Thank you very much for publishing the schematics so as the circuit descriptions.
I wonder why that does not make the most companies of audio devices. I mean, the only reason why many write "strictly confidential - not for release" at their schematics, because they are ashamed to publish this cause bad engineering.
Ok, so I'm in receipt of the bits and pieces Alex kindly agreed to supply me.
I'm looking forward to building the phono stage for my Expert stylus co modded MC DL-103 sat on my SL-1200 (modded of course!!)
I will use premium parts through the build including cerefine electrolytics, silvered mica in the filter and RC55Y resistors throughout. I'm also thinking about mundorf supreme as the output cap as I've used them with great success in the output of several CD players I've messed with.
Alex also supplied me with a std psu to get me going. I intend to build my own using one of my low noise regs with Large mundorf smoothing and compare the 2 supplies.
I'm really looking forward to hearing this phono stage
I'm looking forward to building the phono stage for my Expert stylus co modded MC DL-103 sat on my SL-1200 (modded of course!!)
I will use premium parts through the build including cerefine electrolytics, silvered mica in the filter and RC55Y resistors throughout. I'm also thinking about mundorf supreme as the output cap as I've used them with great success in the output of several CD players I've messed with.
Alex also supplied me with a std psu to get me going. I intend to build my own using one of my low noise regs with Large mundorf smoothing and compare the 2 supplies.
I'm really looking forward to hearing this phono stage
Read over the thread. Thanks, Alex, for publishing your circuit design.
I'm surprised no one has asked the obvious question, so I will:
What are the advantages of using N-channel, depletion mode MOSFETs in a phono stage?
Of course "Why not?" and "Because is sounds good." are both acceptable answers in this game, but from the standpoint of the electronics what are the specific reasons / relative merits to consider?
I'm surprised no one has asked the obvious question, so I will:
What are the advantages of using N-channel, depletion mode MOSFETs in a phono stage?
Of course "Why not?" and "Because is sounds good." are both acceptable answers in this game, but from the standpoint of the electronics what are the specific reasons / relative merits to consider?
Because it sounds very good, that is the most important bit. However from the purely electronics point of view these FETs have one of the highest voltage gains I know in a FET - over 10000, which, combined with high input impedance and fairly low noise, makes some very simple and well performing circuits possible. On top of it the BSS139 has a very good consistency in a batch, usual spread less than 5%, so the Kora 3T SE could be made without pre-selection or matching the FETs which is for a local NFB FET only circuit is quite unusual. I supply FETs for the Kora 3T kits just from a reel, in a factory packaging and the DC voltage difference between channels on the output FETs is usually below 50mV (out of 12V !). And the voltage gain is almost completely defined by passive components so if capacitors and resistors are 1% tolerance the gain difference between channels is usually below 1% (0.1dB).
Cheers
Alex
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Hi Alex, how do you feel about increasing capacitance on the psu? Generally I've found it of benefit. I notice on the PCB there is space for additional caps. How about swapping the 470uF for 1000uF? Also I was going to use a very high value mundorf on both the external psu and inside after the 1st diode?
The original Kora 3T SE version has 2200uF + 470uF. It is possible to increase the capacitance further, I've used 3 x 1000uF Panasonic FM on some units. I would advise against increasing the value of the first capacitor (C15) though, as it would increase the peak current from the power supply on switch-on or on connection.
Cheers
Alex
I ordered a special edition stage from Alex awhile ago and he made it for me and sent to US. I experimented with battery powering it but currently use with an Elpac Linear power supply (which I had gotten as an upgrade for the original Creek OBH 11 headphone amp). This stage sounds very nice to me, it is pretty much like the Hi-fi world review mentions. If you want a ton of snap and detail it might not be for you, it is more easy going and has a liquid "tube like" quality about the sound. The less than ideal noise measurements on paper never intrudes in practical use- the enjoyment of playing records. I might have to contact Alex and get a hold of one of the kits.
I know it's been five years since the last post on this thread but I've recently come across a built up pcb. I've put it in a box and hitched it up to a pair of twelve volt batteries and I'm impressed. It's put my 834P in the shade that's for sure. There are one or two components that deviate from the schematic but I'll replace those in due course. Has anyone added the components to convert one of these to moving coil?
A mate of mine has a made-up one and noticed a significantly better SQ when I made up a 24v SLA PS for him, compared to the SMPS that was supplied with it.
Can I suggest you will get better sound if you put a film cap - anywhere from 40uF to 100uF - across the 24v output terminals of the battery supply.
Interesting to know!
I thought the circuit was MM only?
Andy
Thanks for your reply Andyr. It is primarily a moving magnet phono stage but the board has provision for moving coil by replacing/adding a few components. It can only be one or the other, not both. I will try a cap across the batteries. They're big ones too, 17Ah and top out at 13.7 volts each so should hold their charge for a while.
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