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

[wanvon]

Count me in for one of the stereo versions.

 

[kgt]

Initial custom buffer design/pricing is done (very happy about the price). Not at all finalized, but would be using TI TPS7A49/30 voltage regulators, OPA1612, toggle switch for either "Norrmal" or "Low" gain (26dB/20dB range), slide switch for "On" "12v Trigger" "Auto Sense", PCB mounted Neutrik XLR connectors (with correct Pin 1 wiring), FastOns for connecting my own speaker binding posts (so can easily allow speakON option), Power LED....among other things.

The Hypex SMPS1200A400 is out of stock until end of April unfortunately. Would make a prototype hopefully in May to undergo testing (including tests similar to what Amir does to verify the input board performance, etc). So, fingers crossed, POSSIBLY June/July availability. Not going to take pre orders until the prototype is done and verified.

For a 2ch Purifi, I am shooting for a price range around $1129.

I would be interested in a 3 ch version of this. Just 1 question though:
Would the 26db gain work with an AVR pre-out of 1v? I have an Onkyo TX-RZ50 on order which I am hearing has only 1v pre-outs...
I would be using the pre-outs for the LCR speakers (Sonus Faber Lumina V's that are 4 ohms with 89db sensitivity and a suggested amp output of 50-300w).

Also, any idea on what the 3ch version would price out at?

Thanks

 

[DonH56]

1ET400A output spec = 425 W into 4 ohms which is 41.23 Vrms or 32.3 dBV so you'd need more than 1 Vrms to drive it to full scale. Onkyo does say on their website that subwoofer/pre outs are 1 V (https://www.onkyousa.com/product/tx-rz50-9-2-channel-thx-certified-av-receiver/).

 

[Keened]

1ET400A output spec = 425 W into 4 ohms which is 41.23 Vrms or 32.3 dBV so you'd need more than 1 Vrms to drive it to full scale. Onkyo does say on their website that subwoofer/pre outs are 1 V (https://www.onkyousa.com/product/tx-rz50-9-2-channel-thx-certified-av-receiver/).

Somewhere on the internet, maybe here or maybe AVS, there was speculation that the actual voltage out was higher than 1v but that Onkyo was only promising a minimum of 1V across all pre-out channels. So there might be a higher voltage if you're only sending out the LR channel.

I would like to think they'd include the center in their plans as well but only the LR channels get the nice amplification (according to the manual/box) and I believe there are two kinds of DACs where the LR get a decent one and every other channel get the lesser version; so probably not. We'll know soon enough as the RZ50 review goes up.

 

[TimF]

i want to buy one.

Initial custom buffer design/pricing is done (very happy about the price). Not at all finalized, but would be using TI TPS7A49/30 voltage regulators, OPA1612, toggle switch for either "Norrmal" or "Low" gain (26dB/20dB range), slide switch for "On" "12v Trigger" "Auto Sense", PCB mounted Neutrik XLR connectors (with correct Pin 1 wiring), FastOns for connecting my own speaker binding posts (so can easily allow speakON option), Power LED....among other things.

The Hypex SMPS1200A400 is out of stock until end of April unfortunately. Would make a prototype hopefully in May to undergo testing (including tests similar to what Amir does to verify the input board performance, etc). So, fingers crossed, POSSIBLY June/July availability. Not going to take pre orders until the prototype is done and verified.

For a 2ch Purifi, I am shooting for a price range around $1129.

i want to buy one.

 

[Buckeye Amps]

So if I offer two gain options for my Input Buffer board, what would be the best targets to encompass the majority of equipment out there?

 

[Matias]

So if I offer two gain options for my Input Buffer board, what would be the best targets to encompass the majority of equipment out there?

I guess the gain needed for full power out of 1.5V (damn AV receivers don't reach 2V on their pre-out RCAs....) and 4.0V (balanced standard for DACs).

 

[amper42]

So if I offer two gain options for my Input Buffer board, what would be the best targets to encompass the majority of equipment out there?

Gain setting #1 - High Gain 27dB buffer stage - 1.8V produces 280W in 6 ohms.
(Use with RCA based AVR/DAC to enable full output with 2V)

Gain setting #2 - Low Gain 20.5dB buffer stage - 1.8V produces 65W in 6 ohms.
(Use with 4V Balanced DAC to increase SINAD performance while providing full output with 4V)

 

[goryu]

How about 3 settings: high gain, low gain, no gain (bypass the input board)???

 

[amper42]

How about 3 settings: high gain, low gain, no gain (bypass the input board)???

There isn't enough usable advantage for a flow through option at 0dB in the input buffer to justify the extra cost of a 3 way switch. Or the user confusion it may bring. That configuration produces 10W at 6 ohms with 1.8V. The amp would need to be driven by an ADI-2 or the Benchmark LA4 to offer a reasonable volume with the 12.8dB gain. It might be interesting for testing purposes but I can't imagine recommending that setting for any home audio configuration. Two gain stages for the Purifi would be my preference.

 

[jhaider]

So if I offer two gain options for my Input Buffer board, what would be the best targets to encompass the majority of equipment out there?

One that matches the gain of your existing nCore amps (in case people mix and match), one maybe 6 or 10dB lower for people with very high output line stages.

 

[Buckeye Amps]

Thanks for the responses. Looks like I am on the same page with suggestions as I was looking to do a "Normal" gain of around 26dB and a "Low" of around 20dB

 

[DonH56]

IIRC the input impedance is pretty low without a buffer and the gain is also low. I am not sure 6~10 dB is adequate for anyone except those using "pro" equipment and thus fairly high output levels. I would be inclined to shoot for 20 dB and 30 dB or so but my suggestion would be to look at other amplifier offerings and see what they offer for gain and input levels.

FWIWFM - Don

 

[amper42]

IIRC the input impedance is pretty low without a buffer and the gain is also low. I am not sure 6~10 dB is adequate for anyone except those using "pro" equipment and thus fairly high output levels. I would be inclined to shoot for 20 dB and 30 dB or so but my suggestion would be to look at other amplifier offerings and see what they offer for gain and input levels.

FWIWFM - Don

March Audio P452
20.5dB
26.5dB

Boxem
12.8dB
20.8dB
27.2dB

Buckeye Amps NC502MP
25.5dB

The 26.5dB Purifi based P452 is on the low gain side compared to the 28dB Denon 4700 internal amps. Audyssey adds 2.0dB when setting levels with the P452. The 27dB gain for the Purifi would probably be a better fit for AVR's. On the other hand the current NC502MP is 25.5dB so you may not want to run the Purifi design much hotter than 26.5dB? It's a trade off if people are matching various gain levels with the same system.

 

[goryu]

There isn't enough usable advantage for a flow through option at 0dB in the input buffer to justify the extra cost of a 3 way switch. Or the user confusion it may bring. That configuration produces 10W at 6 ohms with 1.8V. The amp would need to be driven by an ADI-2 or the Benchmark LA4 to offer a reasonable volume with the 12.8dB gain. It might be interesting for testing purposes but I can't imagine recommending that setting for any home audio configuration. Two gain stages for the Purifi would be my preference.

I know of several people using the Okto dac 8 with a 10V output paired with purifi amps, bypassing the buffer. Can't imagine a 3 way switch is materially more expensive than a 2 way....Would give more flexibility.

Also, I agree that one of the gain settings should match the ncore 500 and ncore 1200. Again, I know of several people using those amps for the lower end and it would be nice to have all gains matched.

 

[kgt]

1ET400A output spec = 425 W into 4 ohms which is 41.23 Vrms or 32.3 dBV so you'd need more than 1 Vrms to drive it to full scale. Onkyo does say on their website that subwoofer/pre outs are 1 V (https://www.onkyousa.com/product/tx-rz50-9-2-channel-thx-certified-av-receiver/).

Thanks Don, just curious.
Is this how you are arriving at these numbers?:

Full power output spec of Purifi: 425 into 4 ohms.
Voltage = √(P × R) = 41.23 v
1v pre out out of the Onkyo x 26 gain of amp = 26v
At that voltage, Power obtained = V2 / R = 169 watts
To get the full rated power of Purifi, i would need 1.58v out of my Onkyo pre-outs.
Sound right?
If so, I am having 2nd thoughts on my choice of receiver....

But I might upgrade to a processor in the future (something like the AVM70 or it's successor).

 

[kgt]

Somewhere on the internet, maybe here or maybe AVS, there was speculation that the actual voltage out was higher than 1v but that Onkyo was only promising a minimum of 1V across all pre-out channels. So there might be a higher voltage if you're only sending out the LR channel.

I would like to think they'd include the center in their plans as well but only the LR channels get the nice amplification (according to the manual/box) and I believe there are two kinds of DACs where the LR get a decent one and every other channel get the lesser version; so probably not. We'll know soon enough as the RZ50 review goes up.

@Keened This is what I had heard as well.

I had asked a question on the DAC used on the Onkyo, and someone replied with:
TI PCM1690 and Zone 2/3: TI PCM5101A
I am not knowledgable enough to decipher (from the PCM1690 specs) what pre-out voltage PCM1690 would offer from each of the pre-out channels.

 

[DonH56]

P = V*I = V^2 / R = I^2 * R where P is power, V is voltage, and I is current. Note V = I * R so I = V / R to get P = V^2 / R

Gain in dB = 20*log10(Vout/Vin) = 10*log10(Pout/Pin) -- I usually work in volts since input sensitivity is specified in volts for given power output into given load impedance.

So Vout = sqrt(Pout * R) yes, and 26 dB of gain is a factor of 10^(26/20) ~ 20 V/V, so 1 V input yields about 20 V output instead of 26 V. Then run the numbers... If the overall gain to reach full-power output is 26 dB, then 41.23/20 ~2 V to reach full-scale output.

Check my math, doing other stuff whilst typing... - Don

 

[kgt]

P = V*I = V^2 / R = I^2 * R where P is power, V is voltage, and I is current. Note V = I * R so I = V / R to get P = V^2 / R

Gain in dB = 20*log10(Vout/Vin) = 10*log10(Pout/Pin) -- I usually work in volts since input sensitivity is specified in volts for given power output into given load impedance.

So Vout = sqrt(Pout * R) yes, and 26 dB of gain is a factor of 10^(26/20) ~ 20 V/V, so 1 V input yields about 20 V output instead of 26 V. Then run the numbers... If the overall gain to reach full-power output is 26 dB, then 41.23/20 ~2 V to reach full-scale output.

Check my math, doing other stuff whilst typing... - Don

Thanks Don, i am sure you are right, can you tell me how you calculated gain factor of 20?
You say: 26 dB of gain is a factor of 10^(26/20) ~ 20 V/V.
In that formula, how did you know to use 20 as the Pin value?

 

[DonH56]

Thanks Don, i am sure you are right, can you tell me how you calculated gain factor of 20?
You say: 26 dB of gain is a factor of 10^(26/20) ~ 20 V/V.
In that formula, how did you know to use 20 as the Pin value?

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