Amp Camp Amp - ACA

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leonski66

Member
Joined 2018
Litz Wire? Does that really help RFI?
Litz is certainly useful for SOME things, but typically dealing with skin effects at very high frequencies.

I'm thinking a 3rd wire in a single ended cable....grounded ONLY at the 'send' end, not the amp. The other 2 wires are 'normal'.
Ground is a foil or braided shield. And is 'common' with the ground of the single ended, but ONLY at the one end.

I'd do power cables this way, too. I can't offhand remember the part numbers, but BELDEN makes a 14ga and a 12ga perfect and well regarded for the DIY guy.

Of course a true balanced scheme is best, with a pair of 'hot' and a 3rd ground than a shield, again foil or braid. Common mode 'stuff' is a goner.

Other ways to suppress RFI are testable. I've seen ferrite toroids used and at least one use of copper pieces at each end, that the cable passes thru.
 
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tjw59

Member
Joined 2013
leonski66 said:
Litz Wire? Does that really help RFI?
Litz is certainly useful for SOME things, but typically dealing with skin effects at very high frequencies.

Seem to recall measuring it once into a 50 ohm non inductive resistor. (it = litz wire) And it did not do so well after 850 kHz.

I expect you could make a ground bus and extend litz wire as part of an overall ground system.

If Litz wire is not real good at conducting say 1.8 mHz. You have to find out what is. Normally copper strap is the next choice on the food chain.

---

On a side note. I've driven my ACA(s) with 20 foot unbalanced cables. Nothing special about them. With no ill effect at all. Might try it before you go to all of that trouble and see if it just works.
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Neel007

Member
Joined 2013
Alan4411 said:
I know you have different boards, but on the ACA 1.6 boards Q1 D and Q3 e are on the same track so have to be the same resistance and voltage. Yours are different, so likely you have a fault with the track or soldering going to Q1 where Q3 e, R15, R3 and R4 join it?
Alan
Click to expand...

Hi Alan,

For some reason the copper / soldering broke, hence the measuring results. I had my prints produced professionally, and built the aca up from scratch, and it now runs beautifully again. Still do not understand what happened..

Thank you,
Cheers,
 
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tjw59

Member
Joined 2013
RF Grounding

leonski66 said:
My hearing fortunately gives up WELL below 850khz.

Sure. It seemed like the concern was RF Grounding. And if you are going to use Litz wire to the exclusion of any other wire, it may be a poor choice. But may have misread your intent. If say for example you or someone close by operates in the amateur band at 1.8 mHz. The litz wire under test was super inductive at that frequency. 3 inch copper strap was not.


And my system is fairly 'compact' with current setup including a preamp in the 'center' with about 6 foot runs to each power amp. Power amp has a loop I/O so I than add about an 18" jumper and I'm golden.
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Cool!
 
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dasroot

Member
Joined 2015
Hello All,


In looking for a suitable pre-amp, I came across this:
Hifime UDA38Pro DAC (ES9038Pro + SA9227)

The specs say that it's putting out 2.6vrms into 10k. As that's the input impedance for the ACA 1.6 I'm hoping this is enough. I have been doing some research and I'm unable to find a "hey, look for a preamp with this much gain to use with the ACA" type post. The learning curve for this feels like falling off a cliff a little bit.

Sorry if I missed the answer if it was in an earlier post.I'm building two of the amps and will be driving them into 8ohms, as monoblocks.
 
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RafaPolit

RafaPolit

Member
Joined 2016
Http://rafaelpolit.com
Dasroot,

If you are going with two monoblocks, the power is doubled and therefore the need for a PRE with specific gain values is less critical.

Still, a note of caution with the one you linked in your file: it has only 1.5V output with a traditional 5V power supply. You would need to fetch a 12V one to get to the 2.5, and even a 9V would get you only 2V.

2.5 is hardly any voltage gain, usual line outs are 2 ~ 2.3V. I would not recommend this as a PRE for the ACA myself.

For a similar budget as yours, I bought schiit Magni + schiit Modi. This gives you a DAC, a pre with either 6 or 16dB of gain (switchable) thanks to a nice 14V included transformer (yours apparently does not come with one).

The nice thing about this setup is that you can latter upgrade to a much better DAC, or PRE and you don't have to throw everything away. I really like it.

I recently replaced the pre with a DIY Whammy with 14dB of gain and it makes for a much nicer PRE.

So, I usually suggest to get at the very least 6dB of gain, with something around 10 ~ 15 being MY sweet spot given my setup.

With monoblocks of 24V PSUs you could get away with less, but yours is actually reducing output, depending on conditions.

Hope this helps, let us know what you find out.

Best regards,
Rafa.
 
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Puggie

Member
Joined 2004
Just an update on my ACA build. I have boards done (still need cleaning), its just the chassis manufacture that is holding me up at the moment. The end is in sight though, my aim is to play music on Christmas morning!

DSC_0365 by billbackhouse, on Flickr

and a better pic of the pcb:

DSC_0352 by billbackhouse, on Flickr

I'm building a ASKA Lender pre to sit on top of this as my pre-amp.
 
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dasroot

Member
Joined 2015
RafaPolit said:
Dasroot,

If you are going with two monoblocks, the power is doubled and therefore the need for a PRE with specific gain values is less critical.

Still, a note of caution with the one you linked in your file: it has only 1.5V output with a traditional 5V power supply. You would need to fetch a 12V one to get to the 2.5, and even a 9V would get you only 2V.

2.5 is hardly any voltage gain, usual line outs are 2 ~ 2.3V. I would not recommend this as a PRE for the ACA myself.

For a similar budget as yours, I bought schiit Magni + schiit Modi. This gives you a DAC, a pre with either 6 or 16dB of gain (switchable) thanks to a nice 14V included transformer (yours apparently does not come with one).

The nice thing about this setup is that you can latter upgrade to a much better DAC, or PRE and you don't have to throw everything away. I really like it.

I recently replaced the pre with a DIY Whammy with 14dB of gain and it makes for a much nicer PRE.

So, I usually suggest to get at the very least 6dB of gain, with something around 10 ~ 15 being MY sweet spot given my setup.

With monoblocks of 24V PSUs you could get away with less, but yours is actually reducing output, depending on conditions.

Hope this helps, let us know what you find out.

Best regards,
Rafa.
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Thank you very much for the help with this!!!!
 
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Puggie

Member
Joined 2004
6L6 said:
Place the Lender underneath the ACA, that way you don't heat up the Lender... :D
Click to expand...

The Lender will have the same width front plate as the ACA but a narrower main chassis, so the heatsinks of the ACA will be in free air effectively. I may build a small phono pre to sit under the ACA again same front face but narrower chassis to raise the ACA heatsinks off the deck 50mm to give them more breathing room.

So hopefully the ACA won't cook the whole stack!
 
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bobafet

Member
Joined 2017
TungstenAudio said:
If you are more interested in building a linear power supply than using the readily available and great-sounding 24V SMPS, then you will need to work a little harder. ;-)

Since the ACA is known to perform better with 24V power, then it would be best to choose a 200VA transformer with 2x 20V secondaries. With this option, you can build a quasi dual-mono supply. Use one of the secondary windings for each channel with its own CLC filter. Preferably 15,000 uF caps on either side of the 10 mH inductor.

This will be critical for your ACA, since you do not plan to use a regulator after the CLC filter. The ACA sounds best with minimal ripple on its power.
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Thank you for the answer. I did not find a suitable transformer nearby, but I found the power supply units of the Menville. Series RS and LRS. I will follow your advice and go to build ASA with smps. Chokes will remain for another project.
 
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Steve Luck

Member
Joined 2012
So the ACA despite being Class A isn't hugely power hungry. Could you run it from batteries provided they could deliver the amps?

I understand there are two arguments against batteries

1st in the past was to do with resistance in batteries preventing current draw when it's needed. Would lithium batteries provide all the current and no drop off?

2nd Was just the cost of batteries compared to power supplies.

Could you literally hook up a bunch of lithium batteries in series to provide 24 volts and then multiples in paralell to provide the amp hours for enough listening hours? Lithium batteries wouldn't drop voltage or current until nearly totally depleted.

Could yo do an ACA size battery pack with 6 hours listening built in?
 
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