Nobelium - tube bass preamp project
- Thread starter vigilante398
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vigilante398
Authorized Vendor
Finally has a gain knob in place of the tonestack and is tuned a little differently as far as frequency response and gain. This is part of why Finally can get some drive out of it and Nobelium can't. That being said they were designed with different things in mind, but they're not all that different at the end of the day from a circuit perspective.
Of course, Finally has stopped using LBA and now uses a custom-wound D.I. output transformer, so I feel pretty special for that
Cheers - so the short answer would be “just build one”,Finally has a gain knob in place of the tonestack and is tuned a little differently as far as frequency response and gain. This is part of why Finally can get some drive out of it and Nobelium can't. That being said they were designed with different things in mind, but they're not all that different at the end of the day from a circuit perspective.
Of course, Finally has stopped using LBA and now uses a custom-wound D.I. output transformer, so I feel pretty special for that
but it’s interesting seeing the love the Nobel preamp gets and trying to work out what it is people like about it and where the hype/love comes from- my suspicion is that it’s not magic, just a nicely tuned circuit and a nice transformer packaged in a really well thought out and simple to understand proposition.
(Designer, works in marketing, finds why people buy stuff stuff fascinating)
Lekky
New member
I've been curious about the Noble circuit after seeing all the praise on Talkbass. Reading about the Nobelium made me try to figure out most of the circuit from the BOM and pictures of both sides of the board. I'm planning to build a clone, going single-tube with a MOSFET source follower instead of the White cathode follower.
So, @vigilante398, any mistakes in this schematic?
So, @vigilante398, any mistakes in this schematic?
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vigilante398
Authorized Vendor
You're missing the 6k8 and trimpot before you hit the transformer, but otherwise looks good. The 6k8 inline with the signal is in the original, the trimpot was my addition because I don't like the idea of a fixed level output on a preamp and have heard some people complain the original's output is too hot.
Lekky
New member
Nice, thanks!
There are a few questions regarding Noble's design choices for this circuit. Like using rather high 220k plate load resistors for 12AU7s and a shared cathode resistor for two consecutive gain stages. I suppose the double bypass caps are for stability.
Maybe he landed on this setup after experimentation as it sounded better or "fatter" than the more typical gain stages in other preamps.
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vigilante398
Authorized Vendor
I obviously can't speak to his design process, but I'm assuming it was trying things out and seeing what sounded good.
AgAuthority
Active member
Getting ready to start my build—just double checking
Ag
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vigilante398
Authorized Vendor
The intention is that it be 250V, and that is the only thing I have used in my builds. As mentioned you can expect voltages higher than 50V there.
AgAuthority
Active member
Ooops-Glad I asked.
Ag
Ag
Harry Klippton
Well-known member
Is there a known good schematic out there of the original?
vigilante398
Authorized Vendor
Not to my knowledge, I had to drop a substantial chunk of change to get one in hand to trace. Granted I could have saved a few hundred bucks if I was willing to wait, but a $2k pricetag for used units and 9-month wait for new units is part of what made me want to get the circuit out there in the first place. I did A/B my build against the original (before I sold it to help recoup my costs) and it sounded pretty much spot on, so I have reasonable confidence in my trace.
The only thing I didn't trace was the power supply as the original uses a custom-wound power transformer and rectifier, as well as a 9V regulator to provide the pedal outputs on the side.
vigilante398
Authorized Vendor
I'm with you there, my dude. I don't think it sounds particularly bad, but for the pricetag I was expecting to be blown away and admittedly was not.
It's a great clean preamp, don't get me wrong, the 2-band EQ sounds a lot better than I was expecting, but there's equally good valve DI boxes for half the price (the small trees for one). Probably going to add a mids control if I can find space in the box.
owlexifry
Well-known member
really appreciate you posting this schematic
i’m assuming this is the c2c nobelium?i’m about to start building this one. very excited.
i don’t mean any disrespect to anyone involved in this circuit, but i’m just trying to comprehend why one would choose a 4n7 (C5) coupling cap on a ‘clean’ preamp intended for bass - seems like it would cut a fair bit of low end..
or maybe it’s because that stage is supposed to overdrive if it gets a lot of volume? i guess i could always try a 10n or 22n and see if there’s much change
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isn't that going to the grid of the 4th tube stage?really appreciate you posting this schematic
i’m about to start building this one. very excited.
i don’t mean any disrespect to anyone involved in this circuit, but i’m just trying to comprehend why one would choose a 4n7 coupling cap on a ‘clean’ preamp intended for bass (on the 1/4” out) seems like it would cut a fair bit of low end..
or maybe it’s because that stage is supposed to overdrive if it gets a lot of volume? i guess i could always try a 10n or 22n and see if there’s much change
matmonster58
Active member
Looks like the output cap is 2.2uF to me.
I plan to play around with C8 and try everything from 4n7 to 10n and see what sounds best. I'm guessing 6n8 will start rolling off at ~60Hz which should be great for upright
I plan to play around with C8 and try everything from 4n7 to 10n and see what sounds best. I'm guessing 6n8 will start rolling off at ~60Hz which should be great for upright
