Control Amplifiers?

[davide256]

I've just had a disquieting experience. Have owned  2 integrated amplifiers before, a Bryston B60R and a Prima Luna Prologue Premium. In both cases a deciding

factor for buying the unit was pre  inputs so that I could evolve to separates, do A/B comparisons to the built in pre and any other I had  This also

allowed me to try the DAC's I owned  connected direct to the amplifier section to see if the pre was hindering playback and I found that  the DAC's I had

all sounded better going through the pre amp sections. Last night I tried this with the Chord Mojo and the Hafler amp I'd set aside and was nonplussed to find

that it sounded significantly better without the Linear Tube Audio MZ2 in line as pre, much better dynamics and clarity. But long term I'm going to need a

volume control + input selector that doesn't get in the way, which lead me to start thinking about control amplifiers.

Wondering if anyone here has any personal experience with control amplifiers to share ?

[Norton]

Do you mean a passive preamp like this:

 

http://www.townshendaudio.com/allegri-reference-preamplifier/  Or cheaper version:

 

http://www.townshendaudio.com/allegri/

 

 No experience but I think they get good reviews ( I have one of their turntables though...)

[RickyV]

16 hours ago, davide256 said:

I've just had a disquieting experience. Have owned  2 integrated amplifiers before, a Bryston B60R and a Prima Luna Prologue Premium. In both cases a deciding

factor for buying the unit was pre  inputs so that I could evolve to separates, do A/B comparisons to the built in pre and any other I had  This also

allowed me to try the DAC's I owned  connected direct to the amplifier section to see if the pre was hindering playback and I found that  the DAC's I had

all sounded better going through the pre amp sections. Last night I tried this with the Chord Mojo and the Hafler amp I'd set aside and was nonplussed to find

that it sounded significantly better without the Linear Tube Audio MZ2 in line as pre, much better dynamics and clarity. But long term I'm going to need a

volume control + input selector that doesn't get in the way, which lead me to start thinking about control amplifiers.

Wondering if anyone here has any personal experience with control amplifiers to share ?

 

No experience and not too expensive.

 

https://khozmo.com/index.html

 

 

[fas42]

My solution would be to use the Mojo's volume control; and acquire a completely separate setup for music from other sources - a single chain answer which doesn't compromise the quality will likely cost as much as doing the first thing; and will take far longer to get sorted ...

[Qhwoeprktiyns]

I have tried a few, both active and passive, and settled for "The Truth" preamp, which has a unique design, and gets high praise from some reviewers (notably Arthur Salvatore). I did just what you did: compared the sound quality with my DAC directly connected to my amplifiers using low-volume tracks. This is the only preamp that I have found to be completely "transparent" in my system. It is  not terribly expensive (around 600$), has multiple inputs, but the "DIY" look may not be to your taste. Here is the link to the vendor's site: http://www.thehornshoppe.com/ and a fairly recent user review: https://cheaptubeaudio.blogspot.com/2020/05/the-truth-line-stage-active-buffer-with.html

[Rexp]

23 hours ago, davide256 said:

I've just had a disquieting experience. Have owned  2 integrated amplifiers before, a Bryston B60R and a Prima Luna Prologue Premium. In both cases a deciding

factor for buying the unit was pre  inputs so that I could evolve to separates, do A/B comparisons to the built in pre and any other I had  This also

allowed me to try the DAC's I owned  connected direct to the amplifier section to see if the pre was hindering playback and I found that  the DAC's I had

all sounded better going through the pre amp sections. Last night I tried this with the Chord Mojo and the Hafler amp I'd set aside and was nonplussed to find

that it sounded significantly better without the Linear Tube Audio MZ2 in line as pre, much better dynamics and clarity. But long term I'm going to need a

volume control + input selector that doesn't get in the way, which lead me to start thinking about control amplifiers.

Wondering if anyone here has any personal experience with control amplifiers to share ?

If your turntable sounds great with your pre amp, maybe you need a new DAC. 

[davide256]

What I want to steer  clear of is an active pre amp stage that will add coloration and lose information. Both  Mojo and Hugo 2 have their own gain circuit  and

my phono pre separate has quite a range of gain so I think that a traditional pre + added cabliing in line with them is likely a bad thing, unless something unusual

is going on with the Hafler input circuit?

 

This seems to be 1 example of a "control" amplifier, minimal circuitry between inputs and amplifier stage, volume is regulated in the amplifier circuit.

 

https://conradjohnson.com/cav45-stereo-control-amplifier/

[davide256]

5 minutes ago, Rexp said:

If your turntable sounds great with your pre amp, maybe you need a new DAC. 

I need to try that now direct  into the amp, lets see what happens.

[davide256]

15 minutes ago, davide256 said:

I need to try that now direct  into the amp, lets see what happens.

Ok...too high a db level for night time WAF with a high output MC at lowest phono pre gain setting fed direct to amp inputs. No volume control not friendly to needle

drops and on/off motor switch transients. WIll try again during daylight hours with something less loud than "the Dark Knight"

[Qhwoeprktiyns]

6 hours ago, davide256 said:

What I want to steer  clear of is an active pre amp stage that will add coloration and lose information. Both  Mojo and Hugo 2 have their own gain circuit  and

my phono pre separate has quite a range of gain so I think that a traditional pre + added cabliing in line with them is likely a bad thing, unless something unusual

is going on with the Hafler input circuit?

 

This seems to be 1 example of a "control" amplifier, minimal circuitry between inputs and amplifier stage, volume is regulated in the amplifier circuit.

 

https://conradjohnson.com/cav45-stereo-control-amplifier/

 

I thought you were interested in a preamp - I misunderstood.

The Conrad Johnson CAV45 gets great reviews and I would be curious to hear one.

[bluesman]

On 1/25/2021 at 9:02 PM, davide256 said:

This seems to be 1 example of a "control" amplifier, minimal circuitry between inputs and amplifier stage, volume is regulated in the amplifier circuit.

If I remember correctly, that CJ is “just” a power amp with variable input attenuation.  It’s a wonderful device, as are all the CJ pieces I’ve ever heard.  But if you like your Hafler 200 and don’t want to replace it, any of those passive attenuators will give you what you want.  The leap in SQ with a CJ would probably be quite apparent though, unless your DH200 has all the mods that were popular when it first hit the market and you really love it.

 

You might consider any variant of the Axiom or even a Nobsound (which is a great little box that punches well above its $60 price class).  The upgraded Axiom was about $500 as I recall, but I’ve liked the Nobsounds I’ve heard enough to live happily with one. 

[davide256]

4 hours ago, bluesman said:

If I remember correctly, that CJ is “just” a power amp with variable input attenuation.  It’s a wonderful device, as are all the CJ pieces I’ve ever heard.  But if you like your Hafler 200 and don’t want to replace it, any of those passive attenuators will give you what you want.  The leap in SQ with a CJ would probably be quite apparent though, unless your DH200 has all the mods that were popular when it first hit the market and you really love it.

 

You might consider any variant of the Axiom or even a Nobsound (which is a great little box that punches well above its $60 price class).  The upgraded Axiom was about $500 as I recall, but I’ve liked the Nobsounds I’ve heard enough to live happily with one. 

As a concept the CJ works for me but I don't think its the right choice for current hungry Magnepans. Will investigate the passive Axiom pres,

the only fault I find right now with a fully modded Hafler is transients have a whip crack like accent, otherwise midrange and bass are

much improved without a pre in the circuit.

[sandyk]

2 hours ago, davide256 said:

he only fault I find right now with a fully modded Hafler is transients have a whip crack like accent, otherwise midrange and bass are much improved without a pre in the circuit.

Did these modifications involve the PSU area's filter capacitors ?

 The use of Low ESR electrolytic capacitors can lead to this, as can the inappropriate use of lower value parallel capacitors across large value filter capacitors. Many are overdoing this in their new servers etc. too ,when  adding a lot of low value "boutique" bypass capacitors. 

 

[davide256]

3 hours ago, sandyk said:

Did these modifications involve the PSU area's filter capacitors ?

 The use of Low ESR electrolytic capacitors can lead to this, as can the inappropriate use of lower value parallel capacitors across large value filter capacitors. Many are overdoing this in their new servers etc. too ,when  adding a lot of low value "boutique" bypass capacitors. 

 

I’m not clear what you are referring to. The bridge board power supply capacitors are 4 pole Jenson capacitors which replaced some fairly large capacitors using a standard diode bridge (about 4x the size of the Jensens) 

[sandyk]

1 hour ago, davide256 said:

I’m not clear what you are referring to. The bridge board power supply capacitors are 4 pole Jenson capacitors which replaced some fairly large capacitors using a standard diode bridge (about 4x the size of the Jensens) 

 The Jensen capacitors may be exaggerating HF detail a little if the circuit had already been optimised for normal type capacitors

 

Quote

FOUR TERMINAL ELECTROLYTIC CAPACITORS WITH EXTREMELY
LOW INDUCTANCE/IMPEDANCE FOR HIGH FREQUENCIES - Jensen

 

[davide256]

Found this review of  an inexpensive Val Alstine control amplifier , the SET 120. A little under-powered for Maggies (60W) but sounds like

a good choice for speakers above 90 db efficiency. Continuing to look for its "big brother", something over 100W

 

https://parttimeaudiophile.com/2020/09/19/audio-by-van-alstine-set-120-control-amplifier-review/

[Rexp]

9 hours ago, davide256 said:

Found this review of  an inexpensive Val Alstine control amplifier , the SET 120. A little under-powered for Maggies (60W) but sounds like

a good choice for speakers above 90 db efficiency. Continuing to look for its "big brother", something over 100W

 

https://parttimeaudiophile.com/2020/09/19/audio-by-van-alstine-set-120-control-amplifier-review/

I take it your phono stage also sounded best direct to power amp? 

[davide256]

9 hours ago, Rexp said:

I take it your phono stage also sounded best direct to power amp? 

Couldn't get the gain low enough to go direct, ended up buying Schiit's cheap passive pre  (SYS) just to see if going direct was "directionally" correct.

( no intentional pun here).

As long as there wasn't deep bass transparency was better but deep bass lost definition compared to using pre and compared to same content using DAC direct.

Could be the Phonomena II has impedance matching issue going direct to amp, might have to buy a different phono pre  later if I go this route. Will also have to try

moving the TT opposite the speakers instead of in between, always possible its bass feedback due to greater low frequency output.

[davide256]

This looks promising, the Audio Hungary Qualition APX 200. A 100W stereo tube amplifier with two line inputs  and a gain switch for $5500

 

https://parttimeaudiophile.com/2020/07/17/audio-hungary-qualiton-apx-200-vacuum-tube-stereo-power-amplifier-review/

[Rexp]

10 hours ago, davide256 said:

Couldn't get the gain low enough to go direct, ended up buying Schiit's cheap passive pre  (SYS) just to see if going direct was "directionally" correct.

( no intentional pun here).

As long as there wasn't deep bass transparency was better but deep bass lost definition compared to using pre and compared to same content using DAC direct.

Could be the Phonomena II has impedance matching issue going direct to amp, might have to buy a different phono pre  later if I go this route. Will also have to try

moving the TT opposite the speakers instead of in between, always possible its bass feedback due to greater low frequency output.

Interesting, the Sys must be pretty good, I think your pre should beat it easily though. Maybe your pre has a fault or there is a mismatch with your power amp. 

[davide256]

Possibly. But every pre section I’ve ever had has introduced its own signature and limitations. At this point I view them as a no longer needed added whisper chain member if you can passively switch inputs and manage gain elsewhere

[sandyk]

3 hours ago, davide256 said:

Possibly. But every pre section I’ve ever had has introduced its own signature and limitations. At this point I view them as a no longer needed added whisper chain member if you can passively switch inputs and manage gain elsewhere

 However, at least in this thread, you appear to be basing your conclusion mainly around Vacuum  Rube technology which has MANY dB poorer S/N and Dynamic range compared with the best of Solid State equipment.

 Very few Valve amplifiers would achieve 90dB which is up to 40 dB less than the very best of solid state , and is barely adequate for RBCD, let alone high resolution LPCM and DSD.

[davide256]

3 hours ago, sandyk said:

 However, at least in this thread, you appear to be basing your conclusion mainly around Vacuum  Rube technology which has MANY dB poorer S/N and Dynamic range compared with the best of Solid State equipment.

 Very few Valve amplifiers would achieve 90dB which is up to 40 dB less than the very best of solid state , and is barely adequate for RBCD, let alone high resolution LPCM and DSD.

My Hafler and the van Alstine unit are not tubes.

 

I’m posting what I can find available. Although I haven’t added the Gryphon Diablo or Pass INT 25 integrated which some assert are passively preamped. Tube amps have their charm, but cost a lot to approach the transient response of sold state.

[Rexp]

1 hour ago, davide256 said:

My Hafler and the van Alstine unit are not tubes.

 

I’m posting what I can find available. Although I haven’t added the Gryphon Diablo or Pass INT 25 integrated which some assert are passively preamped. Tube amps have their charm, but cost a lot to approach the transient response of sold state.

I used a tape deck headphone out for a bit while my turntable was in repair. Direct to power amp (Electrocompaniet) it was ok, via pre amp (CJ) it was magical. 

[davide256]

On 2/4/2021 at 10:02 PM, Rexp said:

I used a tape deck headphone out for a bit while my turntable was in repair. Direct to power amp (Electrocompaniet) it was ok, via pre amp (CJ) it was magical. 

The word I'd use for CJ is seductive, not the last word on musical truth but its wiles leave you happy.

 

Turns out that the "whip crack like accent" is coming from the Chord Mojo, putting the Metrum Octave back into use with Sys for volume control eliminated that irritant. An unexpected consequence of eliminating the peak transient damping that it appears the MZ2 used as pre was doing before.