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Amplifiers Which Test Well, Under $1,000 USD

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Knielsen,

The improvements are really remarkable, but from what I see on the photos they are not just related to ground re-wiring.

There seem to be several parts that were changed/upgraded.

I could locate the Acurus 250 schematic here, so it would be interesting to list what you did change, if possible.

The comments by Kaj about the surprising results by using thinner wire for the power lines also deserve an observation.
 

amirm

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The comments by Kaj about the surprising results by using thinner wire for the power lines also deserve an observation.
The extra sidebands are mains harmonics:


You can see their frequencies are multiples of 50 Hz. So grounding did change that. That may be an interaction between his measurement gear and the device though.
 
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But what about the thinner wire? Less induction, perhaps?

It would have been interesting to run other measurements at other frequencies before the parts change to see the possible effect too.
 

DDF

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I was getting quite different background noise measurements of the RTX6001 doing nothing but changing the power cord to the RTX.
In this particular set up, this was best I could get:
https://www.audiosciencereview.com/...udio-measurement-gear.113/page-12#post-153972

The Chintzier power cord had noise levels elevated by ~ 5-10 dB from this. I'm not aware why the two were different, both cords were electrically and mechanically 100% sound. The better one was heavier gauge and had a foil shield.
 
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But what about the thinner wire? Less induction, perhaps?
exactly our thoughts when we measured.. Induction through the power cable.
It seems that the internal construction of an amplifier is highly sensitive to whether the the induction of the cable courses noise or not.
 
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Knielsen,

The improvements are really remarkable, but from what I see on the photos they are not just related to ground re-wiring.

There seem to be several parts that were changed/upgraded.

I could locate the Acurus 250 schematic here, so it would be interesting to list what you did change, if possible.

The comments by Kaj about the surprising results by using thinner wire for the power lines also deserve an observation.
The ground in Acurus is quite messy. Input ground goes to speaker gnd and then to PSU. In this way, there is alot of noise picked up by the input. This is fixed by following the new ground schematic.
Partlist for my amplifier:
- Dale RN60D/70D resistors
- Mills 5w resisters replace the emitterresistors
- Nichicon Muse ES at input and feedback circuit
- Elma Silmic ll (postfuse mod// from Aragon 4004 schematic)
- All bypass caps are Panasonic ECWF(a)
- All micacaps replaced with Charcroft Silver Audio mica
- Zanerdiode D3/6 is coupled with 0.47 cap in parallel for lower noise
- Vishay Precision Group 1k multiturn folie potentiometer
- PSU: Kemet 13.000uf/100V x8, Panasonic ERG 12k ohm in parallel to reach 6 watt, 6kohm. Bridges are HexFred 1200v 55a x2
- All internal wire changed to 10awg
- Input wire changed to sheildtype grounded at chassis

There are other things, but have to open the lid on the amplifier.. can't remember :)
 

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maty

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It should be mentioned that under normal operation the amplifier produces a noise near the boundaries of our testinggear.. that's below 0.01%THD+N!! :D
 
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One thing....

I did ask Kaj to do the starground mod to other amplifiers according to the schematic before publishing the results. It would be fair to see what happens in other applications. Is it the same???
 

Daverz

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Some amplifier measurements by BHK labs here:

https://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=17&Itemid=141

I've heard the Parasound A23 and the Odyssey Khartago often mentioned as affordable class AB amps, but the measurements are a bit disappointing:

https://www.soundstagenetwork.com/i...er&catid=97:amplifier-measurements&Itemid=154

https://www.soundstagenetwork.com/measurements/odyssey_khartago/

Though the Khartago may have had some updates since 2003 and Parasound now has an A23+.
 

Matias

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Matias

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GrimSurfer

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I suffer from a terrible electrical mains in my house. After research I managed to drastically reduce the interference, noise and DC, but I still noticed the sound improvement after 8 pm on weeknight. And the weekend too.

Last Friday I changed the old refrigerator and it improved the sound! I suppose the engine had to inject DC. And not little. It could have been chance, for the weekend, so I had to wait until Monday. Verified, the amplifier heats up less (EI transformer side) and sounds better. In the main system, the same.
Completed a full kitchen renovation two years ago in my 50 YO home. I subbed out the electrical to a respected local commercial contractor.

When laying out their plan, the electrician indicated that new code requirements are to put the fridge on its own dedicated circuit. Microwave too (though I don't use one of these).

Apparently, the boards and power supplies in many new fridges don't share well with others. I suspect that there are times when the current draw momentarily approaches what's available (15 or 20A but depending on what else is on the circuit, the available load could be far less).

Any how, I also had him run a new dedicated line for my system. It was a straight run, so it took less than 30 mins and $100. Frankly, I didn't hear the difference but it's not like I'm running 1000W power amps either.

Just thought the anecdote about new code requirements and fridges connected to Maty's post in a non audio (and perhaps even an audio) way.
 

maty

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It was an old refrigerator that had been repaired. I suspect that something went wrong during the repair because I believe that before, with the same refrigerator, my main equipment sounded very good.

That is why I bought a second-hand amplifier for my second system, to experiment. Days ago I retouched it and I got even better sound. It sounds so good my second system that days ago I decided that I would not build a DIY or buy a new amplifier. The same with the speakers (KEF Q100 5.25" coaxial), with a new crossover designed by Zvu.

I enjoy as never before so better not to touch what so many joys is giving me!
 
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I was surprised and disappointed some weeks ago, with my Breeze Audio TPA3116 amplifier, when it started lowering levels by itself when some level peaks happened.

The weird thing is that I had been using it for several months, and behavior was quite normal, with no such ALC-like events.

Has anyone experienced anything like this with an amp using the TPA3116 chip?
 
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