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-   -   ACP+ Preamp/HPA for Yarra Preamp (https://www.diyaudio.com/forums/group-buys/355617-acp-preamp-hpa-yarra-preamp.html)

MShipmanPE 17th June 2020 05:29 PM

I’ll ask a dumb question. Any resistor changes for HD650 or if I buy a pair of the ESS 422H.

Got any noise floor / harmonic profile graphs?

xrk971 17th June 2020 06:29 PM

This thing runs a pretty hot bias current at 140mA - it can handle 32ohm headphones like 422’s just fine. Certainly 300ohm like HD650 will be more than enough current.

pwagner 17th June 2020 09:43 PM

Like to join the GB for 2 prepopulated boards if you get the minimum # necessary. Otherwise, I take 2 non prepopulated.


pwagner / SMT prepopulated / 2 boards / USA

xrk971 18th June 2020 04:23 AM

Quote:

Originally Posted by MShipmanPE (https://www.diyaudio.com/forums/group-buys/355617-acp-preamp-hpa-yarra-preamp-post6245102.html#post6245102)
Iíll ask a dumb question. Any resistor changes for HD650 or if I buy a pair of the ESS 422H.

Got any noise floor / harmonic profile graphs?

Havenít had a chance to measure it yet. Will see what I can do.

xrk971 18th June 2020 05:59 AM

GB status update.

Quote:

MShipmanPE / SMT Prepopulated / 2 boards/ USA
Carl_Huff / bare PCB / 2 boards / USA
mnichols30030 / bare PCB / 2 boards/ USA
Thompsontechs / bare PCB / 2 boards / USA God Bless it in these trying times!
Aljordan / SMT Prepopulated / 2 boards / USA
Pwagner / SMT Prepopulated (if enough interest) / 2 boards / USA

adn6244 20th June 2020 09:02 AM

Hi X,
Is this project suitable to be used as preamp for class D amp? If not, could you recommend one from your shop?

Kit

xrk971 20th June 2020 01:32 PM

Are you looking for a neutral preamp or one that imparts some SE Class A flavor to the sound? What Class D amp? How much gain do you need?

The Yarra preamp is a great choice because it is a foundation upon which low cost modules like this ACP+, or any number of 7 or 8 other preamp topologies can be selected and used by swapping out the daughterboard.

The ACP+ is a very nice sounding quite neutral preamp with a SE Class A flavor. It is very powerful and can drive low impedance loads like 32ohm headphones.

For general purpose preamp use, I recommend the Melbourne daughterboards.

For simple to build and great resolution and a bit of SE Class A sound, the Hakuin is tops.

adn6244 20th June 2020 06:21 PM

I am looking for preamp for TPA3255 amp that I'm planning to buy or build. At the moment I have a 3116 amp with a bad volume control.

So it's either Yarra + Melbourne or Hakuin/ACP+ depending on the sound signature I'm after.

thompsontechs 20th June 2020 06:28 PM

My advice.... Build them all! The only way to know for sure. :)

adn6244 20th June 2020 06:49 PM

If I have the time, that's ideal !

Can I connect 6 ACP+ or Hakuin to single volume pot and use it as multi channel preamp?


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