Flip up binocular magnifiers are very helpful:
https://www.amazon.com/dp/B003UCODIA/ref=cm_sw_r_cp_api_i_.gAPDbV80J707
These newer ones seem to be top rated and I might try a pair:
https://www.amazon.com/dp/B01H8808H6/ref=cm_sw_r_cp_api_i_siAPDbJ9KM00S
https://www.amazon.com/dp/B003UCODIA/ref=cm_sw_r_cp_api_i_.gAPDbV80J707
These newer ones seem to be top rated and I might try a pair:
https://www.amazon.com/dp/B01H8808H6/ref=cm_sw_r_cp_api_i_siAPDbJ9KM00S
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Wayne’s BA-18 preamp board re-visited, now with output coupling caps. Since I had to install output and input coupling caps on the Yarra mainboard, I thought I would give the WBA-18 another try. It had some pretty bad DC offset drift due to the steep temp dependence of the the transistors. Just wafting your hand over the boards would make it wander 15mV.
Installing it back into mainboard - now WBA-18 also fitted with some serrated fin stamped heatsinks on the output BJTs:
The preamp measures very clean now. The huge sub 1000Hz DC drift hump/hill in the old FFT is gone. Preamp displays natural second order distortion and lower third harmonic. Overall very low levels in the 0.0017% THD range for circa 700mVpp output into 50k load.
MDOT Reference, this is what it looked like before coupling caps:
Installing it back into mainboard - now WBA-18 also fitted with some serrated fin stamped heatsinks on the output BJTs:
The preamp measures very clean now. The huge sub 1000Hz DC drift hump/hill in the old FFT is gone. Preamp displays natural second order distortion and lower third harmonic. Overall very low levels in the 0.0017% THD range for circa 700mVpp output into 50k load.
MDOT Reference, this is what it looked like before coupling caps:
Attachments
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Do you have an 'official' BOM for the 6P1 pre PCBs? I know batty has posted some info. Surely PCB layout software generates very accurate parts lists based on the designers specs?
I just did a dry fit and all parts in the BOM I posted fit the pcb.
Only the alt 470uF 63v did not, but they were a backup.
Pot is used to set grid voltage between 0 and 3.3v and optimum was around 2v. I don’t think the reduced current will be an issue. You can probably use 5k vs 1k.
Ok, here is the Korg 6P1 preamp data in one place.
Setup Instructions: Adjust pot to set voltage = 12.00v at the plate of the 6P1 (same as left leg of R121 or pin 7 or 10 on the 6P1). This achieves the design performance of dominant H2 and monononitcally decreasing higher order harmonics while keeping overall THD low.
Very important: you MUST use AC-coupling caps on the Yarra mainboard for both the input and output or the Korg 6P1 preamp board will not work.
BOM in txt file below or same info in the .xls file zipped as attachment:
Setup Instructions: Adjust pot to set voltage = 12.00v at the plate of the 6P1 (same as left leg of R121 or pin 7 or 10 on the 6P1). This achieves the design performance of dominant H2 and monononitcally decreasing higher order harmonics while keeping overall THD low.
Very important: you MUST use AC-coupling caps on the Yarra mainboard for both the input and output or the Korg 6P1 preamp board will not work.
BOM in txt file below or same info in the .xls file zipped as attachment:
Code:
Part Value Package Description
C101 470µ E5-10,5 POLARIZED CAPACITOR, European symbol
C106 0µ1 C5B2.5 CAPACITOR
C111 10µ0 C5B11
C113 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
C115 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
C116 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
C117 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
C118 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
C122 0µ1 C5B2.5 CAPACITOR
C131 470µ E5-10,5 POLARIZED CAPACITOR, European symbol
C132 10µ0 E2,5-5 POLARIZED CAPACITOR, European symbol
N131 LP2950-33LPRE3 TO92-123
R101 40R2 CMF55-2V
R102 475k CMF55-2V
R103 475k CMF55-2V
R104 1k0 CMF55-2V
R105 1k0 CMF55-2V
R112 1k0 RTRIM74W Trimm resistor
R113 33k2 CMF55-2V
R115 150R CMF55-2V
R117 150R CMF55-2V
R118 270k CMF55-2V
R121 10k0 CMF-55
R122 1k0 CMF55-2V
V104 2N7000 TO92-SGD
V111 6P1 6P1 KORG 6P1
V121 2N7000 TO92-SGD
X101 M3 M3_VIAS_NEU
X102 22-27-2021-02 6410-02 CONNECTOR
X121 M3 M3_VIAS_NEU
X131 M3 M3_VIAS_NEU
X132 M3 M3_VIAS_NEU
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Hello all,
I don't know much about electronic design, but all my builds have been successful (knock knock) primarily because I am careful and can follow directions. I've finally procured enough parts to at least start building the Yarra. I will be running it into M2 (not M2X) and Aleph J builds. Both of these amps have enough gain for my habits to not need much gain from the preamp. I ordered 15 volt transformers, and the WB18, Melbourne and Korg daughter boards. I am going to start with either the Melbourne or the WB18 because I don't have a solid state preamp.
Are both of these boards fine with 15 volt transformers?
Might one of these boards be better suited to the M2 and Aleph J?
Thanks
I don't know much about electronic design, but all my builds have been successful (knock knock) primarily because I am careful and can follow directions. I've finally procured enough parts to at least start building the Yarra. I will be running it into M2 (not M2X) and Aleph J builds. Both of these amps have enough gain for my habits to not need much gain from the preamp. I ordered 15 volt transformers, and the WB18, Melbourne and Korg daughter boards. I am going to start with either the Melbourne or the WB18 because I don't have a solid state preamp.
Are both of these boards fine with 15 volt transformers?
Might one of these boards be better suited to the M2 and Aleph J?
Thanks
My Yarra/Melbourne is using 12+12Vac trafos, and it can drive the M2X Edcor line auto transformer directly without any daughter cards effortlessly, vol knob at 9~10 o'clock position.
I also did bypass the edcor(removed from pcb) and drive the output stages, its around 1~2 o'clock position, thinking to upgrade to 15+15Vac trafos for more ooomph!
For Mofo, think i need 22+22Vac trafo. So happy that this Yarra is so versatile.
I also did bypass the edcor(removed from pcb) and drive the output stages, its around 1~2 o'clock position, thinking to upgrade to 15+15Vac trafos for more ooomph!
For Mofo, think i need 22+22Vac trafo. So happy that this Yarra is so versatile.
First of all, i believe in keeping it simple ...
The Yarra/Melb DB combination actually sound very good driving the Edcor autoTrafo directly, bypassing all the buffer daughter boards. Soundstage is very much lively, a tinge of warmth, good details but not being bright. Basically nothing is lost here.
However, when Edcor is bypassed, i hear slightly more details in the high, a little bright and pretty flat in the bass dept or lower frequencies. Liveliness is gone, music sounds dead to me.
Next for total hums elimination, i will remove the Edcor from the main pcbs and make a interconnect cables with the Edcor along in them. This is to allow me to physically place the Edcor anywhere i like it to be away from any trafos.
Those who have the Yarra and M2/M2x may try the above experiment, hope you like it too.
The Yarra/Melb DB combination actually sound very good driving the Edcor autoTrafo directly, bypassing all the buffer daughter boards. Soundstage is very much lively, a tinge of warmth, good details but not being bright. Basically nothing is lost here.
However, when Edcor is bypassed, i hear slightly more details in the high, a little bright and pretty flat in the bass dept or lower frequencies. Liveliness is gone, music sounds dead to me.
Next for total hums elimination, i will remove the Edcor from the main pcbs and make a interconnect cables with the Edcor along in them. This is to allow me to physically place the Edcor anywhere i like it to be away from any trafos.
Those who have the Yarra and M2/M2x may try the above experiment, hope you like it too.