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Amp Camp Amp - ACA
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Old 28th September 2021, 04:08 AM   #10901
batty is offline batty  Australia
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Running my ACA in my main system now, pre is B1korg, speakers are LK1 Bookshelf kits 86dB/1w1m, DAC is Ares II CD, is Vincent CD-S4, streaming is via Galaxy A7. Analogue is Townshend Rock/RB250/Nagaoka MP11 via DIY Elekit MM phono stage.

Very impressed to say the least.
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Old 28th September 2021, 04:37 AM   #10902
MrJohn is offline MrJohn  United States
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Quote:
Originally Posted by RafaPolit View Post
Very quick read in Wikipedia if my examples are not clear enough:
Amplitude - Wikipedia
Thank you for the link!
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Old 28th September 2021, 06:40 AM   #10903
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by MrJohn View Post
Does anyone use a single ACA to power Klipsch RP-600M bookshelf speakers? These are rated at 96 dB sensitivity, but I can crank up the volume to 100% (PS Audio DAC w/ volume) and I doubt I'll get any noise complaints. It is perfectly clear and distortion-less at 100% volume too, which is amazing, but also not very loud

Also noteworthy is that my DAC only pushes out 1.4V to the RCA outs that feed into the ACA.

I don't believe anything is wrong with my ACA, I'm just curious as to what other people are experiencing with the Klipsch RP-600M + ACA combo.
Have you tried altering the intrinsic gain of the ACA?

Increasing R12 is all you have to to do. Nothing bad will happen and the overall result may well be preferable to adding amplification in front of the ACA. Assuming you fitted a 39k originally then try a 68k, 82k or 100k. Each higher value gives more gain. An 82k will almost double the voltage output for a given input level.
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Old 28th September 2021, 07:37 AM   #10904
Stanislav is offline Stanislav  Australia
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Great advise Mooly.
I find simple solutions the most elegant.
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Old 28th September 2021, 10:22 PM   #10905
MrJohn is offline MrJohn  United States
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Quote:
Originally Posted by Mooly View Post
Have you tried altering the intrinsic gain of the ACA?

Increasing R12 is all you have to to do. Nothing bad will happen and the overall result may well be preferable to adding amplification in front of the ACA. Assuming you fitted a 39k originally then try a 68k, 82k or 100k. Each higher value gives more gain. An 82k will almost double the voltage output for a given input level.
Thank you for this tip. I don't know enough to understand the concept behind what you're talking about, but if it's going to give it more gain, it might be worth a try.

Does this mean I would have to de-solder then solder in another resistor at R12? Can I solder another 39k resistor in the same spot? I take it this is like running in parallel? so.... probably will not work. hahaha

I take it there there are no resistor sockets for quick change?
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Old 29th September 2021, 04:31 AM   #10906
Plott is offline Plott  Austria
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John, it will not work that way. Soldering another 39k parallel will give you 19,5k
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Old 29th September 2021, 04:43 AM   #10907
Stanislav is offline Stanislav  Australia
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What Istvan said above, you'll need to unsolder the old one and solder the new one. Unfortunately there is no other way.
But it's no big deal, the easiest way is to first cut the resistor's legs close to the solder pad on the PCB, then using a solder sucker or some braid remove the remains from the pad. That way the risk of lifting a pad or damaging a component is greatly minimised.
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Old 29th September 2021, 07:15 AM   #10908
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by MrJohn View Post
Thank you for this tip. I don't know enough to understand the concept behind what you're talking about, but if it's going to give it more gain, it might be worth a try.

Does this mean I would have to de-solder then solder in another resistor at R12? Can I solder another 39k resistor in the same spot? I take it this is like running in parallel? so.... probably will not work. hahaha

I take it there there are no resistor sockets for quick change?
The voltage gain of the ACA is approximately given by dividing the value of R12 by R11. So 39,000/10,000 is 3.9

You have to remove the resistor as others have said and then replace it with a different value. No sockets

The value of R11 (10k) sets the input impedance of the ACA. Although you could lower this one instead of raising the other to increase gain (and here you could add a resistor in parallel) the lower input impedance would need to be able to be driven OK by whatever you have feeding it.
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Old 29th September 2021, 08:42 AM   #10909
MrJohn is offline MrJohn  United States
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Quote:
Originally Posted by Plott View Post
John, it will not work that way. Soldering another 39k parallel will give you 19,5k
hahaha ooops! It's a good thing I'm not bashful asking questions. Thank you!

Quote:
Originally Posted by Stanislav View Post
the easiest way is to first cut the resistor's legs close to the solder pad on the PCB, then using a solder sucker or some braid remove the remains from the pad. That way the risk of lifting a pad or damaging a component is greatly minimised.
Thank you for the tips, it's greatly appreciated!

Quote:
Originally Posted by Mooly View Post
The voltage gain of the ACA is approximately given by dividing the value of R12 by R11. So 39,000/10,000 is 3.9

You have to remove the resistor as others have said and then replace it with a different value. No sockets

The value of R11 (10k) sets the input impedance of the ACA. Although you could lower this one instead of raising the other to increase gain (and here you could add a resistor in parallel) the lower input impedance would need to be able to be driven OK by whatever you have feeding it.
I will probably wait for my preamp since it it supposed to have a higher output voltage than my DAC, but thank you for this explanation. When I try to make sense of the schematic against the board again, I will keep this in mind.
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Old 29th September 2021, 10:32 AM   #10910
Mooly is offline Mooly  United Kingdom
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That sounds like a plan

... and if you are feeding the ACA straight from a DAC then it would almost certainly be fine with lowering the 10k. For that you could just tag another resistor across the 10k.

Two 10k's in parallel give 5k and that would increase the voltage gain by a factor of two.

Most DAC's should be fine down to values as low as 1k or even less for a resistor tagged across.

Although we don't have resistor sockets one easy option is to use something like a Veropin which were common decades ago for constructors using stripboard. They are just a pin that would solder in place of the resistor leads and allow you to attach a resistor from the top without having to access the underside of the board.

So lots of options if needed
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