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FSHZ:42 6th December 2008 11:53 PM

Need advice for upgrading an Acurus DIA-100 amp
 
Hello,

I would like to mod/tweak my Acurus DIA-100 intergrated amplifier. I have the schematics for the amp, but not really sure what to do to it. Anyone have any advice to help me with this mod?

Thanks,
FSHZ:42

KevinLee 7th December 2008 12:08 AM

I always start in the power supply. Usually larger/better or additional power supply filter caps sometimes paralled with a film cap. Usually replace bridge with discreet fast/soft diodes. A little more bias is sometimes fun to play with, swapping out the pots for multi turn units helps stop the bias drift. Do this then give it a burn in and listen.

FSHZ:42 7th December 2008 12:38 AM

Quote:

Originally posted by KevinLee
I always start in the power supply. Usually larger/better or additional power supply filter caps sometimes paralled with a film cap. Usually replace bridge with discreet fast/soft diodes. A little more bias is sometimes fun to play with, swapping out the pots for multi turn units helps stop the bias drift. Do this then give it a burn in and listen.

I have the schematics, so I will try and upload it along with a photo of the inside of the amp. I can follow the schematics as to what I would need to do to any of the circuits. So if you would suggest to swap out resistors, caps, diodes,etc, I can do that.

Thanks Again!

FSHZ:42 7th December 2008 12:57 AM

Here is the link for the schematics:

http://s173.photobucket.com/albums/w...=1228614834766

FSHZ:42 7th December 2008 01:02 AM

Here is the link for the Power Supply:

http://s173.photobucket.com/albums/w...=1228615264086

Andersonix 17th January 2009 02:10 AM

2 Attachment(s)
Quote:

Originally posted by KevinLee
I always start in the power supply. Usually larger/better or additional power supply filter caps sometimes paralled with a film cap. Usually replace bridge with discreet fast/soft diodes. A little more bias is sometimes fun to play with, swapping out the pots for multi turn units helps stop the bias drift. Do this then give it a burn in and listen.
I have an Acurus 100X3 (specs 100W @ 8R, 125W @ 4R) that appears to have a similar circuit, and I would also like to beef it up, so I hope my questions will be relevant also to the DIA-100. I have not yet contacted Klipsch for my schematic. My goal is to improve the 4 Ohm power (and make the amp sound its best, obviously!).

1. I noticed the circuit has one 1k pot. Is this to adjust the bias? I don't really understand how to read a circuit. It idles stone cold (The hs is pretty much at ambient temp at idle), which I'm ASSUMING is an indication that the bias is set on the low side. How do I increase the bias?

2. Can we have a recommendation for exactly which diodes to use? I heard that 'soft recovery' was more important than 'fast recovery.' The cheapskate in me wants to just put some caps and resistors across the diodes in the existing bridge.

3. My amp has a 23mF ps cap from plus to ground and one from ground to minus, and what appears to be a 300-350VA torriodal transformer that I measured putting out 93VCT. I see that Apex Jr has a 600VA torroid that is 90VCT and 15mF caps for $3, which I'm thinking about getting and making a CRCC with 0.1-0.2R.

4. I will try to find replacements for all the on-board electrolytic caps. From looking at the schematic of the DIA-100, are there any that could benefit from a different type, increased value, or film by-pass cap?

5. Before the power switch there's a thermistor USS 2R515 (rating says 15A Imax, 2.5 Ohm at 25C, but I measured 4 Ohms) which hardly even gets warm. Isn't this a waste? It does get much warmer while playing loud.

Thanks!

PS. Nicked a pic from ebay.

FSHZ:42 17th January 2009 03:18 AM

Hi Tosh, I recently upgraded my Acurus DIA-100 amp with the following changes: First was to remove caps C-1(.1uf) & C-2(10uf) on the signal path of each board, and replaced them with 1uF Sonicap Platinum on each board. Next was to add a Black Gate WK 220uf cap along with a 1uf Sonicap Platinum (cut-lead type) in parallel with each of the Power Caps marked as C-1 & C-2 located on the power supply schematics. Last mod was replacing the bridge rectifier, making a new one using Fairchild Stealth diodes (30amp/600v). Only problem was that the 1uF Sonicap Platinumís are fairly large caps, so the cap that went on the board closest to the A/C wires going to the on/off switch was causing a slight humming noise, and also created some A/C leakage measuring 60+ mv read at the left speaker output. To correct this, I wrapped copper foil (16awg) around the A/C wires to create a shielding effect, which I then grounded to the chassis. After the mod was complete, I fired it up, and all I can say is WOW! It should be noted that the sonicap platinumís take some time to burn in, say around 300 hours. If your bankroll is a little shallow for this upgrade, you may want to try the Sonicap Gen I's. Also used Cardas Quad-Eutectic solder. Hope this helps out.

Emile

carlmart 17th January 2009 10:30 AM

Quote:

I have an Acurus 100X3 (specs 100W @ 8R, 125W @ 4R) that appears to have a similar circuit, and I would also like to beef it up, so I hope my questions will be relevant also to the DIA-100. I have not yet contacted Klipsch for my schematic. My goal is to improve the 4 Ohm power (and make the amp sound its best, obviously!).
Wow, this amp seems to have very little juice to handle hungrier speakers (4R)! You have to be very careful on what to load it with.

But it seems clear why's that just by seeing the photo: the transformer is very small.

So if you want to improve things, even for 8R loads, I think a transformer upgrade should be considered. At least to double that size.

Perhaps going dual mono, using a similar transformer that size on both channels might do it too.

It's no use upgrading bridges or caps in the supply if you don't feed them with enough current.

If you use just one bigger transformer for both channels, use separate bridges and caps for each channel.

Quote:

1. I noticed the circuit has one 1k pot. Is this to adjust the bias? I don't really understand how to read a circuit. It idles stone cold (The hs is pretty much at ambient temp at idle), which I'm ASSUMING is an indication that the bias is set on the low side. How do I increase the bias?
You increase it by moving this pot. But this should be the last thing to do. You have to be very careful and watch the heatsinks temp, so they can dissipate the additional heat as you increase bias. Also watch the output transistors temp, just in case the heat transfer is not efficient enough. If they get hot to the touch you may need to change the isolators and use more efficient ones, or the transistors may no last.

But beware: not always does increasing bias improve things.

Quote:

2. Can we have a recommendation for exactly which diodes to use? I heard that 'soft recovery' was more important than 'fast recovery.' The cheapskate in me wants to just put some caps and resistors across the diodes in the existing bridge.
Caps and resistors across the diodes may do very little. Fast soft recovery diodes seem to be the best for power amps. Just watch current is high enough.

Quote:

3. My amp has a 23mF ps cap from plus to ground and one from ground to minus, and what appears to be a 300-350VA torriodal transformer that I measured putting out 93VCT. I see that Apex Jr has a 600VA torroid that is 90VCT and 15mF caps for $3, which I'm thinking about getting and making a CRCC with 0.1-0.2R.
That transformer might do it, to feed both channels.

Quote:

4. I will try to find replacements for all the on-board electrolytic caps. From looking at the schematic of the DIA-100, are there any that could benefit from a different type, increased value, or film by-pass cap?
The critical caps are C2 and C7. Put the best you can afford on C2, bypassed or not (try), and check what you have on C7. If C7 is a decent one, designed for audio, just leave it: you will only do better by going for a film cap or a maybe a servo. If not try a Black Gate or something.

Quote:

5. Before the power switch there's a thermistor USS 2R515 (rating says 15A Imax, 2.5 Ohm at 25C, but I measured 4 Ohms) which hardly even gets warm. Isn't this a waste? It does get much warmer while playing loud.
Maybe it's just preserving the switch from burning. I don't think I'd use it, but don't take my advice on that one.

east electronics 17th January 2009 03:14 PM

one of the things i would do .....
 
is to replace the banks with something else

it doesnt look too good ...the way caps are located .... i would go for smaller caps and more but most of everything Placed properly.....

as about the rest of the mods i will agree with most of them ....

looks like a nice amp but ....

i thing cooling is not enough and then the way the amp is biased is not the thing i would keep ..... i could go for something more precise

cheers sakis

Andersonix 18th January 2009 09:31 AM

Quote:

Originally posted by FSHZ:42
First was to remove caps C-1(.1uf) & C-2(10uf) on the signal path of each board, and replaced them with 1uF Sonicap Platinum on each board.
Thanks for that, Emile. But won't replacing a 10uF with a 1uF cut some bass?


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