You can even replace with, or mix in, higher VF generic LEDs but it would not make any performance difference. The four LEDs are fed constant current from Q7 to come up with their added VFs and provide voltage bias to Q3's base. Its a local shunt Vref supply. RC (R22, C6) filters residual noise.
What voltage they achieve plus Q3 Vbe is what the input JFET(s) drain(s) stay at. Typical red LEDs range is alright for that even if their total VF is 7V or 7.5V when in circuit. Having almost the same Q3 base voltage between channels is good for consistency. Q7s must have comparable IDSS and the four LEDs groups comparable VFs to get close. Finally the TP adjustment procedure allows enough rail voltage change for things to bias up correctly.
What voltage they achieve plus Q3 Vbe is what the input JFET(s) drain(s) stay at. Typical red LEDs range is alright for that even if their total VF is 7V or 7.5V when in circuit. Having almost the same Q3 base voltage between channels is good for consistency. Q7s must have comparable IDSS and the four LEDs groups comparable VFs to get close. Finally the TP adjustment procedure allows enough rail voltage change for things to bias up correctly.
For the last word in obsessive-compulsive matching, you could rig up a little circuit on a DIP socket using one or two 9V batteries, your selected Q7, and a string of LEDs, and swap LEDs until you get a voltage in your desired target range, then do the same with the selected Q7 from the other channel and swap LEDs until you get exactly the same voltage as in the first channel. Will this make a performance difference? No. But it might scratch an itch if you desire that level of matching. As DIYers we have the luxury to fiddle around with these things in ways that manufacturers would never dream of. 
It run from the first with no issues. Dead quiet. Sound was very nice, considering it has only few hours of running in, i was very happy with what i hear.
I had high expectations and it did not let me down. Excellent work Salas. Thank you for sharing this brilliant project and Tea-Bag for his support.
I had high expectations and it did not let me down. Excellent work Salas. Thank you for sharing this brilliant project and Tea-Bag for his support.
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After a years of searching for holly grail and synergy between all components i finally settled with the following system. It is built around analogue front end. Turntable was made by one of excellent Croatian TT constructors and enthusiast mr. Lovrincevic. Model is Reference. I have installed two Tonearms, Calista 2 with Nagaoka MP-200 and Kuzma 4point9 Tonearm with Benz Micro LPS cartridge.
Preamp EAR 868 has integrated MM/MC phono section.
Power amp, Luxman M800A is connected to speakers Wilson Audio Sophia 2.
On the other hand, there is Computer audio, as second source, based around modified Mac Mini with changed switching power supply to LPS. Signal goes to Berkeley Alpha USB/SPDIF and then to DAC Bryston BDA-1.
Room is acoustically treated with diffusors/absorbers. Low frequency room modes up to 150hz were controlled by 2 x PSI AVAA C20 active bass traps.
Overall i like the sound very much, neutral, transparent and natural with big stage but i got feeling my BM LPS MC cartridge has still some juice to be squizzed therefore i was building UFSP.
I also plan to build Ultra BiB PSU to feed my DC turntable motor as at the moment it uses switching supply.
And that would be end game for me. At least for some time...
Preamp EAR 868 has integrated MM/MC phono section.
Power amp, Luxman M800A is connected to speakers Wilson Audio Sophia 2.
On the other hand, there is Computer audio, as second source, based around modified Mac Mini with changed switching power supply to LPS. Signal goes to Berkeley Alpha USB/SPDIF and then to DAC Bryston BDA-1.
Room is acoustically treated with diffusors/absorbers. Low frequency room modes up to 150hz were controlled by 2 x PSI AVAA C20 active bass traps.
Overall i like the sound very much, neutral, transparent and natural with big stage but i got feeling my BM LPS MC cartridge has still some juice to be squizzed therefore i was building UFSP.
I also plan to build Ultra BiB PSU to feed my DC turntable motor as at the moment it uses switching supply.
And that would be end game for me. At least for some time...
I’m watching these guys on eBay for quite time and they do manufacture several turntables types with flexibility of some parts choices. In did it is nice (at lease visually) units. It is SAM eBay store attached as image.
Other subject:
I remember it was already discussed here on form in the past, but lets refresh it: what is
our best option to connect our amazing phono to fully balance preamp? If somebody already did that, then please share with you experience.
Other subject:
I remember it was already discussed here on form in the past, but lets refresh it: what is
our best option to connect our amazing phono to fully balance preamp? If somebody already did that, then please share with you experience.
Use SMPS
Hi, I have just received one of these, however no transformers from a local auction. Was advised it was working OK, but the guy wanted the trans for another project.
I have Meanwell 48 VDC dual outlet unit, that I can set down to 42 VDC, can I use this to trial the phono amp.
Cheers
Hi, I have just received one of these, however no transformers from a local auction. Was advised it was working OK, but the guy wanted the trans for another project.
I have Meanwell 48 VDC dual outlet unit, that I can set down to 42 VDC, can I use this to trial the phono amp.
Cheers