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Amp Camp Amp - ACA
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Old 16th February 2019, 04:26 AM   #7141
laserscrape is offline laserscrape
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Join Date: Dec 2017
Originally Posted by TungstenAudio View Post

The addition of R15 will increase the quiescent current through Q1 and Q2. This gives a performance boost for both 19V and 24V power. Remember that the source of Q4 (maybe BF862) runs at the gate voltage necessary to turn on Q1, or about 3.5 Volts. So Q4 does not have the full power supply voltage across it.

The Chinese kit parts are cheap, but they may or may not be original or good. You get what you pay for. You might be better off buying the bare boards, which are also available, and get the rest of the components from reliable suppliers. But then you might as well buy the bare boards from the diyAudio store and get the genuine article.
ah ok, lucky you mentioned this before a transformer was bought,
still not sure about using a lm338 supply or CRC supply for it.

you can buy certain things from china ebay sellers that are really good value, examples were presoldered DIP OPA1622 and TPS7A regulators, this will be a real test.
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Old 16th February 2019, 02:12 PM   #7142
Alan4411 is offline Alan4411  Wales
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Whats visible is a different layout with awkward placement power transistor, BC550 replaced with ztx450 and 2sk170 reaplced with k246 mosfet and a diode added.
I guess they replaced rare transistors with common ones with the intention of producing cheaper kits without fakes... edit:that mosfet isnt common at all

all other components are the same so the original transistor might drop in.

as for capacitors the nichicons look authentic in the pic at least.[/QUOTE]

I used a pair of those kits for my first ACA build, (The DiyStore kits were out of stock for ages.) and I had that itch...
I ditched all the parts except for the trim pots and MosFets, they tested fine and are still working.

Everything else I replaced. The ZTX450s are easy to find and cheap, the 2SK170s were available in the UK at the time too. Just be aware if you do use these devices in the 'copy' kit you have to reverse them both and not follow the screen print on the boards. You can just see that on the picture.

The limitations are the size of output capacitor you can fit on the board, they are much smaller than the official ACA boards, and no space for 2.2K R15 as stated. You need to fit it to the rear which is easy enough.

They perform identically to my proper ACA 1.6 kits.

The last picture shows the £5 Chinese 24 volt SMPS I used / use.
Cheaper than all the parts to build a linear supply and again has worked flawlessly. I even tried a 10,000uF cap across it, but found it just as good without...

If you do go the linear route, don't forget each board needs 1.5 amps (class A) so build at least a 4 or 5 amp supply.
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Last edited by Variac; 20th February 2019 at 07:01 AM. Reason: 1.5 amps...
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Old 17th February 2019, 05:57 AM   #7143
laserscrape is offline laserscrape
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amazing how small it is

I see you included the diode even with original transistors, any ideas what they're for?

Im still sure how to approach the build, at first it looked like a cheap and simple amp aimed at beginners but really if power isnt a big concern then this amp is as good (if not better) than most other amps youll find. Might aswell use quality parts and a really good supply.
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Old 18th February 2019, 05:51 PM   #7144
fmalloy is offline fmalloy  United States
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Join Date: Nov 2018
Finally did it! I figure as a degreed EE if I can't build this I may as well just hang it up and quit my job in shame. I had almost no experience soldering but I was surprised how well it all turned out. I had a little trouble soldering the barrel-type connections like the power jack and RCA connectors; I was concerned about them falling out, and it took a few tries. Tabs are much easier. I also had difficulty mounting the LEDs, the heat shrink method didn't do it for me, but Gorilla glue did. I also realize I should have used heavier gauge wire for the power to the boards.

I feel like a young kid again, listening to this incredible class-A sound from something I put together. I connected it to my TV's fixed-level audio out, and the TV audio input is fed by an AppleTV streaming music. As such I didn't have a gain control (!) and it's just a line-level signal but surprisingly I got a decent room-filling volume on my efficient 99dB Klipsch Heresy speakers.

My next step will be to pull the jumpers on my NAD integrated amp and use that as a preamp and get proper preamplification and a volume control.

Thanks SO much to Nelson Pass and everyone here for making me feel young and happy!

Link to photos with a couple of videos:

Amp build - fmalloy

Last edited by fmalloy; 18th February 2019 at 06:03 PM.
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Old 18th February 2019, 06:09 PM   #7145
Mazeppa is offline Mazeppa  United States
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Amp Camp Amp - ACA
Glad to hear of your success.
ACA's are just good fun all around.

Be forewarned; The Pass Class A sound will get to you. It wasn't long after my ACA's went into service that I was starting my 2nd build, an Aleph J and planning a 3rd, the M2x.
I am in no hurry, though, these ACA's in parallel mono sound good enough that I could stay here, but being one of the GreedyBoyz I wanted more.....
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Old 19th February 2019, 09:18 PM   #7146
jjacek is offline jjacek  Sweden
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Default finished

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Old 22nd February 2019, 08:56 PM   #7147
udailey is offline udailey  United States
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My friend is a guitarist in our church band. Built my first guitar amp for my step mom and he loved the sound, especially the smoothness. So I figured I will build one for him, but with an ACA.
I'll probably have a few questions in the next week or so.
If I remove, and leave open, the 2k2 resistor I will have a bias current around 1 amp, right? Heatsink is 8x3x3 so it might handle 1.5 but if not I'd like the option of dialing down.
If I replace the 5k pot with a panel mount pot and allow him to dial it how he likes in an effort to change distortion.. will there be any downside to the longevity of the amp? This might not matter a lot as I think I will build an H2 to insert distortion but I wondered if this might be an option. I can add a series resistor to keep voltage from hitting extremes.
Thanks guys and gals
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com

Last edited by udailey; 22nd February 2019 at 08:59 PM.
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Old 23rd February 2019, 01:59 AM   #7148
6L6 is offline 6L6  United States
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Amp Camp Amp - ACA
udailey - Get a guitar speaker, wire up a guitar jack to RCA cable, and attach the output of the ACA to that speaker and see what it sounds like. Might be totally awesome, but you'll want to try it first and make sure it sounds the way you want.
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Old 23rd February 2019, 01:57 PM   #7149
propitious is offline propitious  United States
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Amp Camp Amp - ACA
Hi U-man, great to hear from you. I built a ACA from the first kit series offered, which just had a HeatsinkUSA 8.46 heatsink, which is 8.46" x 1.3" by 3' tall. It was fine for the earlier 1 amp bias current, but I would not want to put much more heat through it. Your heatsink should take the higher bias and 24 VDC. I took that ACA to a friend, and we rigged up a temporary output from one of his guitar amp preamp sections (I do not remember which one). He tried it on several different guitars and even a bass guitar. We were very impressed. It was more smooth, clear and detailed than his other solid state amps. It let through what was sent to it (more undistorted distortion, or is that an oxymoron?) We decided a necessary component would be a good tube preamp that would allow you to overdrive it to get the desired distortion and not try to overdrive the ACA. Zen Mod knows a lot about that and might chime in here with ideas.The best sounding guitar speaker we tried it on was the one that came with the Orange Tiny Terror.
Give me a PM or call me some time and we will talk more about it.
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Old 23rd February 2019, 03:09 PM   #7150
LongRoad is offline LongRoad  Russian Federation
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Tell me which transistors are better for the amplifier, who has experience?
My head is spinning
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