Amp Camp Amp - ACA

[aljordan]

My personal opinion is that if ACA is not sufficient in normal single ended mode ACA is the wrong amp for the job. There are better alternatives such as M2, Aleph J, MoFo, F5 etc.


For me the ACA works very well with my upgrades such as linear PSU, caps. It would probably work well also just "as is".

What benefits does the linear PSU and caps give you over the 24 volt switching supply?

Thanks!

 

[aljordan]

After consultation with those who understand this better than I do, here's a table which helps explains the pros and cons of the various monoblock operation modes, including the effect on damping factor. This table as well as wiring diagrams for each mode will soon be added to the ACA guide.

Jason, thank you for posting this. I just want to make sure that the standard 1.6 build guide wiring (with the back stereo / mono switch and XLR input) does not account for parallel mono configuration. If I wired the amps as shown in the build guide, then I would still need the RCA Y adapter to run in parallel mode, correct?

Thanks!

 

[RafaPolit]

Yes, indeed the guide accounts (as of the current online version) only for two options:
- RCA Stereo + XLR Mono (it's the base configuration with the XLR pins routed to each RCA Input) - Back switch down
- RCA Mono (left channel fed to right channel through resistor) - Back switch up.

The Parallel config has not yet been described in detail, there's a placeholder in the guide.

Hope this helps,
Rafa.

 

[jaaptina]

Not having a separate dac I was wondering how to feed the ACA. Bought a second hand Yamaha WXC-50. It works. Connection wise it is great and easy. It streams Tidal over wifi. However it doesn't sound nice. Then I had a bright idea and connected my laptop directly to the ACA. It works and sounds even a little better! Now there is room for improvement!

First I will try this with a dac in between. Got a Chord Mojo coming [emoji41]

Mojo is here!

Even with my 4 Ohm 86bB Penaudio Cenya speakers volume is not a problem anymore at all in my 3 by 4 meters room.

Laptop > Mojo > ACA sounds really nice.

Sonore ultraRendu (streamer) > Mojo > ACA sounds really great.

 

[MEPER]

What benefits does the linear PSU and caps give you over the 24 volt switching supply?

Thanks!

I can't compare the sound between the original ACA and my version as I never built the original. But to my ears the sound is extremely good and so says my "HiFi friends".

My linear PSU is a LCLC version using a 300 VA trafo. The advantage is that such a PSU is very silent. No switching noise. Ripple is less than 1 mV. I use schottky diodes for the bridge. It is an expensive solution (around 1000 USD).

In the ACA itself I use a KEMET R75 series 160 VDC 10 uF MKP cap instead of the Silmic (input cap) and for the output cap I use two Jensen 3300 uF Audio grade caps (the two orange in the picture). They have very low ESR and very low inductance. Much lower than the cap in the kit. I have a LCR bridge so I have measured the parameters. How much this affects the sound I can't say but I am very satisfied. I think it gives me better low end because the caps has lower loss and lower impedance at low frequencies. But that is a guess only.

If some of you hit Copenhagen you can have a listening test ….then you can hear yourself.

I have no sound in the speakers during power on/off.

 

[rnjorge]

Meper


Your "simple" mods outdo any of the ACA configurations listed, don't you think?

 

[MEPER]

Meper


Your "simple" mods outdo any of the ACA configurations listed, don't you think?

I can always think that but it has to be tested against each other to make a conclusion. 6L6 og Mr. Pass should have my setup shipped to them to perform a test (but the trafo is for 230V not 110v ). Or someone with the original ACA should visit me and we could compare…..


But I can ensure you that it sounds really good…..and more than enough power for a 94 dB speaker.


I would like other to try the KEMET R75 160 VDC series as input cap….not only for the ACA but as in general. I think it is very good…...and cheap…...it is not "audio branded".....so it cost 10 times less……


Often it is the same factories which makes the "audio caps" (as the one making the normal industrial caps).....then they get another name on it......and costs 10 times as much…..

 

[Old'n'Cranky]

Meper.
Your power switch, is it for the mains into the power supply, or for the dc to the aca modules ?

 

[6L6]

Silver bearing solder -

It’s not audiophile quackery, but instead good metallurgy...

The addition of 2-3% silver in a tin/lead solder will keep any silver (silver contacts, silver plated copper wire, etc...) from being dissolved by the solder, causing corrosion and joints that go bad over time.

Euctectic solder, commonly 63/37 SnPb, is a solder where the metals will freeze (solidify) at the same time, making for a mechanically solid joint, as a non-euctectc solder will have the consistutent metals freeze at slight different times, making the joint susecptable to cracking and is at risk of movement during the (slushy) cooling down period.

A bit of copper Cu in the mix keeps the tips of soldering irons from burning up and eroding.

So, the perfect solder, in my opinion, is a euctectic mixture of tin, lead, silver, and copper, which will make smooth solid joints, not dissolve silver, esentally stop whiskering altogether, and let your soldering iron tips last longer. That is to say, a mixture that places all the metallurgical advantages in your favor.

Silver bearing being advantageous in audio (because all our most, if not all of our soldered connections are copper or tin/copper or silver/copper) is not audiophile quackery — but sadly the audiophooles have blindly latched onto the idea that Silver=Better, not understanding the chemistry behind it.

The Wiki article on solder is quite good;

Solder - Wikipedia

And whiskering is something to be avoided (and easily done by using leaded solder);

Whisker (metallurgy - Wikipedia)

Also, a simple and effective argument against lead-free solders, which in my opinion are all undesirable compared to leaded solders; Aviation is one of the very few industries that is exempt from the RoHS regulations, precisely because of whiskering problems. You don’t want that happening in an airplane!

 

[mraudioguru]

Silver bearing solder -

So, the perfect solder, in my opinion, is a euctectic mixture of tin, lead, silver, and copper, which will make smooth solid joints, not dissolve silver, esentally stop whiskering altogether, and let your soldering iron tips last longer. That is to say, a mixture that places all the metallurgical advantages in your favor.

That's why I use only Cardas Quad Eutectic solder exclusively. Best solder I've ever tried. Expensive, but well worth it, IMHO.

Cardas Solder

 

[6L6]

Yes.

 

[Natural Sound]

My boss back in the 80's gave me two 1lb. roll's of Kester solder when he closed down his shop. One is really fine and the other is "normal" diameter. I don't know the specifics off the top of my head. I've built a bunch of kits, built some DIY tube amps, repaired a ton of electronic devices and restored a bunch of old radios. Judging by how much is still on the rolls I'd say I have enough solder to last the rest of my life.

I think that having a good soldering iron and properly sized tip is equally important. I started out with Weller and didn't really like them mainly because I burned through tips like crazy. Then I switched to Unger with their iron clad tips which seemed to last forever. Ironically I think those two companies merged several years ago. I've since moved on to a nice Hakko soldering station about ten years ago. That will probably outlast me too.

I haven't tried any of the more exotic solder that's available. I'm just saying that regular generic Kester has served me well all these years. Maybe I'm just old school or cheap or both.

I did enjoy the explanation 6L6 gave of different solder types. Interesting stuff.

I received the second box of Amp Camp parts last week. I'm looking forward to that build. I plan on using a battery powered pre amp I built a few years ago and some Blumenstein Orca speakers with the Amp Camp. It should be a nice combination.

 

[MEPER]

Meper.
Your power switch, is it for the mains into the power supply, or for the dc to the aca modules ?

I have no power switch on an ACA. I in "XLR hole" I have mounted a 2-pole Neutrik Speakon connector and use that for the power. It was recommended by Neutrik as it can take some current. So ACA gets 24 VDC via this connector. I like is as simple as possible so I dropped the switch on the ACA and also the LEDs. I have a main switch on the PSUs (on the 230 VAC side). I also use one ACA chassis for just one channel as I needed the space for the output capacitors. So it is a dual mono setup with two of those PSU's.


I use all 4 speaker terminals as I use it for bi-wiring.


All wires are with PTFE insulation and mostly 1.3 mm2 (AWG 16). Some leftovers for playing with tube amps.

 

[MEPER]

I have some kilos of old stock solder so I use that until it is finished…..it will probably never be. There are different variations.....some 60/40.....some with Cu and some with Ag. It all works….but not the ALU-SOL.....it is for aluminium......it is awful ….once I used it by a mistake….apart from that I get very nice solder joints with all of the other.

 

[oc11]

Natural Sound, I think what you are saying is that you can add price in many ways to whatever it is that you are building. The real key to adding price to the project is the value you get, in terms of the music, on the other end. The solder example is a good one, I also have a fat roll of Kester (I think mine has some silver in it but I am not sure) that has lasted forever. Surely there are better quality solder rolls out there but I still have my inexhaustible Kester roll. There are better quality hook up wires available, and better quality interconnects, and better everything if you think about it. Ultimately your bankroll is the factor that will limit the scope of the project. How much do you wish to spend extra and how much you hope to get in return for the additional expense in terms of music quality are or should be the determinant factors.

For example in terms of my coming 2 mono amps ACA build, I decided to standardize all the capacitors by using Nichicon Muses (KZs for the 10 uF and 1000 uF, + KG level II for the 3300 uF). I looked to replace the 10 uF capacitors with metallic film ones, but the size of the non-electrolytic caps put a stop to that. The total cost of this upgrade, assuming it turns out to be an upgrade, was $39 at Digikey (including some spares just in case). I also bought 2 Allo CMs to deal with ripple. Judging by the datasheet one of the major features of the Chemicon 3300 uF in the kit is ripple control at the output, not much is said in the datasheet about sound purity. I got the Allos for ripple control and the Nichicons 3300 uF Kgs level II for the music. The Allo CMs cost around $31 at Amazon. The last thing I plan to do is to improve ventilation by drilling the top and bottom plates. That is primarily labor that goes for free in this case. That is about $70 extra for the project so far which I think is not too bad for my bankroll, now let's hope the music coming on the other end justifies the expense, which I think it will.

 

[Extreme_Boky]

That's why I use only Cardas Quad Eutectic solder exclusively. Best solder I've ever tried. Expensive, but well worth it, IMHO.

Cardas Solder

I use Mundorf
Specifications: 88.6%S-Sn/1.8%Cu/9.5%Ag/0.1%Au
Melting point 290C / 554F

I like to heat the solder joint with 430deg C tip, and then strictly allow it to coll down "naturally".

But, I also double-up the important PCB tracks with pure silver ribbons, or pure copper ribbons... the silver ones are sometimes annealed, sometimes not.

 

[Puggie]

290degC is a massively high temperature for soldering, that thermal shock cannot be good for things like ceramic caps and boards? At least its eutectic and has a single melting point.

 

[poseidonsvoice]

To all,

Lots of good advice here, particularly 6L6. I also use Cardas Quad Eutectic due to the ease of soldering with it and I find the costs to be a mere pittance in this hobby in all honesty (YMMV). I have smaller diameter solders (Kester) for SMD work. Flux, Chemtronics "Flux Off No Clean Plus" with KimWipes and an antistatic (ESD rated) brush to me is absolutely vital. You guys probably won't believe it but I use an Ultrasonic machine with deionized and distilled water washes to clean nearly all of my boards. I rapidly dry them both mechanically and with a heat gun to eliminate the presence of all water.

I also think that Christiansen's advice here is golden: Choosing solder: A guide for hobbyists and pros alike.

Best,
Anand.

 

[Puggie]

I'm about to undertake an ACA build off the back of this thread:

Looking for a little power amp project (spoilt for choice on here)

And I have a couple of issues:
1) No PCBs available, is there a gerber file about for a single or double sided PCB? I can etch no problem but single sided would be prefered if the SQ trade of is not significant.
2) UK component availability, RS is my goto for components and they have no stock of any of the transistors (apart from ZTX) are there UK available equivalents or am I best just using Mouser.

My chassis will be a DIY affair from a heatsink I have available. I will keep my progress posted on here.

thanks

Bill.

p.s. FWIW for soldering I like the Alpha telecore HF-850 63/37

 

[oc11]

Puggie, be patient just wait a year and sometime next summer you will be able to order ACA 1.7, PCBs, components, and cases.