I recently purchased a second ACA 1.6 to run a monoblock pair. I built the second amp with a modified build to better match my low impedance speakers.
R11=20k
R12=90.9k
C1=4700uf
C2= 1000uf
C4= 100uf
R4=.50k
The second amp with the mods sounds great. When I used both amps as monoblocks (1st one original spec, 2nd one modded, parallel rca) the second was louder and seemed like it had more gain. I had to use the balance knob to even out the sound. I figured the second amp did have more gain due to the mods and I just needed to update the 1st original amp to match the 2nd.
I used the extra set of mod parts I ordered and updated the 1st amp. And it still has less gain than the 2nd amp. I’ve compared the two amps and can’t see any differences in parts or wiring. ( attached is a pic of the modded 1st amp board).
Any thoughts where to start?
R11=20k
R12=90.9k
C1=4700uf
C2= 1000uf
C4= 100uf
R4=.50k
The second amp with the mods sounds great. When I used both amps as monoblocks (1st one original spec, 2nd one modded, parallel rca) the second was louder and seemed like it had more gain. I had to use the balance knob to even out the sound. I figured the second amp did have more gain due to the mods and I just needed to update the 1st original amp to match the 2nd.
I used the extra set of mod parts I ordered and updated the 1st amp. And it still has less gain than the 2nd amp. I’ve compared the two amps and can’t see any differences in parts or wiring. ( attached is a pic of the modded 1st amp board).
Any thoughts where to start?
Attachments
I don’t think so.
When I noticed the difference in volume, I disconnected the amps and switched the amps to the opposite channel. I figured it was the easiest way to eliminate the room, cables, source and preamp. I found the same issue: my first amp wasn’t playing as loud as the second amp, no matter what channel it was driving.
When I play the first amp only, that amp driving both channels, it sounds good. No odd sounds, no missing sounds, no hum.... When I play he second amp only, it’s sound great. More dynamic, more interesting.
Some of that or most of it might just be the difference in gain. I don’t have a golden ear, so it’s hard to hear subtle differences.
A few questions,
Are both the PSUs 24 volt units? Have you swapped them round?
Are both the amplifier 'modules' in the quieter side working correctly? I.e. are they both as loud as each other if you do not use them in mono-block mode.
Have you used 'bridge' or parallel mode for the mono-blocks?
Are both the PSUs 24 volt units? Have you swapped them round?
Are both the amplifier 'modules' in the quieter side working correctly? I.e. are they both as loud as each other if you do not use them in mono-block mode.
Have you used 'bridge' or parallel mode for the mono-blocks?
Thanks for the help.
Yes, both PSUs are 24 volt and I left each one with a channel as I swapped the amps. The lower volume signal followed the first amp.
If I compare the two amps when one amp is driving both channels, playing the same music with the same preamp settings, I’d say he first amp is quieter than the second. Both channels on the first amp play and there’s no difference in volume between the two channels, though.
I’ve only played them as monoblocks using the bridged monoblock RCA input from the build guide. I’m not sure if that is parallel mode.
I do have a balanced preamp and I ordered XLR cables, due to arrive this week. I’ll try them with the bridged monoblock XLR input next.
Update- I re-biased the amps and set up them up as bridged monoblocks using balanced connections to my preamp. Everything seems to be working well and each channel seems correct.
The overall system sounds great. It's a noticeable improvement over running a single ACA with single ended connections. It's worth the time and investment.
Thanks to Papa for the ACA and TungstenAudio for the ACA mods.
The overall system sounds great. It's a noticeable improvement over running a single ACA with single ended connections. It's worth the time and investment.
Thanks to Papa for the ACA and TungstenAudio for the ACA mods.
Has anyone compared the single ended monoblocks vs the balanced monoblocks sound wise? Should they be identical?
Also I still can’t wrap my head around how the single ended monoblock works. With balanced inputs, one channel is inverted, but singleended you don’t have that inverted channel? How is it doing the same amplification? Is that one resistor flipping the signal?
Thanks
Also I still can’t wrap my head around how the single ended monoblock works. With balanced inputs, one channel is inverted, but singleended you don’t have that inverted channel? How is it doing the same amplification? Is that one resistor flipping the signal?
Thanks
The resistor isn't inverting the signal, the first side of the amplifier is. The resistor just connects one channel to the other.
Signal goes into the left side, is amplifier and inverted. Speaker output black is connected to this speaker post. Resistor takes that inverted signal, feeds it to the other amp board (right) and the signal is amplified and inverted again (making the phase positive) and the speaker output red is connected there. The speaker posts are 180deg out of phase with each other, which is precisely what balanced bridged is.
With XLR, the connection between the 2 boards never happens at the output (I.E., the resistor connecting the two) because the + and - leads of the XLR are already inverted when compared to each other.
As for sound, there is more 2nd harmonic overall when feeding the signal with the RCA, as the distortion spectra of the two sides of the amp end up being additive. It actually sounds quite nice overall. But it's absolutely different.
Signal goes into the left side, is amplifier and inverted. Speaker output black is connected to this speaker post. Resistor takes that inverted signal, feeds it to the other amp board (right) and the signal is amplified and inverted again (making the phase positive) and the speaker output red is connected there. The speaker posts are 180deg out of phase with each other, which is precisely what balanced bridged is.
With XLR, the connection between the 2 boards never happens at the output (I.E., the resistor connecting the two) because the + and - leads of the XLR are already inverted when compared to each other.
As for sound, there is more 2nd harmonic overall when feeding the signal with the RCA, as the distortion spectra of the two sides of the amp end up being additive. It actually sounds quite nice overall. But it's absolutely different.
Thanks that does help a lot. To be clear we should be connecting our speakers to both black output terminals correct? When you said the right channel output red you meant the wire to the speaker not the binding post itself, right?
The reason I’ve asked this is because, to my surprise, I’m finding that a single aca in stereo mode is sounding better to me than unbalanced bridged monoblocks. This is totally subjective and I have nothing to back it up but my gut, but there is something to me that I can’t put my finger on.
I was wondering if a balanced bridge connection would sound more similar to the stereo connection. I don’t have a balanced source at the moment so cannot test.
The reason I’ve asked this is because, to my surprise, I’m finding that a single aca in stereo mode is sounding better to me than unbalanced bridged monoblocks. This is totally subjective and I have nothing to back it up but my gut, but there is something to me that I can’t put my finger on.
I was wondering if a balanced bridge connection would sound more similar to the stereo connection. I don’t have a balanced source at the moment so cannot test.
I wouldn't think distortion will be cancelled.
Certainly the start up "fart" sound disappears (I can vouch for that). Stray noise will be cancelled as a function of balanced operation:
Balanced audio - Wikipedia
plus, you get a bit more grunt as a bonus:
Balanced audio - Wikipedia
I am using the 1st version of AmpCamp now, and would like to upgrade to the balanced mono block version.
But I am not able to understand the power rating versus impedance.
The reason for upgrade is to enjoy the benefits of 15W RMS power at much lesser distortion.
But I find that the power rating even in the balanced mono mode is given as only 5 watt RMS on 4 ohm load whereas 15 watt RMS on 8 ohm load.
Am I missing something here.
My bookshelf speakers are rated at 4 ohm, so does this mean I have no advantage in upgrading my AmpCamp.
But I am not able to understand the power rating versus impedance.
The reason for upgrade is to enjoy the benefits of 15W RMS power at much lesser distortion.
But I find that the power rating even in the balanced mono mode is given as only 5 watt RMS on 4 ohm load whereas 15 watt RMS on 8 ohm load.
Am I missing something here.
My bookshelf speakers are rated at 4 ohm, so does this mean I have no advantage in upgrading my AmpCamp.
I understand the term "upgrade" in this context indicates modifying the amp to alter/increase performance.
It sounds as if you may be referring to changing the operating mode of the amp(s). Should that be the case, the "ACA V1.6 Operating Modes" chart may be helpful to you.
https://cdn.shopify.com/s/files/1/1006/5046/files/ACA_Monoblock_Operation_RevA.pdf
Grounding of heatsinks?
I’m putting together and ACA with a custom chassis and pillaged heatsinks.
The diyaudio build guide says to check that your pcb’s have no stray leads extending down /touching the heatsink because the heatsink is grounded.
How/where is the heatsink grounded in the kit? Does it need to be grounded?
I’m asking because my design has the pcbs mounted to wood, not directly to the heatsinks; the connections from the transistor legs are jumped to the pcbs with some wire. Do I need to add an additional ground connection from the heatsinks to the board?
Sincerely,
Hawley
I’m putting together and ACA with a custom chassis and pillaged heatsinks.
The diyaudio build guide says to check that your pcb’s have no stray leads extending down /touching the heatsink because the heatsink is grounded.
How/where is the heatsink grounded in the kit? Does it need to be grounded?
I’m asking because my design has the pcbs mounted to wood, not directly to the heatsinks; the connections from the transistor legs are jumped to the pcbs with some wire. Do I need to add an additional ground connection from the heatsinks to the board?
Sincerely,
Hawley
The heatsinks in the kit ACA are 'grounded' in 2 ways.
Primarily via the outer ring of the power connector (step 30 of the 1.6 Build guide) directly to the rear chassis then through the metal work to the heatsink.
Second the metal stand off (step 15) to the -ve track on the ACA board, though some standoffs are nylon.
It is not strictly necessary to ground the heatsinks, but it is best practice. Try it and see...
Alan
Primarily via the outer ring of the power connector (step 30 of the 1.6 Build guide) directly to the rear chassis then through the metal work to the heatsink.
Second the metal stand off (step 15) to the -ve track on the ACA board, though some standoffs are nylon.
It is not strictly necessary to ground the heatsinks, but it is best practice. Try it and see...
Alan
