The Tisbury Audio Mini Passive "preamp"

Andre Marc · Aug 27, 2014

The Tisbury Audio Mini Passive "preamp"

135 British Pounds, approx $225 US.

http://www.avrev.com/home-theater-p...reamps/tisbury-audio-mini-passive-review.html

Andre Marc · Aug 29, 2014

The manufacturer is interested in starting a US Tour for this review sample...any interested parties?

DonH50 · Aug 29, 2014

Had to use a different link after a search: http://www.avrev.com/home-theater-p...reamps/tisbury-audio-mini-passive-review.html

Had to chuckle reading this from your review: "Of note: there is no remote, as this was designed with a purist approach." The vision of an a simple passive device like this saddled with a remote just seems wrong, as well as un-passive...

Maybe I missed it, but how many steps and what resolution are the attenuators? And why would it take 25 hours to break in?

Curious - Don

Andre Marc · Aug 29, 2014

DonH50 said:
Had to use a different link after a search: http://www.avrev.com/home-theater-p...reamps/tisbury-audio-mini-passive-review.html

Had to chuckle reading this from your review: "Of note: there is no remote, as this was designed with a purist approach." The vision of an a simple passive device like this saddled with a remote just seems wrong, as well as un-passive...

Maybe I missed it, but how many steps and what resolution are the attenuators? And why would it take 25 hours to break in?

Curious - Don

Hi Don:

Thanks for reading!

Actually, my CIAudio passive, of similar design, with more inputs and two outputs uses a remote. The "active" part of the circuitry simply controls the microprocessor that selects input and control the volume knob. When we have designs like this it gets into semantics as far as active/passive. Clearly their is power required to control the aforementioned functions, but there is no active circuitry in the signal path.

Even Music First, which uses a TVC design, offers a remote option. (That is an amazing, but costly piece)

I counted about 25 volume steps. I have no idea what resolution are the attenuators.

I don't know why the break in was needed, but this was par for the course for all the passive units I have had in house.

Connectors, wiring, etc all settle maybe.

DonH50 · Aug 29, 2014

Active usually implies active devices in the signal path. I would think that adding active components, especially things like microprocessors and digital stuff, would require extremely careful design to prevent leakage into the signal path. I've always suspected break-in was more about us learning a component's sound vs. the component breaking in but there are exceptions.

I have had passive controls in my systems at various times but by and large prefer active for the isolation and buffering (drive). Not for the noise, distortion, and need for power, natch, but all that is pretty small for good gear.

Enjoy! - Don

Andre Marc · Aug 30, 2014

DonH50 said:
Active usually implies active devices in the signal path. I would think that adding active components, especially things like microprocessors and digital stuff, would require extremely careful design to prevent leakage into the signal path. I've always suspected break-in was more about us learning a component's sound vs. the component breaking in but there are exceptions.

I have had passive controls in my systems at various times but by and large prefer active for the isolation and buffering (drive). Not for the noise, distortion, and need for power, natch, but all that is pretty small for good gear.

Enjoy! - Don

Perhaps the word "active" is not appropriate. As I said much of it is semantics.

The fact is that
a passive controller has absolutely zero gain, remote, or no remote.

I don't think it is the least bit difficult to prevent "leakage" from micro processor control components into the signal path in a passive
unit than any more than it is for an standard preamp with gain, which to my way of thinking is theoretically going to be far
more susceptible to passing on noise, especially from power supplies etc. Hence the SOTA, over the top approach of some designers in
using outboard power supplies.

Johnny Vinyl · Aug 30, 2014

DonH50 said:
Active usually implies active devices in the signal path. I would think that adding active components, especially things like microprocessors and digital stuff, would require extremely careful design to prevent leakage into the signal path. I've always suspected break-in was more about us learning a component's sound vs. the component breaking in but there are exceptions.

I have had passive controls in my systems at various times but by and large prefer active for the isolation and buffering (drive). Not for the noise, distortion, and need for power, natch, but all that is pretty small for good gear.

Enjoy! - Don

Sorry for the slight off-topic, but I agree with Don' s statement that I bolded.

Andre Marc · Aug 30, 2014

Johnny Vinyl said:
Sorry for the slight off-topic, but I agree with Don' s statement that I bolded.

Actually, I agree totally as well. I believe listener break in is a huge factor in some cases.

Knowing this, I take steps to try to differentiate, like "breaking in" a component or speaker in another system
without listening to ti.

Johnny Vinyl · Aug 30, 2014

Andre Marc said:
Actually, I agree totally as well. I believe listener break in is a huge factor in some cases.

Knowing this, I take steps to try to differentiate, like "breaking in" a component or speaker in another system
without listening to ti.

I'm a little confused by this. Can you elaborate?

Andre Marc · Aug 30, 2014

Johnny Vinyl said:
I'm a little confused by this. Can you elaborate?

Sure, on more than a few occasions I took a speaker, and other electronics and hooked them up
in my home theater and left it playing 24/7 for a specified time, so that I, the listener, was not
assimilating to the sound. Then I install in the reference systems. Many times my "break ins" are at
the request and guidance of the manufacturer.

BTW, this is after giving it a good listen out of the box, so I know what, if ANYTHING, has changed.

MOST of the time they are correct. Sometimes there is no change.

DonH50 · Aug 30, 2014

Andre Marc said:
Perhaps the word "active" is not appropriate. As I said much of it is semantics. The fact is that
a passive controller has absolutely zero gain, remote, or no remote.

I don't think it is the least bit difficult to prevent "leakage" from micro processor control components into the signal path in a passive
unit than any more than it is for an standard preamp with gain, which to my way of thinking is theoretically going to be far
more susceptible to passing on noise, especially from power supplies etc. Hence the SOTA, over the top approach of some designers in
using outboard power supplies.

I agree a device comprising a controller to adjust the volume of a stepped attenuator (or whatever, motor-driven potentiometers are also available) can be considered a passive device as far as the signal is concerned. The microprocessor ain't in the signal path. I don't know a good way to describe that scenario; "actively-controlled passive preamp" is pretty verbose.

From designing mixed-signal circuits, active signal path or not, I think it would be difficult to suppress the noise from a processor to below 80 - 100 dB. That is a challenge no matter the architecture.

I am not sure I agree that in general passive or active is more susceptible to noise and such. The active path has more devices, finite PSRR/CMRR and all that jazz, but noise and distortion for a good active circuit is extremely low. And active devices are much less sensitive to load and driving impedances since they can be designed to have very high input impedance and very low output impedance simultaneously. The passive device may be more sensitive to noise because, without active buffers, the attenuator must be high enough in impedance to not load the source, at the same time keeping a low enough impedance so as not to add noise to the load. And hopefully not significantly change the frequency response or other characteristics from source or load. It will always be a compromise.

I would be hard-pressed to say in general one is better than the other. I would not say one is less sensitive to noise; the argument can be made that a stepped attenuator of any reasonable design will not add more distortion than an active gain stage. It will probably not add more noise, either, but as stated above that may not be true when the whole system is taken into account. I think it is going to be very dependent upon the load and source components. As a final comment (and the crowds go wild), with a passive "preamp" (no amp, technically) there are still active sources and amplifiers in the chain...

Andre Marc · Aug 30, 2014

DonH50 said:
I agree a device comprising a controller to adjust the volume of a stepped attenuator (or whatever, motor-driven potentiometers are also available) can be considered a passive device as far as the signal is concerned. The microprocessor ain't in the signal path. I don't know a good way to describe that scenario; "actively-controlled passive preamp" is pretty verbose.

From designing mixed-signal circuits, active signal path or not, I think it would be difficult to suppress the noise from a processor to below 80 - 100 dB. That is a challenge no matter the architecture.

I am not sure I agree that in general passive or active is more susceptible to noise and such. The active path has more devices, finite PSRR/CMRR and all that jazz, but noise and distortion for a good active circuit is extremely low. And active devices are much less sensitive to load and driving impedances since they can be designed to have very high input impedance and very low output impedance simultaneously. the passive device may be more sensitive to noise because, without active buffers, the attenuator must be high enough in impedance to not load the source, at the same time keeping a low enough impedance so as not to add noise to the load. And hopefully not significantly change the frequency response of other characteristics from source or load. It will always be a compromise.

I would be hard-pressed to say in general one is better than the other. I would not say one is less sensitive to noise; the argument can be made that a stepped attenuator of any reasonable design will not add more distortion than an active gain stage. It will probably not add more noise, either, but as stated above that may not be true when the whole system is taken into account. I think it is going to be very dependent upon the load and source components. As a final comment (and the crowds go wild), with a passive "preamp" (no amp, technically) there are still active sources and amplifiers in the chain...

Don, well written and informative post.

As I said in the review, passive controllers (let's face it, they are not "preamps") are not for everyone. I'm a convert myself,
but I totally understand why someone would want an active unit, especially a tube pre!!

I am also waiting for the day when affordable DACs hit the market with transparent volume controls.

The Simaudio Neo 380D I have in house is fantastic in that regard, but it is $5000.

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