vigilante398
Authorized Vendor
So the Unagi fits and sounds great, but it gets pretty tight as the can is slightly wider than a Jensen. It kind of forces the ground lift toggle outwards a hair.
Nobelium - tube bass preamp project
- Thread starter vigilante398
- Start date
Mentaltossflycoon
Well-known member
Hey @vigilante398, I'm thinking about nixing my radial bassbone since the di on the nobelium crushes it handily. Without the use of the di, the radial only really serves as an a/b leveler for my p bass and upright. I intend to just simplify by making an ab switcher with perhaps a comp on the upright input.
This means I'll have a spare 500mA 15v gigrig converter that I'd like to utilize. I remember you saying that one of your pedals (maybe the black eye?) can go above 9v with no problems other than shorter life span on the tubes. Is this true of the nobelium or am I flirting with disaster?
This means I'll have a spare 500mA 15v gigrig converter that I'd like to utilize. I remember you saying that one of your pedals (maybe the black eye?) can go above 9v with no problems other than shorter life span on the tubes. Is this true of the nobelium or am I flirting with disaster?
vigilante398
Authorized Vendor
It's going to be the same with all of my pedals, 9-12V is the suggested operating voltage. Because the tube filaments are fed directly from the input voltage, 15V makes me nervous because of how much higher it is than the 12.6V called out in the 12AU7 datasheet. This could severely impact the life of the tubes.
Additionally, the filaments act more or less as a fixed resistor, which means the higher the voltage across it, the greater the current draw. So with a 12.6V input we have 150mA draw per tube, with a 9V input it's 107mA, and with 15V you would be at 179mA per tube or 357mA total just for the heaters. Even if I wasn't concerned about the pact to the tube life (which I am), I'm not confident that 500mA would be enough to run the pedal at that voltage. I do not recommend running the pedal on a 15V supply.
Mentaltossflycoon
Well-known member
That's what I thought, guess l I'll find something else to run at 15v. Thanks!
chris.knudson
Well-known member
I just bought the PCB, the enclosure, the tubes, the transformer, the XLR jack, and all the parts to build this thing. If I threw in the cost of a power supply, I could have probably afforded a Noble pre-amp -- but where's the fun in that?
matmonster58
Active member
I have all premium expensive parts in my cart and I'm coming in at like $300. I don't know exactly how much because I have like 10 projects lumped together
vigilante398
Authorized Vendor
Yeah if you're approaching actual Noble price ($1259 for 10 month wait or $2019 for 6 week wait) for a Nobelium build, you're doing something wrong.
chris.knudson
Well-known member
No, you're right. I just wasn't expecting the transformer to be that expensive.
vigilante398
Authorized Vendor
Yeah it's definitely the most expensive part of the build. I'm still on the fence about offering Unagi transformers as an add-on for Nobelium as they would be a little cheaper (probably $65 or so). They fit, but you really have to squeeze it in there with the ground lift switch.
Thinking about this for my build and trying to get an idea of what effect this trimpot has on the output volume. If I changed this to a full sized pot and mounted it on the enclosure as a "DI output level" control would it be worth it? I'd hope it'd work in the same way as the existing volume pot, but if it's more like a "0.5->0.7" control than a "0->1", then I probably wouldn't bother.
vigilante398
Authorized Vendor
That would absolutely be worth it and is something I do on my personal Nobelium builds. The original Noble just has a fixed output level for the XLR, but an independent volume control for 1/4" output and XLR output is a win in my opinion.
That's great, thanks - I'm also quite tempted to move the ground lift switch onto the top as well, partly to keep it obvious and accessible, but also because I'm hand drilling the enclosure and I'd quite like to not have to get the jewelers saw out. Are your personal builds in 1590XX enclosures as well? Are you putting the XLR volume above the vol/bass/treble controls?
vigilante398
Authorized Vendor
My personal builds are also in 1590XX, but I actually have a different PCB set for my builds (because I'm special) that has the XLR volume control mounted on the side with the ground lift switch and XLR jack.
Heyho everyone! What an awesome thread!
I'd like to thank vigilante for being so open and offering the traced out schematic! That's just awesome. When I saw it, I decided immediately to build my own preamp, not complicated at all
I will do a handwired one without the PCB though...well at least for the amplifier part. For the smps I will make a small PCB. Further I will use a different transformer, since I have it already here, it will be an AMI UT10. So I will need a different housing as well...let's see what it will be I'm the end... probably a DIY case made from sheet metal. I also do like the idea of an volume pot for the XLR port....ahh I'm.very enthusiastic right now 
Out of interest: Vigilante, can you tell me what the quiescent current of the tubes are in idle state? You use 250V for B+ for your builds, correct?
Cheers
Root
I'd like to thank vigilante for being so open and offering the traced out schematic! That's just awesome. When I saw it, I decided immediately to build my own preamp, not complicated at all
I will do a handwired one without the PCB though...well at least for the amplifier part. For the smps I will make a small PCB. Further I will use a different transformer, since I have it already here, it will be an AMI UT10. So I will need a different housing as well...let's see what it will be I'm the end... probably a DIY case made from sheet metal. I also do like the idea of an volume pot for the XLR port....ahh I'm.very enthusiastic right now Out of interest: Vigilante, can you tell me what the quiescent current of the tubes are in idle state? You use 250V for B+ for your builds, correct?
Cheers
Root
vigilante398
Authorized Vendor
Depends on the tube, but it's all in the datasheet. Filaments are 150mA on a 12.6V supply or 300mA on a 6.3V supply, plates are around 10mA. The B+ of my builds depends on the build. For the boards I sell to DIYers I set the B+ around 235V, for pedals I sell commercially I set them at 350V.Heyho everyone! What an awesome thread!
I'd like to thank vigilante for being so open and offering the traced out schematic! That's just awesome. When I saw it, I decided immediately to build my own preamp, not complicated at all
Out of interest: Vigilante, can you tell me what the quiescent current of the tubes are in idle state? You use 250V for B+ for your builds, correct?
Cheers
Root
owlexifry
Well-known member
at least you don't reamed dry for shipping
Components have arrived. I still, however, dont know which transformer i should use. I have 3 to choose from:
Sowter 4243
AMI UT10
Triad A-66j
While the UT10 and the sowter are DI transformer, the triad is not a typical DI transformer though. It input/output ratio is a bit lower (5:1 or 7.75:1). But since the XLR out is rather hot without a trim pot in series it might work.
Sowter 4243
AMI UT10
Triad A-66j
While the UT10 and the sowter are DI transformer, the triad is not a typical DI transformer though. It input/output ratio is a bit lower (5:1 or 7.75:1). But since the XLR out is rather hot without a trim pot in series it might work.
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flashmotroniks
New member
With the power in, should the center pin connect to ground or V+?
vigilante398
Authorized Vendor
That's kind of up to you and up to the supply you're planning to use, but the standard for guitar pedals is center pin negative (ground).
