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The Great Bass Preamp/DI Comparison

#4,262
Littlewing6283 said:
Have you used to for anything else ? Tracking vocals ? Other instruments
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Haven't tried it for anything else besides bass and vocals where it absolutely shines.

Forgot to mention it's also a great standalone DI. There's a separate DI output to connect to a different mic pre, say you prefer something more Neve-ish or whatnot. But of course you would be bypassing the killer comp and EQ sections too.
 
#4,263
Robal said:
With a separate AC power supply, the Teegarden Fatboy is too big for a pedalboard obviously -- you are stretching the size boundaries (what's next? Eclair Evil Twin, Tonecraft, Tab Funkenwerk V71, etc.) and coming perilously close to rack mount tube DIs (Kern IP777, REDDI V2, Demeter, etc.). . . pretty soon all hell will break loose! :hyper:
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That power supply is an optional upgrade that provides more current headroom, a connected non-floating ground, and the ability to operate at 240v overseas. Normally the Fatboy ships with a wall wart type plug. This means the Fatboy is actually quite small, relatively speaking, at 8" long by 5.25" wide.
 
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#4,264
I'm a bit curious about how to think about the tube preamps that are available.

I recently received (after many weeks of COVID delay) one of the AMT Bricks A Bass preamps. I also have the SLO Mark IIIs, currently on a CIOKS7 powered board. I guess the reasons I bought the A Bass were that it was a) (relatively) inexpensive and b) claimed to emulate the Alembic rack preamps.

Well, I hooked up the A Bass and immediately noticed something that I'm quite sure is obscured by the LED in the tube compartment in the SLO. Which is that powering a 12AX7 tube from a wall wart / pedal power unit doesn't supply enough current to fully charge up the tube. Or, at least, the photon emission is significantly less than when the same tube is in a conventional amp chassis.

Yet, the apparently less energized tubes still seem to sound pretty decent.

So, I'm not really sure how to think about this. I initially steered clear of the tube preamps, which require 120VAC power, because at that point I can just use my Demeter Bass400 as a preamp. So, the feature of going on a board, and being driven by a board power supply seemed differentiating. Though, at this point, the Noble's design with the DC supplies might make more sense.

Anyhow, is there any way to understand the tube performance vs the power supply designs? I'm not sure I can readily distinguish the differences in sound; but, still it bugs me not to drive the tube properly. How much of this difference is academic and how much of it is real?
 
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#4,265
bucephylus said:
Anyhow, is there any way to understand the tube performance vs the power supply designs?
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That's a tough question. Define power supply design. Wall wart versus built in power supply? Impossible to know how that impacts the final supply to the tube.

The tube heater requires a certain amount of current at, typically, 6.3 V or 12.6 V (AC or DC). For a 12AX7 that is somewhere around 300 mA or 150 mA, respectively. You either properly supply that or you don't. Whether AC or DC and whether it is floated at a raised voltage or not can make a difference in noise and hum.

Generating a suitable B+ which has a low current requirement is not all that difficult. Especially these days with tiny switching supplies able to step 9 V, 12V DC up to 250 V or more.

So, I'll give you two answers to your question. 1) Yes, power supply design impacts tube performance. Properly or under supply the heater, low plate voltage versus high plate voltage. 2) No, you can't predict tube performance on external versus internal power supply. It is completely possible to have a high plate voltage, properly heated tube circuit from a 9 V DC input.
 
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#4,266
JKos said:
That's a tough question. Define power supply design. Wall wart versus built in power supply? Impossible to know how that impacts the final supply to the tube.

The tube heater requires a certain amount of current at, typically, 6.3 V or 12.6 V (AC or DC). For a 12AX7 that is somewhere around 300 mA or 150 mA, respectively. You either properly supply that or you don't. Whether AC or DC and whether it is floated at a raised voltage or not can make a difference in noise and hum.

Generating a suitable B+ which has a low current requirement is not all that difficult. Especially these days with tiny switching supplies able to step 9 V, 12V DC up to 250 V or more.

So, I'll give you two answers to your question. 1) Yes, power supply design impacts tube performance. Under supply the heater, low plate voltage versus high plate voltage. 2) No, you can't predict tube performance on external versus internal power supply.
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Thanks, but I pretty much understand all that. To simplify my question, is the "if it sounds good, it is good" axiom still true, even if the tube emissive glow is not happening? Because apparently you can check all the boxes you just summarized, but the tube isn't emitting nearly as brightly. So, are the standard amp chassis overpowering the tubes?

I would have thought that at least the filament should be optically bright to enable the required thermionic emission.
 
#4,267
Hmm.. judging whether a tube is getting enough current by the glow isn't really satisfactory. For one, some tubes glow more than others. When we are talking the 12XX family of tubes its not like they put out a ton of glow anyway. You'll see the filaments glowing a little orange.

As @JKos was mentioning, the design of the circuit matters too. I.E. starved plate vs high voltage.

If it sounds good, don't worry about it. :D
 
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#4,270
scubaduba said:
Hmm.. judging whether a tube is getting enough current by the glow isn't really satisfactory. For one, some tubes glow more than others. When we are talking the 12XX family of tubes its not like they put out a ton of glow anyway. You'll see the filaments glowing a little orange.

As @JKos was mentioning, the design of the circuit matters too. I.E. starved plate vs high voltage.

If it sounds good, don't worry about it. :D
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@scubaduba and @JKos , thanks for the replies. Here are two images of the Bass 400 and the A Bass with basically the same 12AX7 in each.
710627A9-4B5C-4B59-88A7-181A698993D3.jpeg

9CD6F1BA-2070-420E-9A8A-556198DF1146.jpeg


I wouldn't have asked the Q, if it were a matter of minimal perceived differences. It seems pretty clear to me that different things are going on with those tubes in the respective circuits. I'm not just sitting around Chong style going, "oh, wow man, those tubes don't glow as much." Both make sound. No question that the Demeter sounds much fuller.

Further I suspect the SLO may well be doing the same thing as the AMT; which may explain the otherwise superfluous LED in the tube compartment.

Yeah, I know about starved plate etc. But, even my old and trusty ART Tube MP, which was starved plate, had pretty reasonable emission from the tube - much more similar to the Demeter pic. So, I don't think that explains what's going on here.
 
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#4,275
chadhargis said:
I'm regretfully selling my FEA DE-CL. And yes, I still think it sounds a little better (to my ears) than the LA-1A
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Valveman said:
it's all about the tubes!
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Shouldn't it be all about what sounds best? I feel like this thread is starting to become a "how many tubes can I show that I have on my board" thread....even to the point where we're now selling stuff that we think actually sounds better just because it doesn't have a tube in it.

I mean, if I didn't mention tubes and said you can either have a pedal with a small form factor that's built like a rock with simple power requirements....or you can have one that's 3 times the size, fragile, with extremely high power requirements, and doesn't sound as good to you. Would you really choose the latter?

I get that tubes sound great, and I'm totally interested in this thread from a point of actually comparing the quality/sound of preamps/DIs (whether tube or not).....but I'm starting to feel like opinions are now purely subjective based on tube count.
 
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#4,277
JKos said:
That's an LED at work.

- John
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Fer cryin out loud, that emission is white and coming from within the tube. I'll take another picture without the dove cage tomorrow.

[Edit: mea culpa, I stand corrected. Didn't realize the tube socket had an LED built into it. OK, I'll go back to the stoopid corner now.]
 
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