Discussion in 'Preamps / Channel Strips' started by mark4man, Oct 28, 2004.
i was not quite correct. tubes actually act as a rectifier in a power supply. read this
That’s a good link. I wish I understood it more. Anyone know of a book that breaks down the electronics and componentry and their roles and effects as they pertain to audio?
There seems to be a ridiculous amount of care and quality control put into these boutique tube peices. Aspen Pittman said 57 man hours to put one Vipre together. He outsourced to China, stating it’d raise the asking price from 3.5k to 10-15k had it been assembled in USA. Damn. Lol.
No they were real tubes but they didn't do much to the sound. (there is only 2 in this unit)
I did try to change them in hope that I could fix the nazal sound but it nearly didn't change the sound. So I sold it. (so glad I could)
Thats the one. Thanks. Interesting ain't it. Best piece of gear I've ever heard or seen.
Absolutely fascinating. Makes me wish I’d gotten one, or ‘the brick’ at least while they were new. Seems groove tube mics are now named ‘sterling audio’ and nowhere near what they were. It’d be nice if these companies didn’t buy great, successful brands, then change everything about them lol. If it ain’t broke...!!
I also am interested in Pittman’s method of using out-sourced labor in a high end piece. Makes me wonder if some of these boutique units in the 2-4K range could be made for people shopping on the 1k range. And perhaps smoke the otherwise well received warm audio type things.
At some point there’s got to be the ability to bring pro standard gear into project studio price points. I’m guessing bulk fabrication, simple circuits, and reasonable QC prior to sale would be part of the recipe.
I watched a bunch of Aspen Pittman vids all day lol, great dude.
Possibly regulating tubes... I hope so !
That's an excellent point. In fact, it is for this very reason we made sure the 12AX7 in the 583 was powered the same way as those in the 992EG; a full 250v on the plates and 12v on the filament. Once you stray from that the tube begins to sound weaker and distort much quicker. That's just reality. One of our early proto type 583's has a 125v supply and it sounds horrible! Distortion comes waaaay to early and the frequency response is laughable. Give tubes what they want and need! The result should be pristine, beautiful analog tone.
Is that what you were referring to in Tape Op about getting the +/- rail spacing right, and why you were paying attention to it? Sorry, not trying to pester you, or have you give away any secrets. Just trying to understand the gear I use better, and make more informed purchase decisions.
It's never a pester ... but yes, that's what I was referring to in the TapeOp review. I find it necessary to emphasize that point as much as possible with our 583S mk2. A lot of folks think we've somehow "cheated" or compromised in our approach to powering the tube. After all, the 500 series is a low voltage format and yet we're claiming to power-up a tube. It naturally requires more investigation on the buyer's part.
The D. W. Fearn preamp is a good unit. Good classic design. Tubes should last a long time. If you need to replace tubes, send the unit back to Mr. Fearn for service or install NOS tubes from known source. Mr. Fearn has tubes on hand to select the best ones for your unit. Tubes are selected for lowest noise, and the most quiet tubes go in the first stage which sees mic level signal. The usual warning with tube gear, DO NOT work on this unit unless you are familiar with working around tube circuitry using 300 volts DC or higher.
Scott... agreed you need at least 250 volts HT on the supply rails to any preamp using the 12A*7 dual triodes. I personally don't like the 12AX7 because of noise and microphonics. High gain (u = 100) is good, but the "baggage" can be unacceptable. Work out the load line for those tubes... if the plate voltage is varying by 8 volts (at the plate itself) and is coupled into a 10:1 transformer to talk to the outside, then the variation across the secondary is around 0.8 volt. (Also note that 0 dBm is around 0.775 volt across 600 ohms.) The 12AX7 is a voltage amplifier, has a HIGH plate output impedance, and not intended to furnish power. This may be part of distortion issues using this tube for some applications. 125 volt supply rail is WAY too low... expect a garbage sound. Regulating the HT rail never hurts...even if inexpensive OA2 or OB2 tubes in series are used for this.
For triodes, I personally prefer the 6072 (12AY7), triode connected D3a (7721), triode connected EF86, 5879, etc. The 417a (5842) is an old Western Electric triode; these are expensive and one has to be careful about biasing due to high transconductance and extremely close element spacing... The self noise of the industrial tubes in most cases is better than "garden variety" types like the 12AX7....
Man, do we have some REALLY smart people here on RO or what??!!
Just sayin' ...
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