B'ASS Current Amplifier

[doublelife]

[PeterSt]

[Mamba315]

And please notice that back at the time (2010 I guess) I did not even know really much about the importance of differential (balanced) needing to be 100% the same, while this light stuff - now I think of it - won't be "the same" at all. I recall that it even requires some means of calibration and that the leds will deviate from that over time.

http://www.tortugaaudio.com/products/ldr3x-v2-1/

This guy claims he is "approaching" 99.9% accuracy from his LDR modules ( target attenuation vs actual measured), and he has an auto-calibrate feature since the LED do deviate over time.  Still, that's not to say he has solved the fundamental issues that LDR's may have.

Regarding the need for "investigation," I agree of course.  No doubt I'm limited by my knowledge and lesser experience, which is why I like hearing from others with more of both.  I will say that a huge reason why a disproportionate amount of my audio budget goes to Phasure is that your (Peter's) standards are simply higher than everyone elses.

Should Phasure release an outboard attenuator, I'll be first in line.  I think that's the bottom line here

I don't mind forgetting about those other things in the meantime.  My current solution (Benchmark DAC2) is certainly not ideal either, but at least it's already paid for and offers many other features besides.

[AlainGr]

Peter,

For someone (I will not name him ) that uses a preamp, does the B'ass and/or that preamp become redundant ?

Regards,

Anonymous

[acg]

Anthony, I hope one of your ideas is left; I only mention these to be ahead of things instead of nagging afterwards.
And (Matt) never ever hunt hear-says. First investigate the leage you're in and in what leage that "shouting" is. It can be really fine, but always needs thorough investigation.

Regards,
Peter

Well, two of my ideas are still left.  I had thought of the auto former (Intact Audio would be my choice) but I would have needed convincing that its varying output impedance, non-constant resistance and the tendency of magnetics for inductance for LF changing to capacitance for HF could work in this situation.  That would have been a long shot I reckon.

The problem with any passive attenuator is that it is basically a voltage divider, whether that be discrete resistor based on a switch or relays, LDR type, or magnetics.  They all act as high pass filters and LF suffers plus they are incapable of driving any length of cable or wire. For them to work best they should be used right before the gain stage with as little pcb trace or wire following them as possible...think in centimetres rather than metres. What is the B'ass?  My understanding is that it is a gain stage or an active buffer to my way of thinking, so we have an opportunity for the best possible results from a passive attenuator if it is jammed in nice and snug before the unity gain stage.

How would I do a passive attenuator in this position?  Well, I would use sealed relays rather than switch.  These relays would of course be powered from a completely separate power source.  On top of this, this power source would only be active when the volume is being changed...for the moment of changing a relay...then shut down.  I would use Vishay VAR precision trimmed resistors and have an attenuator step of about 1.5dB just like XXHE, plus a mute function.  Note that as far as I am aware this is not like the Tent Labs attenuator (I admit that I did not look at it too hard) that you linked to Peter, and I am not sure how you used that device when you tried it, but it may well work differently immediately before the gain stage in the B'ass.  That is impossible for me to find out.

My other, and prefered option is the Muses 72320 chip.  Have you noticed them before Peter?  They also make some very good  opamps by all accounts.

Regards,

Anthony

[PeterSt]

so we have an opportunity for the best possible results from a passive attenuator if it is jammed in nice and snug before the unity gain stage.

Anthony, I'd say this is correct. Anyway during reading your text onwards to this sentence I was thinking "but no problem in this case".
This doesn't tell it really is no problem - only that the short run of length can be in order. Mind you (please) outside of the PCB's now present. So exactly as you just said.

Peter

[PeterSt]

For someone (I will not name him ) that uses a preamp, does the B'ass and/or that preamp become redundant ?

Alain, please pass this on to Mr Anonymous :

I don't think so;
The attenuator "undoubtedly" will fail anyway (but yet to see of course), although it may not be worse than what you are used to, Mr Anonymus. For the remainder part it should be for the better or at least it is the very best, plus all explicitly tested as matching with the NOS1(a) (not only technically but also audibly). Also, because it measures as non-existent, it should work anywhere (a bit the same as the heaphone story, where I vaguely claim it should be "a best").

And of course, if the B'ASS is taken for its volume control (now assumed it wil be in there) then it is redundant when Mr Anonymous already has a volume control to satisfaction.
But then I'm responding in a pestering kind of way ...

Give my regards,
Peter

[AlainGr]

Peter,

Thanks on behalf of Mr Anonymous. He is telling me that he should send his NOS1 to have it upgraded, then he will make an order for a B'ass (#2). Damn conservative he is

Ala(In)tona

[Nick]

A #2 BNC type please for me Peter.

One question, does the B'ASS have unity (or less ) gain ?

My NOS1a is driving 8 gain clones from its balanced outputs so the current capacity of the B'ASS would be very welcome but very loud volume is -34 db in XX so extra gain would not be a good thing for my system.

Regards,
Nick.

[PeterSt]

Hi Nick,

B'ASS is unity gain.

Regards,
Peter

Edit :

A #2 BNC type please for me Peter.

Don't you mean RCA + XLR ?
Otherwise #4 is balanced BNC ...

[Nick]

A #2 XLR type please for me Peter.

One question, does the B'ASS have unity (or less ) gain ?

My NOS1a is driving 8 gain clones from its balanced outputs so the current capacity of the B'ASS would be very welcome but very loud volume is -34 db in XX so extra gain would not be a good thing for my system.

Regards,
Nick.

Oops !

Sorry I meant to say;

A #2 balanced XLR type please for me.

Thank you Peter,
Nick.

[acg]

so we have an opportunity for the best possible results from a passive attenuator if it is jammed in nice and snug before the unity gain stage.

Anthony, I'd say this is correct. Anyway during reading your text onwards to this sentence I was thinking "but no problem in this case".
This doesn't tell it really is no problem - only that the short run of length can be in order. Mind you (please) outside of the PCB's now present. So exactly as you just said.

Peter

Well I hope it can work well Peter...I really do.  Thanks for even considering the VC as an option.

[PeterSt]

So ...

Yesterday's afternoon was spent for a large deal on sorting out solutions with the Muses chip.
Not unimportant side note : I have the idea that you just as well can use another ladder DAC to control the volume, but alas (although it is quite unclear, that chip looks to be an R2R ladder DAC).
Also ... no real relevant specs thar I can find in that "Japanese" style datasheet. Only the plots may tell something, but they are without real numbers anywhere while I am used to the numbers.

I only sorted out one path of solution (say with ready components) and for SE it looks that for ~225 euros for cost price of "foreign parts" something can be tested. And, this then can be tested for balanced as well (one channel), IMO. N.b.: Balanced looks to be ~100 euros more but this is not 100% clear to me yet.

I mentioned "foreign parts" because this is outside things I can arrange for myself. So the cost price tells nothing but that this is mandatory to set up a test, which btw undoubtedly (say by guarantee) will lead to a working whole.
It is more difficult to envision what more parts come along, like connectors, the wireing and regulators of various voltages. All I have seen is that all can be done with the PSU which was planned to begin with, but which possibly now require two, doing the job right, including an additional transformer. It would be end to end 2x mono, although at this moment I doubt whether this is the best to do. So FYI, you might think this works nicely but it thus assumes no common ground anywhere between the two channels of which you are not going to tell me that this stays separate at the other (poweramp) end. Then what ? I feel this brings misery only and my feelings are often correct.

In the end the work is maybe 2-3 fold of what it would have been for the original B'ASS and I envision a whole day of work to put one SE together outside of the base SMD soldering in order for the "amp". This means that this day now about equals the original price, so my mentioned 1200 was not a bad estimate at all.

BUT

For this all you would have 3 inputs as well and everything is remote controlled. The idea of having the "source" of D/A converter always connected directly, remains (that would be one of the three). But of course it can be connected to one of the controlled inputs, might one not hear a difference anyway.

I am not sure whether this would be "a best" preamp, but it could be equally good to e.g. a Pass XP-30 (uses the same chip) because it just will, measurement wise - at least for the direct connection. One thing : that XP-30 costs 16K and possibly that is because it is as good for each input.
http://www.stereophile.com/content/pass-laboratories-xp-30-line-preamplifier-measurements#DRiKWUSY2BvRCGYe.97
... Well, to be honest, the B'ASS measures better (direct connection - http://www.phasure.com/index.php?topic=3592.msg38254#msg38254 with the notice that this includes the NOS1a which is feeding the test signal).

That's it for now and only starting. So :
Disclaimer : This is all very premature and "fast". Don't pin me down on any mentioned prices.

Not sure what's next ...

Peter

[PeterSt]

My NOS1a is driving 8 gain clones from its balanced outputs so the current capacity of the B'ASS would be very welcome [...]

Nick,

In my proto-box there's currently still the switch hanging around that can add ~240mA per channel (I think I mentioned it in between the lines in the first post). So what I planned at some stage, is adding more current by means of, say, two switches (engage them both and the current is double the native). But it did not sound well. Not for me ! But I never thought of a situation like yours, where indeed it would be so that "double the drive" implies double the required current, all else being equal (read : if in my case and one 50K input impedance amp, the ~500mA is the best, then with two amps 1A should be required - well, sort of because the length of the interlink stays the same). So while I ditched the switches, I shouldn't ...

The additionally attached current ("chips") are only switched in the output signal path and I think/claim this is allowed at this higher level (of current). Measurement really shows no difference at flipping the switch (while it thus surely is audible). Side note (or not) : In my situation this additional current sounds chaotic, but this is not because of the switch; it already does with the chip nicely on the PCB like the others. Still, I can't judge the switch for that merit (of "switch").

Anyway ... thinking more inputs and what not it is not so difficult to again think "switches" (in the case). And if I do what I planned, then 2 switches plus electronics supplying the current, will cost 150 more for SE (300 for Balanced). It goes like this :

One switch can serve two "channels" and a channel is regarded one SE channel. Thus, stereo RCA (= SE, Single Ended) requires one double pole switch (think power switch sized) to attach one step of more current; with Balanced, the one switch would attach one functional channel (like the left channel) for both plus and minus of the differential channel. So it requires two switches to attach current for the left and right channel for one step of more current.
Thus two steps require 4 switches.

The switches would be at the outside of the case, reachable at any time without lifting the lid.

Peter

[doublelife]

Peter,

I would also like my #2 to be dual-mono if you think it can be done successfully.

Paul