2 Watt 1% Metal Film Resistors - Pk.8 - Jaycar Electronics
Regards, Felix.
62 K (metal film) resistors are a standard value at my component suppliers locally. 62Kohm 1/2 Watt 1% Metal Film Resistors - Pk.8 - Jaycar Electronics
Regards, Felix.
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