Amp Camp Amp - ACA

AX tech editor
Joined 2002
Paid Member
Unless you live in sunny California, then you do it as we did at my buddy Dana's place...

Amp Camp:
On the extreme left, "sparky", to the right of him is Papa Pass. I'm in the yellow T-shirt.
Of course you need a "land yacht" for decor

Looks very well set-up. Yes Mark I recognise you even from a distance ;-)
If we do it this side of the pond we'd have to do it indoors.
I was thinking of a (technical) school - they would have the space and facilities and stuff. Hmm.

My hat off again for a very generous NP!

jan
 
Loved Amp Camp, speakers next for newbie

That’s me and my daughter in #58 of this string. We loved amp camp! We arrived as complete beginners, learned from a great team of experienced people, and walked away with a pair of amps and the sure understanding that we are, in fact, complete beginners. Now we are looking for recommendations for a beginner-level set of speakers to build for my daughter’s dorm room. The room has painted concrete walls and ceiling. It measures 18'1" long by 11'4" wide with a 57"x57" window centered in the rear wall. The floor is covered with very low pile carpet. Furniture includes two beds, two desks, and all the stuff of two sophomore college soccer players. This turns out to be a lot of stuff. And, it is most often distributed around the room in a fashion which exemplifies the concept of entropy. A plan of the room can be found at:
http://virtualhousing.njit.edu/index.php?bid=4&fid=5&rid=01

She and her roommate listen to a wide range of music including rock, hip-hop, country and show tunes. We would like a design that: 1) takes advantage of the Amp Camp amps. 2) fits in her crowded dorm room. And, 3) can be mocked up at home and shipped in parts to school for final assembly with simple tools.

Thanks in advance for your suggestions.
 
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As about boards...
xampcamp1_pcb_500.png


Do i see a connection between one of the pins of P1 to the minus pin of output cap?

xampcamp1_sch_500.png
 
Soldersucker, I suggest you take a look at: http://www.planet10-hifi.com
Dave offer drivers, plans, flat panels for the Frugal horn and is working on new flat panel set for other of his designs.

I once had the Fonken with modified Fostex drivers from Dave. It was truely great.

I had several other speakers using bigger 8" Fostex drivers (also modified Fostex drivers) and they made my ears bleed...
So stick to the small ones but be aware that it will not be a party speakers but they can play pretty high in a small room.

Happy building to your daughter.
 
diyAudio Editor
Joined 2001
Paid Member
This article we have from Morgan Jones seems to be perfect for an easy to build speaker that's efficient and easy to drive.. and would fit in a dorm room.

http://www.diyaudio.com/forums/diyaudio-com-articles/158899-arpeggio-loudspeaker.html

np mentions in a comment on the article that it would work well with a small amp he's designing, however that was back when the article was published,
no reason to think that our amp is the same one, but I suspect it has similar needs and issues..


Here's the driver but its a slightly newer model. We should compare the specs of old and new.. :

Madisound Speaker Store
 
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This article we have from Morgan Jones seems to be perfect for an easy to build speaker that's efficient and easy to drive.. and would fit in a dorm room.

http://www.diyaudio.com/forums/diyaudio-com-articles/158899-arpeggio-loudspeaker.html

np mentions in a comment on the article that it would work well with a small amp he's designing, however that was back when the article was published,
no reason to think that our amp is the same one, but I suspect it has the same needs and issues..


Here's the driver but its a slightly newer model. We should compare the specs of old and new.. :

Madisound Speaker Store
That's good , I am very tempted to buy it . It seems also the FE206 has been emproved ...
 
A nice accessible amp for first time builders

The real neat thing about this amp that makes it unique from many other pass designs (not counting non-passLabs\FirstWatt commercial work) is the low power consumption. If compared to the F2 it uses the same gain device has the same output power and similar distortion numbers but the dissipated power goes from ~75 watts/channel to ~20watts /channel. Obviously there are some caveats, feedback Mu-Follower… but non-the less it’s an archetypal pass amp. Perhaps it should have been called the pass-eco-amp.

But is this a teaching tool or is it an amp you could listen to for a few years? I would love to know from some of the builders how it sounds into full range drivers (reviews). I would like to know if it could beat my current class-D demo board for an ADAU1592 with diy power supply to drive my Fostex full range speakers (all subjective I know).

One thing that I think would encourage more people to "jump in the pool", If the parts to populate the PCB are provided. To my everlasting shame I have purchased some PCB’s I have never populated, and will most likely never do so. However I am happy to say that I have built every kit I have ever purchased (mostly headphone amps) where the parts to populate the PCB were provided. This is what Glass Jar Audio does.

Questions?
I have a bag of 2SK170. I have measured the drain currents (Idss) of each of these using a 9v battery a resistor and a multi meter and I have attached a sticky tag to each with the current labeled. I don’t have a distortion analyzer, but I was wondering if there is a way this information could be used to pick the 2SK170 which will yield the lowest distortion in this amp. I have a guess at how to do this based on the B1 article, but I am just guessing you could measure the gate threshold voltage of the MOSFET Q1, then figure out how much voltage would be flowing across R9 and select the JFET with the Idss closest to that. Is that correct?

An upgrade path is always nice and gives people more of an encouragement. So I was doing simulations in LTspice to see how well a SJEP120R100 would work in this amp (I am just assuming it would improve things). That would make it an all JFET amp. I didn’t have a model for it so I just put a 3.5V voltage source on the source of an IRFP240 to model the lower turn-on gate voltage threshold of 0.75v – 1.25v. The amp was not happy. The solutions I could find were to connect P1 and R9 to a -3.5v voltage source (which I did not like because it needs an external supply). Or to decuple by use of a cap the JFET stage from SJEP120R100. This required many changes. I also tried putting a diode (to act as a voltage source) under the source pin of the SJEP120R100, which introduce funny harmonics, but worked, at least in simulation. Any ideas as to how this could be easily done. After all we want to keep SemiSouth sales healthy so they will keep producing power JFET for years to come.

Leve
 
I have a bag of 2SK170. I have measured the drain currents (Idss) of each of these using a 9v battery a resistor and a multi meter and I have attached a sticky tag to each with the current labeled. I don’t have a distortion analyzer, but I was wondering if there is a way this information could be used to pick the 2SK170 which will yield the lowest distortion in this amp. I have a guess at how to do this based on the B1 article, but I am just guessing you could measure the gate threshold voltage of the MOSFET Q1, then figure out how much voltage would be flowing across R9 and select the JFET with the Idss closest to that. Is that correct?

An upgrade path is always nice and gives people more of an encouragement. So I was doing simulations in LTspice to see how well a SJEP120R100 would work in this amp (I am just assuming it would improve things). That would make it an all JFET amp. I didn’t have a model for it so I just put a 3.5V voltage source on the source of an IRFP240 to model the lower turn-on gate voltage threshold of 0.75v – 1.25v. The amp was not happy. The solutions I could find were to connect P1 and R9 to a -3.5v voltage source (which I did not like because it needs an external supply). Or to decuple by use of a cap the JFET stage from SJEP120R100. This required many changes. I also tried putting a diode (to act as a voltage source) under the source pin of the SJEP120R100, which introduce funny harmonics, but worked, at least in simulation. Any ideas as to how this could be easily done. After all we want to keep SemiSouth sales healthy so they will keep producing power JFET for years to come.

Leve

Surely you haven't checked here: http://www.diyaudio.com/forums/pass-labs/190438-ss-120r085-depletion-mode-jfet-22.html