How convert Creek OBH-8 to MC cartridges?

[Calvin]

hi,

I assume that the only way to satisfyingly accommodate for MC pickups with this stage would be to use a dedicated lownoise MC-Prepre or stepup transformer.
In all sims of amplification stages with this or similar topology, noise was an issue.
Noise figures may be good enough for MM-pickups but not for MC-pickups.
A drawback of this otherwise clever and elegant circuit.

jauu
Calvin

[x-pro]

Originally Posted by Calvin

hi,

I assume that the only way to satisfyingly accommodate for MC pickups with this stage would be to use a dedicated lownoise MC-Prepre or stepup transformer.
In all sims of amplification stages with this or similar topology, noise was an issue.
Noise figures may be good enough for MM-pickups but not for MC-pickups.
A drawback of this otherwise clever and elegant circuit.

jauu
Calvin

Some while ago I've published the "2010" version of this circuit - specially for DIY.

Simple Phono Stage 2010





That version can work with either MM or MC cartridge. For a medium-output MC cartridge (~0.4-0.7mV@1kHz) the input FET J1 should be 2SK170BL, R2=68 Ohm, for a low-output MC (~0.2-0.3mV) on top of these changes R2 needs to be shunted by 1000uF 6.3V quality capacitor - that doubles the gain to ~65dB @1 kHz. The input resistor R6 should be chosen for the required cartridge load (100 Ohm - 1kOhm), R15 replaced by a wire link and I usually use C11 = 1nF for MC variants.

For input FETs a selected pair should be used.

Noise levels in this circuit are very good both for MM and MC.

Cheers

Alex

[x-pro]

Originally Posted by tiefbassuebertr

For bigger capacitor values in the RIAA network I have to increase significantly the idle current through the SRPP stage.
How I can realize this?
Genuine schema you will find about post #5+7.

Why do you need to use larger capacitors in the RIAA network? This circuit is nicely balanced and it would be not easy to change the values without some drawbacks.

Originally Posted by tiefbassuebertr

And another question: why is the emitter current through Q2 not defined by a resistance, rather depends on the Hfe of Q3 ??

For me it sounds better this way .

Cheers

Alex

[tiefbassuebertr]

Thank you very much for reply.

Originally Posted by x-pro

For me it sounds better this way .
Cheers Alex

I see. In some cases there are no correspondence between the measurement results and the audible sonic results. The same thing you will find in follow topology:
Jean Hiraga's Super Class-A Amplifier

Originally Posted by x-pro

Why do you need to use larger capacitors in the RIAA network? This circuit is nicely balanced and it would be not easy to change the values without some drawbacks.

the smaller the capacitance values for the RIAA network ​​(and the greater the internal impedance values of the gain stage), the larger is the influence through accessories like follow:
6moons audio reviews: Acoustic System Int. HeartSong Rack
Franck Tchang.com: HeartSong Racks
because the unwanted microphonic effect does a too strong influential (usual and obvious at tube RIAA head amplifiers).
This I don't like.

If you perform a listening test (sound check) with A3i or Atac-3 include Phono Modul (RIAA operation - select "Phono") - and compare the sonic results both with and without an absorber plate like follow
http://www.finite-elemente.de/de/zubehoer/soundbase
or similar. Then you understand, what I mean.

[x-pro]

Originally Posted by tiefbassuebertr

the smaller the capacitance values for the RIAA network ​​(and the greater the internal impedance values of the gain stage), the larger is the influence through accessories like follow:
6moons audio reviews: Acoustic System Int. HeartSong Rack
Franck Tchang.com: HeartSong Racks
because the unwanted microphonic effect does a too strong influential (usual and obvious at tube RIAA head amplifiers).
This I don't like.

Larger capacitors could be actually more microphonic and more problematic in general. I prefer polystyrene capacitors in the RIAA network and had no problems of this kind with these. With a good layout and quality components this circuit is capable of a very good sound quality, far surpassing it's modest cost.

Cheers

Alex

[tiefbassuebertr]

Originally Posted by x-pro

Larger capacitors could be actually more microphonic and more problematic in general. I prefer polystyrene capacitors in the RIAA network and had no problems of this kind with these. With a good layout and quality components this circuit is capable of a very good sound quality, far surpassing it's modest cost. Cheers Alex

For cost effectice solutions you are clearly right. But I want to reach the leading edge concerning the sonic quality by RIAA preamps. Unfortunately the gain stage for driving the RIAA looks then like a big power amp stage, because big caps in an RIAA network needs large currents.
The Outline of such an RIAA head amp looks then like the largest vintage phono stage from Plinius Audio - go to
http://www.pliniusaudio.nzld.com/doc.../m14manual.pdf

[x-pro]

Originally Posted by tiefbassuebertr

I want to reach the leading edge concerning the sonic quality by RIAA preamps.

http://www.ant-audio.co.uk/reviews/ANT%20Kora%20LTD.pdf

FYI - the A.N.T. Audio Kora 3T phono stage uses exactly the same values in the main RIAA network as the "2010" circuit. However it is a FET only design and it is still a commercial product so the circuit is not available.

Cheers

Alex

[tiefbassuebertr]

Originally Posted by x-pro

http://www.ant-audio.co.uk/reviews/ANT%20Kora%20LTD.pdf

FYI - the A.N.T. Audio Kora 3T phono stage uses exactly the same values in the main RIAA network as the "2010" circuit. However it is a FET only design and it is still a commercial product so the circuit is not available.
Cheers
Alex

Good advice. Is the circuit topology also based on a SRPP ?
Perhaps also similar to the OBH15 MK-II ??
Creek Audio - OBH-15mk2

[x-pro]

Originally Posted by tiefbassuebertr

Good advice. Is the circuit topology also based on a SRPP ?

Yes, the topology is similar.

Originally Posted by tiefbassuebertr

Perhaps also similar to the OBH15 MK-II ??
Creek Audio - OBH-15mk2

From the description - nothing like it.

Cheers

Alex

[tiefbassuebertr]

Originally Posted by x-pro

Some while ago I've published the "2010" version of this circuit - specially for DIY.

Simple Phono Stage 2010





That version can work with either MM or MC cartridge. For a medium-output MC cartridge (~0.4-0.7mV@1kHz) the input FET J1 should be 2SK170BL, R2=68 Ohm, for a low-output MC (~0.2-0.3mV) on top of these changes R2 needs to be shunted by 1000uF 6.3V quality capacitor - that doubles the gain to ~65dB @1 kHz. The input resistor R6 should be chosen for the required cartridge load (100 Ohm - 1kOhm), R15 replaced by a wire link and I usually use C11 = 1nF for MC variants.

For input FETs a selected pair should be used.

Noise levels in this circuit are very good both for MM and MC.

Cheers

Alex

Which parts are determine the line gain factor after remove the RIAA network consist of C5+10/R8+9/C4 ?
One part is the resistor R2 + the forward transfer admittance.