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Old 17th February 2012, 04:34 AM   #21
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One very neat relay attenuator I've seen in a preamp at an audio show in Montreal was using a hybrid type volume control. They were using digital or PGA type volume control when changing volume (slow or fast), so it was totally silent during this operation and when set, they where calculating the exact same value on the latching relay R-2R ladder so only one "click" would be heard. Sounded really good as well.

I don't know if anyone has attempted this here?

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Old 17th February 2012, 04:38 AM   #22
neb001 is offline neb001  United States
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That's an interesting idea....
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Old 17th February 2012, 04:49 AM   #23
qusp is offline qusp  Australia
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seems to me the attenuator would be several times the size of the amp =D
as for Titan, i'm not entirely sure they are for general sale yet. its the same tech as in the davinci, but the USB board by itself is multichannel 8 x 32/192, 4 x 32/384

the cost will probably be about the same as the rest of your dac, think its about 500EU I have a prerelease prototype, but i understand its same as the final one

yeah i thought of using the PGA to drive something else with a control voltage too, seems to me it would make a good solution and avoid putting 2 opamps in the signal for no reason

Last edited by qusp; 17th February 2012 at 04:51 AM.
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Old 17th February 2012, 09:55 AM   #24
sek is offline sek  Germany
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Hi,

about volume control and complexity. I can see that people here are trying totally different things for volume control - and anything pre-WIRE, actually.

I don't seem to fit right into the minimalist approach of leaving out every non-essential component, like avoiding additional opamps or pots. See attachment.

Quote:
Originally Posted by hochopeper View Post
What devices are upstream of your wire?
I'm still in the stage of finding that out, but there certainly won't be a number of devices in front of it. It'll of course go as close to the DAC as possible.

Seeing that my headphone amp (ultimately) will have a volume control (pot on the right, see pic), I don't know why not having separate gain presets for each input would be a big problem in general.

Considering a DAC like a BII/BIII as the single (i.e. only) source of analog signals, isn't having a relay-type attenuator with predefined input levels the functional equivalent of telling your controller to switch both channels and volume in the digital domain simultaneously?

Then again, I own a record player...

Quote:
Originally Posted by opc View Post
I love my BII digital domain volume control, but before that I used a relay based shunt volume control and it was by far my favorite volume control setup, and offered much more flexibility than the digital volume control does.
Would you please explain? What flexibility did you have to give up that was caused by digital volume control in the BII per se (and not by different topology of signal routing and management in your shunt volume control device).

Quote:
Originally Posted by opc View Post
6. PGA
7. Dual gang resistive element pot
8. Full volume while wearing earplugs
Haha, glad you didn't put "no volume control" right at the top of that list.

I was always under the impression that the general culprit (going from larger to smaller influence, assuming quality gear) are things like the number of devices (as in: interconnected units) involved, the number of plugs, the length of cabling, the degree of pollution outside and inside the devices, etc.

Quote:
Originally Posted by qusp View Post
[...] PGA (i dislike going to all this trouble with the signal and then putting everything through the integrated opamps)
Considering the above I'd favor a PGA close to the amp over a separate unit just for volume control...

Cheers,
Sebastian.
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Old 17th February 2012, 11:27 AM   #25
qusp is offline qusp  Australia
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Quote:
Considering a DAC like a BII/BIII as the single (i.e. only) source of analog signals, isn't having a relay-type attenuator with predefined input levels the functional equivalent of telling your controller to switch both channels and volume in the digital domain simultaneously?
functionally yes, but adding 7 components in each phase, including 2 integrated circuits (at least one of which has THD numbers worse than the dac) and a transformer, with what is likely not a small amount of feedback, where nothing at all is needed; is hardly the same thing.

i'm not against opamps, i quite like them (obviously), but cleverness for cleverness sake is not what i consider clever. adding extra components can only degrade performance and in your circuit, linearity, noise and expense are all increased for no reason.

i'm not quite sure what you mean....separate unit just for volume? nothing in my list is a separate unit and my top 3 are actually part of the transport/source signal path whether any attenuation is applied or not. titan is a usb-i2s convertor of the highest order that happens to have 64bit floating point volume control, puremusic is player software and sabres volume, well thats obvious.
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Old 17th February 2012, 12:38 PM   #26
neb001 is offline neb001  United States
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Quote:
Originally Posted by qusp View Post
functionally yes, but adding 7 components in each phase, including 2 integrated circuits (at least one of which has THD numbers worse than the dac) and a transformer, with what is likely not a small amount of feedback, where nothing at all is needed; is hardly the same thing.
When you say integrated circuits, are you referring to the IC's that control the relays? In a relay attenuator, the specs of any ICs in the attenuator control circuit shouldn't matter since they're not in the signal path.

I think in the end it depends on our own needs/priorities. I'll probably build a wire amp without a volume control for fun, but I like to have the flexibility that having a volume control in the amp provides.


Quote:
i'm not quite sure what you mean....separate unit just for volume? nothing in my list is a separate unit and my top 3 are actually part of the transport/source signal path whether any attenuation is applied or not. titan is a usb-i2s convertor of the highest order that happens to have 64bit floating point volume control, puremusic is player software and sabres volume, well thats obvious.
I believe by separate unit, he means a volume control that is external to the amp. I know that's kind of the point, but that brings us back to that whole personal priorities thing

Last edited by neb001; 17th February 2012 at 12:44 PM.
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Old 17th February 2012, 01:14 PM   #27
qusp is offline qusp  Australia
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afaik the PGA volume control is buffered with at least 1 OP internally; but i think 2, one before and one after and it is this I object to, any efforts to create an individual high performance dac and amplifier combination are thrown away and rather limited to the performance of the internal opamps. i was referring to his schematic, in fact the whole post was directed at sek, no relay attenuator there. i presumed by PGA we are talking about the Ti electronically controlled analogue attenuator ICs; if i'm mistaken my apologies. i'm certainly not having a shot, i just dont understand the need/want to add such a complicated circuit to accomplish something you already have covered.... rather well

indeed one of the MAJOR points of the controls i favor are they are not external or separate to anything, they are integral to a device that is in the critical signal path whether you like it or not, but happen to provide completely transparent volume control hat has no effect on channel matching, input or output impedance, allows simultaneous control of multiple channels and also practically free for as many channels as you like.

sure you have the disadvantage that you cant use the amp with other peoples gear that doesnt have volume control, but for me, who gives a toss! I build gear for me. with my bal-bal its taken another step, it'll be integrated into the dac itself as the IV stage that happens to drive headphones very well

Last edited by qusp; 17th February 2012 at 01:19 PM.
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Old 17th February 2012, 01:25 PM   #28
neb001 is offline neb001  United States
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Ah, I missed the schematic. Please excuse my post then
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Old 17th February 2012, 04:23 PM   #29
fualcr is offline fualcr  Canada
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Smile More photos

I just thought I would add some photos of my build. This is a BAL-SE. I was very careful with the ICs when soldering them since they are so freaking expensive. The small residual amounts of flux remaining are non-reactive rosin type, meaning it is 100% safe to leave on for centuries. The tiny 0805 chip parts are a quite a challenge - some of mine look a little drunk, but I assure you, they are rock solid in place and the sound obviously speaks for itself. Another high five to OPC!

Shown below in daylight on a ESD safe bag - taken with an ancient digital camera with a nice macro mode. Remember, this amp is tiny (like I could probably hold ten of them in my palm)!

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Old 17th February 2012, 05:14 PM   #30
qusp is offline qusp  Australia
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nice work, pictures taken before the wonderous sounds sprang forth i take it? =P or you are commenting on the superbly black background?

also sek, i think i misunderstood your statement back there but i cant edit it, still not quite sure i follow, i think i was just reeling from your volume control schematic that shows 2x more parts (and of lower performance) than the amp its attenuating!

it seems totally against the theme of the amp, but i didnt mean it to be snarky with the cleverness thing. more flexible maybe, but its a bottleneck

anyway i'm just waiting for the epoxy to cure on the mini T connectors i'm lashing together for the low impedance battery umbilical, i'll grab some pics of the build on the bench tomorrow and some impressions
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