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Old 18th October 2012, 07:30 AM   #431
mc297 is offline mc297  Italy
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Default Amp Camp Complete!

I completed my Amp Camp #1 from the DiyAudio Kit! Here you have some pics.
It is stereo version case, made from scrap aluminium; the top is plexyglass.
The channels are completely separate, isolating the pcb GND from the dissipator.
The sound is AMAZING. I didn't think it would have played so well, the sound comes alive at very low levels and is full and rich at any frequencies.
I don't know if it is because of my setup (Arcam CD73, Kingrex Preamp, Klipsch RF82) but from my first listening I noticed surprisingly bass response!
I will do more listening sessions and I let you know in a few days time.
The only issue I have is a turn off thump one the loudspeakers, but I'll investigate later.
This is my first class A amp and I recommend it to everyone because it has excellent quality/cost ratio!
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Old 18th October 2012, 12:44 PM   #432
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Quote:
Originally Posted by JRKO View Post
How are everyone's builds going?

I'm getting things in place to build the amp now. Just ordering power supplies.

Seems the more advanced among us are planning modifications/alterations before some noobs may have completed the build - could we have a new thread for builders questions & completed builds, or maybe another for mods to the ACA so the learners don't get blown away?

I know how you guys like to mess with Mr 's designs and, hopefully the ACA will set more of us on that path with confidence
Thank you JRKO for your post. Fortunately, I did not suggest in my previous post to modify ACA#1. It is a special and perfect amp as designed, and thus untouchable. I am 100% for assembling it and using it exactly as recommended with the Arpeggio loudspeaker etc. After doing all this, then the DIYer may consider my suggestion to expand or diversify the use of ACA#1 in a compound setup which maybe a transient experiment or a permanent integration.
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Old 18th October 2012, 01:00 PM   #433
billyk is offline billyk  United States
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My kit arrived yesterday! Very nicely put together. Thanks to those who put in the effort to make such a fine thing available! Can't wait to get building!
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Old 18th October 2012, 07:53 PM   #434
ejfud is offline ejfud  United States
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Thought I'd share a mock up of what I'm thinking about for chassis for my ACA #1's. Never worked with aluminum so it's all wood.

Think I'll do some holes in the top and lay some old ADS mess grill underneath.
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Old 18th October 2012, 08:10 PM   #435
Zen Mod is offline Zen Mod  Serbia
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yummy .........

Q405-like
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Old 18th October 2012, 09:23 PM   #436
zany is offline zany  Australia
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Nice work ejfud, I have been looking for some
nice wood for the front panel also.
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Old 19th October 2012, 10:02 PM   #437
LBHajdu is offline LBHajdu  United States
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I tried a little experiment. I put a jumper (alligator clips) across the 10k (R11) feedback resistor shorting it out. I am not sure what the input impedance becomes (I think it goes way down), but the dac was able to drive it. The result was a lot more gain. The base output went up and the top end went down. It sounded a lot more like my SE 300B but that’s not to say I prefer it. However it’s worth trying just to see the effect. But you have to be careful to make sure your jumping out the right resistor otherwise you could blow your amp check it twice.
Leve
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Old 20th October 2012, 01:37 AM   #438
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Quote:
Originally Posted by mc297 View Post
The only issue I have is a turn off thump one the loudspeakers, but I'll investigate later.
You could use a double pole power switch and just disconnect the speaker when the amp is powerered off. There is no turn-on thump because C2 charges up slowly thus the current ramps up slowly giving C1 time to charge up.
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Old 20th October 2012, 02:06 AM   #439
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Quote:
Originally Posted by LBHajdu View Post
I tried a little experiment. I put a jumper (alligator clips) across the 10k (R11) feedback resistor shorting it out. I am not sure what the input impedance becomes (I think it goes way down), but the dac was able to drive it. The result was a lot more gain. The base output went up and the top end went down. It sounded a lot more like my SE 300B but thatís not to say I prefer it. However itís worth trying just to see the effect. But you have to be careful to make sure your jumping out the right resistor otherwise you could blow your amp check it twice.
Leve
You can come pretty close to the closed loop distortion numbers without feedback by adding a resistor in the source of Q1 and adjusting the R1-R2 / R3-R4 ratio. Search for my previous posts in this thread. Frequency response and high frequency distortion may suffer. Perhaps paralleling Q4 and reducing R9 would help in that area. I tried a bigger Q1 and the results were bad.

It seems to me that Nelson choose the R1-R2 / R3-R4 ratio to create 2nd harmonic distortion for a more pleasing sound. I'm not very good at making those kind of judgements, try it and tell me what you think.
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Old 23rd October 2012, 06:03 AM   #440
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Default Napoleon Complex

This is a great amp....sounds much bigger than its output suggests!! Operating at 25-30V, CLC (68mF-4mH-68mF), and double bias....sounds amazing!!
Thank you Nelson and the diyAudio team for putting this together!!
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