Do not confuse amplifier output power (watts) with amplifier gain (dB or amplification factor if you like).weird: 15w vs SIT 3's 18 but... sounding louder (everything else being the same)
might be just bad memory (not swapping back to the FW for a while)
An amplifier with more gain will require less signal input for the same output power. Hence the volume pot on your pre amp does not need to be turned so far up.
As Dennis said.
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Most power amps ( including the ACA) do two things, step up the voltage gain and step up the current gain. , Usually with different circuit stage sections. So the preamp gives some voltage gain, then the power amp adds MORE voltage gain, then sends the signal to it’s current gain stage for the essential current. Then you the have POWER, voltage and current....
Interesting Pass variations:
The F-4 amp has no voltage gain, so ALL the voltage gain comes from the preamp! The preamp has to put out hefty voltage, up to almost 20volts! Most CD players and other sources put out about 2 volts.
The Burning Amps (BA-1,2, and 3) have the 2 stages as mentioned above. But the voltage gain stage is a separate PCB so lots of people just take that voltage gain stage and put it in a box creating
reasonably high power preamp, the BA-3 preamp.
The ACA doesn’t have a lot of voltage gain, so that’s why it doesn’t work especially well with passive preamps which have no voltage gain (ie only a potentiometer, or a buffer only pre:the Pass B-1 which matches impedance between components but also has no voltage gain)
The ACA puts out enough power to work in most situations but one has to think about the total gain of the system: preamp with some gain, not necessarily huge, to make sure the amp can put out rated power, using 2ch ACA or 2 monoblocks, and using reasonably efficient speakers, or very efficient speakers. OTOH, if you have very efficient speakers, you probably don’t care if the amp puts out more than a couple of watts so perhaps preamp gain isn’t necessary. So there are trade-offs one can make!
The gain of the ACA can be changed by merely changing a resistor, but Nelson seem to feel that having too much gain in a power amp can often harm the sound.
Interesting Pass variations:
The F-4 amp has no voltage gain, so ALL the voltage gain comes from the preamp! The preamp has to put out hefty voltage, up to almost 20volts! Most CD players and other sources put out about 2 volts.
The Burning Amps (BA-1,2, and 3) have the 2 stages as mentioned above. But the voltage gain stage is a separate PCB so lots of people just take that voltage gain stage and put it in a box creating
reasonably high power preamp, the BA-3 preamp.
The ACA doesn’t have a lot of voltage gain, so that’s why it doesn’t work especially well with passive preamps which have no voltage gain (ie only a potentiometer, or a buffer only pre:the Pass B-1 which matches impedance between components but also has no voltage gain)
The ACA puts out enough power to work in most situations but one has to think about the total gain of the system: preamp with some gain, not necessarily huge, to make sure the amp can put out rated power, using 2ch ACA or 2 monoblocks, and using reasonably efficient speakers, or very efficient speakers. OTOH, if you have very efficient speakers, you probably don’t care if the amp puts out more than a couple of watts so perhaps preamp gain isn’t necessary. So there are trade-offs one can make!
The gain of the ACA can be changed by merely changing a resistor, but Nelson seem to feel that having too much gain in a power amp can often harm the sound.
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Very nice explanation, Variac! Thank you very much!
I am also puzzled by the power difference of all the FW amps into different loudspeakers.
Say, both Aleph J and F5 are kind of "normal" amps, not requiring anything special of pre-amp or speakers (as NP puts it), but:
Aleph J: 10W into 8ohms, 7W into 4ohms
and F5: 25W into 9ohms, 40W into 4 ohms
How comes one is giving more W into 4ohms than 8ohms and other the other way round?
What is the story behind this?
And what difference would 4 or 8 ohms make with the gain of these amps?
Could anyone be so kind to explain the working of that?
-Alvis
I am also puzzled by the power difference of all the FW amps into different loudspeakers.
Say, both Aleph J and F5 are kind of "normal" amps, not requiring anything special of pre-amp or speakers (as NP puts it), but:
Aleph J: 10W into 8ohms, 7W into 4ohms
and F5: 25W into 9ohms, 40W into 4 ohms
How comes one is giving more W into 4ohms than 8ohms and other the other way round?
What is the story behind this?
And what difference would 4 or 8 ohms make with the gain of these amps?
Could anyone be so kind to explain the working of that?
-Alvis
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Are these normal bass speakers (like a multiway speaker) or are they just mid or HF units via a crossover?
Also bridged mode might get you very little thump noise as both amps would do the same thing at the same time and the switch on/off voltage difference between the bridged output terminals would be minimal.
Also bridged mode might get you very little thump noise as both amps would do the same thing at the same time and the switch on/off voltage difference between the bridged output terminals would be minimal.
Hi All,
After protracted labour I can confirm that another ACA1.8 entered the world last night alive and kicking; father and baby doing fine.
Just a quick thank you for the prompt responses I received on this thread.
Looking forward to getting stuck into the next project - F5 or another ACA for mono?
Cheers
David
After protracted labour I can confirm that another ACA1.8 entered the world last night alive and kicking; father and baby doing fine.
Just a quick thank you for the prompt responses I received on this thread.
Looking forward to getting stuck into the next project - F5 or another ACA for mono?
Cheers
David
Attachments
I built my initial ACA 1.8 for a friend to use in her system and it has been working very well for her. I was impressed with the sound myself and decided to build two more so I can use it in balanced mode. I made some minor substitutions of parts as detailed in the ACA Amp with Premium Parts and the build went well and in testing the voltages everything looked okay. However, I am running into some problems with the operation which I will detail below:
1. Stereo Mode: Adequate sound is only achieved from the right channel. Very low output can be heard from the left channel and increasing volume brings distortion pretty quickly. This occurs regardless of the position of the toggle switch. If I swap the speaker cables the opposite occurs, so I know the left channel is capable of producing adequate sound, just not when everything is hooked up correctly.
2. Monoblock operation, unbalanced connections: With the toggle switch set to the middle (stereo/balanced mono) or top (bridged) position the left channel produces sound but it is distorted and the right channel has low output. If the switch is in the bottom (parallel) position everything is fine. Speaker cables (outer posts of each amp) and interconnect cables (Chanel A input of each amp) are connected per the 1.6 build guide.
3. Monoblock operation, balanced connections: This one is a little stranger as I get buzz regardless of the position of the toggle switch. Due to balanced operation I have to use a different preamp here so that may be the issue. When the toggle switch is in the up (bridged) or middle (stereo/balanced mono) positions everything sounds is fine. In the bottom (parallel) position no sound at all.
I went back and checked over the wiring which looked okay, I did re-solder the wire to the input jacks and speaker terminals more out or precaution than anything else. I am stumped though so any help would be appreciated.
1. Stereo Mode: Adequate sound is only achieved from the right channel. Very low output can be heard from the left channel and increasing volume brings distortion pretty quickly. This occurs regardless of the position of the toggle switch. If I swap the speaker cables the opposite occurs, so I know the left channel is capable of producing adequate sound, just not when everything is hooked up correctly.
2. Monoblock operation, unbalanced connections: With the toggle switch set to the middle (stereo/balanced mono) or top (bridged) position the left channel produces sound but it is distorted and the right channel has low output. If the switch is in the bottom (parallel) position everything is fine. Speaker cables (outer posts of each amp) and interconnect cables (Chanel A input of each amp) are connected per the 1.6 build guide.
3. Monoblock operation, balanced connections: This one is a little stranger as I get buzz regardless of the position of the toggle switch. Due to balanced operation I have to use a different preamp here so that may be the issue. When the toggle switch is in the up (bridged) or middle (stereo/balanced mono) positions everything sounds is fine. In the bottom (parallel) position no sound at all.
I went back and checked over the wiring which looked okay, I did re-solder the wire to the input jacks and speaker terminals more out or precaution than anything else. I am stumped though so any help would be appreciated.
Post some good quality pictures of your build/s.
Is it one ACA with the problem or two ACAs both with the same issue?
Low power and distortion sound is normally a shorted output. Check the resistance between the red and black terminals, should be 500 to 1000 ohms.
Do the same for the inputs too. You should get about 50k ohms from the RCA outer ring to the centre pin.
Is it one ACA with the problem or two ACAs both with the same issue?
Low power and distortion sound is normally a shorted output. Check the resistance between the red and black terminals, should be 500 to 1000 ohms.
Do the same for the inputs too. You should get about 50k ohms from the RCA outer ring to the centre pin.
Check you haven't stuffed one of the plastic insulators that isolate the speaker terminals from the chassis - same for the RCA connectors. Cost me a few hundred dollars to have a professional diagnose I'd stuffed my valve amp up with a tiny metal bur when I opened up binding post holes to fit new ones. Both the pro and I went all over the soldered joints checking for continuity before it got tracked down. To a tiny metal spike shorting a terminal.
@Alan 4411 - Thanks for the suggestion, here are the measurements:
Amp 1: Channel A and Channel B inputs = 111k ohms. Speaker output Channel A = 0 ohms, speaker output Channel B = 1k ohmns.
Amp 2: Chanel A input = 111k ohms, Channel B input = 45k ohms. Speaker output Channel A = 0 ohms, speaker output Channel B = 1k ohms.
@Steve Luck - I should note I am not using the stock binding posts. I put in Cardas binding posts that required me to drill the hole a bit bigger. I will remove the Channel A binding posts on both amps and clean things up a bit. I have a surplus of the Cardas posts so I will put another set in.
I will try and post pictures later if I can't get things going. Any other suggestions are welcome.
Amp 1: Channel A and Channel B inputs = 111k ohms. Speaker output Channel A = 0 ohms, speaker output Channel B = 1k ohmns.
Amp 2: Chanel A input = 111k ohms, Channel B input = 45k ohms. Speaker output Channel A = 0 ohms, speaker output Channel B = 1k ohms.
@Steve Luck - I should note I am not using the stock binding posts. I put in Cardas binding posts that required me to drill the hole a bit bigger. I will remove the Channel A binding posts on both amps and clean things up a bit. I have a surplus of the Cardas posts so I will put another set in.
I will try and post pictures later if I can't get things going. Any other suggestions are welcome.
The Channel As 0 ohms is one fault, you have a 'short' there somewhere. First make sure you have the speaker OUT + and - wires in the correct locations at the board. (Do not forget the + OUT is ground / 0 volts).
If they are correct, unsolder the wire from the - OUT on the board. Measure the resistance from OUT - and + at the board. It should now be 1k ohms. If not there is a problem at the board. If it is correct, the black output socket is shorted to the chassis or there is a wiring problem...
Not sure why you have different input resistances? They should all be the same. Standard build ACAs measure about 50k. If you have altered the values of R11 and R12 the figure should be the addition of those two values.
Alan
@Alan4411 - speaker wires are connected correctly per 1.8 wiring diagram. Unsoldered the minus output wire at the board and measured to plus wire and got 1k ohms on both amps.
In my setup R11 (20k) and R12 (91k) are why I get 111k ohms. I rechecked and this time everything was 111k so I guess I am good there.
I will focus on the output terminals on the left channel.
In my setup R11 (20k) and R12 (91k) are why I get 111k ohms. I rechecked and this time everything was 111k so I guess I am good there.
I will focus on the output terminals on the left channel.
As an update one of the amps is now working. I ended up going back to the stock binding posts and now it plays both channels in stereo and the correct channel in bridged mono. This is with an unbalanced RCA connection. I haven't tried the balanced XLR input yet as I wanted to wait until the other amp was up and running. Unfortunately after replacing the binding posts in the second amp the left channel would still not produce any sound. In addition, while the input and output measurements were within the specified range, on the board I could only get the voltage to go up to about 8V DC, and after checking the other test points, only Q2 D was within range. All other values were off by a good amount.
I tried to up load photos but it didn't work. I will try again later.
I tried to up load photos but it didn't work. I will try again later.
So, I'm building a B1 to drive my ACA. All in a bigger chassis with much larger heatsinks.
My question, since the B1 and the ACA both invert the signal, I figure I'll wire it up with the ACA Out + (with is grounded) to the negative (Black) speaker post and the Out - to the positive (Red) speaker post to get the signal corrected, right?
Obviously, I will not wire the positive speaker post to the ground. And I am single ended, not balanced.
Thanks
Dan
My question, since the B1 and the ACA both invert the signal, I figure I'll wire it up with the ACA Out + (with is grounded) to the negative (Black) speaker post and the Out - to the positive (Red) speaker post to get the signal corrected, right?
Obviously, I will not wire the positive speaker post to the ground. And I am single ended, not balanced.
Thanks
Dan
