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DIY Purifi Amp builds

boXem | audio

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Backplate holes & cutouts all done, polish & paint next.

Ribboncable question, is it possible to have two ribbons into one connector?

View attachment 94669
One ribbon, no more, no less :).
Binding posts look nice, what are they?
 
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JimB

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Yes, agree, just investigating if the aesthetics of cable management can be improved in my build ... ;-) not breaking the symmetry ... I know, it’s just me.
How about the strain relief type? Both ends of the ribbon will come out the same side. I've done this in computers. Neat.
1605908741620.png
1605908812973.png

EDIT: Use it in the middle of your cable.
 
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Dear audiophiles,

A quick question - given that the stock Purifi EVAL input buffer (as amirm mentioned) reaches max volume at just 1.5V input with the extra gain, how do you guys drive the amp unit? If I am not mistaken, most balanced (XLR) DACs max out around 4V. How do you control the volume?

I am trying to procure a completely new setup from scratch with the Purifi amp, likely a pair of Klipsch RP-8000F speakers and a new balanced DAC that I still need to decide on (currently leaning towards either the Gustard A18 or the SMSL SU-8). My concern is that if the maximum volume is reached at just 36.5% of the max volume of the DAC (1.5/4) that the incremental volume steps are actually quite large. Furthermore, what would happen if the DAC reverts to full output/volume (4V) for example because there was a power reset or something like that, that could mean the end of the speakers. Very keen to find out how to best tackle the volume issue or how you guys drive the amp!

Cheers
 
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Dear audiophiles,

A quick question - given that the stock Purifi EVAL input buffer (as amirm mentioned) reaches max volume at just 1.5V input with the extra gain, how do you guys drive the amp unit? If I am not mistaken, most balanced (XLR) DACs max out around 4V. How do you control the volume?

I am trying to procure a completely new setup from scratch with the Purifi amp, likely a pair of Klipsch RP-8000F speakers and a new balanced DAC that I still need to decide on (currently leaning towards either the Gustard A18 or the SMSL SU-8). My concern is that if the maximum volume is reached at just 36.5% of the max volume of the DAC (1.5/4) that the incremental volume steps are actually quite large. Furthermore, what would happen if the DAC reverts to full output/volume (4V) for example because there was a power reset or something like that, that could mean the end of the speakers. Very keen to find out how to best tackle the volume issue or how you guys drive the amp!

Cheers
Upon further research I think the best option would be to add an inline attenuator, such as a fixed Rothwell attenuator. Pardon my ignorance, but which gain reduction level should I aim for (-10, -15 or -20 dB), to bring the EVAL1 back into balance with a typical balanced DAC that has a 4V output Voltage?
 

boXem | audio

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Upon further research I think the best option would be to add an inline attenuator, such as a fixed Rothwell attenuator. Pardon my ignorance, but which gain reduction level should I aim for (-10, -15 or -20 dB), to bring the EVAL1 back into balance with a typical balanced DAC that has a 4V output Voltage?
20log(1.5/4) = - 8.5 dB so -10 dB
 

TimoJ

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Upon further research I think the best option would be to add an inline attenuator, such as a fixed Rothwell attenuator. Pardon my ignorance, but which gain reduction level should I aim for (-10, -15 or -20 dB), to bring the EVAL1 back into balance with a typical balanced DAC that has a 4V output Voltage?
You could also change two SMD resistors (R17) on the Purifi preamp board. I think that would give better performance than using an external attenuator. (Theoretical performance that you won't hear.)
 
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JimB

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Dear audiophiles,

A quick question - given that the stock Purifi EVAL input buffer (as amirm mentioned) reaches max volume at just 1.5V input with the extra gain, how do you guys drive the amp unit? If I am not mistaken, most balanced (XLR) DACs max out around 4V. How do you control the volume?

I am trying to procure a completely new setup from scratch with the Purifi amp, likely a pair of Klipsch RP-8000F speakers and a new balanced DAC that I still need to decide on (currently leaning towards either the Gustard A18 or the SMSL SU-8). My concern is that if the maximum volume is reached at just 36.5% of the max volume of the DAC (1.5/4) that the incremental volume steps are actually quite large. Furthermore, what would happen if the DAC reverts to full output/volume (4V) for example because there was a power reset or something like that, that could mean the end of the speakers. Very keen to find out how to best tackle the volume issue or how you guys drive the amp!

Cheers
The nominal gain of the EVAL1 with buffer stage enabled is 27 dB, or ~22.4x. It takes 1.8V to reach the nominal rated 200W output (8 ohms), though the actual drive required to hit hard clipping will depend on your supply and mains voltage. Having up to 2V is not excessive.

And having a little extra gain upstream is not crazy. You might want to turn up some low level recording. So the concern then seems to be volume control resolution. What will you be using? If a simple linear stepped attenuator, then yes, you'll be maxing out at about half position, with crude steps down the range where you will listen most of the time. But, if not, then it won't behave that way. If, for example, you use the volume control on the Gustard (right?), you would have good control in reasonable dB steps, all the way up.

Maybe try your chosen volume control method first, and then, if the potential to overdrive the amp in some cases still concerns you, add a good in-line attenuator.
 
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JimB

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The nominal gain of the EVAL1 with buffer stage enabled is 27 dB, or ~22.4x. It takes 1.8V to reach the nominal rated 200W output (8 ohms), though the actual drive required to hit hard clipping will depend on your supply and mains voltage. Having up to 2V is not excessive.

And having a little extra gain upstream is not crazy. You might want to turn up some low level recording. So the concern then seems to be volume control resolution. What will you be using? If a simple linear stepped attenuator, then yes, you'll be maxing out at about half position, with crude steps down the range where you will listen most of the time. But, if not, then it won't behave that way. If, for example, you use the volume control on the Gustard (right?), you would have good control in reasonable dB steps, all the way up.

Maybe try your chosen volume control method first, and then, if the potential to overdrive the amp in some cases still concerns you, add a good in-line attenuator.
Thanks JimB, appreciate your response. Your suggestion to try a DAC first and add an attenuator later if required seems the most sensible way to go. Your post, if I understand you correctly, made me realise that DACs that have volume control in steps of 1dB are not linear stepped attenuators, so the actual difference in volume per step will not be too drastic.
 
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JimB

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... Your post, if I understand you correctly, made me realise that DACs that have volume control in steps of 1dB are not linear stepped attenuators, so the actual difference in volume per step will not be too drastic.
A dB of change is a dB of change, regardless of full scale limit.
 

Murray A

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Nice assembly. Very orderly and good layout.
Thanks for your kind comments.

I've been amp building for 55 years. I had the opportunity to test the Purifi Eval1 with my APX555 for one of the online webzines and was blown away by the eval1 technical and aural performance. This is truely a game changer and I believe the future of audio.

L1010316_00001.jpg
 

Doodski

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Thanks for your kind comments.

I've been amp building for 55 years. I had the opportunity to test the Purifi Eval1 with my APX555 for one of the online webzines and was blown away by the eval1 technical and aural performance. This is truely a game changer and I believe the future of audio.

View attachment 95189
Nice HP 11C too. :D I used a regular calc all my life and decided to pick-up a HP 11C for my electronics study many moons ago. Much easier for many operations. Those are collectors items now.
 
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