B1 with Korg Triode

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#4,862
Microphony -

A very simple and quite effective tweek to deal with microphony of the nutube .
As you can see on the picture under each extremity of the nutube I have stick under it a patch of blue tak about 1cm by 1 cm .

I can tap lightly on the nutube and it does not ring at all .
 

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#4,863
borlotti said:
here is my PSU 24V for the Korg Nutube Preamp

View attachment 844224


Power supply Model H (24V)

the “model h” power supply is a linear high performance power supply, which provides digitally supervised voltage monitoring and very low noise output. thanks to the partial shunt regulation design, the power supply can also provide clean output voltage to small loads. the toroidal transformer prevents unwanted emissions and radiation is minimized to suppress noise in sensitive analog circuits. the output voltage can be precisely adjusted with a potentiometer.

Features
-high security: primary and secondary side are fused
-suppressing house power line noise (from microwaves, motors, …) by using a special mains filter
-protection against overvoltage coming from mains
-different output voltages selectable by switching resistors. fine tuning using potentiometers
-big capacitance (ca. 24mf) to stabilize short power pulses from the load
-protection against big capacitive loads
-digital voltage monitoring (adjustable). monitoring over- and undervoltage for output
-overvoltage, overpower and over temperature protection
-exact output voltage independent from the connected load by using a specialized partial shunt regulation. therefore the power supply doesn’t need a minimum load to be stable and can power very small loads with low noise.
-ultra fast diodes to prevent ringing
-different filters, including inductive ones, to prevent low and high frequency noise
-specialized filters to suppress 50hz mains noise

the default version of the power supply is adjusted to 28v. the maximum current per rail is 5a. peak load up to 5.1a. for different voltages and/or higher currents, feel free to contact me.

Transformer
the toroidal transformer must be configured as follows: primary 1x 230v, secondary 2x 27v, 230va (please adjust power and voltage according to desired output voltage and power of the power supply; you can get information about this by contacting us). the secondary windings will be connected in serial on the power supply pcb. please pay attention to the polarity of the windings!
Click to expand...

Very cool. If you make these available I'd be happy to order one PCB.
 
#4,864
Hi, I build my B1 buffer preamp years ago.
I have just upgrade it with new "better" / pricier parts.
Im very happy with it.
Then a friend call me and speak of the Korg Nutube B1.
Damn!! He say "this you must have", must I ? :scratch2:
 

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#4,870
OK, I could use some help.


I built the full kit about 3 months ago, but have been having problems with it ever since. I've been double checking polarities and values ever since.


I get the correct in-spec voltages for T1-T6. When it is first powered on, I also can adjust T7,T8 to around 10 volts. I let it sit to warm up, but after a minute or so, T8 starts dropping, eventually going down to about 3 volts. I've left it on for 24 hours, and it still stayed at 3 volts. Also, it's side of the NuTube doesn't have that nice blue glow.


I used to have this problem with both T7 and T8, but now it seems to be confined to T8.


I've put an oscilloscope probe on T8 and noticed it is quite noisy and unstable.


Does anyone have any ideas on what to check next?
 
#4,871
I had the same problem with mine but on T7 only. When I checked, one of the resistors was loose. Could not remember exactly which one, the 100 the 33.2k or R1. I re-soldered the loose one and all components around T7 and got problem fixed. Hope this helps.
 
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#4,873
The output being in the 200R region depending on your output transistors, and this preamp having IMHO an optimal operational range below 2V, I would say there shouldn't be any problem driving such a load (although unusaly low for a power amp)

As a side note, I also drive directly my 600R speaker, through a 100R resistor, so make that 700R load, without any problem and at circa 1V level...

I hope this helps

Claude
 
#4,875
I assembled the preamp and fired it up. Right side tube seems ok, nice glow. Left side only half the grid glows, I have to turn the potmeter significantly further clock-vice to get the voltage at T7 down to 9.5V. When T7 and T8 both are at 9.5V, the voltage at G1 is 2.66V and G2 is 2.29V.

Double checked everything on the pcb, seems ok. Desoldered the nutube from the board and hooked it up with wires, left to right and right to left. Glow/voltage issue remained on the left side of the tube. Seems to indicate an issue with the nutube?

Btw, it’s also super microphonic. Dont know If it relates to the same issue.

Some advice on this would be much appreciated.
 
#4,876
Bjerrolini said:
I assembled the preamp and fired it up. Right side tube seems ok, nice glow. Left side only half the grid glows, I have to turn the potmeter significantly further clock-vice to get the voltage at T7 down to 9.5V. When T7 and T8 both are at 9.5V, the voltage at G1 is 2.66V and G2 is 2.29V.

Double checked everything on the pcb, seems ok. Desoldered the nutube from the board and hooked it up with wires, left to right and right to left. Glow/voltage issue remained on the left side of the tube. Seems to indicate an issue with the nutube?

Btw, it’s also super microphonic. Dont know If it relates to the same issue.

Some advice on this would be much appreciated.
Click to expand...


I had this apparent issue, too. On one channel the grid did not completely glow and I had to set the trimmers on different positions, but other than this, I had no problem. Beautiful sound! Put a couple of stacked pencil erazers on the nutube and you will almost completely get rid of the ringing. The try to seal every hole on the chassis with adhesive tape. It will help, too. Some posts ago another user showed some isolating rubber spacers to secure the circuit to the baseplate of the chassis, instead of metal ones. I've bought them, but I've still to try. You could do the same!
Best,
Gaetano
 
#4,877
ghitus said:
I had this apparent issue, too. On one channel the grid did not completely glow and I had to set the trimmers on different positions, but other than this, I had no problem. Beautiful sound!
Click to expand...

I read in the article that the plate voltage measured at T7, T8 sets the distortion level, just figured the higher voltage drop over G1 -> T7 surely would affect the distortion as well. Guess I'll have to box it up and give it a proper go. Thanks for the advice regarding ringing, I have drone gyro dampers that i think will work beautifully for this.
 
#4,878
BOM please

Anyone have a current BOM for the Korg B1 PCB's on sale right now?

Anyone have files for the chassis that sold out?



The store doesn't give the info and i'm a bit tired of searching, there are different boms and schematics out there.



Could somebody involved perhaps put together a new list of info, and post it somewhere people can find it? perhaps, consider - a files tab on the top menu organized by project..?
 
#4,879
BillBr said:
Anyone have a current BOM for the Korg B1 PCB's on sale right now?

Anyone have files for the chassis that sold out?



The store doesn't give the info and i'm a bit tired of searching, there are different boms and schematics out there.



Could somebody involved perhaps put together a new list of info, and post it somewhere people can find it? perhaps, consider - a files tab on the top menu organized by project..?
Click to expand...

Have you read this from First Watt website?

http://www.firstwatt.com/pdf/art_diy_nutube_preamp.pdf
 
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