Salas,
I have already built the Preamp you are looking for. It is a combination of the DCB1 (mez) and the "Super Simple Preamp" . I have a switch which can include or exclude the "SSP" which will add gain if needed (not often) to the chosen recording. Gain can be changed with different resistors. I have not noticed any denigration in sound, although some may argue against having the "chips" in the circuit. (hence the switch) This pre is in front of my F5 and it sounds fantastic on quality recordings. Not forgiving of poor recordings though.
SSP link: DIY Simple Active Preamp - Page 17 - AudioKarma.org Home Audio Stereo Discussion Forums
Post #248
Ron
I have already built the Preamp you are looking for. It is a combination of the DCB1 (mez) and the "Super Simple Preamp" . I have a switch which can include or exclude the "SSP" which will add gain if needed (not often) to the chosen recording. Gain can be changed with different resistors. I have not noticed any denigration in sound, although some may argue against having the "chips" in the circuit. (hence the switch) This pre is in front of my F5 and it sounds fantastic on quality recordings. Not forgiving of poor recordings though.
SSP link: DIY Simple Active Preamp - Page 17 - AudioKarma.org Home Audio Stereo Discussion Forums
Post #248
Ron
Excellent. It'll be going into a GFA-535....in the next ten minutes. Have heard the relays clicking on and off. Thank you for a wonderful project 
. Should mention now, the DCB1 will be used with the aforementioned GFA-535 ( which I believe is DC coupled ) and a SCHIIT bifrist DAC that is for sure DC coupled. Should I take precautions of some kind?
. Should mention now, the DCB1 will be used with the aforementioned GFA-535 ( which I believe is DC coupled ) and a SCHIIT bifrist DAC that is for sure DC coupled. Should I take precautions of some kind?
hello everyone.
I read the first 40/50 pages and i gathered the information i need to build a buffer DCB1 with mezmerize pcb but with 200ma hot rod configuration (by the way, nice work guys!).
Now I just want to have some solid proof before buy the components. Clear and precise answers i think will be helpful also to other people that read this ...
1) to be used n.4 resistor 8.2R 3W, n.2 per side, in place of 64R, right? (someone has item code to purchase on mouser?)
2) to be used transformer 50Va 2x12V or 50Va 2x15V? Secondary output schema is 1x 0 1x or +1x 0 -1x? (I'm sorry but I'm not very knowledgeable on the subject of transformers). Any issue on using Rcore in place of toroidal, better or worse?
3) to be used MUR820 in place of MUR120 for security reason(heat)? If yes, audio quality remains the same, better or worse? (someone has item code to purchase MUR820 on mouser?)
4) to be used dissipators for IRFP240, IRFP9240 and 7812?
only another one ...
5) does the potentiometer ALPS stereo RK27 fit on the pcb? What is the
maximum usable value, 20K? Any suggestions on other pots (better?) to use?
I repeat, these questions are designed to make a hot rod 200ma mezmerize buffer with good audio quality but also with good reliability over the long term and for many hours of continuous use.
Thanks to anyone.
I read the first 40/50 pages and i gathered the information i need to build a buffer DCB1 with mezmerize pcb but with 200ma hot rod configuration (by the way, nice work guys!).
Now I just want to have some solid proof before buy the components. Clear and precise answers i think will be helpful also to other people that read this ...
1) to be used n.4 resistor 8.2R 3W, n.2 per side, in place of 64R, right? (someone has item code to purchase on mouser?)
2) to be used transformer 50Va 2x12V or 50Va 2x15V? Secondary output schema is 1x 0 1x or +1x 0 -1x? (I'm sorry but I'm not very knowledgeable on the subject of transformers). Any issue on using Rcore in place of toroidal, better or worse?
3) to be used MUR820 in place of MUR120 for security reason(heat)? If yes, audio quality remains the same, better or worse? (someone has item code to purchase MUR820 on mouser?)
4) to be used dissipators for IRFP240, IRFP9240 and 7812?
only another one ...
5) does the potentiometer ALPS stereo RK27 fit on the pcb? What is the
maximum usable value, 20K? Any suggestions on other pots (better?) to use?
I repeat, these questions are designed to make a hot rod 200ma mezmerize buffer with good audio quality but also with good reliability over the long term and for many hours of continuous use.
Thanks to anyone.
1) 8.2R 3W 1 per side or 17R 2W 2 per side for about 200mA current per side. Use 100ppm or under, metal film.
2) 50VA 15+15VAC (dual secondaries i.e. 4 secondary wires). Rcore better for low magnetic field and lower capacitance from primary to secondary. Not Chinese.
3) Same quality, you need 820 in more hot rod than 200mA which I don't recommend in Mez, too much trouble. Just mount MUR120 standing upright with a little space from one body end to board, 2mm when using 200mA. Or get 820 if you feel better, little more difficult to arrange them there, your choice.
4) Use the chassis for IRFP sinks (dissipators you say) by mounting those under board this way _| like in power amplifiers. Use insulation pads! Good enough for 200mA setting. If mechanically impossible or you don't like it, then use 2 to 2.3C/W common sinks per 2 Mosfets per side. Insulators again. Use a small clip or screw sink for 7812.
5) Yes it fits exactly. 20K is good. Its not a strict technical maximum, it is a recommended about sound quality around 25K max because it works better for more supersonic bandwidth, i.e. faster squarewave test risetime, in combination with the JFETs input capacitance. Better is switch pot with resistors, even cheap Ebay switch pot, or TKD for classic wiper pot.
Use 105C over 2000 hours spec electrolytic capacitors for long stable life.
2) 50VA 15+15VAC (dual secondaries i.e. 4 secondary wires). Rcore better for low magnetic field and lower capacitance from primary to secondary. Not Chinese.
3) Same quality, you need 820 in more hot rod than 200mA which I don't recommend in Mez, too much trouble. Just mount MUR120 standing upright with a little space from one body end to board, 2mm when using 200mA. Or get 820 if you feel better, little more difficult to arrange them there, your choice.
4) Use the chassis for IRFP sinks (dissipators you say) by mounting those under board this way _| like in power amplifiers. Use insulation pads! Good enough for 200mA setting. If mechanically impossible or you don't like it, then use 2 to 2.3C/W common sinks per 2 Mosfets per side. Insulators again. Use a small clip or screw sink for 7812.
5) Yes it fits exactly. 20K is good. Its not a strict technical maximum, it is a recommended about sound quality around 25K max because it works better for more supersonic bandwidth, i.e. faster squarewave test risetime, in combination with the JFETs input capacitance. Better is switch pot with resistors, even cheap Ebay switch pot, or TKD for classic wiper pot.
Use 105C over 2000 hours spec electrolytic capacitors for long stable life.
Thinking of it (+12dB gain, great sounding and neutral in character, using +/-10V PSU, no coupling caps and designed in compliance with B1/Pass concepts) I came to this idea (in attachment) based on Mr. Pass' proposal from BAF2013. Having LSK/LSJ JFETs available makes this possible.
J310 CCS provides about 20mA each, LSK/LSJ JFETs work at Vds of 7.5V and with Id at about 80% of Idss. P1 enables dynamic matching/distortion profile optimizing and P2 sets the DC offset.
Preamp's max. output is about 7V_peak of clean swing.
Zout is determined by value of R9 and it's not critical (R9/R6 ratio determines the gain of the circuit) since we have a Mesmerize buffer stage next to it.
I think they will work great together. AFAIC, it would be very difficult to find a better sounding gain stage...
