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 Post subject: My Budget ACA
PostPosted: Thu Sep 13, 2018 8:38 am 
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Location: London, ON, CA
I didn't say low budget. I also didn't want to say anything until I had the thing assembled and running.

It isn't broken in and it's only about 8 watts but so far I'd say it has good detail and great mids. A bit thin to my ears but that may change. Runs cooler than I expected but it's not 100w of Class A.

I'm one of those people who says if it ain't broke you didn't fix it hard enough; go big or go home; I can make it better; you get the idea.

Bought 2 complete kits so I can run them in parallel for a mighty 15 watts but I've only run them in stereo so far 'cos I have to borrow back my preamp with balanced connections.

mods:
- vishay z-foil resistors in the low signal points
- AN non-polar (or bi-polar if that's your thing) C2
- Nichicon audio cap for C1
- DH Labs OFH hook-up wire
- LED and resistor not connected
- power switches omitted; direct feed from power supply
- trio of steel cones for feet
I have a linear power supply here that I'll try one of these days. For now I'm just going to listen.

It was a nice simple build and I couldn't have done it without a decent soldering iron.

Here are a couple of pix:


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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 8:59 am 
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Location: Toronto, ON, CA
fjferal wrote:
Here are a couple of pix:



For what it's worth:

Your pics show all of the parts sticking very high off the boards. This increases inductance in the circuit and will also capture more noise.

I've only ever seen power resistors lifted off the boards to assist in cooling, as they get hot.

I've looked at some pics of the amp camp amp builds at DIYaudio and everything is tight to the board. I'd try to minimize the length of leads as well.

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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 10:02 am 
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Erik wrote:
fjferal wrote:
Here are a couple of pix:

Your pics show all of the parts sticking very high off the boards. This increases inductance in the circuit and will also capture more noise.


Good catch, Erik.

A couple of months ago I had an unfortunate incident with a tube power amp that involved smoke and probably tiny flames. I was too busy running for the off switch to really notice but after I calmed down and the stench of overheated electronics had dissipated I was left with serious scorch marks on the PCBs under the burned resistors. Fortunately none of the traces were damaged.

After that experience I thought I would lift all components in this build a bit just in case the gremlins attack again. It's a simple circuit and has been running trouble free for several hours now so maybe I'll go back in and drop things down.

Thanks for the tip.

BTW, I can't believe how well the heatsinks work with Keratherm. The heatsinks almost feel warmer than the transistors (my thermometer finger says around 40 deg. C.). I thought nothing would work as well as goop but clearly that's not so.

Cheers. Al


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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 10:05 am 
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Location: Markham, ON, CA
fjferal wrote:
I didn't say low budget. I also didn't want to say anything until I had the thing assembled and running.

It isn't broken in and it's only about 8 watts but so far I'd say it has good detail and great mids. A bit thin to my ears but that may change. Runs cooler than I expected but it's not 100w of Class A.

Bought 2 complete kits so I can run them in parallel for a mighty 15 watts but I've only run them in stereo so far 'cos I have to borrow back my preamp with balanced connections.

I have a linear power supply here that I'll try one of these days. For now I'm just going to listen.

It was a nice simple build and I couldn't have done it without a decent soldering iron.

Here are a couple of pix:



Can you contrast the sound as compared to your previous amp(s)? I have two of them here, Nakamichel is building me a power supply. And I am going to mono them as well. They will replace a McIntosh 754.

How many hours do you figure it took you to do them both?

Tom


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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 11:12 am 
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brownslane wrote:

Can you contrast the sound as compared to your previous amp(s)? I have two of them here, Nakamichel is building me a power supply. And I am going to mono them as well. They will replace a McIntosh 754.

How many hours do you figure it took you to do them both?

Tom


Geez, you know how to open a can of worms, Tom.

Sound
Guess I'll work backwards here, timewise. And it won't be very scientific as the rest of the gear changes, too.
My main amps are AudioNoteKits Artiste EL34 monoblocks. Dead quiet, great tonal balance, great detail and depth. Completely non-fatiguing. If it gets any better than this I probably can't afford to know about it.
The ACA is also dead quiet. I just went and turned the volume up to max (without anything playing) and can't hear a thing. That's using the Meanwell PSU. On a casual listen I'd say the frequency extremes are reduced, detail and depth almost as good. Non-fatiguing.
A secondary rig is Paradigm Active 20s. Not so quiet, not so much detail, good depth. ACA a better listening experience.
I spent a lot of years with the NAD 2400. Limited detail, limited top end, good depth, loud as you want. ACA a much better listening experience.
I've also played around with a 3886 chip-amp. Harder to name a preference there. My recollection is the chipamp played louder but might have been more fatiguing to listen to.
I'm using speakers around 90 db efficiency. The ACA doesn't play loud but it will fill a 13' X 17' room fine. Since anyone who orders the kit should know they're getting 8 watts, I can't imagine anyone will complain about lack of volume.
I have no MacIntosh experience so can't help you there. I just checked and that's a 100 watt amp so be kind in your comparisons.

Build Time
Short answer - if I did it all at once I probably have 8 hours in.
Longer answer - I have good manual skills. I've been building (and un-building) stuff all my life. I've soldered and welded before. I'm slow. I had to wait for parts to come in and I had to go over the 1.5 and 1.6 assembly manuals a few times to make sure I was doing the right thing. It looks like there are 3 monoblock options and the 1.6 manual isn't quite complete yet so you might want to wait to see which direction you want to go. I've opted for the balanced input option. I had to go back and undo a couple of things because I didn't fully understand the options before I started.

Irrelevant comment
I ran a 125 enduro kart for a few seasons in the 90s. I blame it on mid-life crisis. It was fun but I prefer analogue audio as my black hole to pour money and time into.

Good luck with your build when you get started. Al


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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 12:25 pm 
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fjferal wrote:
Erik wrote:
fjferal wrote:
Here are a couple of pix:

Your pics show all of the parts sticking very high off the boards. This increases inductance in the circuit and will also capture more noise.


Good catch, Erik.

A couple of months ago I had an unfortunate incident with a tube power amp that involved smoke and probably tiny flames. I was too busy running for the off switch to really notice but after I calmed down and the stench of overheated electronics had dissipated I was left with serious scorch marks on the PCBs under the burned resistors. Fortunately none of the traces were damaged.

After that experience I thought I would lift all components in this build a bit just in case the gremlins attack again. It's a simple circuit and has been running trouble free for several hours now so maybe I'll go back in and drop things down.

Thanks for the tip.

BTW, I can't believe how well the heatsinks work with Keratherm. The heatsinks almost feel warmer than the transistors (my thermometer finger says around 40 deg. C.). I thought nothing would work as well as goop but clearly that's not so.

Cheers. Al


The power rating of the part will determine the height off the board. For the small resistors, like 1/4 watt, 1/2 watt, it's fine if they are touching.

When those low wattage parts scorch the board, you can be sure they are trying to pass more than their rating -- in other words, something is shorted out / miss-wired.

When you see 3W or more, you'll want a bit of circulation -- so really as long as the resistors don't touch the board, you should be fine. There is still no need to raise them proud. 1.8" should do -- it's convection/air flow that works to dissipate the heat, so as long as the heat/air is not trapped below the higher wattage resistor, you're fine.

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 Post subject: Re: My Budget ACA
PostPosted: Thu Sep 13, 2018 2:14 pm 
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further thoughts (as one of the audio mags used to say)
- this is my initiation to Class A. Run it for 4-5 hours and the whole unit gets hot. It's all aluminum so I guess that makes sense. It's nothing to get worried about but if it was anything else I own I would be concerned. I'm upping my finger reading to close to 50 deg. C. Not hot enough to burn but more than I'm used to.
- the bias dropped about 150 mV during the trial. I put it back to 12V and I'm going to leave it alone. The bias adjusting pot is very sensitive. If you can get within 10 mV you're doing great.
- I hate sheet metal screws, which are used to hold the top and bottom lids in place. Brownslane, it sounds like you have the skills - maybe put rivnuts in instead.
- nice little amps. Glad I got them.

I'll report back on XLR bridging next week when I have the gear.


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 Post subject: Re: My Budget ACA
PostPosted: Fri Sep 14, 2018 5:52 pm 
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If you want a few spares, Allied Electronics has a large stock of the power transistors for a good price. I have bought from them before and shipping is very fast and relatively reasonable.
https://www.alliedelec.com/view/search? ... P240PBF%20
Time to try out a 48 volt power supply.


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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 8:49 am 
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Well I've had them running in XLR bridged mode for a couple of days now. Sound is the same to these tired old ears. Only difference I noted was that the funny buzz when starting in un-bridged stereo with the Meanwell PS is gone.
It may play louder. I didn't try to find out. My headbanger days are over.
Still like the sound. Bass could be a bit better defined.
I got out the IR thermometer and after an hour they read 49 deg. C.
Lastly, I tapped the side pieces for 8-32 machine screws and I like that a lot more for cover removal than the sheet metal screws.
To everyone building these - have fun, they're nice little amps


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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 10:34 am 
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Probably common mode power supply noise rejection is better in bridged mode.

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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 11:23 am 
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Irrelevant comment
I ran a 125 enduro kart for a few seasons in the 90s. I blame it on mid-life crisis. It was fun but I prefer analogue audio as my black hole to pour money and time into.

Good luck with your build when you get started. Al[/quote]

Thanks for the detailed response Al. Funny, back in the eighties, I raced 100CC direct drive. Was National champ for a couple of years. Then I moved onto Formula cars, ran a few different cars including F2000, Atlantic, then moved to prototypes. If you think Audio can be expensive, try wadding a Stohr into the wall; bye bye to $100,000.!!! I still have a number of cars, various race motors (Have 4 5-valve race Yamahas on the shelf, a couple of Per-ported rotaries, etc......

I am also no longer looking for volume.....it is about quality versus quantity. I am looking forward to listening to my units (once I get off my butt and build them).

Best, Tom


Last edited by brownslane on Wed Sep 19, 2018 1:16 pm, edited 1 time in total.

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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 12:23 pm 
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fjferal wrote:
Only difference I noted was that the funny buzz when starting in un-bridged stereo with the Meanwell PS is gone.

Was that buzz through the speakers or in the PS case?

I only bought the one amp. I better not hear any buzzing when it's done! :lol:

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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 12:58 pm 
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ripblade wrote:
fjferal wrote:
Only difference I noted was that the funny buzz when starting in un-bridged stereo with the Meanwell PS is gone.

Was that buzz through the speakers or in the PS case?

I only bought the one amp. I better not hear any buzzing when it's done! :lol:


It's nothing to worry about, Rip. It's less than a second, a very quiet bzzt in the speakers. It's dead quiet once up and running. Al


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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 1:17 pm 
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fjferal wrote:
ripblade wrote:
fjferal wrote:
Only difference I noted was that the funny buzz when starting in un-bridged stereo with the Meanwell PS is gone.

Was that buzz through the speakers or in the PS case?

I only bought the one amp. I better not hear any buzzing when it's done! :lol:


It's nothing to worry about, Rip. It's less than a second, a very quiet bzzt in the speakers. It's dead quiet once up and running. Al


I read somewhere that this is a common to all their builds; something about powering up the caps.....


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 Post subject: Re: My Budget ACA
PostPosted: Wed Sep 19, 2018 3:16 pm 
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fjferal wrote:
ripblade wrote:
fjferal wrote:
Only difference I noted was that the funny buzz when starting in un-bridged stereo with the Meanwell PS is gone.

Was that buzz through the speakers or in the PS case?

I only bought the one amp. I better not hear any buzzing when it's done! :lol:


It's nothing to worry about, Rip. It's less than a second, a very quiet bzzt in the speakers. It's dead quiet once up and running. Al

Oh...well that's ok then. My S150 hums quite a bit when I turn it on, in this case, a cold transformer mounted to the front panel. I leave it on 24/7 for that reason. Wouldn't want to do that with a class A amp....even a small one lol.

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