Thank you for your replies.
Am I correct in assuming the Board is a Pass B1 ? Just not a variation of the board referred to earlier ?
I have a DACT Stepped Attenuator sitting idle, is this type of Volume Control the right choice for the B1 ?
Any suggestions on he Power Supply, as the device will need one ?
I purchased the Board from the AnalogueAssociation.de forum.
Am I correct in assuming the Board is a Pass B1 ? Just not a variation of the board referred to earlier ?
I have a DACT Stepped Attenuator sitting idle, is this type of Volume Control the right choice for the B1 ?
Any suggestions on he Power Supply, as the device will need one ?
I purchased the Board from the AnalogueAssociation.de forum.
I have slightly more than 100 of the basic kits going to the shipping
department on Monday.
The attachment is a Schematic that was forwarded following the purchase.
I was not aware of needing to express any concerns for the authenticity of the board when I purchased it.
In hindsight the vendor was encouraging communication through private mail.
If the Schematic attachment is unwelcome on here, then please remove it.
View attachment B1Korg.pdf
I was not aware of needing to express any concerns for the authenticity of the board when I purchased it.
In hindsight the vendor was encouraging communication through private mail.
If the Schematic attachment is unwelcome on here, then please remove it.
View attachment B1Korg.pdf
So far, the preamp sounds great piping music through my McIntosh MC240 tube amp; however, the microphony is a problem. I used the double side foamed tape to mount the NuTube to the PCB, but the ringing is audible. I will comb through this forum on remedies, but I would think that builders would like a proven solution for this.
I can say that aside from the microphony, the preamp presents a tonally warm, musical presentation. It is also very quiet as I did not hear any noise through my sensitive Klipsch Forte II speakers.
I can say that aside from the microphony, the preamp presents a tonally warm, musical presentation. It is also very quiet as I did not hear any noise through my sensitive Klipsch Forte II speakers.
I used these rubber mounts for the PC board. Used them on my B1 Korg along with Vibrapods (Thanks 6L6), for feet on the enclosure.
I have no ringing, even at high volumes
https://www.walmart.com/ip/3mm-Thre...ibration-Isolator-Mounts-8x8mm-8pcs/136047444
I have no ringing, even at high volumes
https://www.walmart.com/ip/3mm-Thre...ibration-Isolator-Mounts-8x8mm-8pcs/136047444
if putting preamp enclosure on more rubbery feet isn't helping , think about moving a preamp to neighbor's
Best is to purchase from either the GB thread or the DIYAudiostore because the sales are open to all to see and most importantly, you get the support when you are stuck. I know this because many have helped me along the way. It’s not too late to use the authentic boards.
I put the soft/fuzzy side of velcro behind mine. Sticky side attached to the PC board and fuzzy side supporting the Korg chip. I have nothing else isolating it and have had zero problems. But Zen's suggestion of next door installation seems a certain solution to me! May want a remote volume control though...
I suspect the magnet damps the 5K filament wire resonance. I had a Millett NuClassD amp with one tube that had filament resonance much worse than the other. The amp uses a separate tube for each channel with the tube sections in parallel, so you get 2X the filament ringing problem. Loudspeaker bass notes would excite the ringing, even inside a covered chassis.
The NuClassD circuit has a variable resistance connected directly between the plate and the input JFET gate to provide a small amount of negative feedback. It is a 475K resistor in series with a 1 meg pot wired as a variable resistor. Pete put it in ostensibly to balance channel gains. I found that increasing the NFB just a bit got rid of the ringing and totally improved the sound of the amp without the NuTube H2 magic going away. I had previously changed the plate resistors to allow tube biasing at less than half supply, to provide a higher H2 than the circuit can provide as drawn. So I guess I had some H2 "to burn" when increasing the NFB.
My next experiment will be adding adjustable NFB to my B1Korg to play with the sound character. I know NFB is supposed to be this "awful" thing, supposedly avoided at any cost, but in the NuClassD situation it really made a positive difference. I used a fixed signal input level at 1 KHz and lowered the output voltage in small fixed steps until the problem went away, then balanced the other channel to match. It should be easy enough to add this to the B1K and see what happens. Then, not only can the harmonic content be adjusted with the bias pot but low level tube resonances can be dialed out with NFB.
Attachments
Well I tried Zen Mod’s first suggestion and so far, so good. I am using these rubber and foamed EVA polymer composite pads used for vibration isolation of HVAC equipment. I have these under my ARC phono stage and ARC line stage preamps, and they seem to do a good job with those components.
On switching inputs, it did trigger some ringing, but once that disappeared, the preamp was quiet. Before using the rubber pads, the ringing never went away.
With the absence of sustained microphonic ringing, I can really enjoy the music. This little preamp is impressive indeed.
Thank you all for your help. Glad I don’t have to ask my neighbor if I can put my preamp in their house.
On switching inputs, it did trigger some ringing, but once that disappeared, the preamp was quiet. Before using the rubber pads, the ringing never went away.
With the absence of sustained microphonic ringing, I can really enjoy the music. This little preamp is impressive indeed.
Thank you all for your help. Glad I don’t have to ask my neighbor if I can put my preamp in their house.
Options on the complete kit later?
Any chance of options for 4 inputs (rotary selector) and XLR outputs to match up with AMP Camp Amp ?
Cheers
Steve
Any chance of options for 4 inputs (rotary selector) and XLR outputs to match up with AMP Camp Amp ?
Cheers
Steve
My microphony mitigation is a bit over the top but it’s worked. No ringing at all. A bit hard to see in the photo. Under the Nutube is a piece of 3mm thick double sided gel tape, a 1/2” thick piece of very dense hardwood and another piece of 3mm thick gel tape to stick the stack to the pcb. Flexible wiring between the Nutube pins and the pcb. My “add mass and damping” solution..
As well as that... The pcb is mounted on rubber isolating standoffs similar to those mentioned above. The kind that drone builders use to mount flight controllers into quadcopter frames..
As well as that..... I’ve put soft felt feet on the box.
As well as that... The pcb is mounted on rubber isolating standoffs similar to those mentioned above. The kind that drone builders use to mount flight controllers into quadcopter frames..
As well as that..... I’ve put soft felt feet on the box.
Attachments
A fellow drone builder /RCer? I've done RC Cyclic Copters for years too as well as fixed wing planes. If you think Amps are hard to build and make correctly, try building a Cyclic RC helicopter and actually flying it. It's more like trying to keep a crash above the ground.
Great hobby though. Being a a stubborn masochist is helpful, I have to admit.
Steve Luck - more inputs and balanced outputs is absolutely something you can do... this is DIY!! 
You’ll need a bigger chassis to have room for the additional input jacks, and either a doubling up of the PCB to run balanced at the circuit level, or a pair of SE to BAL output transformers.
Sounds like a great project!
You’ll need a bigger chassis to have room for the additional input jacks, and either a doubling up of the PCB to run balanced at the circuit level, or a pair of SE to BAL output transformers. Sounds like a great project!