B1 with Korg Triode

[Soundhappy]

Do builders have the same gain from twin triodes ?
My one output have much less..
I do ready incrase plate resistor to ~ 380 K but no equilibre.
Thanks in advance for the solutions

 

[Soundhappy]

Last week I do the trick with two separated mono potentiometers , channels balance equilibrum is better
but You know one side have this " juice " the other don't.
It's probably two different transductances or tube was broken maybe ??
My Korg are very little microphonic no problem is quiet 😀

 

[Soundhappy]

I see Korg tester photos

 

[RobertHaze]

Yes Soundhappy, My Korg B1 had a weak left channel. The NuTube was also extremely microphonic. My B1V2 got a brand new NuTube which thankfully is not very microphonic. The channel balance is better too although still not perfect.
The B1 also got plain top and bottom plates for the enclosure, just in case the new tube still had issues with microphony. Both plates were treated with Dynamat sound deadener. The new plates only had the mounting holes along the sides. I had to drill and bevel the holes for the standoffs. This was good because the big Solen output capacitors I had stuffed on the board had been crowded against the input jacks. I moved the mounting holes about 1/2 inch forward so the PCB is almost but not quite under the volume control PCB. That gave me ample clearance for my capacitors.
The blank plates are available directly from Italy.
Aluminium cover GALAXY 247-287 without any hole

 

[Soundhappy]

My all test mesurements values from T1 to T8

 

[nashbap]

Do builders have the same gain from twin triodes ?
My one output have much less..
I do ready incrase plate resistor to ~ 380 K but no equilibre.
Thanks in advance for the solutions

How much difference did you measure?
nash

 

[nashbap]

My B1V2 got a brand new NuTube which thankfully is not very microphonic. The channel balance is better too although still not perfect.

What is a B1V2? Thanks. Could you post a pic?

nash

 

[Soundhappy]

Yes Soundhappy, My Korg B1 had a weak left channel. The NuTube was also extremely microphonic. My B1V2 got a brand new NuTube which thankfully is not very microphonic. The channel balance is better too although still not perfect.
The B1 also got plain top and bottom plates for the enclosure, just in case the new tube still had issues with microphony. Both plates were treated with Dynamat sound deadener. The new plates only had the mounting holes along the sides. I had to drill and bevel the holes for the standoffs. This was good because the big Solen output capacitors I had stuffed on the board had been crowded against the input jacks. I moved the mounting holes about 1/2 inch forward so the PCB is almost but not quite under the volume control PCB. That gave me ample clearance for my capacitors.
The blank plates are available directly from Italy.
Aluminium cover GALAXY 247-287 without any hole

Thanks Robert for interesting advice and link.
Yes is weak left channel. Strange such big inbalance.
First time after all Korg bench test's was OK I play this record Dawn of the Forest
This high frequency rings with subtles vibratos sound haevenly with B1Triode.
My caps are mixture of Elna Silmic and Fine Gold Nichicon for the moment
3.3 uF MKP in drawers waits for the future modification..work in progress.
Best regards
Christophe

 

[Soundhappy]

How much difference did you measure?
nash

It's deep night I need go to sleep 😴 .. tomorrow

 

[Soundhappy]

How much difference did you measure?
nash

And Your Nutube mesurement are ?
My have half or less of the other channel..

 

[DQ828]

My all test mesurements values from T1 to T8

Geeks rule the world 🙂

 

[Soundhappy]

How much difference did you measure?
nash

Volume pot at full o clock my channels outputs difference is 1:16
max left = 0.5V , max right = 8V

 

[avtech]

That's a big difference. Have you double checked all component values on the LH side? Dry joints?

What about the voltages either side before the nutube? Are the input buffers working correctly?

 

[Soundhappy]

Thanks DIYers

Meantime, I learn more about scope use and how do precise gain measurements
Oscilloscope: DC & AC, Signal Tracing in Amp Circuit, RMS Output Measurement

 

[Soundhappy]

Perfect balance in less 5 minutes

Yes Soundhappy, My Korg B1 had a weak left channel. The NuTube was also extremely microphonic.
My B1V2 got a brand new NuTube which thankfully is not very microphonic.
The channel balance is better too although still not perfect..

I have a good time today: amplitudes measurements with scope and search for the same distortion value for both channels.
Photo 1 low % THD, photo 2 Right, photo 3 Left "weak" channel signal amplitude at maximum with the same V/ Division scale.
The solution is simple and no need for laboratory tools.
Only ears and music.
Play Your favorite song with B1 Korg in the audio chain.
Do with trimmer adjustment on the strong channel slowly.... step by little, step.... tube light does glow less than the other triode
and You hear two channels is perfectly balanced now on both sides. Enjoy

 

[soundwavesteve]

Just finished this version today, nice Christmas gift to myself having it work first time 🙂. I’ll post thoughts tomorrow but first thing I noticed is I am getting a noticeable 60hz hum, measurable from listening seat. It is volume dependent, though it goes away at full volume. The case is a Chinese piece from eBay. Beautiful machining, not a single flaw. I did have to machine out one of the knobs to get it fit over the Tubecad Select2 selector shaft.

 

[dewdrop]

Very nicely done! I didn't see analog ground.

 

[elwood625]

I had the same problem with my build, I had wired the RCA grounds separate up to the selector and then to ground twisted with the positive side of each RCA. I had to wire all the RCA grounds together at the jacks and then wired it to the closest mounting point of the PCB, which is connected to ground, to solve my 60 Hz hum issue.
My build used the wall wart power supply, and yours has the power supply in the chassis, so it probably isn't the same.

 

[elwood625]

Nice build, great looking chassis. I hope you find the cause, what a great sounding preamp IMHO. I love the ability to 'tune" the sound to your liking. I've had preamps in the past where you could make small changes to the sound, nothing like the B1 Korg where the changes are so dramatic.

 

[soundwavesteve]

Thanks for the tip elwood, I will investigate tonight. Dew, my Bugle 2 phono pre is grounded and I get no additional hum when listening to vinyl with the setup as it is.



I have not read every post on this unit but I do recall that a few people say the B1K does need some time to burn-in to sound its best. So far, with the B1K having been used for just 40min, it isn't yet as good sounding in my system as the modded Dynaco Pas2 I have been using. Being a triode I am already used to the overall character, but the PAS2 has a more tangible tone. The B1K is noticeably darker with less high frequency energy, a plumier bass range and less vertical soundstaging. The cables are inverted at the speaker and the trim pots are set at exactly 9.50VDC. I will try putting the cables at normal polarity just to see if it makes a difference. My amp is the Akitika GT101. The B1K does have a 'blacker' background though (even with the hum) as it has lower distortion and power supply noise than the upgraded PAS2.



Side note, inside that closed aluminum case with the B1K board on drone anti-vibration stand-offs and the NuTube sitting on foam double-sided tape there is no microphonics from the room or tapping on the case. However you do hear ringing when changing inputs. With the onboard Meanwell PS and eight 2200uF audio caps, there is no turn-on/off thump.