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.
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.
Heat management
I thought I would share some recent experience I've had with the ACP+ circuit.
My application is using this circuit as a gain stage for my MoFo monoblocks. Due to the limited room I have inside the chassis, I'm using a strip board layout that is just a little bit larger than the Yara Preamp IPS. As such, I happen to be using the same size and style heatsinks on the output transistors as those used for the Yara version. I have found that the IRF610 devices run very hot with the standard bias current of 150 mA. With the original circuit parameters, the output devices were rapidly heating up to 70 °C before I shut off the power. This is hot enough that device life is likely to be adversely affected, both for the transistors and possibly also for the adjacent electrolytic capacitors.
The original PCB for the ACP+ had enough room for much larger heatsinks, which look like they should do a good job of managing the temperature. With the reduced board space available on the Yara implementation, as well as my own, the small heatsinks are not quite up to the task. That is, unless other measures are taken to reduce power dissipation or improve thermal performance.
So far I have managed to lower the power dissipation by reducing the quiescent current through the output stage from 150 mA to 133 mA. This gave a noticeable reduction in device temperature. I can now hold my finger on the heatsinks for about one second before having to let go. That translates to about 60 °C using the Nelson Pass temperature estimate. This is still hotter than we would like for reliable lifetime, but an improvement nonetheless. I changed R111 from 1.5k to 3.0k and R115 to 3.2Ω, which is 4.7Ω in parallel with 10Ω. The lower current may affect power delivery for some of the lower impedance headphones, but should be fine for most everything else.
The next thing I plan to do is increase the size of the heatsinks. Since there is only room to go up, I will attach two of the small heatsinks together, one on top of the other, using thermal conductive epoxy. This is a slightly tricky operation, as one needs to avoid clogging the mounting hole. I did spend some time on the Mouser website looking for taller heatsinks with the same small footprint, but came up empty. So epoxy it is.
I thought I would share some recent experience I've had with the ACP+ circuit.
My application is using this circuit as a gain stage for my MoFo monoblocks. Due to the limited room I have inside the chassis, I'm using a strip board layout that is just a little bit larger than the Yara Preamp IPS. As such, I happen to be using the same size and style heatsinks on the output transistors as those used for the Yara version. I have found that the IRF610 devices run very hot with the standard bias current of 150 mA. With the original circuit parameters, the output devices were rapidly heating up to 70 °C before I shut off the power. This is hot enough that device life is likely to be adversely affected, both for the transistors and possibly also for the adjacent electrolytic capacitors.
The original PCB for the ACP+ had enough room for much larger heatsinks, which look like they should do a good job of managing the temperature. With the reduced board space available on the Yara implementation, as well as my own, the small heatsinks are not quite up to the task. That is, unless other measures are taken to reduce power dissipation or improve thermal performance.
So far I have managed to lower the power dissipation by reducing the quiescent current through the output stage from 150 mA to 133 mA. This gave a noticeable reduction in device temperature. I can now hold my finger on the heatsinks for about one second before having to let go. That translates to about 60 °C using the Nelson Pass temperature estimate. This is still hotter than we would like for reliable lifetime, but an improvement nonetheless. I changed R111 from 1.5k to 3.0k and R115 to 3.2Ω, which is 4.7Ω in parallel with 10Ω. The lower current may affect power delivery for some of the lower impedance headphones, but should be fine for most everything else.
The next thing I plan to do is increase the size of the heatsinks. Since there is only room to go up, I will attach two of the small heatsinks together, one on top of the other, using thermal conductive epoxy. This is a slightly tricky operation, as one needs to avoid clogging the mounting hole. I did spend some time on the Mouser website looking for taller heatsinks with the same small footprint, but came up empty. So epoxy it is.
I'm back in the game X!
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
jwjarch / bare PCB / 2 boards / USA
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
jwjarch / bare PCB / 2 boards / USA
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
jwjarch / bare PCB / 2 boards / USA
meanie / SMT Prepopulated / 2 boards / SGP
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
jwjarch / bare PCB / 2 boards / USA
meanie / SMT Prepopulated / 2 boards / SGP
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
jwjarch / bare PCB / 2 boards / USA
meanie / SMT Prepopulated / 2 boards / SGP
diy40 / 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
jwjarch / bare PCB / 2 boards / USA
meanie / SMT Prepopulated / 2 boards / SGP
diy40 / SMT Prepopulated / 2 boards / USA