Amp Camp Pre+Headphone Amp - ACP+

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#1,982
Autodidactosaurus said:
OK, I did some "testing". First, I connected the fixed outs to the Peachtree. At roughly 12 O'clock, the volume at the speaker was 82-92db on program music, so not even 1 watt (meter closer than 1M). I chose a Van Halen 5150 track because as you all know this has a lot of continuous noise as opposed to the huge dynamic swings of an orchestra. I guess what I am saying is that Van Halen is a good surrogate for white noise ;-) in the absence of testing equipment... Next I swapped to the variable outs. I did not expect to see any difference but in fact, at "100%" output, with the same volume position on the Ptree, I was up about 6db over fixed, 88-98. So there does appear to be gain in the variable (4x?), which means the second tech was wrong.

I did try to test the fixed outputs off the Marantz with a multi-meter but was not able to get any meaningful readings. I didplug it into the wall and saw 120.5 so I know it is working and in the AC range. Readings at the RCA were anywhere between nothing and 3.3V but appeared to have no relation to the music program (I even got 2.9V when the CD was not playing), so that's garbage. At least there was no magic smoke...

Next I tried boosting the volume on the Ptree. With fixed outputs, I think I began to hear distortion about 4PM on the knob, but frankly it was also playing very loud so I did not stay there for long. Plus, Van Halen is distorted by definition. Repeating with the variable set to 100%, I heard distortion around 3PM. In any case, the peachtree definitely drives the F7 much harder than the Marantz. I'm going to guess about 6db at least but my ears are not that well trained.

So I am not sure where this leaves us, without knowing what the Marantz is actually putting out voltage-wise. I read somewhere yesterday that your typical consumer source (CD/DVD) puts out -10dbV by industry convention, which is about 0.32V. If my math is right, this would be enough to drive the F7 to about 0.3W, which would be consistent with my db SPL observations when driving my F7 at 100% output with just the Marantz with classical redbox program. I'm not sure what relation any of this has to Marantz's stated specs of 4.5V but it's clear by now to me that it does not put out anywhere near this number in actuality.

Yesterday, I did not know anything about Ohm's Law. So there's progress....

And thanks Zen for directing me to that article on system gain and attenuation. I understand much better now how this all works.

I'm thinking there is no harm in building an ACP+, right?
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I've been using an ACP+ on the 1.8 ACAs driving some decently-efficient custom MTMs to very satisfyingly loud levels for my workshop. And it sounds great. Give it a try.

--Tom
 

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#1,984
Autodidactosaurus said:
I'll probably wind up building one just for fun - if I can make time from my other hobbies. The CIY store kit looks about as plug and play as it gets for an electronics noob. Then, I'll have to build an amp to gp with it. ;-)
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Cool. The build guide 6L6 put together is your guide, but if you need more help check here or ping me. 🙂

Autodidactosaurus said:
Thomasnadeau - I like those ACA monoblocs
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I love these little ACAs. Im building another stereo one right now with my son. 🙂

--Tom
 
#1,986
I built the ACP+ from the kit, and I’m really happy to say that it works on the first try.
I had huge problems with the ACA, but it seems I learned from my mistakes there.
(I was using way too much soldering paste there and I didn’t clean it off…)

Just some funny things about the kit.
I think there were a bunch of resistors that were missing, while there were a set of capacitors that I did not end up using. I could not find any 125Ohm resistors so I replaced them with 120Ohm (would 130ohm have been better in this circuit?)
also the resistors I had at hand were 5% instead of 1%, so the values were a bit biased on the lower end of the scale though they did not spread very much.

Anyway it works and I will let it burn in, and then give it a proper test.
I’m really happy that it works on the first try!
 
#1,990
Yes it will!
Next time, if you are in doubt, when you click on the Manufacturer Part # and you see that it is in back order, you can find a replacement and compare the specs when you check the tick boxes under "Specifications"", search similar. As you plug in the parameters, it will show you similar products found including the quantity available.
 
#1,991
amandarae said:
Yes it will!
Next time, if you are in doubt, when you click on the Manufacturer Part # and you see that it is in back order, you can find a replacement and compare the specs when you check the tick boxes under "Specifications"", search similar. As you plug in the parameters, it will show you similar products found including the quantity available.
Click to expand...
Copy, thanks for the quick response!
 
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