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PecanPi® DAC, Streamer and USB - Rev 2.0

orchardaudio

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The PecanPi® DAC just underwent an upgrade and is now able to drive balanced headphones.
https://orchardaudio.com/pecanpi

All measurements below are for XLR outputs driving 300ohm loads, performance does not change with load and the outputs are able to drive all the way down to 32 ohms.

I will start off with bench mode as Amir likes to do.
Capture.JPG


Dynamic Range (No Weighting)
Dynamic Range - AES17_NO_Weighting.jpg


Frequency Response
Frequency_Response.jpg


Linearity
Linearity.jpg


Signal to Noise Ratio (No Weighing)
SNR_No_Weighting.jpg


THD+N Ratio Vs Level
THD+N Ratio vs Level.jpg


Jitter Spectrum and Noise (256k FFT, 16 Averages)
Jitter_Spectrum_and_Noise .jpg


THD+N Ratio vs Frequency
THD+N Ratio vs Frequency.jpg


Intermodulation Distortion (IMD)
SMPTE Ratio.JPG


128k FFT of -20dB 1kHz Output
FFT_-20dBFS.jpg
 

Veri

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That 1kHz FFT looks very clean indeed. Up to par with Topping D90. Jitter is very very low, too! I wonder why SINAD isn't higher though. Some inherent noise? In any way, you seem to have squeezed the maximum out PCM1794A

Some questions though
-Any way to see what is PecanPi rev 2.0? Currently I see no indication on the site
-Could you tell us briefly about the changes from 1.0 to 2.0? :)
 
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orchardaudio

orchardaudio

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Any way to see what is PecanPi rev 2.0? Currently I see no indication on the site
All pictures on the website are of Rev 2.0 board, except for the PecanPi USB, I have not yet updated those.
https://orchardaudio.com/pecanpi-dac -- scroll down to the photo gallery
https://orchardaudio.com/pecanpi-streamer -- scroll down to the photo gallery

Could you tell us briefly about the changes from 1.0 to 2.0?
Changes are as follows:
  • DAC is now able to drive balanced headphones directly, supporting impedances down to 32-ohm.
  • DAC no longer has built-in RCA connectors but comes with included custom XLR to RCA adapters.
 
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Veri

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  • DAC is now able to drive balanced headphones directly, supporting impedances down to 32-ohm.
  • DAC no longer has built-in RCA connectors but comes with included custom XLR to RCA adapters.

  • Does this require some kind of adapter? 2x XLR 3-pin to XLR 4-pin?
  • custom XLR to RCA, I suppose pin 3 is floating?
Cheers
 

Veri

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Yes adapter needed if your headphones do not plug into 2x 3-pin XLR

Note that this is most of all headphones :) 2x 3-pin XLR is a pretty niche headphone cable/termination. Really.
I think pairing the XLR>RCA breakout with a RCA-headphone adapter would be a more common use case :)
 

Pillars

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Well, it's kind of a DAC streamer that happens to be able to drive headphones... I don't know, for the money it's a pretty hard place to be in.

For the price I think the unit should be

Streamer, DAC w/XLR+RCA, Digital volume control (remote if possible) - just scrap the headphone ability if you don't have space. If able, just do 1/4 plug.

I really like the chip choice though.
 
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orchardaudio

orchardaudio

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Streamer, DAC w/XLR+RCA, Digital volume control (remote if possible) - just scrap the headphone ability if you don't have space. If able, just do 1/4 plug.

It already has all this minus the 1/4'' plug and remote...

You control the unit remotely with your smart phone...
 

Veri

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Hey Orchard this terminates to 4-pin male. Balanced headphones tend to also be terminated on 4-pin male, so that won't work.
You'd need such an adapter that goes to 4-pin female, so you can plug your headphones into that.

That's why I mentioned it, this is a pretty niche/uncommon set-up. Very few headphones terminate on 3-pin xlr connectors.
XLR>RCA adapter, and RCA>headphone adapter would still be far easier to connect a headphone to.. :)
 
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orchardaudio

orchardaudio

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Hey Orchard this terminates to 4-pin male. Balanced headphones tend to also be terminated on 4-pin male, so that won't work.
You'd need such an adapter that goes to 4-pin female, so you can plug your headphones into that.

That's why I mentioned it, this is a pretty niche/uncommon set-up. Very few headphones terminate on 3-pin xlr connectors.
XLR>RCA adapter and RCA>headphone adapter would still be far easier to connect a headphone to.. :)

I posted the link to wrong one sorry:
https://www.amazon.com/Female-Balanced-Adapter-Hi-end-Silver/dp/B018ZN9IXI

Also, a headphone adapter for the RCA is already sold as an option with the unit.
 

Music1969

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Hi @orchardaudio

For headphone use, I see an important measurement missing - output impedance.

Can you share the maximum output impedance of 20-20kHz ?

If it can drive 16ohm headphones I hope maximum output impedance is < 1ohm?
 

Veri

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Hi @orchardaudio

For headphone use, I see an important measurement missing - output impedance.

Can you share the maximum output impedance of 20-20kHz ?

If it can drive 16ohm headphones I hope maximum output impedance is < 1ohm?
From the first thread:
Single ended output impedance: 0.05 ohm
So I expected Balanced XLR output impedance: 0.10 ohm

The headphone driving stage is built around parallel OPA1622s (if that is still the case in Rev 2).
 

Music1969

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Noted but this is Rev2 - just checking with the designer for latest info ;-)

Plus Rev2 now has an adapter for RCA outputs...

Also @orchardaudio - I see power input is 9Vdc but can it work with a 7.5Vdc 3A power supply?

If so, measured performance will be identical to 9Vdc power supply?
 
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orchardaudio

orchardaudio

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Single ended output impedance: 0.05 ohm
So I expected Balanced XLR output impedance: 0.10 ohm
This is correct.

Also @orchardaudio - I see power input is 9Vdc but can it work with a 7.5Vdc 3A power supply?
It will not work with 7.5V. 8.5V is absolute lowest I would recommend.

The headphone driving stage is built around parallel OPA1622s (if that is still the case in Rev 2).
This is still correct, for balanced it is 4 parallel OPA1622 two per side.
 

Veri

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I see power input is 9Vdc but can it work with a 7.5Vdc 3A power supply?

If so, measured performance will be identical to 9Vdc power supply?

To stay on the safe side you should go with 9V +/- 0.5V max fluctuation, otherwise you could have undervoltage or overvoltage problems.
7.5V is too little if you don't want to break down the device over time, and to prevent very unstable operation. It could randomly drop out.
 
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