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 Post subject: Amp Camp Amp
PostPosted: January 31st, 2021, 9:12 am 
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Joined: February 28th, 2013, 1:19 pm
Posts: 567
To all,

I just finished building one of these amps for my desktop near-field system in the basement. If you have not heard of it, it is a design for a simple single-ended MOSFET amplifier by Nelson Pass that can be done in a day. Looks alot like an Aleph from a circuit standpoint. It is available as a kit from DiyAudio.com, for around $350, which includes a nice chassis. Power supply is a 20V/5A switcher from MeanWell. You can read all about it on DiyAudio.com. I built it stock, with the exception of an upgrade of the output capacitor from the stock 3300uF/50V CDC industrial snap-in electrolytic, to a Nichicon KG(M) Gold electrolytic of the same value, about $4.50/channel upgrade, available from Mouser. It is a 8W/ch ampifier for 8 ohm loads, and 5W for 4 ohm loads. For a desktop amp is probably does not need to be very much.

The sound, as it breaks in, is very nice for a near field setup. I have had a much more powerful tube/MOSFET hybrid amp and a pair of 2A3 SET monoblocks in the same system (powering a pair of Aria 5R MTM 4ohm monitors). Compared with both of these amps, it produces a much more expansive soundstage and a more warmth to the sound that even the 2A3 amps provided. No doubt a bit of second order distortion in the profile, it does sound like a single-ended tube amp. Detail is nice, can really hear instruments and their locations. Instrument colors are spot on. Listening to a recording of Rachmananoff Symphony No. 4 with the Philadelphia Orchestra under direction of Yannick Nezet-Seguin, at 24/96 recording on Qobuz, and is beautifully full bodied, expansive and engaging.

It is not a headphone amplifier, there is no volume control (though some have modified the design to add both). I am driving the amplifier using my computer as a source through a Topping D50s DAC and companion A50s headphone amp/preamp (using the P50 linear power supply). Plan on having something that can provide addition gain, the amp only has 14dB of gain, so needs 3 to 4 volts at the input for full output.

I have another on order (have the parts kit already, waiting on the chassis), so I can hear what it does as mono amplifiers. There is a lot of flexibility, as a mono amp you can run it with balanced input, bridged (for more power at 8ohm and 16ohm) or parallel (for more power at 4ohm loads).

Anyway, I am really pleased so far with how it sounds. It is a relatively cheap project if you have a need or purpose for it, or just want to have some fun building something that does not take a lot of planning or effort (an instant gratification project). It is obviously not an end-all amplifier, when I build my second one, I will try it in my main system just out of interest. But if you want to put together a nice little system for a bedroom, computer workstation, or a small little hideaway, it could fit the bill. Obviously, a companion project would be a pair of nice high efficiency single driver full range speakers if you were setting up a system.

David


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 5:28 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 429
I read the original article by Nelson Pass where the cost per channel was $14.25 plus heatsinks and power supply. Even with needing to buy a couple of LSK170s, there seems to be a considerable markup to $350.

https://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca.html

I've sometimes wondered if a simple roll of aluminum flashing would be adequate for a heatsink. Just let it unroll a bit so that air could pass through it.

https://www.lowes.com/pd/Union-Corrugating-14-in-x-10-ft-Aluminum-Roll-Flashing/3499742

I do have everything I need to build an F6 but I'm proceeding on the Roscoe (6V6 - 6550) first. It gets too hot in the afternoon at my workbench (85 F) so progress is slow. Mornings are when we get things done here during summer. I'm also about to start on the bucket subs.

https://www.transcendentsound.com/bucket-sub.html

ray


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 6:31 pm 
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Joined: February 28th, 2013, 1:19 pm
Posts: 567
Ray,

I think the boards may cost $15, but there is a lot more than you think for the $350. You get a nice chassis from Italy with robust heatsinks, a nice 10mm thick front panel, a high quality switching power supply for the price you would pay from Mouser, etc., as well all the parts you otherwise would have to source, packaged up in a way that makes it an easy project for the neophyte builder. That is really the purpose of the project, to get new builders started. This won't be the last amp they will build.

Also, do not underestimate the amount of heat dissipation there is from a Class A MOSFET amplifier. You really need to have good heatsinks. That little 8W/ch Amp Camp Amp gets mighty warm. I can keep my hand on it for a while, but it does put out the heat. My 20W/ch Class A tube/MOSFET hybrid amp uses a well heatsinked 4U chassis, and it gets pretty warm as well. You can get by with wimpy heatsinks for a Class AB amp, but you are dissipating alot of power all the time in Class A, and the device temperature can be pretty high. As with so many components, the longevity of the parts is heavily dependent on temperature. Aluminum flashing is not going to cut it unless you are inventive on making a decent multi-fin heatsink out of it. You still need to have thermal mass at the device to sink the heat quickly and transfer it to your dissipative fins.

Hope you get that soldering iron warmed up and start sniffing the rosin fumes again, on Roscoe's project or anything else that crosses your mind.

David


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 7:02 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 429
My first project was a Son of Zen and as somebody said, 'you could roast a chicken in there'.

https://www.passdiy.com/project/amplifiers/son-of-zen

Image

There were three parts - the above was for the output. It barely got hot at all.

Image

The tower for the 8 ohm resistors (3 x 25 ohm 50 watts). The chicken would have gone in here if it could have been stuffed in.

Image

Power supply with the resistor tower on top.

It sounded pretty good but was just too unwieldy and heavy so I eventually dismantled it. I will be reusing the heatsinks in my F6 build.

After this, I moved on to tubes.

ray


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 7:11 pm 
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Joined: February 28th, 2013, 1:19 pm
Posts: 567
Ray,

Impressive. I should just shut up!

I think the F6 should be nice and cool!

David


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 7:22 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 429
My wife just shook her head and remained silent.

I was just thinking about a flat plate heatsink with the flashing, particularly for inexpensive experimenting.

https://www.heatsinkcalculator.com/free-resources/flat-plate-heat-sink-calculator.html

ray


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 Post subject: Re: Amp Camp Amp
PostPosted: January 31st, 2021, 7:40 pm 
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Joined: February 28th, 2013, 1:19 pm
Posts: 567
Ray,

Nice calculator. I was just trying to model a 300mm x 300mm x 2.5mm plate, but have to look up info on the thermal interface material and junction to case thermal resistance.

Obviously, vertical orientation is the the best, to get good convective air flow on both sides of the plate.

David


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