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Balanced B1 with Korg Triode
Balanced B1 with Korg Triode
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Old 4th September 2019, 12:27 AM   #11
elwood625 is offline elwood625  United States
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I finally finished my Balanced B1 Korg preamp, rainy day made the difference. I gave up marking the PC boards Left and Right, now they are marked + for positive 2H and - for negative 2H. This way I can change the boards from right and left if I want positive 2H or negative 2H. Far to many double negatives for me to keep track of.

I used a 6 position solder strip, grounds on the ends and then the four test positions to measure plate voltage for the two PC boards. A 3 position 4 pole selector switch, make before break with 1 M ohm resistors from L+,R+ and L- R- to ground on the inputs, A nice trick from NP to reduce noise while selecting inputs. Twisted pairs with a shield for input wiring.
I had a scare when I first powered it up, after completing all the internal wiring, the on-off switch LED was slowly flashing and the Korg Nutube did not have the cathodes glowing. The $10 wall wart, which works perfectly with the regular B1 Kord triode preamp, does not work with the Balanced version. My lab power supply powers it up along with the Meanwell power supply from an ACA v1.6 amplifier.
I'm using the preamp with the ACA mono blocks in balanced mode with my Threshold FET 10Pe phono section, it has balanced outputs and the Music Hall 25.3 DAC, which also has balanced outputs.
I have to admit, the Balanced Zen line stage is a better match for the ACA's. I built this preamp for the F5T v3 mono blocks I'm building.
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File Type: jpg IMG_0876.jpg (1.00 MB, 396 views)
File Type: jpg IMG_0878.jpg (974.3 KB, 392 views)
File Type: jpg IMG_0879.jpg (803.2 KB, 364 views)
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ACA v1.6 monoblocks, Balanced Zen Line Stage, M2x, Aleph J, H2, B1 Korg triode, 12AX7a Phono amplifier, Balanced B1 Korg triode, 6FG6 "Magic Eye" tube VU meter, FS NJFET RIAA
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Old 4th September 2019, 03:07 PM   #12
nashbap is offline nashbap  United States
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Balanced B1 with Korg Triode
Just so that I understand after inversion you have a positive H2 in both Left and Right channels?
nash
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Old 4th September 2019, 06:58 PM   #13
elwood625 is offline elwood625  United States
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"To the extent the balanced channels are matched, they will cancel, leaving
5th. You can unbalance the 2nd harmonic if you like - the channels are
adjustable as described in the article. You could set one side at negative
phase and the other at positive, or simply make them unequal in
amplitude but not phase"
I adjusted so that they are unequal in amplitude but equal in phase, this adjustment provided the lowest 3H for each channel.



"If you want more 2nd, then you would set them differently, for example:
Keeping mind that the individual channels are inverting, if you have a
+ incoming signal it becomes the - outgoing signal and vice versa.

+ in to L ch = -out

- in to R ch = +out"



Which is how the boards are installed. Once the F5T amps are finished, I plan on changing the R channel to positive and with the inversion, negative 2H on both channels.
I'm curious as to what the sound will be with one channel positive and one channel negative. Since I have recorded all the measurements, all I will need to do is set each side to the plate voltage from previous measurements. I can set them to either negative 2H on both channels or positive 2H on both channels.
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Old 5th September 2019, 02:09 AM   #14
nashbap is offline nashbap  United States
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Balanced B1 with Korg Triode
Since this is a balanced setup each channel input signal has a +phase and a - phase.
The procedure you outlined shows that you matched overall the Left channel and the Right channel spectrum. Does this imply that you matched the Right + to the same spectra as the Left +? And similarly the Right- and the Left -?
Not sure of your exact procedure but in setting up my BA3bal I treated each phase as a separate channel so that all 4 phases have the same spectra.


nash
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Old 6th September 2019, 02:21 PM   #15
elwood625 is offline elwood625  United States
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When I was making the adjustments, I adjusted R+ and R- together along with L+ and L-. First, I made a rough adjustment for 1.5% 2H on either R+ or R-, then I would go back and forth adjusting R+ and R- so that I would have the 1.5% 2H and 3H decreasing. It is easy to adjust for 2H, however, 3H amounts will increase at times. The adjustments required me to wait 30 seconds for the results to stabilize, if I saw 2H rising above the 1.5% or 3H increasing, I would back off the previous adjustment.
When I would find the sweet spot of 1.5% 2H and 3H to the lowest level, I recorded the plate voltage for each L+, L-and R+, R-.
It took me about 1 - 1.5 hours for each channel, for each 2H level I chose. Since I recorded each channel for 1%, 1.5% positive and negative phase and the 2H null point, I tested each channel by un-adjusting each pot, and then setting each adjustment to the values I recorded. I was very concerned with being able to duplicate the adjustments each day I worked on them. At times I thought it would be nice to be able to see positive 2H and negative 2H, the REW software just gives 2H amplitude, not phase. However, knowing the plate voltage for the 2H null point, then when adjusting lower plate voltage was positive 2H and increasing plate voltage gave negative 2H.

It took me 4 days of work to make and record all the adjustments, patience making the adjustments made all the difference. It reminded me of adjusting multiple carburetors on an engine, set idle speed, then mixture and readjust idle speed, repeat, etc.

Once I was able to find the settings for each channel where 3H would decrease, and 2H stabilized, it was a very rewarding feeling. I had so much fun with this project, it got me away from the drill press drilling holes endlessly for my F5T amps, now that it is done, it's back to drilling more holes.
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ACA v1.6 monoblocks, Balanced Zen Line Stage, M2x, Aleph J, H2, B1 Korg triode, 12AX7a Phono amplifier, Balanced B1 Korg triode, 6FG6 "Magic Eye" tube VU meter, FS NJFET RIAA
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Old 6th September 2019, 04:47 PM   #16
nashbap is offline nashbap  United States
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Balanced B1 with Korg Triode
Yes the pots can be fiddly tiresome and repeatability is not that great.


If you can, try setting each phase separately, essentially treating as 4 separate channels matched identically. The individual and the balanced work out differently.



Hope you find a setting that you are happier with.


nash
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Old 8th September 2019, 12:39 AM   #17
elwood625 is offline elwood625  United States
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Here are the final adjustments which provides 1.5% positive 2H on both channels. Notice the variations in plate voltage for each channel, Korg Nutube production variances? Each channel has 3H at the lowest level I could adjust to and keep noise and 4H to low levels.
With the speaker connections swapped, the final result is 1.5% 2H negative phase.
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Old 8th September 2019, 12:43 AM   #18
elwood625 is offline elwood625  United States
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Solution to the power supply, scope pattern is almost identical to the wall wart supply. $14.95 with free shipping from Mr. Bezos and friends. I used it for the right channel adjustment, lab supply for the Left channel.
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File Type: jpg IMG_0882.jpg (377.7 KB, 66 views)
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ACA v1.6 monoblocks, Balanced Zen Line Stage, M2x, Aleph J, H2, B1 Korg triode, 12AX7a Phono amplifier, Balanced B1 Korg triode, 6FG6 "Magic Eye" tube VU meter, FS NJFET RIAA
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Old 15th September 2019, 04:24 PM   #19
elwood625 is offline elwood625  United States
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Here are the final plate voltage numbers for the Right channel:
R+ = 9.53 vdc
R- = 8.87 vdc
This gives 1.5% positive 2H, with the speaker leads swapped, the final result is 1.5% 2H negative.
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File Type: jpg Right channel Balanced R+ = 9.53 vdc R- = 8.87 vdc.JPG (173.8 KB, 43 views)
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ACA v1.6 monoblocks, Balanced Zen Line Stage, M2x, Aleph J, H2, B1 Korg triode, 12AX7a Phono amplifier, Balanced B1 Korg triode, 6FG6 "Magic Eye" tube VU meter, FS NJFET RIAA
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Old 15th September 2019, 04:26 PM   #20
elwood625 is offline elwood625  United States
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Here are the final plate voltage numbers for the Left channel:
L+ = 10.51 vdc
L- = 9.56 vdc
This gives 1.5% positive 2H, with the speaker leads swapped, the final result is 1.5% 2H negative.
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ACA v1.6 monoblocks, Balanced Zen Line Stage, M2x, Aleph J, H2, B1 Korg triode, 12AX7a Phono amplifier, Balanced B1 Korg triode, 6FG6 "Magic Eye" tube VU meter, FS NJFET RIAA
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