DIY Power Amp for Toaster- 'Alien Boost'

smfelton · April 1, 2015 at 10:30 PM

I just wanted to start a thread to document my DIY amp for my Kemper Toaster. I've been saving to get one of the other offerings, although I did really want the option of stereo. So I was talking to an old work colleague who reminded me of previous electronics I had done, and together we put together a plan.
The amp will be 50w+50w stereo into 8Ω. I'm still looking into some options for using it mono too, but for now stereo will do as I have a stereo cab.
I've ordered all the parts and so far has come to around £50ukp i'll put more accurate pricing up later.

So today I have cut out the aluminium panel, i've gone with 2mm as it seems more than stiff enough, and is relatively easy to work. So the panel is shaped and fits perfect, and i've cut out the hole for the power switch.

So like I said I will keep updating this thread with my progress, in case anyone else with some basic soldering skills fancies giving it a go too

Kempermaniac · April 2, 2015 at 10:53 AM

Pics or it didn't happen!

smfelton · April 2, 2015 at 1:00 PM

It hasn't happened yet haha, everything is ordered hopefully will soon be here. This is where i'm at so far

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Kempermaniac · April 2, 2015 at 1:02 PM

Good looking evidence so far!

smfelton · April 2, 2015 at 7:09 PM

Todays meagre progress, unluckily no post until tuesday now will have to wait for more bits.

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greenblob · April 2, 2015 at 9:55 PM

Awesome. Not sure if you've seen my DIY poweramp build post, but I put lots of pic's in there and there is some discussion on transformers etc that you may find helpful.

The thread is HERE if you want to take a look.

smfelton · April 3, 2015 at 12:47 PM

Quote from greenblob

Awesome. Not sure if you've seen my DIY poweramp build post, but I put lots of pic's in there and there is some discussion on transformers etc that you may find helpful.

The thread is HERE if you want to take a look.

Hi yes I had seen your thread thanks, it was one of the reasons I decided against using a toroidal transformer in the end. How warm/hot does your back plate/heatsink get ? I have been wondering if I ought to go to a 3mm panel to give better heat soaking.

greenblob · April 3, 2015 at 3:24 PM

After an hour or so of playing at band volume the plate is only just warm to the touch directly where the amp chip mounts. An inch or two away the plate is room temp. I did use good quality Arctic Silver thermal paste (i had some spare from some pc stuff I was doing) between the two. My plate was 1/4" but I'm now confidant I could have gone with a thinner aluminum plate and still been ok. I believe the Ambrosi uses a thinner plate and they have no cooling issues (and their plate is painted which reduces its thermal efficiency even further).
Hope it helps.

smfelton · April 3, 2015 at 4:43 PM

Good, that's what I hoping, i've got some Artic Silver too so that is the way I was going to go, I do have a large heat sink I can bolt on too if needed.

ibanez270 · April 3, 2015 at 6:10 PM

I leave mine on through the whole gig about 4.5hrs. The back plate is about 1/8". and it barely gets warn were the chip is.

What did you get for a transformer? I went with the toroidal.

smfelton · April 4, 2015 at 2:19 PM

Thats good news.
I went for a Laminate Core Farnell Transformer, if its too noisy i'll just change it as it was cheap enough.

smfelton · April 9, 2015 at 8:44 PM

Afternoon spent soldering

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smfelton · April 9, 2015 at 8:46 PM

Enough for today, looks like it will just fit.

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ibanez270 · April 9, 2015 at 9:13 PM

Looking good. How are you going to mount the board? Did you measure the voltage after the rectifier?

smfelton · April 9, 2015 at 9:23 PM

I've not connected it up yet, was waiting for an old colleague to double check the caps etc before I power it up. The board will be mounted at right angles with the amp chips bolted through the plate. I'm going to make two plastic brackets to support the board, have decided with what yet, will raid the shed tomorrow and see what I've hoarded.

Zapman · April 10, 2015 at 12:36 AM

Lookin great Shane, nice work so far!!

greenblob · April 10, 2015 at 4:29 AM

Nice! It looks like everything will fit beautifully. A tidy looking build so far.

What is the relay above the speaker out terminals for?

Whats the specs on the transformer you used? As you know I did a lot of research to try and find an optimal transformer for mono use and would be interested see what direction you've gone in your build.

I believe this is the first stereo DIY Kempamp build.. Looking forward to seeing some more updates!

smfelton · April 10, 2015 at 8:46 PM

Assembly started, not rushing it though, hopefully first test will be tomorrow.

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Front panel done, not perfect but it is only the first prototype.

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ibanez270 · April 10, 2015 at 9:00 PM

Looking real good.

smfelton · April 11, 2015 at 5:06 PM

It's finished !!!!!

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Had a little bit of fun getting it too fit, but it's tested and works, might be a little bit load though haha, got to 1.4 on Kemper master volume and the dog ran out of the house and I was requested to TURN IT DOWN !!!!!

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