I had a thought about a different way to do a phono preamp and EQ system -- as a series of API 500
"Lunchbox" modules. You save some design time and expence because there's pre-made and standardized
power supply and connection interface. There might be a deal to be made with Radial or API itself or
another 500 series frame-maker to fabricate a custom frame allowing for unbalanced RCA connectors on
the back, or you could just include adapters with the modules. The 500 series if full of
preamplifiers and equalizers, both tubed and solid-state (and hybrids), so this is all within known
and done territories.
I can envision this sort of system:
1. a separate phono preamp module. Perhaps such things as tube and solid-state options can be
offered. You'd need to build in unbalanced inputs and also direct outs for flat transfers. The tube
version would likely be 2-wide (that seems to be what's required for true-to-spec tube voltages plus
enough real estate to allow for tube heat-venting).
2. a separate EQ module, two channel or perhaps one module for each channel. There would need to be
channel-to-channel level and phase-relation controls to allow for a wide variety of vintage disks.
Perhaps also some sort of low-frequency phase control, which can sometimes very much help the sound
quality while not lopping off the bottom end via a "dumb" rumble filter. A choice of EQ curves, of
course. I advocate separate turnover and rolloff controls. Perhaps there could also be a separate
super-high-grade RIAA EQ module, maybe with a choice of tube or solid-state topology.
3. there could also be an output/routing module. This would be helpful because it could put the
power demand for the output line/buffer amp in a separate module (perhaps necessary in 500 series
standards), plus the extra real estate could be used for such things as a processor loop (either
external or looped to the next slot or slots in the 500 frame) and perhaps a transformer output
4. in a Radial 500 frame, there would still be room for two channels of dynamics processing or
mastering EQ modules.
Being a modular systen, the user could have at least these options: tubed or solid-state preamp;
many-curve or super-hifi RIAA EQ module.
-- Tom Fine
----- Original Message -----
From: "Paul Stamler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, April 18, 2015 10:27 PM
Subject: Re: [ARSCLIST] "Best of both worlds" disk preamplifier
> On 4/18/2015 1:25 PM, Richard L. Hess wrote:
>> On 2015-04-18 3:07 PM, Paul Stamler wrote:
>>> Well-designed tube circuits can have transient response as good as
>>> transistor circuits, and incredibly low distortion as well (with the
>>> application of negative feedback). I'm sorry, but the idea that
>>> "euphonic distortion" is an inherent characteristic of tube circuits is
>>> one that's been carefully nurtured by the purveyors of tube hi-fi gear.
>>> I'll go on record as saying categorically that it ain't necessarily so.
>> They key to this is circuit design/topology and paying attention to gain
>> staging through the device as well as component selection.
>> Tubes can handle rather large voltage swings and if the R/C rolloffs are
>> properly controlled they may actually provide a cleaner representation
>> of the transient--if the A-D converter can accept it without excessive
>> noise. Again, gain-staging is of paramount concern.
> It is, and it's important to pay close attention to load impedances. Most common tubes (high-mu)
> have trouble driving lower impedances like the common 10k without a transformer. Low-mu tubes like
> the 6SN7 can do it, but they're bigger, use more current, etc.
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