BUILD THREAD - A New Take on the Classic Pass Labs D1 with an ESS Dac - Page 48 - diyAudio
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Old 27th January 2013, 08:34 PM   #471
opc is offline opc  Canada
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bigpandahk:

The short answer is no... it's an inherently balanced circuit and just taking one phase of the output results is significantly diminished performance.

If you absolutely must have SE output, the I suggest using an op-amp to perform the BAL-SE conversion. A transformer can also be used, but I generally don't recommend it.

If you're looking at a DAC with this sort of performance, IMHO the next stage in the system really should have a differential input, be it a preamp or a power amp.

pinnocchio:

Your secondary AC voltage is a little high if it's a loaded voltage. You'll get about 56VDC on the high side of the regs, and 9V of drop is pretty high.

If I were you, I'd target more like 36-38VAC at nominal (operating) load.

For the connectors, just use standard SIP 0.1" headers and sockets, but remove every other pin.

Cheers,
Owen
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Old 27th January 2013, 09:40 PM   #472
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Quote:
Originally Posted by opc View Post
bigpandahk:

The short answer is no... it's an inherently balanced circuit and just taking one phase of the output results is significantly diminished performance.

If you absolutely must have SE output, the I suggest using an op-amp to perform the BAL-SE conversion. A transformer can also be used, but I generally don't recommend it.

If you're looking at a DAC with this sort of performance, IMHO the next stage in the system really should have a differential input, be it a preamp or a power amp.

Cheers,
Owen
Thanks Owen
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Old 28th January 2013, 12:52 AM   #473
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Can anyone suggest a good BAL-SE conversion circuit? As my 300B must have SE input.

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Old 28th January 2013, 08:13 AM   #474
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Well, if it's really necessary, check this one out: THAT1646.
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Old 28th January 2013, 08:20 AM   #475
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nah, those things are well below the capabilities of this IV stage, but then as far as numbers I suspect so are the amps. I have to say i'm somewhat confused at the building a dual mono balanced dac to use with a SE tube amp. I would suggest a nice yet simple discrete opamp normally, but building 2 of them and stuffing in the same case as this... so maybe transformers or a couple of Owens BAL-SE the wire headphone amps if he has any PCBs left. lol in joke
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Old 28th January 2013, 08:38 AM   #476
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nah, those things are well below the capabilities of this IV stage, but then as far as numbers I suspect so are the amps.
Well, if you wanna go crazy you can try paralleling devices and stuff, but, as already stated, these are going to be the sub-optimal outputs anyway. I wouldn't waste a sexeh and precious Wire there.
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Old 28th January 2013, 12:53 PM   #477
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yeah... it's a tough call on that side of things.

If it's a 300B amp, then there is at least one transformer, and possibly two in the signal chain already, which would probably push me to suggest simply using another transformer to perform the BAL-SE conversion. If you like the sound of the amp, then you're clearly not bothered by the way transformers sound, so more of the same might be the safer bet.

Using a transformer also lets you reduce the output capacitor count to 1, which can be placed between the two primary windings of the transformer. If you're really adventurous, you could be the first to try it with no coupling caps at all and just slap the transformer across the output of the NTD1 before the output coupling caps.

Lastly, is your amp a 300B SE or 300B PP? If it happens to be push-pull then you could do a little circuit modification and bypass the phase splitter which would essentially make the amp a "differential" amp which could be driven from the NTD1's differential outputs.

If your amp is PP, then the last option is by far the best, and would certainly result in much better performance for both the amp and the DAC.

Cheers,
Owen
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Old 28th January 2013, 01:03 PM   #478
qusp is offline qusp  Australia
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Quote:
If your amp is PP, then the last option is by far the best, and would certainly result in much better performance for both the amp and the DAC.
but.... it would result in a much cleaner sound sig, which may not actually be desirable, since it may lose some of that really densely harmonic soundstage that 300B lovers can hold dear. difficult that making recommendations in these circumstances with objectives that can turn out to not be aligned, even though its objectively the 'right' thing to do.

it really depends on the style of tube amp, ive heard some pretty damn clean 300Bs as well. not many admittedly but its not the sort of thing I search out. Its usually the surrounding components that screw with tube amps linearity

Last edited by qusp; 28th January 2013 at 01:07 PM.
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Old 28th January 2013, 01:19 PM   #479
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After so much speculation let me add mine as well.

Amp won't be a 300B PP. I believe this is a dirty word in HG

As it most probably is a SET i just cannot understand all the obsession with a super duper bal/se convertor. Taking just one phase out appears to be the cleanest solution which will only bring negligible in this context increase in second harmonics and noise.
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Old 28th January 2013, 01:25 PM   #480
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you clearly dont have much of an idea of how the ES9018 works then, you wont 'just' get a small increase in 2nd harmonic.

also its all in series, some of the distortion wont add but not as little as you may think and all of the noise will.

basically all the careful on chip routing and element matching, all the power supply fiddling, all the careful layout, all the mosfet matching, all the zfoil matching and all the expense of dual mono, would be utterly pointless....

it would come to nothing, how exactly are you minimizing that?

Last edited by qusp; 28th January 2013 at 01:29 PM.
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