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RE: November Stereophile - Western Electric 91E Review

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In Reply to: RE: November Stereophile - Western Electric 91E Review posted by stellavox on October 08, 2022 at 09:46:09

Just a brief comments on the passages you chose to quote.
"in essence this microprocessor-controlled stepped attenuator.......emulates a DAC".
Your ellipsification here is misleading. Here's the quote in its entirety--and please note that these are Charles Whitener's words:
"Stepped attenuators have a lot less noise and superior channel-to-channel tracking ability compared to motorized potentiometers. In essence, this microprocessor-controlled stepped attenuator uses relays to engage each discrete resistor in circuit and is accomplished with software that emulates a DAC."
As to the second point, obviously there are some solid-state electronics inside the chassis--for switching and control at least. There's even a DAC, for Bluetooth. Is there solid state amplification involved, as suggested in this post? That's not a determination I can make, but I have no reason to think so.
Jim Austin, Editor
Stereophile

Edits: 10/08/22

Follow Ups:

RE: November Stereophile - Western Electric 91E Review - stellavox 13:01:05 10/09/22 (2)
Thanks for your input Jim,

Regarding amplification, from what I'm aware of - for a power amplifier, assuming that what I will call a "High level input" into it is around 1-2VRMS, then to power the speakers requires a gain of 20-30dB. The second paragraph of JA's measurements mentions a gain of 29.6dB. There may be some "apples to oranges" comparisons here but I believe we're in the ballpark.

The review's specifications section mentions that the amplifier has two tubes ECC81/300B. Again I assume this is per channel. A gain of 30dB for these together is not unreasonable.

HOWEVER - again from my experience with phono preamplifiers, to output a same "high level" 1-2VRMS requires in the neighborhood of 40dB gain for MM cartridges (with millivolt outputs) and maybe 60dB for MC cartridges (many? microvolts output). JA's measurements of what I guess was the total preamplifier/amplifier gain was 71.5dB (MM) and 82.1dB (MC). SO SOMEWHERE/SOMEHOW to amplify a phono cartridge, the 91E was picking up an additional 40 to 50dB of gain - and it's NOT from the listed TUBES - unless there are some lurking deep inside.

SO I reassert that at least in the phono section there is a LOT of amplification going on and that it must be solid state - whether discrete or IC-based is yet to be ascertained. And assuming this is the case, could there be other amplifying devices in the "chain" before, say, a signal enters a high level input and is then connected to the ECC81. And per an original question, can this "chain" be bypassed?

Thank You
- The phono stage in the 91E - Jim Austin 18:48:10 10/17/22 (0)
  is solid state.
  
  Jim Austin, Editor
  Stereophile
- am sure they would have mentioned if they stuck a 6088 tube in there~nT - Cleantimestream 01:15:33 10/13/22 (0)
  ~!
  The Mind has No Firewall~ U.S. Army War College.
Moreover.............................. - Kal Rubinson 07:16:57 10/09/22 (3)
Decades back, AR/Teledyne marketed a device called the SRC (System Remote Control) which one could insert into an analog stereo system to provide remote control for input selection, volume and balance. I owned one and it was reviewed in Stereophile

This device used the R2R-Ladder resistor array of an early DAC as a stepped attenuator for volume and balance. The designers found this to be the best way, at the time, to implement such an attenuator with precision and economy.

Everything old is new again.
- https://www.stereophile.com/content/acoustic-research-stereo (Open in New Window)
- Thanks for the memories Kal, I recall~nT - Cleantimestream 01:17:58 10/13/22 (0)
  ~!
  The Mind has No Firewall~ U.S. Army War College.
- And Moreover.............................. - Kal Rubinson 13:09:37 10/09/22 (0)
  A blast from the past.
  
  Posted by John Atkinson (R) on October 4, 2014 at 10:52:34
  In Reply to: RE: Ladder DACs for volume controls. posted by rick_m on October 2, 2014 at 07:24:42:
  
  > Some are, or at least were, just R-2R networks and transmission gates so
  > you could use them for four quadrant multipliers (one axis being digital,
  > the other the "reference voltage" port) with a little biasing.
  
  I always thought this was an elegant piece of lateral thinking: rather than
  connect the DAC's voltage-reference pin to a steady DC voltage, you feed it
  the audio signal The value of the DAC's internal resistor ladder is then
  set by applying an 8-bit word to the data port.
  
  I first knowingly saw it used in the Mark Levinson No.38 preamp from the
  early 1990s, so I am astonished to learn that the Acoustic Research SRC,
  which I used 30 years ago, also featured it. I believe that this kind of
  control gives an improvement in S/N ratio as the volume setting decreases.
  
  John Atkinson
  Technical Editor, Stereophile
- RE: Moreover.............................. - Ivan303 08:29:45 10/09/22 (0)
  Everything you wanted to know about resister volume controls.
  
  More than everything, IMNSHO
  - Resistor-Switch Networks for Audio Volume Control (Open in New Window)

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