Amp Camp Amp - ACA

[gideon]

Originally Posted by Loudthud

It looks like all the transistors are functioning correctly. The problem must be that one or more of R1, R2, R3, R4 are not the correct value, or current is flowing through C1 to the speaker.

The voltage from the Drain of Q1 to the plus side of C1 should be 0.366V and 0.253V from the plus side of C1 to the Source of Q2. A low voltage on one side points to which side has too low a resistance. If the sum of the voltages is not 0.62V, some current is flowing in C1 or somewhere else.

With no signal, the DC voltage at the speaker (-Out on the schematic) should be very close to zero volts. Verify that the polarity of the capacitor is correct. I made a mistake on one of my builds. I connected the +Out to +19V instead of ground.

Note that it's a good idea to mount transistors low on the heatsink for best cooling efficiency. The top of a heat sink is usually several degrees warmer. I suggest about 1/3 the length from the bottom.

Ok Some more findings and an action plan:
(please let me know if it's more appropriate to start a new thread around this, don't mean to hijack).

- Seems like its a faulty R3 or R4 on the hot block (Loudthud, you nailed it!!
The resistance across both of them sum up to be 0.9R where it should be around 1.36R (0.68x2) as it is on the good block.

Action plan is to just buy a new set of R1-R4 resistors and replace in both, probably not the white brick kinds

Measurements from what Loudthud suggested:

Running temperature:

On the hot block: C1+ to Q1 Drain = 0.348v / -0.254v
On the cooler block: C1+ to Q1 Darin = 0.366v / -0.22v

While warming up:

On the hot block: C1+ to Q1 Drain = 0.35v / -0.22v
On the cooler block: C1+ to Q1 Darin = 0.40v / -0.18v

With no signal:

On the hot block: -OUT = 0.01v
On the cooler block: -OUT = 0.09v

Thanks again, and I will report back with results.. until now the amp sounds amazing!

Gideon

[mikegranger]

Gideon,

These resistors are in parallel, meaning the total of their resistance is half the value of one (0.34 ohms). If you hand wired the board, perhaps you hooked them in series instead of in parallel.

[gideon]

Originally Posted by mikegranger

Gideon,

These resistors are in parallel, meaning the total of their resistance is half the value of one (0.34 ohms). If you hand wired the board, perhaps you hooked them in series instead of in parallel.

you have a point there!

I guess I was jumping to quickly to conclusion after finding the first anomaly. I'll try to replace them and see if this solves the problem, hopefully I can do it today before I go to my friend and play the amp through his mysterious new speakers (fei-le full rangers).

[Eric]

Some time ago, my daughter was working on her "circuits" unit in science class. She was telling me about the fun she and her friends had making light bulbs light up, etc with a small battery circuit. So, I got out my my Snap Circuits kit and we played around for the afternoon making all kinds of circuits. The one that she thought was the most fun was the radio that we built.

Seeing all of the fun she had building some circuits, I spent the next few weeks gathering all of the parts necessary for an Amp Camp Amp and and a small pair of speakers. I also spent a few days cutting and finishing a nice piece of hard maple for the chassis and drilling holes (I used the 2U sinks from the DIYAudio store) and routing holes in the speaker cabinets.

Fast forward a few weeks to her birthday. She was thrilled to unwrap a box full of little electronic parts and pieces. This past weekend, we spent the afternoon putting it all together. She bent all of the resistor legs, populated both boards, and helped me solder everything in place. After each part was in place, she clipped the legs off. We mounted the boards to the sinks and then attached the sinks to the wooden pieces for the chassis. We did a quick adjust to the pot (man, that is a REALLY sensitive adjustment) and then moved on to the speakers. I got her a pair of Mark Audio CHR-70 drivers (thanks to Planet10 for the suggestion!) and we put them in the Parts Express 0.25 cu ft cabinets. Finally, it was time for a listen. What a GREAT sounding little system for her iPod and MP3 player!

It's too bad we couldn't travel to California for Amp Camp to be with everyone, especially the master himself! But we brought a little bit of amp camp to our house for my daughter's birthday! Thank you, Nelson, for sharing another great design with all of us!

We had a great time working together and she has the satisfaction of knowing that she helped build her new stereo. It is the perfect size and power for her bedroom. I told her to be sure to keep an eye on it - I think it sounds so nice that I might just take it to work with me

Pics are below.

[6L6]

I think we might have a contender for

BEST POST OF THE YEAR!!

What a fantastic project!!

[Zen Mod]

kiss for both little builders/helpers

I also have one and I must admit ( proudly ) - she's smarter than I am

[bcmbob]

Looks like you have what you need, but I bet they would get a kick out of doing some Foam Core Cornu horns - Just for fun.

Great Story!!

[Eric]

Thanks for the kind comments, guys! We really had a great time working on it. It's kinda interesting that my daughter's first stereo features a Class-A amplifier designed by Nelson Pass.

Cool speaker design, Bob!

[vdi_nenna]

That's just awesome! Nice job!

[bcmbob]

xrk971 and Cal are leading the threads on foam core, but even I get a bit of a child like thrill playing with all the gooey glue.