Hi,
I want to build my first solid state audio amp, and I've decided to build an ACA. I have built vintage clone guitar tube amps, a few active speakers, repaired vintage integrated amps, turntables, and speakers, and built various small solid state projects, so I'm not anticipating difficulty. I'll be using a linear power supply (AnTek toroidal Xformer, etc), it will not be monoblocks, just one stereo amp.
My quandry is that I don't know how to deal with the input. Do I have to use a preamp? If so a passive one or an active one or just a buffer? I've never owned separates before, just integrated amps all my life, and I'm ignorant about this. I thought "line level" was a standard thing but apparently it varies from one source to another. Of courses the ACA doesn't have input sensitivity control.
The music sources that I imagine using are
1) a turntable
2) a CD player
3) a Raspberry Pi music server with a DAC hat.
Any advice or knowledge on this would be greatly appreciated.
Thanks,
Rob
I want to build my first solid state audio amp, and I've decided to build an ACA. I have built vintage clone guitar tube amps, a few active speakers, repaired vintage integrated amps, turntables, and speakers, and built various small solid state projects, so I'm not anticipating difficulty. I'll be using a linear power supply (AnTek toroidal Xformer, etc), it will not be monoblocks, just one stereo amp.
My quandry is that I don't know how to deal with the input. Do I have to use a preamp? If so a passive one or an active one or just a buffer? I've never owned separates before, just integrated amps all my life, and I'm ignorant about this. I thought "line level" was a standard thing but apparently it varies from one source to another. Of courses the ACA doesn't have input sensitivity control.
The music sources that I imagine using are
1) a turntable
2) a CD player
3) a Raspberry Pi music server with a DAC hat.
Any advice or knowledge on this would be greatly appreciated.
Thanks,
Rob
I am aware that a phono input must have a preamp, not just because the voltate level is so low, but RIAA equalizing.
Looks like you need 1.7 volts input to clip the ACA. So with digital you'd be fine with a buffer, but if you're going to play records you may need an active preamp. Have a look thru this thread: Which preamp for Amp Camp?
jeff
jeff
Thanks Jeff. I had a look at that thread. There are a lot of recommendations there, and it's a bit confusing still, but I think I'm starting to get the picture. The DAC on the Raspberry Pi outputs "line out" through two RCA jacks, so probably that's enough output to be fine for the ACA? Similarly for a CD player. So my main need is to have input selection (say a switch to select between the CD player and DAC), and a volume control?
A buffer circuit would be to make sure the output impedance is appropriate for the ACA? So how do I choose a buffer? The FirstPass site has a nice manual for a "B1 Buffer", I could make one of those. Would that B1 be a suitable buffer?
A buffer circuit would be to make sure the output impedance is appropriate for the ACA? So how do I choose a buffer? The FirstPass site has a nice manual for a "B1 Buffer", I could make one of those. Would that B1 be a suitable buffer?
Try using the digital volume control in your playback software temporarily. Before hitting "play", make sure it's all the way down, then gradually increase it. Listen to it that way for a little while. Vary the volume over the course of a few days the way you normally would.
If you never turn it up to 100%, then a buffer will be fine for the music you listen to, in your room, at your comfortable volume levels, using your sources, with an ACA, with your speakers.
If you never turn it up to 100%, then a buffer will be fine for the music you listen to, in your room, at your comfortable volume levels, using your sources, with an ACA, with your speakers.
The gain of the ACA is very very low compared to most other designs, in voltage terms just a gain of approx 3.3 or just over 10db. It needs around 2.2vrms at the input for full output into 8 ohms.
I suspect you will struggle without a preamp of some sort or another.
I suspect you will struggle without a preamp of some sort or another.
That is correct and the ACA performs best driving very sensitive speakers. The OP of the thread that Jeff linked to (post #3), Skylar88, is currently using a B1 + H2 with his ACA to drive (around 94+dB I think) sensitive speakers. Neither the B1 nor H2 has any gain but he is extremely happy with this setup. For lower sensitivity speakers the ACA benefits from a preamp with some gain. I used a Class A headamp (xrk's PCA) with the ACA to drive FHXL's with Alpair 10.3 drivers and they sounded gorgeous.
I'm realizing now that maybe I'm overthinking this. I guess there's no one-size-fits-all answer for matching a source/preamp/amp. There is variation. I like the suggestions of just trying the source with the ACA and seeing what I get. There is a software volume control on my DAC. Depending on the result, I can always build and add a buffer/preamp. Thanks!
On the system in the bedroom I used the software volume out of my Rpi DAC and it worked well. Then I added Pete Millet's NuHybrid Headphone Amp as a preamp and the ACA really came alive. Now I have preamps on all my ACA's.
The B1 Korg is a great option. My B1 drives an F6 and to me sounds fantastic. There are a lot of choices in the DIY store just add more inputs and a switch.
The B1 Korg is a great option. My B1 drives an F6 and to me sounds fantastic. There are a lot of choices in the DIY store just add more inputs and a switch.