Why does the EQ module have to have active EQ? Why not take the pre-amplified signal from the preamp
module, do passive EQ and then end the EQ module with a gain stage to bring it back up to line
-- Tom Fine
----- Original Message -----
From: "Corey Bailey" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, April 19, 2015 2:03 PM
Subject: Re: [ARSCLIST] "Best of both worlds" disk preamplifier
> Hi Tom,
> Let's start with the fact that active equalizers make better filters than they do gain amplifiers.
> I proved this on the bench years ago. In fact, it caused me to re-think the way I approached
> recording: listening for what I wanted to remove instead of boosting what I thought was lacking.
> When boosting frequencies with an active equalizer (API, MCI, Neve, Radial, etc.) you get unwanted
> phase distortion, not to mention running out of headroom if you are talking about the amounts
> required for record EQ. The reason is that, from a design standpoint, the vast majority of
> equalizers used in pro audio equipment (at least, all of those you mentioned) have the RC
> components in the feedback loop. Thus, the phase distortion when boosting beyond 3dB or so.
> In the case of record EQ, we are talking about only boosting the low frequencies for playback but,
> that is the area where phase distortion can be most difficult to hear. However, it is certainly
> My $0.02
> Corey Bailey Audio Engineering
> On 4/19/2015 7:02 AM, Tom Fine wrote:
>> 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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