Quite right Pete. I knew full well that the Allegri Reference is single ended through and through, but conflated the two things as I typed. Sloppy of me. What I meant was whether it’s likely to make a jot of difference by having the cables be terminated as RCA or XLR, i.e.
Hi all, apologies, I realise I’m rehashing some points already covered in this thread, but I want to make sure I’m not misunderstanding and I’d appreciate your thoughts/views.
I currently connect, fully balanced, from my Bartok to an MFA Baby Reference V2 pre-amp and then into my Karan KAS600 power amp. The preamp is passive and the Karan has an input sensitivity of 2v. My speakers are Magico A3s.
I set my Bartok output to 6v, my preamp to approx 2/3 volume and end up listening with volume on Bartok set to between -15 and -5db. It’s reasonably loud, not as loud as I’d like but I usually listen after others have gone to bed so I have to be reasonable! Everything sounds very nice indeed…
However, I’m trying to determine if my preamp is really adding any value, or whether I can sell it to raise some funds for use elsewhere (ideally an upgrade to a Rossini). The preamp doesn’t have a remote control so it doesn’t really give me the ability to set the Bartok to 0db and control volume via the preamp, hence the reason for me controlling the volume from the Bartok. So therefore it has to deliver sonic benefits to justify keeping it.
In order for me to compare against a direct output from Bartok to Karan, I need to decide what output voltage to set on the Bartok. My first test was at 2v to match the amp but the volume is much too high - I have to set the Bartok to around -25db for normal listening levels. 0.6v turns out to be the right setting, enabling me to get the Bartok back to approx -10db (+/- 5).
I’ll be doing more listening tonight but initial impression was I couldn’t really hear a difference - sounded great both ways. I’ll do doing more listening tonight.
Does anyone have any thoughts on whether I’m (at least in theory) losing anything by removing the preamp and setting the Bartok to 0.6v? Am I right to be setting the preamp at 2/3 volume to get the best from it?
I realise it’s my ears that ultimately need to decide but I’d like a view as to what you would EXPECT to be the best arrangement and settings.
O.K. let’s start from here. With a preamp the Bartok should be set to 0.0dBfs and all of the volume adjustment done with the preamp’s control. Why? By setting the Bartok to 0.0dBfs you are effectively removing its volume control. The output is then at line level and there is no question of any loss of resolution ( even if it is inaudible ).
Is 6V OK for your amp? It is specified as 2v input sensitivity. That means that your amp provides full output for that level of input. If it receives a signal in excess of 2V it is delivering more than rated full output. In practice that means an increase in distortion. However we do not know ( unless Karan quote it) what the distortion level is that they define for full output. 2V means full output for x% distortion. If they are very conservative the distortion may be very low anyway and there is a leeway before it is an issue. This also depends upon the harmonic spectrum of the distortion.
Of course when you set the Barok to 6V line output it will rarely, if ever, actually be sending a 6V signal to the amp’s input. This is because the maximum level on the recording will not have been mastered at 0.0dBfs (putting aside “Loudness Wars” questions). A competent mastering engineer will leave a few dB in hand so to avoid distortion ( output in excess of 0.0dBfs is just distortion. 0.0dBfs is the maximum output there can be).
So it looks from your description that 0.6V may be correct for you everything taken into account as far as is possible. As I have mentioned in other posts on this subject there is no "Correct " setting that can be generally adopted as there are so many variables including how loud you like to listen, the sensitivity of your loudspeakers, the size of your room, the type of repertoire you listen to etc.
As I have already indicated NOT if you are also setting the Bartok to -10 or 15 dB. Analogue volume potentiometers have various " rules" as to the mathematics they apply for volume control. Most are not linear but give differing increase/diminution of attenuation depending where they are set in their degree of rotation. Normally they require a fair amount of advancement to produce a big change in volume over the first 50% then smaller degrees of advance give larger amounts of increased ( decreased ) volume. The only thing to avoid with many stereo analogue volume controls is that during the initial few percent of travel the two channels may not track each other accurately leading to imbalance. So try not to have your volume pot set at e.g. 7 o’clock.
Whether you like using a pre-amp or not is dependent on many things including your personal expectations and, of course, the pre-amp concerned. I would only say that , generally, good ( active) pre-amps are not cheap pre-amps.
As for a bit of click-bait, I wonder if some who prefer 6V into inputs specified for significantly less voltage are actually enjoying that additional distortion because it seems to add , what, punch etc? . NB: I have nothing at all against enjoying what you like.
Many thanks for the comprehensive response (as always!)
The reason I don’t set my Bartok to 0db and adjust the volume via the preamp is that my preamp doesn’t have a remote, so it would be a big inconvenience to have to keep getting up and down to adjust the volume depending the music being played. Therefore there will always (for me) be a range in which I operate the Bartoks volume control - but it does sound as if I need to try adjusting the Bartok output voltage and/or the preamp volume setting to get the Bartok closer to 0db than it is currently. Maybe set the Bartok to 2v and turn up the volume control on the preamp.
Btw, the Baby Reference preamp is a passive design, not sure if that affects any of your comments?
The other question was whether folks felt the performance of the Bartok was regarded as better or worse at the various output voltages - if I remove the preamp I think I have no choice but to go down to 0.6v, so the question was whether than in itself wasn’t optimal for the Bartok. Or whether it’s just a case finding the level that best matches the downstream components. In which case it really is a case of me deciding which sounds best to my ears, or whether they all sounds similar enough that I may as well offload the preamp…
The Music First Audio Baby Reference passive preamplifier uses transformers to control its volume out.
This type of preamps are usually called transformer volume controls (TVC), or magnetic passive preamplifiers. Generally speaking, they use an auto-transformer designed so that the user can tap in to different sections of its windings via a switch. As each section is engaged, the voltage level swings up or down, as does the output impedance. In this/ your case there are 23 separate taps for a total of 24 discrete volume steps.
There are several advantages to this. A transformer acts to isolate your power amp from whatever radio-frequency interference (RFI) your source components are trying to send it. Also, compared to a simple, conventional, less-expensive potentiometer, a transformer passes along more of the incoming voltage from those source components. Less power is lost.
A key point is that a passive preamp’s output impedance drops the more you attenuate the signal, which means that the sound actually improves at lower volume settings. This has a very practical benefit: You don’t have to crank up the volume to get more detail and better dynamics.
From:
So, best would be to output your Bartók at 6V out (highest SNR, less distortion), at unity gain 0.0 dBfs (line level), and let the passive preamp do the attenuation, to fit your power amp, and listening level, giving the best SQ.
Rule of thumb: never use a preamp before a preamp. But your need to overcome not having a remote is complicating the situation.
Your preamp is passive, so it is not connected to mains. In order to have a working remote on it, it would need to be connected to mains, to feed a motorised volume control.
So, the choice is up to you: either enjoy the best SQ by using your Baby Reference, with Bartók at 6V out, 0.0 dBfs, and walk to it to adjust volume, or go for convenience, drop the preamp, loose some SQ, and use the Bartók at 0.6 or 2V directly into your power amp, and remotely adjust its output volume.
To add: if you look at the official dCS spec sheets, they give the specs at 6V out (where it applies). They do this of course because at 6V out they are at their best.
This may not be very helpful, but I also use a passive preamp after my Vivaldi for volume control. In my case, it’s a Townshend Allegri Reference. I run the Vivaldi DAC at 6V, and the Allegri does all the volume work. The Baby was one of the preamps I looked at before landing on the Allegri. The remote control of the Allegri was a significant factor in my decision. There is no question I get better low level detail and dynamics with this arrangement.
Another vote for a passive preamp being a potential approach that sounds fantastic @Mnemarks. I’m a day or so into the same Townshend Allegri Reference that Greg has — and it sounds gorgeous. No proper comparisons yet, just a big smile on my face
(The difference between the Allegri’s Apple remote and the dCS remote is hilarious, though — a mate suggested I reenact the opening scene from Star Wars with one chasing the other…)
A question (perhaps @PAR, @Anupc, @PaleRider or @Ermos?) — given that my power amps do their peak output at 1.1V input and the Allegri Reference is effectively at pass-through at full volume (129, or 0dB attenuation on the front display), how does the maths work for the table part-way down this page?
At what point would the Allegri be passing 1.1V through to the monoblocks? I run the Bartok at 6V and don’t want to sizzle anything.
I’ve not needed to crank it much, but it’s only a matter of time/wine…
Actually, perhaps I’m just being dim — if I’ve not driven myself out of the room with this system and an active preamp before it’s unlikely that I’ve been anywhere near 1.1V with ANY of the different configurations I’ve tried.
Does that make sense, or am I yet dimmer than I thought?!
I had a good listen late last night with the Bartok set to 6v and 0db and the Baby Ref set to just before 12am (15 out of 31 steps), getting up and adjusting it ocasionally as necessary. I have to say that this is the best I’ve yet heard my system sound, all the things others have described, it was fabulous. Tbh I don’t think I need to do any more comparisons, I’m keeping the Baby Ref and I’ve already sent an email to MFA asking if they’re able to retrofit the optional remote control. I’ve also asked their opinion on what effect this might have on SQ as I have to assume it must have some negative impact.
Thanks again for everyone’s input, this has been a bit of an eye opener for me in terms of getting settings matched correctly.
The difference between Bartok set to 6V [email protected] and 1.1V input to your power amp with no attenuation by the Allgegri (129 setting) is ~14.74 dB. So according to the table the Allegri volume control should be set somewhere between 99 and 100 to deliver circa 1.1V in that circumstance.
However, as I said Bartok will rarely pass 6V as that requires a level from the recording to also be at 0.0dBfs. That level can only be for maximum peaks in practice and the mean level of the recording will be way below that given a wide dynamic range e.g. well recorded orchestral music. Modern pop/rock will be much closer to 0.0dBfs as a mean level as it typically has a narrow dynamic range. Even a 16 bit recording is way, way more than sufficient to capture it .
Yes, you may never have been near 1.1V input in practice but that depends on how loud " loud" is to you. I remember the designer of the ATC SCA2 preamp visiting me many years ago. The ATC 50 actives I run have the tri-power amp section biased to run in class A for 80% of output. Looking at my typical volume setting on the pre-amp he remarked that I had probably never run the power amps outside of class A. If I had that would result in an SPL in excess of 100dB as a guesstimate. I would rather keep my hearing and neighbours.
The Allegri Reference is a microprocessor-controlled, passive, autotransformer volume control (AVC) pre-amplifier. There are 129 individual 0.5dB steps, which give very fine volume adjustment at all listening levels. This incredibly wide range can accommodate very high source levels and very high sensitivity power amplifiers.
Although the signal path is totally passive in the Allegri Reference, the electronics and display require 12V DC. A universal power supply is supplied, with the appropriate plug, to suit your country’s mains supply. Power and music signal are always separate. There is no direct connection between the power supply and the signal conductors or ground.
The table below illustrates the extremely wide volume setting possibilities:
Maximum signal level: 4V RMS 8Hz; 10V RMS 20Hz and up.
Impedance: At 0dB, input impedance is 20kohm. At -10dB (normal listening, volume setting at 109, see above) input impedance is 200kohm, for a power amplifier load with 20kohm input impedance.
Since the decibel is defined with respect to power, not amplitude, conversions of voltage ratios to decibels must square the amplitude, or use the factor of 20 instead of 10. To convert decibels to voltage, see the link below:
If you set your Allegri to -10dB, its voltage ratio loss output will be 0.316228. So, if you set your Bartók to 6V out, your Allegri at -10dB will output 0.316228 x 6V = 1.9 V to your power amp. With normally mixed source material this would not overload your power amp’s input sensitivity. But if you set your Allegri to -15dB (volume setting 99), its output voltage will not exceed 1V. So, if you keep your Allegri’s output setting between -10 and -15dB (between 99 and 109) you will be safe.
I demo’ed the Bespoke Audio preamp; I loved those folks and their dedication to their craft. But for me, I concluded the Townshend Allegri Reference was preferable.
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