Amp Camp Amp - ACA

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#2,142
Well, I managed to have a chassis and the parts to stuff the board coming from a gracious gentleman who, like me, seems to have unfinished projects around.

What SMPS bricks have ya'll been getting that do a good job and arent' junk? They need to be 19V at 2.5A or better correct? Is there a BOM of part numbers for stuff like the power switches and panel components that work on the store chassis someplace?
 
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#2,144
A cheap $7 power brick from ebay went into the trash after I first hooked it up. Too much noise, both physical and electrical. It bled noise back into the house AC system. I replaced it with an actual Dell power brick and all is right with the world. The amp draw 1A per channel in its stock configuration, so you need a PSU that will provide twice that: 2A per channel, 4A per stereo chassis. I think the Dell power bricks are 19v at 4.6A, which is perfect for a stereo chassis.

Power switches, RCAs, and speaker terminals are whatever you have or can find. Check Apex Jr.Home Page for parts, you can also find what you need at PartsExpress.com and ebay.
 
#2,146
I think I've ordered from everywhere at one point or another it seems. Digikey, mouser, parts express, parts connexion, apex, aes, Angela, edcor, and numerous others.

I just asked about a BOM for the diyaudio chassis because the holes are already there for the power switches and whatnot, and bolt length for board mounting, stuff like that where the measurements had been done already but where I'm going to need to order those parts. If I was building a chassis from scratch I'd just order the parts I wanted and make the appropriate hole size, etc...

I'll have to check our drawers of leftovers at work for some Dell supplies. We keep all the old ones from retired laptops.
 
#2,150
running too cool?

I'm in the proces of moving my aca amp to another chassis (power supply and 2 mono channels into 1 chassis). Now because I had lying a robust chassis with VERY big cooling onto the sides (can easily dissipate 100W per side) I fixed everything into that chassis. Now the power transistors hardly become luke warm at all. I have around 25 Watt of dissipation per channel (same as before). Still I think the sound has changed.

Can the chassis by itself and/or the temperature of the transistors affect the sound quality (everything else remaining the same, I did not change components, not even binding posts and wires). Or is it just my changed perception? I googled for 'sound effect of chassis' etc but did not find useful information.
 
#2,152
That's interesting. The bias is the same, so it should be the junction temperature which is much lower now (could be 30 degrees or more lower now, that's case temperature, don't know about junction temperature). I've never seen a discussion that the so-called sweet spot is also dependent on junction temperature itself. Everybody is warning against too high a temperature and shorter live-span, I never did see warnings against too low a temperature (again: assuming the same voltage and current).
 
#2,153
Let's look into what might have changed.
1) We assume you readjusted the pot after it has reached operating temperature in the new chassis.
2) The ACA pcb has a connection from signal ground to the mounting holes. We will have to see pictures to get a better idea of your p.s. and chassis grounding, but this means that now you have a connection from each signal ground to the other channel signal ground and probably also to chassis ground to earth. If this is the case (check with an ohmmeter), then try isolating the pcb mounts from their heatsinks. It has been mentioned before to make sure the RCA connectors are isolated from chassis for a similar reason.
3) If all else fails, send in pictures and a schematic of your new power supply.
 
#2,154
No no, nothing has changed electically speaking. I had the same power supply before, just moved the stuff into another chassis. Everything works fine, no hum, no hiss and probably somebody else would be pleased by now. I never did any connection to the chassis, not then, not now. Before it was a common normal powersupply (CRC) in separate enclosure with 2 ACA enclosures, nothing grounded (floating ground that is).

Now exactly the same but put everything into one chassis (no ground connection to chassis itself) but the power transistors mounted to bigger heatsinks.

So let's not digress into grounding issues (though that can be important too, but as said nothing has changed).

It just seems to sound slighty different (less good) but could be the local power plant situation or some kind of pollution from wifi or whatever (maybe a bad solder joint, but did check that of course several times). Most probable it is bad memory of subjective illusion?

Okay, let's forget about it, scientifically speaking it can't happen.
 
#2,155
The parts kits are now 90% completed, the chassis' are now ordered but will take a couple of months to be made and shipped. Quite sure we'll have them in stock in 2 months. Probably silver/black only




bloozestringer said:
As always I'm late to the party. Does anyone know if the full kits (or even the chassis) will be restocked. I have a possible lead on a silver chassis with boards and the bits for the board, but really like the looks of the red/black. If they're not gonna be restocked then I'll most likely go for the silver. Shallow, I know, but red is my favorite color 🙂
Click to expand...
 
#2,156
Variac said:
The parts kits are now 90% completed, the chassis' are now ordered but will take a couple of months to be made and shipped. Quite sure we'll have them in stock in 2 months. Probably silver/black only
Click to expand...

Thanks. I should have responded last week. I found someone here on the forum that had a pair of unbuilt silver/black chassis with most of the parts except power switch, jacks, PS, etc. Should have it this Friday! Now to build a preamp which I've never needed and match some smallish speakers as well. Kind of starting from scratch this time coming from integrated amps and large speakers trying to downsize everything for smaller living quarters.
 
#2,157
You may not need a preamp if your source has a volume control. Something like a Dragonfly DAC or other DAC/small headphone amp combo is probably is enough for most listening. Reasonably efficient speakers will help like 90+ dB efficiency, but give it a try With what you've got.
 
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#2,158
Jacks and connectors for the ACA chassis or other chassis actually

Switch
https://www.parts-express.com/parts-express-spst-automotive-round-rocker-switch-black--060-776

DC Power Jack
https://www.parts-express.com/parts-express-panel-mount-metal-dc-power-jack-25-x-55-mm--090-496

Speaker Binding Posts
https://www.parts-express.com/parts-express-gold-plated-binding-post-pair--091-1150

RCA Jacks
https://www.parts-express.com/parts-express-chassis-mount-rca-jack-pair--091-1120


If you add up all the parts costs the parts kit is cheaper than buying parts individually.
When it's available. And if it is sold separate from the chassis which it may not be
 
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#2,159
Thanks Variac! The "kit" I got from jdubs supposedly has all the resistors, caps, fets, pcb's, etc. I'll have to inventory when it gets here. I purchased it for a fair price I think from what the entire diyaudio kit would be (very comparable taking into account what the missing parts cost). I just wasn't sure if you'd have them again and didn't want to pass up an opportunity. Now to find suitable ps bricks.

None of my sources have a volume control. I'm still old school and have never ventured into streaming or beyond mid-fi at best. I'm looking into a simple RasPi2 with IQAudio dac and external drive to give it a go. But not having a pre and getting the ACA's gives me a reason to build a 9-pin Aikido 🙂
 
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