Amp Camp Amp - ACA

Hoping that the ACA would be able to drive newly purchased speakers

I'm trying to find an amp that will match nicely with a pair of Wharfedale Diamond 225's, rated at 87db. I'm using a small 15 watt integrated amp now, that gets loud around 2/3rds volume. I'm in a small room and almost in a nearfield type set up...around 6' or so away. I'm hoping this will work because they're very deserving of better amplification. Guess I should try the voltage test.
 
I'm trying to find an amp that will match nicely with a pair of Wharfedale Diamond 225's, rated at 87db. I'm using a small 15 watt integrated amp now, that gets loud around 2/3rds volume. I'm in a small room and almost in a nearfield type set up...around 6' or so away. I'm hoping this will work because they're very deserving of better amplification. Guess I should try the voltage test.

I can just report on what I found. Finished my ACAs this weekend and ran some tests tonight with Tannoy E11 (88dB) speakers. Using a B1 as a pre, the ACAs do not drive the Tannoys to satisfactory levels on certain recordings. But when I use a Class A Headamp as a preamp - boy oh boy, the ACAs have no problem driving the Tannoys to uncomfortable levels. The headamp perhaps have too much gain here.

So yes, with a preamp with some gain, the ACAs will drive those Wharfdales just fine I think, without clipping. And they will sound fantastic. I used a TDA7297 15W amp before. The ACAs just sound so much better and creates a better soundstage and imaging.
 
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Finished my ACA build this past week. Did the final tweaks today and ran some tests tonight. Using a 28V 6A smps and Juma cap multipliers to supply 24V. Bias set to 12.5V. Did both the R15 and R12 mods. This amp sounds fantastic on the speakers tested.

Beefy heatsinks can handle the heat and the "enclosure" has enough breathing space. Here is my ACA - The Meccano version.
 

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Finished my ACA build this past week. Did the final tweaks today and ran some tests tonight. Using a 28V 6A smps and Juma cap multipliers to supply 24V. Bias set to 12.5V. Did both the R15 and R12 mods. This amp sounds fantastic on the speakers tested.

Beefy heatsinks can handle the heat and the "enclosure" has enough breathing space. Here is my ACA - The Meccano version.

Looks fantastic! Nice job, very clean and nice enclosure work.
 
Do I see a plexiglass pcb ? What components are on it ?


Yes, I use plexiglass a lot. That is how I started off with diy 2 years ago - building simple circuits using plexiglass. It is a cheap medium. Basically point-to-point with a layout close to the schematic. I did my B1 this way. See here : B1 Buffer Preamp


The ones you see on the ACA, sharing the heatsink are Juma Easy Peasy Cap Multipliers.
 

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Which output capacitor is used?
It is quite small in physical size so it must be an electrolytic capacitor?
Is it a special version made to transfer audio frequencies?
It is this component I worry most about if I am going to build the amp.
I have a LCR meter and all the electrolytic capacitors I have tested measure quite bad already at 1 kHz. The phase angle is not -90 degree anymore as it should be and at 10 kHz the phase angle has often showed someting like -60 degree caused by internal loss. But maybe I should just listen and not be so worried :)
 

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Exactly! :)

The JLH is push-pull. The topology is dictating damping factor, not the output cap.

Definitely. I also like your suggestion of the Aleph.

Meper, here's a quote from Papa (from the Son of Zen article):

"A lot of people are really concerned about capacitors, almost as many as worry about wire. Capacitor distortion is small compared to the sins committed by output transformers and the gain devices (tubes or semiconductor), but occupies a disproportionate share of audiophile angst."
 
Think it would be a good learning experience to build the AmpCamp. Then I could try different coupling caps to test if there is a difference. I guess the value of 3300 uF is not critical. An e.g. 4700 uF would probably also work. A 3300 uF foil capacitor is difficult to get. 10 x 330 uF will be physical large......and expensive. It also seems that high value and low voltage in foil capacitors is not that common.......?
 
The ACA is a wonderful sounding amp. The electrolytic capacitors in the signal path are not a big deal. The electrolytics in the power supply of any amp are indirectly in the signal path. I remember Nelson saying that the active parts ( tubes , transistors ECT) have a bigger influence on the sound than the passive parts. I used Nichicon`s from Digikey part number 493-11043ND. I encourage to build the amp. I am enjoying mine.
 
To demonstrate why I worrie about using electrolytic caps as coupling caps I found a good quality 6.8 mF / 16V cap. I made measurements using a professional LCR bridge. Parameters measured was Rs, Cs, D and Phase angle. On an ideal cap phase angle should be -90 degree, Rs = 0 and D = 0 at every frequency. I measued at 10, 100, 1k, 10k, 20k and 100k. Pictures attached of screen showing the values. At 10 and 100 Hz everything look Ok but already at 1 kHz things starts to get not so good and at 10k and 20k it gets very bad. Pure film caps measure much better. That said I have not measued a 6.8 mF film cap. But looking at the results I think you would worrie a bit also?


The real world seems to be a bit better as the measurement on the real amp shows good transfer function from 10 to 20 kHz.


The manual for the measurement equipment are 200 pages so there might something I have missed or need to learn when performing measurements like this. I am not an expert in measurement techniques.......yet :)
 

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If you are concerned, you could bypass the big 3300uF cap with a 1-2,2uF film cap. As you possess nice measurement equipment, you could measure the frequency dependent changed outcome of this new 3300||1,5uF cap, and later on, just hear the 3300uF a couple of days and then add the bypass film cap.
Bypassing caps is a highly controversial topic, so you can find many different opinions. Some prefer here caps with MKC (obsolete), just good metalized film, or PPS caps.
Linear audio has some articles about capacitors, which I enjoyed a lot. They are worth their price.

The same for the cap in the signal input. Here you can just use a film cap, or trust Papa'a decision, or, and he for sure will like it, play around it.

Kind regards,
Matthias