Phonostage with balanced input

[Khom]

My phonostage with balanced input based on schematic of Konstantin Musatoff described here: http://musatoffcv.narod.ru/Projects/RIAA5.htm , see also attached picture for convinience. The main features are:
- no common feedback loop
- passive correction
- relative high (+/-24 V) power supply.
- relative powerful output stage, so it should be non-sensitive to the interconnect

Unfortunately, there is no EN translation for device, so I will describe it in short.

R* - additional HF-correction for some cartridge with lack of HF
R7 - tau1 (75 us)
R26 - tau2 (318 us)
R29 - tau3 (3180 us)
R15, R21 - 7950 us
R12 - bias for output stage (Q9)
SW1 - switches between balanced and asymmetrical input

DA1 (low-noise opamp with MOSFET input, for example LF353) and components around it works as integrator and maintain DC zero output. As you see, all correction RC-circuits are passive, i.e. there is no frequency correction in feedback. Of course, output stage Q9 works in Class A.

So, it's basic schematic. I make some changes:

1. C3R7 excluded, I make tau1 correction (75 us) on input by reducing R3 and R4 to 3.1 kOhm each. Calculated value is (R3+R4)=6.2 kOhm for my AT-440MLa (moving magnet, approx. 480 mH inductance). I used this solution for tau1 with different schematic a long time ago since 80-th and it works well.

2. Integrator DA1 with it components removed, RIFA polypropylene 10 uF capacitor installed before R35. My opinion - one good PP capacitor is better than integrator circuit with a lot of active and passive details plus additional power supply for it.

3. 2SK184 replaced with 2SK170 (or 2SK117). Reason is enough simple - I didn't find here supplier for genuine 2SK184 . Of course, all transistors in differential stages and in current mirror should be matched in pairs.

All capacitors in "sound" way are polystyrene ones, C7 polypropylene, other big caps C4, C6 are PTFE.

Phonostage powered by Two-transistor Shunt Regulator, it has low noise at the wide frequency range and good performance regarding 50*n Hz. Regulator recalculated to 24 V, I used two identical ones with two separated Shottky rectifiers.

Sound. Unfortunately I'm rather technician than poet. It sounds light and airy, with soft deep bass. By the way, I don't see significand difference in sound with balanced and unbalances modes, maybe result will different with other interconnect from TT to PhS.

Used with upgraded Technics SL-1200Mk2, MM AT-440MLa. Tonearm rewired by litz, stock interconnect replaced with DIY Klotz MC5000 (twisted pair in common shield each lead, it's very suitable for this FS) and XLR connectors, external PSU, internal onboard regulator replaced with LM317, control board fully recapped, main bearing upgraded in first iteration... I see a long way ahead!)
RIAAPhono5.jpg

[Colin Wonfor]

Interesting circuit, I do like the idea of the shunt reg.
But I hate the idea of DC servo on the output, I always found then troublesome.

[Audio Advent]

Owchen prekrastnui!

(I studied Russian at school and visited Borisov - home of the 1812 victory and therefore symphony - in Belarus as part of my exchange. Sadly things like "very nice" are all I can remember now. "Slon igrayet na barabanye" = "The elephant plays the drums".)

[Khom]

Interesting circuit, I do like the idea of the shunt reg.
But I hate the idea of DC servo on the output, I always found then troublesome.

Yes, I also prefer more simple and straight solution. That's why my version looks as shown here (C3 removed, but I saved it's place on PCB for using in future with MC where my 75 us correction is unusable):

Owchen prekrastnui!

(I studied Russian at school and visited Borisov - home of the 1812 victory and therefore symphony - in Belarus as part of my exchange. Sadly things like "very nice" are all I can remember now. "Slon igrayet na barabanye" = "The elephant plays the drums".)

Thanks for russian words! Borisov is old city not so far from Minsk, historical Berezina crossing well known. I have vinyl Tchaikovski "1812 Overture" (canonical variation, i.e. with "God save the Tsar" ("Боже, царя храни") old russian hymn).

[Audio Advent]

Боже мой!

[Barry]

Valery,

I would be interested in a balanced output version of your circuit. Could that be achieved by taking the output from the junction between the 100R resistors and the output FETs? That is, there would be two 10u + 62R combinations.

Thanks

Barry

[Khom]

I'm afraid it's not so simple and in order to get balanced output you have to take differential signals from J4, J5 FET's and make two additional output stages instead of push-pull on this schematic. Or (may be better?) to add medium-power differential amplifier instead given output. My PA has unbalanced input, so I newer think about it.

BTW, this schematic is not mine, I took it from Konstantin Musatoff site.