Modding Parasound Halo A21

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michael12345

Member
Joined 2009
Hi

I'd love to have JC-1 monoblocks, but these are big (like two of my A21), and I do not like their 35W constant power consumption..

A21 is fabulous, I compared it against two much pricier amps and still preferred A21 :)

What I would like to improve:
imaging, more transparency and lower noise floor..
and Class A bias.. now is it 10W? 15W would be likely better..

I like the sound signature, so I merely looking for 'more of the same'..
I am not so strong in electronics, so the advises here I will bring to my engineer..

thanks in advance,
--Michael
 
DCPreamp

DCPreamp

Member
Joined 2005
Like I mentioned in a previous message about Parasound amps , anything you do will likely make them sound worse and compromise their longevity. Those are fantastic amps just as they are. I know it's a DIYers nightmare, but I wouldn't do a thing to them.

Paul.
 
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captain hook

Member
Joined 2010
michael12345 said:
Hi

I'd love to have JC-1 monoblocks, but these are big (like two of my A21), and I do not like their 35W constant power consumption..

A21 is fabulous, I compared it against two much pricier amps and still preferred A21 :)

What I would like to improve:
imaging, more transparency and lower noise floor..
and Class A bias.. now is it 10W? 15W would be likely better..

I like the sound signature, so I merely looking for 'more of the same'..
I am not so strong in electronics, so the advises here I will bring to my engineer..

thanks in advance,
--Michael
Click to expand...

hello, i am an owner of halo a21 and i'd like some mods but i don't have the schematic. please help.
 
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Cjohnson6

Member
Joined 2013
Schematics are available from Parasound... Or if I can figure out how to attach them I'll do so... Else, pm me you email and I'll send them over to you that way.

To be honest , I sort of agree with Paul, although have been tempted to try other brands of feedback resistors.
 
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smatteo

Member
Joined 2004
hello Mr J.Curl

I haven't schematic, so I cannot be precise. Anyway, VFA amplifier has a resistor partition as feedback, the idea was to switch to caddoc resistors (same values). A21 has a trimmer to modify the gain.. May you suggest some ideas to us ?
Thanks in advance.
 
tvrgeek

tvrgeek

Member
Joined 2009
Best way to improve an A21 is to buy better speakers. I don't care what ones you already own, the amp is better than they are. For that matter, so are my 1200's not that I would not love to have a A21 or A23.

Don't be fooled by "class A bias". It has been shown there is a correct bias. Set it correctly and worry about something else.
 
vzaichenko

vzaichenko

R.I.P.
Joined 2010
smatteo said:
hello Mr J.Curl

I haven't schematic, so I cannot be precise. Anyway, VFA amplifier has a resistor partition as feedback, the idea was to switch to caddoc resistors (same values). A21 has a trimmer to modify the gain.. May you suggest some ideas to us ?
Thanks in advance.
Click to expand...

That's actually an interesting point. Two questions:

1) Why do you think caddoc resistors will improve the sonic qualities?
2) Why do you think feedback resistors are the ones that need to be changed?
 
john curl

john curl

Member
Joined 2003
If you want to change to A21 for the best, learn to adjust the output bias (pots) current and push it up until the heatsinks get too hot to touch, OR the overtemp protection kicks in. Of course, keep the heatsinks off the rug, and allow free air circulation. I have actually used 'Whisper' fans on occasion to minimize overheating. The smallest fan (hopefully quiet) can make a big difference. Still air is not a good heat conductor.
 
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smatteo

Member
Joined 2004
Thx for suggestion.
I don't have schematic of A21 so where is the pot ? Anyway, from your feedback seems you just increased A class working in A23 compared to A21, previous you said that has impact on device life time...
My A21 is cold, touching it, after 1h powered on. Pumping a lot my pioneer 1ex I can feel only a bit of heat. The A21 heat-sinks seem oversized to me. I may verify the correct polarization current that I can check on big white resistor close final transistors, may you tell me the correct voltage that I should read ?
Grazie :)
 
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smatteo

Member
Joined 2004
Maybe I confused A23 with A31 :) sorry for mistake.
I discovered than I cannot connect 2 devices together to unbalanced and balanced inputs and using the switch, on A21 back side, to select the source to hear.
Last question: any plan to release a DAC for Halo line to pilot directly my A21 soon?
 
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smatteo

Member
Joined 2004
Hello

Is it safe to use the switch on back A21 to switch between balanced and unbalanced source of sound signal ?
I have connected my pc and anedio d2 dac to my A21 inputs but switching the two sources ( balanced or unbalanced) on back switch of A21... I had the impression that amplifier works better when only one source is physical connect
to the inputs.
Is it only a my impression ?
Someone with A21 scheme may check?

thanks in advance.
 
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