Buckeye Amps: Purifi Mono, 2ch, and 3ch Official Thread

[amper42]

From my experience, it's a bit difficult to drive a Purifi based amp to full output using the Denon 4700 even with a 26.5dB gain stage. Audyssey increases the level of the Purifi speaker chain by 2dB compared to when using the internal amps or a Monolith 7x200 external amp. At volumes higher than the Audyssey pink noise calibration, the Purifi connected speaker volume lags a bit when playing multi-channel stereo (measured via SPL meter). It's harder to detect with Atmos in 7.2.4 mode as all speakers don't play the same content and people don't normally listen to pink noise via ATMOS.

If I was going to use the Purifi amp with an AVR I would appreciate a 27dB gain especially if I was using the 28dB internal amps or the Monolith. Having all amps on the AVR with a similar gain voltage spec is a plus.

When I use the 26.5dB Purifi amp with the RME ADI-2 DAC FS it can easily rock the room with volume as low as -32. The higher voltage on the RME allows the volume control to stay relatively low at a higher SPL.

 

[kgt]

The formula for voltage gain in dB is: Voltage Gain (dB) = 20*log10(Vout/Vin) -- it is a fundamental equation. You can re-arrange the equation to get Vout/Vin = 10^(Vgain_in_dB/20) and use 1 V as Vin for reference. Note that is for voltage, Vin, and not power, Pin.

The equation is similar for power, but with a factor (constant) of 10 instead of 20: Power Gain (dB) = 10*log10(Pout/Pin)

I cannot vouch for this site but the equations for power and voltage gain look correct: https://en.wikipedia.org/wiki/Gain_(electronics)

HTH - Don

Thanks Don.
So, starting with: Gain in dB = 20*log10(Vout/Vin). So, Vout/Vin = 10^ Gain in db/20 i.e. Vout/Vin = 10^ 26/20 = 19.95v
So a 1v input = 19.95 v output for 26db gain.

So, using the same formula to calculate expected input voltage to get a output voltage of 41.23v would be:
Vout/Vin = 10^ 26/20 = 19.95v
So, Vin = Vout/19.95 = 41.23/19.95 = 2.06v

I get it now...
So I guess I won't be getting the full power out of these amps with my receiver until i upgrade to a processor that outputs 2v RCA or 4v XLR right?

 

[Buckeye Amps]

Update:

With the buffer board well underway in prototype design/testing (to come soon), the final price point for the 2-channel will be $1149

 

[thegeton]

Update:

With the buffer board well underway in prototype design/testing (to come soon), the final price point for the 2-channel will be $1149

Excellent! Do you have a current confirmed feature list?

 

[Buckeye Amps]

Excellent! Do you have a current confirmed feature list?

If all pans out with testing:

Low and High Gain (20dB/26dB), built-in 12v trigger on the input board (super low mA draw) with slider to choose always on, trigger, or auto sense on. OPA1612. TI voltage regulators. Emphasis on the design to minimize cross talk.

 

[thegeton]

If all pans out with testing:

Low and High Gain (20dB/26dB), built-in 12v trigger on the input board (super low mA draw) with slider to choose always on, trigger, or auto sense on. OPA1612. TI voltage regulators. Emphasis on the design to minimize cross talk.

Still projecting a June/July 2022 lead time?

 

[Buckeye Amps]

Still projecting a June/July 2022 lead time?

Yea, July to be safe. I am going to have a completed build tested thoroughly (similar to Amir's slate of tests) first so want to leave a little time cushion in case of revisions

 

[DonH56]

Thanks Don.
So, starting with: Gain in dB = 20*log10(Vout/Vin). So, Vout/Vin = 10^ Gain in db/20 i.e. Vout/Vin = 10^ 26/20 = 19.95v
So a 1v input = 19.95 v output for 26db gain.

So, using the same formula to calculate expected input voltage to get a output voltage of 41.23v would be:
Vout/Vin = 10^ 26/20 = 19.95v
So, Vin = Vout/19.95 = 41.23/19.95 = 2.06v

I get it now...
So I guess I won't be getting the full power out of these amps with my receiver until i upgrade to a processor that outputs 2v RCA or 4v XLR right?

Correct.

 

[thegeton]

Yea, July to be safe. I am going to have a completed build tested thoroughly (similar to Amir's slate of tests) first so want to leave a little time cushion in case of revisions

Apologies for peppering you with questions; which case will you be using? (doing some space planning)

 

[BoredErica]

Something below 20db would be nice, but 20db gain is already a lot better than 26db.

 

[Buckeye Amps]

Apologies for peppering you with questions; which case will you be using? (doing some space planning)

No apologies needed.

It will still be the "small" sized case but likely an inch wider and an inch deeper. Same height. Should have a specific case design done soon (just waiting for the board to be 100% finalized for prototype production before I start looking at the case layout/design).

 

[tifune]

Update:

With the buffer board well underway in prototype design/testing (to come soon), the final price point for the 2-channel will be $1149

Have you found a little time to consider 3/5ch options and/or their pricing? Ty!

 

[christr]

Have you found a little time to consider 3/5ch options and/or their pricing? Ty!

I would be very interested in this as well

 

[Buckeye Amps]

3ch will be an option but most likely not til Fall. I can only roll out one at a time right now (unless someone feels like becoming an investor in my company).

Good news is the Purifi modules for testing have been ordered. So far so good with timeline

 

[magic44ken]

I'd be interested in seeing a x3 L/C/R build with the modules oriented vertically on heat sink trays, or the traditional horizontal orientation if vertical would be too tall. They could probably all share one SMPS1200A400 with a three-way splitter and still be fine for most purposes.

Would the Neurochrome do anything better than the EVAL1 or EVAL2 buffers?

I'm also interested in a LCR version to be use in home theater.

 

[Buckeye Amps]

 

[Keened]

You're making it very hard to justify DIYing when we know this is just around the corner...

 

[Buckeye Amps]

You're making it very hard to justify DIYing when we know this is just around the corner...

Hey, I'll never talk someone out of DIY'ing (I know the fun/love of doing things yourself)....but I know the cost of the Purifi as a small purchase by a consumer is quite expensive. And I am not sure how easy it is for a consumer to get an SMPS1200A400.

The custom board prototype is expected to be assembled within the next week or two. So I should have an idea in mid March how everything looks. Limiting factor for actual availability is still, at this point, the SMPS1200A400's being on back order. If the prototype goes as planned and doesn't need revisions, I hope to have the first 2chs available by mid to late May

 

[SuperDave]

Must...not...regret...going...Hypex...

No, I don't regret it for a moment. But I will have you know, as a downstream consequence of having bought one of your amp builds and a good pre/DAC, I just bought a pair of KEF R3's, and I blame you for all of it.

 

[kgt]

Hey, I'll never talk someone out of DIY'ing (I know the fun/love of doing things yourself)....but I know the cost of the Purifi as a small purchase by a consumer is quite expensive. And I am not sure how easy it is for a consumer to get an SMPS1200A400.

The custom board prototype is expected to be assembled within the next week or two. So I should have an idea in mid March how everything looks. Limiting factor for actual availability is still, at this point, the SMPS1200A400's being on back order. If the prototype goes as planned and doesn't need revisions, I hope to have the first 2chs available by mid to late May

Thanks Buckeye for the update, I will be (im)patiently waiting for availability of the 3 channel one.
Also, any idea when you plan on sending the 2ch to Amir for review? Hopefully, one of the first ones so that you can incorporate his feedback, if any, to customer shipping versions?