Yes, all 6 were of the incorrect value.
Would that also explain why R1 by T5 measured 00.8 millivolts and R1 by T6 measured 0.13 millivolts?
Well, I am not sure. The much small resistor value will draw more current from the power supply, 36mA per channel. However if your power supply is rated for 0.50A the power supply should be able to handle it. The voltage will drop about 1.4V but that shouldn't affect the J113 CCS current. The much smaller resistors would drastically drop the audio signal level but that is not the immediate issue of concern and besides, when the correct resistors are in place, it would be moot.
If you have four resistors of about 100k or higher in value, you can install them at the input buffer locations. The exact value is not critical, as long as both in each channel are the same value and the value is high enough so that the current draw is small. The other two resistor locations can be left open. Then you can check the R1 voltage drop. To be sure of R1, check that it is 150R.
This way you can check to see if the input buffer JFETs are okay.
If you have four resistors of about 100k or higher in value, you can install them at the input buffer locations. The exact value is not critical, as long as both in each channel are the same value and the value is high enough so that the current draw is small. The other two resistor locations can be left open. Then you can check the R1 voltage drop. To be sure of R1, check that it is 150R.
This way you can check to see if the input buffer JFETs are okay.
Hi Ben,
I received the correct 332K resistors super fast from Digi-key and installed them just a little while ago. Everything is up and running within specification.
I was able to bring the the voltages on T7 and T8 down to the 9.5v recommendation that Mr. Pass suggested as the starting point.
All the other voltages look good too.
T1= 23.7v
T3=22.9v
T4=8.87v
T5 measures .628v and T6 reads .641v
Thank you once again for your help, time, and sharing your electronics trouble shooting wisdom and expertise.
Kind Regards,
Benjisan
I received the correct 332K resistors super fast from Digi-key and installed them just a little while ago. Everything is up and running within specification.
I was able to bring the the voltages on T7 and T8 down to the 9.5v recommendation that Mr. Pass suggested as the starting point.
All the other voltages look good too.
T1= 23.7v
T3=22.9v
T4=8.87v
T5 measures .628v and T6 reads .641v
Thank you once again for your help, time, and sharing your electronics trouble shooting wisdom and expertise.
Kind Regards,
Benjisan
That's great news.
Did you measure the voltage drop across the R1 resistor at the input JFETs at both channels?
Did you measure the voltage drop across the R1 resistor at the input JFETs at both channels?
Hi Ben,
The voltages for R1 near T5 measured 1.251v and R1 near T6 measured 1.242v
It sounds really good as I have been listening to the preamp for the past few hours.
I'm pretty happy now because this preamp has absolutely no discernible microphonics like my first build and I can now box it up and give to my brother for his Christmas gift.
Hi Ben,
My brother loves it and says the sound is detailed, expansive and pleasing. He has an Anthem Pre-2l and gives the Korg Nutube circuit Mr. Pass designed a big thumbs up.
It's just setting in this temporary setup on top of the Adcom GFA 555 until he can put it in a more appropriate spot in his system. Right now it's being played through a Dell Laptop, Topping E30, Korg, Adcom, Magnepan Magneplanar MG1's that he completely refurbished and rebuilt from the inside out.
Again, thanks for the assistance and hope you had a very Merry Christmas.
My brother loves it and says the sound is detailed, expansive and pleasing. He has an Anthem Pre-2l and gives the Korg Nutube circuit Mr. Pass designed a big thumbs up.
It's just setting in this temporary setup on top of the Adcom GFA 555 until he can put it in a more appropriate spot in his system. Right now it's being played through a Dell Laptop, Topping E30, Korg, Adcom, Magnepan Magneplanar MG1's that he completely refurbished and rebuilt from the inside out.
Again, thanks for the assistance and hope you had a very Merry Christmas.
@pitbul I want to thank you personally, I rebuilt it using your guidance. I did have a wiring error with one of the power connections just touching the chassis. I rewired the signal routes as you suggested and went a little further - I bypassed the switch altogether (I only have one output) and wired the two outputs parallel (so I can run 2.2).
Sounds much better and the PLC noise echo is gone. There's a bit of hiss though I'm not convinced it's the pre's fault.
Sounds great.
@rmpfyf
glad to hear that you have better results, I recommend that you check resistors as some people wrote in the previous threads, check the voltages and determine if they are correct.
I don't have such device, but I know that my way of wiring is much, much better then suggested, it will for sure give much better stereo.
I always like to help when see someone is trying to diy.
glad to hear that you have better results, I recommend that you check resistors as some people wrote in the previous threads, check the voltages and determine if they are correct.
I don't have such device, but I know that my way of wiring is much, much better then suggested, it will for sure give much better stereo.
I always like to help when see someone is trying to diy.
Yes, I didn't like the sound of my Purifi Eval1. No emotion. After adding B1 Korg I like it a lot.
Well, just finished the kit and it worked right out of the gate. I’m very very happy with it, looks great, sounds great, is a great match my ACA amps.
OK, I do have one question. The resistor in position T3 gets very hot, about 130°F. Is that normal?
Is that the 10 Ohmer in the power supply filter? I think Pa said 24V at T1 and 23V at T3. Approximately. T1 is the power in. There are two 10 Ohm resistors so 1V drop will give you 50mA current. A hot resistor indicates excessive current draw.
Several things:
1. Confirm that the resistor is 10 Ohm.
2. Confirm that the resistor is 3W.
3. Measure the voltage drop across the resistor. The current draw is supposed to be about 60mA so the voltage drop should be about 0.6V across a 10 Ohm resistor.
4. How was the 130 degrees F (54 degrees C) determined? Infrared thermometer or a thermometer in contact with the resistor, or by feel?
1. Confirm that the resistor is 10 Ohm.
2. Confirm that the resistor is 3W.
3. Measure the voltage drop across the resistor. The current draw is supposed to be about 60mA so the voltage drop should be about 0.6V across a 10 Ohm resistor.
4. How was the 130 degrees F (54 degrees C) determined? Infrared thermometer or a thermometer in contact with the resistor, or by feel?
Tested with commercial contact temp probe.
My schematic shows it to be a 270 Ohm 3W resister in that position.
https://www.diyaudio.com/archive/galleries/korg-b1/nutube final schematic.pdf
I am measuring 150 Ohm, but it is still in circuit, so that is probably not correct.
Test points as described in the assembly manual are showing correct 24V.
My schematic shows it to be a 270 Ohm 3W resister in that position.
https://www.diyaudio.com/archive/galleries/korg-b1/nutube final schematic.pdf
I am measuring 150 Ohm, but it is still in circuit, so that is probably not correct.
Test points as described in the assembly manual are showing correct 24V.
I looked at the schematic and that showed T3 next to the 10 Ohm, with the 270 Ohm on the other side of T3. I see now that the PCB has T3 next to the 270 Ohm.
Approximately 55mA passes through the 270 Ohm, so the dissipation is about 0.8W. I can see a 3W resistor getting hot dissipating 0.8W. If you have a spare 270 Ohm 3W resistor and 15V power supply, you can hook it up and check the temperature and compare.
I don't have a 270 Ohm 3W resistor to try, but one of my amps has 0.1 Ohm 3W resistors passing 3.0A for 0.9W dissipation at each resistor, and they get quite hot, probably around 50 to 55 degrees C by touch.
So I think the temperature of your 270 Ohm resistor is probably normal.
Approximately 55mA passes through the 270 Ohm, so the dissipation is about 0.8W. I can see a 3W resistor getting hot dissipating 0.8W. If you have a spare 270 Ohm 3W resistor and 15V power supply, you can hook it up and check the temperature and compare.
I don't have a 270 Ohm 3W resistor to try, but one of my amps has 0.1 Ohm 3W resistors passing 3.0A for 0.9W dissipation at each resistor, and they get quite hot, probably around 50 to 55 degrees C by touch.
So I think the temperature of your 270 Ohm resistor is probably normal.
Hi all,
I have a question for the DIY gurus here.
As noted in this thread I had built a second Korg B1 Nutube and gifted it my brother. After a faux-pas with a resistor purchase screw up, and some help from Ben Mah, I can say the unit is working fabulously.
Now I need some advice on a possible add-on L-R balance pot modification to the Korg in order to help my brother out. He has a slight hearing loss in his left ear. He audiologist determined that he has about a 25 db difference of hearing loss starting just above 10-kHz between his left and right ear.
What this translates too is that he needs to now position himself slightly closer to the left speaker to maintain true stereo. With his prior preamp he just simply adjusted the balance to favor the left channel ever so slightly. This was very convenient and helped tremendously with his hearing impairment. He doesn't really have the capability to rearrange the current listening environment (it's shared and not a dedicated sound room) because of the way the furniture in the room is setup.
So I was thinking that it would make more sense to add a balance pot to the unit, but would like to seek some guidance on the feasibility or pitfalls of adding such a modification.
Please let me know what you guys think.
Kind Regards,
I have a question for the DIY gurus here.
As noted in this thread I had built a second Korg B1 Nutube and gifted it my brother. After a faux-pas with a resistor purchase screw up, and some help from Ben Mah, I can say the unit is working fabulously.
Now I need some advice on a possible add-on L-R balance pot modification to the Korg in order to help my brother out. He has a slight hearing loss in his left ear. He audiologist determined that he has about a 25 db difference of hearing loss starting just above 10-kHz between his left and right ear.
What this translates too is that he needs to now position himself slightly closer to the left speaker to maintain true stereo. With his prior preamp he just simply adjusted the balance to favor the left channel ever so slightly. This was very convenient and helped tremendously with his hearing impairment. He doesn't really have the capability to rearrange the current listening environment (it's shared and not a dedicated sound room) because of the way the furniture in the room is setup.
So I was thinking that it would make more sense to add a balance pot to the unit, but would like to seek some guidance on the feasibility or pitfalls of adding such a modification.
Please let me know what you guys think.
Kind Regards,