Massdrop x THX AAA™ 789 Linear Amplifier - Impressions Thread
Jul 30, 2019 at 8:42 AM Post #1,681 of 2,613
Hi @AndrewM888

If I have a DAC with only XLR outputs... but I don't want to use the XLR inputs of THX789 because the gain is too high (even on lowest gain setting) - do XLR-to-RCA cables provide the same benefits as the RCA-to-XLR cables you've recommended for RCA-only output DACs?

No issues with XLR (DAC end) to RCA (THX789 end) cables?
Hi,
Unfortunately you can't take XLR bal out from DAC and reduce to RCA because it will short one of your DAC bal outputs.
Just use XLR DAC out to AMP XLR in. For a given headphone jack e.g. 1/4", the 789 gain is same whether using RCA or XLR input. It has a diff input stage.
 
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Jul 30, 2019 at 8:44 PM Post #1,683 of 2,613
Is there any point getting a balanced DAC for this amp if I'm not running super long interconnects? Does a balanced source just provide more power??
 
Jul 30, 2019 at 8:51 PM Post #1,684 of 2,613
Jul 30, 2019 at 8:52 PM Post #1,685 of 2,613
None of the lengthy reviews I've read have mentioned the balanced XLR input being significantly better or louder than the single-ended RCA.
 
Jul 30, 2019 at 9:01 PM Post #1,686 of 2,613
None of the lengthy reviews I've read have mentioned the balanced XLR input being significantly better or louder than the single-ended RCA.
But has anyone here done an AB between RCA and XLR input to settle this issue?
 
Jul 30, 2019 at 11:04 PM Post #1,687 of 2,613
None of the lengthy reviews I've read have mentioned the balanced XLR input being significantly better or louder than the single-ended RCA.
if signals are true balanced when reaching XLR inputs, you should get +6dB (double power) and much less crosstalk than single-ended RCA.
if you carry a non true balanced signals (i.e., single-ended) into XLR inputs, there shouldn't be noticeable difference with single-ended RCA (the only difference would consist of plugs and jacks quality and conductivity: small one)
 
Jul 30, 2019 at 11:22 PM Post #1,688 of 2,613
if signals are true balanced when reaching XLR inputs, you should get +6dB (double power) and much less crosstalk than single-ended RCA.
if you carry a non true balanced signals (i.e., single-ended) into XLR inputs, there shouldn't be noticeable difference with single-ended RCA (the only difference would consist of plugs and jacks quality and conductivity: small one)

But this amp isn't fully balanced. Before it gets to the amplification stage, it takes half of the balanced input (ditching the other half) and then doubles it, just like it does with the single-ended RCA inputs. I have yet to hear it for myself, but I think that brings both input types closer together in terms of power and quality.
 
Jul 30, 2019 at 11:49 PM Post #1,689 of 2,613
But this amp isn't fully balanced. Before it gets to the amplification stage, it takes half of the balanced input (ditching the other half) and then doubles it, just like it does with the single-ended RCA inputs. I have yet to hear it for myself, but I think that brings both input types closer together in terms of power and quality.
humm.. didn't know this. then, guess it creates its own balanced signal when doubling, instead of getting and amplifying the balanced input signal.
but doubling is adding negative signal for XLR-4 balanced output, which is different than adding ground for RCA single-end output. that's why you get double power and much lower crosstalk in balanced XLR-4 output (check the specs).
if it works this way, you could get balanced output from a single-ended input signal. so the 3.5TRS cable to 2*XLR (single ended) gets sense. this is not usual, i'll search for further info.

EDIT: yes, it generates its own balanced signal from single-end signal, coming from either single-ended (RCA/XLR) or balanced (XLR) inputs.
using single-ended signal via XLR input, gets the benefit of removing possible ground loops (hum) and decreasing the chance of RF noise (XLR cables use to be full shielded), like if it was a balanced input signal. so it's much preferred than RCA input.
i like this very much.
 
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Jul 31, 2019 at 3:18 AM Post #1,691 of 2,613
Still not 'sold out' at Drop. Either the interest has dropped (thanks to Atom?:)) or they finally managed to have bigger stock than before. :)
 
Jul 31, 2019 at 5:20 AM Post #1,692 of 2,613
Jul 31, 2019 at 6:52 AM Post #1,694 of 2,613
But this amp isn't fully balanced. Before it gets to the amplification stage, it takes half of the balanced input (ditching the other half) and then doubles it, just like it does with the single-ended RCA inputs. I have yet to hear it for myself, but I think that brings both input types closer together in terms of power and quality.
No, we don't just use half the input signal. We use it all, through an instrumentation opamp differential input stage.
Both 789 input types are extremely high quality with impeccable measurements. For most setups, indistinguishable.
Choose the DAC you like best, and if you must use RCA use short cables 1-2ft. It'll be awesome. Cheers!
 
Jul 31, 2019 at 8:44 AM Post #1,695 of 2,613
More stock definitely, @escalibur.

Otherwise they wouldn't have it available to order for a month.

Hope you have a great day !
I think that technically it isn’t that they have more stock (if it were in stock they could ship it right away at the end of the drop rather than waiting till mid November). They probably have secured more production capacity at their contract manufacturer and/or they have secured more of the scarce components from their supply chain, allowing them to build many more units than before,

In either case, a great development indeed.
 

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