Cookie sheet build of the Amp Camp Amp by Nelson Pass

[ALL212]

I've gone through my box 'o treasures and found a pair of Amp Camp Amps that I had rebuilt a year or so ago but then updated another set of boards and just packed these away.  Inspired by the sheet build of the Bottlehead kits I designed and had cut a sheet that combined the two mono block boards into a single chassis.  The heat sinks aren't quite big enough and it gets quite hot without some fans on it. 

I found that if you preheat and then bake the aluminum on a portable room heater (no open flame please!) using a hammered finish paint you get a very nice even matte type finish on this.  A complete accident that I got this good a finish on this and I'm very pleased with it.

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[mcandmar]

I like the BH style chassis layout

I think the biggest problem with your heat is the fact the transistors are mounted to the very edge of the heatsinks, and also insulated from the heatsink by the chassis plate. Personally i would cut out the chassis plate under the heatsinks, then drill and tap holes directly into the heatsinks to mount the fets into the center of them.  It all looks doable by just rotating those boards 180 degrees and it should work fine then. I know on my F4 each mosfet sources around 10watts so they need a fairly substantial sink to carry that heat away.

How are you powering them, laptop supply's or a big chunk of iron power supply in a box?

[ALL212]

Thanks!  I didn't think of rotating those heat sinks - that might be the next build mod.

I didn't paint the chassis where the heat sinks attach and I used thermal paste in that area.  The plate heats up very evenly as do the heat sinks.  Any air flow keeps the temp reasonable.  Those heat sinks come from old Dell servers as CPU heat sinks and the holes line up perfectly with the transistors on the board - that's why I used them.  I've got a couple of very quiet fans that sit on top of the heat sinks and it works just fine. 

Power is dual laptop power supplies and Neutrik connctors.

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[JamieMcC]

Nice job, the ACA is a good sounding easy and fun project I have done a couple as well in the past and found it does a nice job of driving my HiFi Man HE-6 headphones and some Fostex full range drivers I have.

I use a Bottlehead Quickie in front and have been pleased with the results.

My two diy builds
First
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Second was a bit more headphone friendly
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[ALL212]

What kind of wood did you use?  That top one is beautiful (the other is no slouch but that top one - WOW!).

Did you have to do anything special to get headphones to run on it?  And just place a volume pot before the outputs?  Cool idea!!

And where did you get that headphone hanger? 

So many questions...so little time!!!

[SCompRacer]

I'd watercool it....

Pretty neat, what do those old CPU's do?

[ALL212]

Those old CPU's...ahh....well they ah...you know, RIAA curve, imbalance of the flux, secret arms storage in Iran, ah...you know....stuff.





Absolutely nothing - I thought they would look cool sitting on the plate.

[JamieMcC]

What kind of wood did you use?  That top one is beautiful (the other is no slouch but that top one - WOW!).

Did you have to do anything special to get headphones to run on it?  And just place a volume pot before the outputs?  Cool idea!!

And where did you get that headphone hanger? 

So many questions...so little time!!!

Top one is Zebrano wood, bottom one is out of a bamboo chopping board I picked up in a sale. The headphone out is just connected to the speaker posts. The volume pot is passive and the rca inputs connects straight to it before any amplification.
If the dac has a decent output the amp will work fine straight from it without the need for a preamp so the volume control is handy. While this ok for moderate listening with the HE-6 using the Quickie preamp in front give it a nice boost.  I have a the boards for another and was thinking about a Bottlehead Pass mash up building the Quickie in to the enclosure. Funny enough was only the other day pondering over using some cpu passive heat sinks there are some weird and wonderful looking options about.

I recently sold the second one which had some nicer specified parts compared to the first. The guy who brought it also had a pair of the ACA monoblocks and swore the better resistors and internal cabling used made a noticeable improvement compared to his Monoblock version.

I would add while they are nice amps I do prefer my Bottlehead Sex with my speakers. The HE-6 headphones on the other hand need the extra oomph the ACA brings to get them to sing. I have tried the HE6 on a handful of integrated amps ranging from 40W-150W all off of the speaker posts but found I have preferred the little 6W ACA to them all.

I make the headphone hangers they have become a bit of a self funding hobby of mine

[ALL212]

Finis

Added a couple of Nanoxia 60mm fans running at 7 volts.  These have about 6db of noise - you really can't hear them unless your ear is in the blades.   

Used Scotch clear mounting tape cut into some thin strips.  It's been on for about 6 hours - warm to the touch and the tape is holding beautifully.

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[ALL212]

Every power amp needs a matching preamp.    I did one similar to this awhile back but with no volume control, just a switcher.

Three inputs, three outputs and a volume control stuffed in between.  I have new knobs coming in but these are kinda cool!  Streetwires damping layered on to take the boing out of the plate when turning the switches.

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[Paul Birkeland]

Just an "FYI", a 100K control will have a pretty tough time driving interconnects, and often times will also struggle with the input of many solid state circuits (they tend to be 10-50K).  You'll typically find 10K-15K level controls in a passive control.   (The Amp Camp 1 has 10K input impedance, so a 5-10K passive control would be in order)

[ALL212]

Thanks Paul!

By struggle do you mean overwork the amp?  Volume issues? 

Tell me more! I'd like this thing to work as well as possible and I'm not opposed to dropping in the correct pot.

[Paul Birkeland]

The amp won't know what volume control is sitting behind it.  There are a few considerations in selecting an appropriate level control.

1. The control has to drive your cable capacitance.  You'll need to look up your cable's capacitance per foot, then consider the highest possible output impedance from your source, in combination with the highest output impedance of the control, then see how much high frequency roll off there will be from your cables.  A calculator for this can be found here: http://www.sengpielaudio.com/calculator-cable.htm  You don't want any treble attenuation from your cable, so a 200kHz or higher corner would be nice.

2.  Your control impedance must be high enough to not load your sources down.  The general rule is at least 5X source output impedance, or 10X source output impedance, depending on who you talk to.  Going higher than this does not present problems to your sources, going lower than this can load your sources down and degrade their performance.

3.  Your control in conjunction with your source must be able to drive your amplifier.  The highest output impedance of your source and passive control will be roughly the output impedance of the source plus 1/4 of the passive control impedance.  In your case, this will be over 25,000 Ohms, and not suitable for driving a 10K load. Even with a 10K level control, you're still a bit on the high side for driving a 10K load. 

This kind of analysis suggests that your amplifier would benefit from an active linestage, or a 5K passive control if your sources will permit it.

[ALL212]

Kinda what I'm hearing also??  ...volume at 95% or not much coming through.  At 100% it's not bad.

Intent is (could become was) to use this at the office on a PC running media monkey to a USB converter.  So I just set this up here at home.  USB device has a volume control on it so I bypassed the pre and ran it straight to the amp.  Plenty of volume!

Cables will all be under 3M so I'm not sure if capacitance will play a roll there.  Based on the calculator I've got to get some pretty long cables before the freq drops.  Mogami W2534 is my standard @ 97pF/m conductor to conductor.

Is there more or less a standard impedance for SS devices?  I'll probably be moving this thing around so being selective on input source is going to be iffy.  I can get a 5k but I don't want to end up with too low impedance if that is possible.

Green horn math nube here so please forgive the massive quantities of ignorance!!

[JamieMcC]

Edit just realised I mis read your post but will leave up my ramblings in case they are of anyhelp .

Having run the ACA straight off a few different dacs and also my phono amp (variable gain up to 9Vrms) I feel I have had similar experiences. FWIW I think you really need more gain.

With a dac with a output is 2.35V straight from the dac the ACA was ok for easy listening levels only (speakers sensitivity 89dB) and volume controlled via pc software at maxed out and it didn't start to come alive until I reached around 4Vrms

Putting the Quickie with PJCCS in front and 5-7vrms made a massive difference I able to easily drive the wife from the room (12'x20') and the combination I feel makes for a nice sounding set up. FWIW its also an epic and inexpensive combination for use with Hifiman HE-6 (Mainline+HD800 as my bench mark)

PS Being a low voltage system its also the first time I didn't have to take a deep breath to calm the nerves when it came time to carry out the voltage checks 

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I sold mine about a month ago and have just found a nice heatsink to build another but this time am going to build both the quickie and ACA in to a larger enclosure the same size as the Mainline so it can then sit on top.
The dacs in the pic have all now been superseded by a Leema Acoustics Elements dac. Interestingly the Leema and Eastern Electric Minimax both have preamp function but I found after a lot of ABing I preferred the Quickie in front of the ACA.