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Universal Buffer achieving -140 dBc (0.00001 %) THD
Universal Buffer achieving -140 dBc (0.00001 %) THD
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Old 8th February 2020, 11:33 PM   #271
studiophone is offline studiophone  United States
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Very cool thank you Tom for creating this balanced buffer! I have a few questions. If you wanted to build three of these in one box would the power supply amp rage yeah thanks auto correct I know I have amp rage but Iím working on it... amperage required just triple and the voltage stays the same? 150 mA.. or should I get three units like the recom in the picture above? It would be for splitting an xlr out of Dac to 3 amps a hard wired balanced pad for each would be part of this with slightly different attenuation for each.

Also, I know this is a little vague but here goes... right now I have a pro gear Dac Mackie blackbird but eventually want to try new/other stuff like a topping D90... as far as I can tell the best scenario is to have the output on the source all the way up (digital volume or really no digital attenuation) and then attenuate with a preamp or passive pre. Update me if Iím wrong... my question is this can the buffer handle these types of Dac outs with some attenuation in between?

Right now with my Dac straight to power amps I have to use the volume control in jriver and keep it at around 33% or less to be comfortable. So what I think Iíll end up doing is padding it at the buffer so in jriver when itís at 90% itís about all I can take... what tangled webs we weave. What data should I be looking at to tell if a Dacs output will or wonít work? My main interest in buffering is impedance matching, I donít want to worry about it.
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Old 11th February 2020, 11:17 PM   #272
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by sledwards12375 View Post
Just completed the build of my Universal Buffer. I built it with one goal in mind only, and that was to add 6 dB of gain between my Matrix Audio X-Sabre Pro DAC and Neurochrome Modulus-686 amplifier. The build substantiates Tom's claim; it IS sonically transparent...period. No need for audiophile superlatives.
Awesome. Thank you for sharing. I'm glad you like the buffer. very nicely done with the chassis and build as well!

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Originally Posted by sledwards12375 View Post
Tom, thank you for another no-hassle, does what the numbers say it's supposed to do product.
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Originally Posted by mocenigo View Post
I have to thank Tom Christiansen for building this very very transparent and revealing buffer, which is serving in my Purifi build
You're quite welcome. I'm glad you like it.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 11th February 2020, 11:18 PM   #273
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by studiophone View Post
Very cool thank you Tom for creating this balanced buffer! I have a few questions. If you wanted to build three of these in one box would the power supply amp rage yeah thanks auto correct I know I have amp rage but Iím working on it... amperage required just triple and the voltage stays the same? 150 mA.. or should I get three units like the recom in the picture above? It would be for splitting an xlr out of Dac to 3 amps a hard wired balanced pad for each would be part of this with slightly different attenuation for each.
I would budget 100 mA per board to make sure you have enough current for the load current. So a Ī15 V, Ī300 mA supply would be my choice.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 14th February 2020, 08:31 AM   #274
s666foto is offline s666foto  Netherlands
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Hi Tom,

Stil enjoying my par-86 amp everyday! Now looking into building a preamp and... perfect timing, enter the Universal Buffer I want to build a preamp with 1 rca input, 2 xlr inputs and 1 xlr output, with volume control and possibly HT bypass funtion on one of the xlr inputs. I'm not sure how many UB's i need for this and what the considerations are for the position of the volume control in the scheme.

Could you perhaps sketch an example of such a preamp? Connections, boards needed etc. (For instance do i need UB's before and after the volume control or not?) This would be of great help, maybe not just to me...

gr, Sander
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Old 14th February 2020, 05:23 PM   #275
tomchr is offline tomchr  Canada
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Yeah. I need to get some block diagrams together for common use cases.

Attached "Instagram-ready" drawing should help you get going.

Basically: If your source can drive the volume pot directly, you can connect the RCA input directly to the pot through the input selector switch. That would be the "basic" version of the preamp. Some may prefer to add a buffer between the volume pot and the source, which leads to the "deluxe" version.

I know you said you only needed the XLR output, but with the Universal Buffer, you get both the XLR and RCA outputs, so I drew both. I'll leave it up to you as to whether to connect one, the other, or both to chassis connectors.

For the volume pot, I'd go with a 10 kΩ audio taper. Alps RK271-series "Blue Velvet" would be a good choice. Alternatively, a stepped attenuator would be nice as well.

Tom
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__________________
Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 14th February 2020, 06:18 PM   #276
zgtc is offline zgtc  Europe
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Universal Buffer achieving -140 dBc (0.00001 %) THD
wouldn't it be possible (and cheaper) to run a single input UB between the switch and the pot?
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Old 14th February 2020, 06:34 PM   #277
tomchr is offline tomchr  Canada
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Originally Posted by zgtc View Post
wouldn't it be possible (and cheaper) to run a single input UB between the switch and the pot?
If all your inputs are XLR or all your inputs are RCA, you can certainly do that. However, once you have a mix of XLR and RCA inputs, you have to be careful with the connection to XLR Pin 1 from the RCA shell. You could make it work with a three-pole switch, though.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 14th February 2020, 06:43 PM   #278
zgtc is offline zgtc  Europe
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Universal Buffer achieving -140 dBc (0.00001 %) THD
ah yes, that makes sense, thank you
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Old 14th February 2020, 07:05 PM   #279
studiophone is offline studiophone  United States
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Hereís what Iím wanting to do to split 3 ways. Tell me what you think. The first pad would be a high z voltage divider to take 1 volt down to .93 or so so the input sees a high z across all 3. (Help needed here to figure what is the best) Then the middle pad does the main attenuation then out to 3 separate amps. Deluxe version.
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Old 14th February 2020, 07:09 PM   #280
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by studiophone View Post
Here’s what I’m wanting to do to split 3 ways. Tell me what you think. The first pad would be a high z voltage divider to take 1 volt down to .93 or so so the input sees a high z across all 3. (Help needed here to figure what is the best) Then the middle pad does the main attenuation then out to 3 separate amps. Deluxe version.
That should work, though, I wonder if you can combine the two pads such that you get the required attenuation up front. That would save you three buffers.

I'm obviously quite happy to sell you six buffers instead of three, but ya know... I like to be honest and that.

Keep in mind that the input impedance of the UB is 48 kΩ, differential.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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