Amp Camp Amp - ACA

From the beginning of my ACA build, I planned to bridge two amps on each channel because I have 16 ohm speakers. As I tested each large heatsink with two amps as a stereo single-ended amp (not bridged), I found that they powered my 95 db sensitive speakers very well. Don't hesitate to listen to those nice 3 watts just because it doesn't seem like enough to work well. I really like the now-finished bridged amps, but it probably wasn't necessary to bridge them -- the difference is very subtle.

Skip
 
Official Court Jester
Joined 2003
Paid Member
no apples and oranges ..... meaning - you can't find two speakers same in everything , except in impedance

even if you translate what's needed in db/W/m figures , there are few more factors in speakers world - most important being impedance module - in other words - how speaker is easy to drive

so , listening test is only way to compare things like that
 
no apples and oranges ..... meaning - you can't find two speakers same in everything , except in impedance

even if you translate what's needed in db/W/m figures , there are few more factors in speakers world - most important being impedance module - in other words - how speaker is easy to drive

so , listening test is only way to compare things like that

I was meaning in theory anyway, to tease out the effect of impedance alone. But I've got the sense of it I need. Thanks to you both.
 
Hello,

I built ACA and love it! Have the opportunity to test it on a high end system (same kind of speaker as Nelson Pass Kleinhorn in smaller).
Conpetitor amp was a Pioner M22, the ACA (ACA 1.1 with single 120W meanwell 24V PSU) and the ACA was good!
Off course M22 is best on low medium and bass especially when huge power is required, then I would love design my own amp based on ACA active current source.
I think this is due to the poor reactivity of my psu (also poor wattage for 2 channel), would like to try with a 350W fly back psu.
But the idea is to lower the output impedance, since I'm far away to be an electronic audio expert, after reading the whole thread I decide to explore lowering output impedance this way:
modify the ACA design and reuse the lovely active current source, in fact transform the active source to active sink using a common drain instead of common source. Then the gain of output stage goes to unity and design a low noise, low distorsion JFET voltage gain stage with common nsource topology.

Then I ask to you if this kind of idea worth try or if I'm totally wrong ?

For my presentation I'm a french electrical engineer who after lurking some Nelson Pass design for years decide to go in bath and build some amps!
 
No idea is totally wrong.

You need to determine whether the problem is not enough voltage swing or damping factor. Current clipping is unlikely to be a problem in stock form.
If you can't figure that out, just mod both. You'll need bigger heatsinks though.

Alternatively build an F6. I've modded mine to have almost identical distortion character to ACA but at around 0.05% and damping factor is over 20 in mine.
 
OK, the idea is wrong for the lack of low medium/bass of the ACA I built.
Then maybe it's not the good topik for such questions.

Here a picture of my ACA 1.1, I did the PCB with kicad and manufacture it to seeedstudio (5 pcb for 75$).
I made a mod to avoid OFF pop: I connect speaker directly between the power resistor on one side and the other side is AC coupled with two big caps between power rails. In a such way voltage rise and fall same potential at the two pole of speaker. And this serve also as a power tank for whole circuitry. I also add a common mode 1mH self and a big 3900µF tank for each channel.

I also upload the ltspice shematic with THD run of the idea I would like to test, THD measurment seems to show good results from the unity voltage/current gain output stage.
 

Attachments

  • aca.jpg
    aca.jpg
    823.5 KB · Views: 820
  • amp.jpg
    amp.jpg
    305.7 KB · Views: 774
I have completely built the ACA partner with BOZ pre. I found the sound is not loud enough. The BOZ volume control I'm using is ALPS 20k. Let say at 6 o'clock the volume is zero, when I turned up till 1 o'clock the sound is not loud. My speaker is a DIY by own. The speaker is 88db @ 8ohm. Anyway to make it louder? The sound is great.
 
I have completely built the ACA partner with BOZ pre. I found the sound is not loud enough. The BOZ volume control I'm using is ALPS 20k. Let say at 6 o'clock the volume is zero, when I turned up till 1 o'clock the sound is not loud. My speaker is a DIY by own. The speaker is 88db @ 8ohm. Anyway to make it louder? The sound is great.

More details about the speakers are needed.
 
Please check heatsinking, I suspect MOSFET’s are getting too hot and then their power decreases....are you using Keratherm pads in between?
The heatsink is hot but still be able to touch in 10secs. I added an usb fan directly blow at the heatsink and it runs much more colder. I could leave my hand touching it for whole day without a problem. One side I'm using Keratherm and another side I'm using mika. The reason is I'm running out of Keratherm. The funny thing is using mika side is hotter than another.
 
One side I'm using Keratherm and another side I'm using mika. The reason is I'm running out of Keratherm. The funny thing is using mika side is hotter than another.


I tend to agree with you, Moppy. I also found that a mica pad and paste transfers heat better than Keratherm.

I guess the popularity of Keratherm is due to the fact that it's not messy. But is it better? I personally don't think so. Obviously, I'm open to being proven wrong. :p