Acurus A250 and starground

[KNielsen]

Thank you Mondialfan
I put the R20 of 10k ohm in as on the schematic shown and the DBT was bright then i measured the R20 in the working channel it showed 1k ohm so i replaced R20 with 1k ohm and the DBT was not bright up what value should be used and would you please show me how to measure and set DC bias thank you for helping.

I can't comment about your findings on R20. I have 10Kohm in mine...

Bias is measured across any of the emitterresisters R24-32 and set the bias to 8-10mVdc... This setting should work without any problems with heat

Regards

 

[Jdk07]

I can't comment about your findings on R20. I have 10Kohm in mine...

Bias is measured across any of the emitterresisters R24-33 and set the bias to 8-10mVdc... This setting should work without any problems with heat

Regards

I can't comment about your findings on R20. I have 10Kohm in minBias is measured across any of the emitterresisters R24-33 and set the bias to 8-10mVdc... This setting should work without any problems with heat

Regards

Thank you KNielson
Should i turn the music off then measure and adjust or leave the music play while measure and adjust. It reads about 3.5mVdc now i should turn up until it reads 8-10mVdc

 

[KNielsen]

Yes adjust without music. Let the amp settle for a while and remeasure the bias, play some music and measure again when the amp is in idle.. This process can take some time to get right.
I always let the amp play pretty loud when finished (for about an hour or so) just to check that the amp doesn't get to hot to touch under a hard load.
When I'm satisfied with the heatsink temp I always measure once again before putting the cover back on, just to make sure the bias haven't driftet and is identical on both channels.

 

[KNielsen]

My own amp were adjusted to approx 13.7mV at first. When we did the performance test on the amplifier (watt, THD ect..) we measured 45°c (113°f) on the heatsink . At home with my 4ohm speakers the temperature raised to about 55-57°c (131-135°f) when loaded pretty hard.
After this I lowered the bias to 11mV to keep the temp at approx 50°c (122°f).. It seemed like at good balance for my setup!
With my new speakers (6ohm) the Acurus have further lowered the heatsink temp, and I'll guess I could go to the area around 15mV now without the amp getting to hot. We'll see

Regards

 

[mondialfan]

Thank you Mondialfan
I put the R20 of 10k ohm in as on the schematic shown and the DBT was bright then i measured the R20 in the working channel it showed 1k ohm so i replaced R20 with 1k ohm and the DBT was not bright up what value should be used and would you please show me how to measure and set DC bias thank you for helping.

If you're talking about the potentiometer that would be R11 not R20? A 10k pot will work but it will make the bias adjustment very sensitive. A 1K multi-turn is much better. Manufacturer recommended bias is 6mV, if you can set it higher and not have excessively high heatsink temps in normal operation then 10mV is fine.

 

[Jdk07]

If you're talking about the potentiometer that would be R11 not R20? A 10k pot will work but it will make the bias adjustment very sensitive. A 1K multi-turn is much better. Manufacturer recommended bias is 6mV, if you can set it higher and not have excessively high heatsink temps in normal operation then 10mV is fine.

I am using a 1k potentiometer, it is the R20 i use 1k instead of 10k on the schematic. I try to read the R20 resistor color code but not 100% sure of red or brown but it measured 1k ohm. The amp is working i turned it up to 8mV now and the heatsink is not even warm with normal volume level. Would it sound better with higher bias i rather have it runs cool unless it sound better when running hot and should i leave R20 with 1k or replace it with 10k ? thank you Mondialfan

 

[Jdk07]

If you have 8 Kemets and two bridges I would run the two bridges separately instead of bridged. One bridge and 4 Kemets per channel. This will break the supply up to what I call pseudo dual-mono. The two channels use the same transformer windings but everything after that is channel dependent. This should help to minimize channel interaction.

Definitely leave out the big 10uF film and go with the Nichicon Muse and an ECWF on the input coupling cap. You should be able to squeeze a .33 or .47uF ECWF in a similar physical size into the C1 location.

You can use the 50uF/100V but I usually go with a 100uF/100v polar on the rails, ECWF films are good. There is a lot of open area on the board so I usually opt for a radial cap and drill a couple of small holes to install it then a small dab of glue to hold it in place and then P2P wire on the back side of the board. In this manner it looks like the factory installed it.

I like to add the post fuse cap to my amp would you please instruct me how to do it thank you for your time

 

[KNielsen]

I like to add the post fuse cap to my amp would you please instruct me how to do it thank you for your time

I've attached the Aragon 4004 schematic. There the postfuse caps are shown.

Combined with the info in this thread, there should be enough info to do the job

If you are still unsure I wouldn't continue.

 

[Jdk07]

I've attached the Aragon 4004 schematic. There the postfuse caps are shown.

Combined with the info in this thread, there should be enough info to do the job View attachment 1458511

If you are still unsure I wouldn't continue.

Thank you KNielson I should use
(1) 1 electrolytic100uf/100v or 2 caps in parallel 47uf/100v electrolytic // 1uf film cap (radial polar cap)
(2) The positive lead of the cap should connect to the fuse on the positive side of the board and negative lead to ground
(3) On the negative side of the board the negative lead of the cap should connect to the fuse and positive lead to ground
Thank you for your help

 

[KNielsen]

(1) go with 100uf/100v Elna Silmic ll... They are good for this application. Use a small film cap for bypass with at voltage rating from 200v and up.. I use Panasonic ECWF(a) 1uf/250v
(2) yes
(3) yes

 

[Jdk07]

T

(1) go with 100uf/100v Elna Silmic ll... They are good for this application. Use a small film cap for bypass with at voltage rating from 200v and up.. I use Panasonic ECWF(a) 1uf/250v
(2) yes
(3) yes

Thank you KNeilson can I add this mod to my other Acurus A150 too?

 

[KNielsen]

Thank you KNeilson can I add this mod to my other Acurus A150 too?

Yes

 

[mondialfan]

T

Thank you KNeilson can I add this mod to my other Acurus A150 too?

This mod works on all of the Acurus amps, its just that there's no guide on how or where to add the new caps. I usually use a small wire gauge drill bit mounted in a finger drill to drill the new holes needed.

 

[Jdk07]

This mod works on all of the Acurus amps, its just that there's no guide on how or where to add the new caps. I usually use a small wire gauge drill bit mounted in a finger drill to drill the new holes needed.

Thank you Mondiafan
I see that the A150 got more fuses could you please show me which one to connect the caps to thank you for your help.

 

[mondialfan]

No the A150 still has 4 fuses just like the big brother A250. The new caps do not necessarily connect to the fuses, in fact I've never attached any of the ones I've installed directly to the fuses as there are better areas on the board to attach them. They just need to be installed after the fuses as the schematic that KNielsen posted shows.

 

[Jdk07]

No the A150 still has 4 fuses just like the big brother A250. The new caps do not necessarily connect to the fuses, in fact I've never attached any of the ones I've installed directly to the fuses as there are better areas on the board to attach them. They just need to be installed after the fuses as the schematic that KNielsen posted shows.

Thank you i see it now. I could not tell what part of the circuit related to the schematic yet I am still trying to learn how. I saw that on KNeilson amp board has a wire going from one end of the fuse clip to the caps and another wire from the caps to ground. I don’t know what after the fuse yet from looking at the board

 

[KNielsen]

Thank you i see it now. I could not tell what part of the circuit related to the schematic yet I am still trying to learn how. I saw that on KNeilson amp board has a wire going from one end of the fuse clip to the caps and another wire from the caps to ground. I don’t know what after the fuse yet from looking at the board

I just attached the wire to the caps after the fuse on both sides (+/-).. but don't look to much at my pictures, as there are other repairs involved with wire also

At the feedback circuit the copper sliped the board and had to be replaced so space were becoming a bit limited with a bunch of new wires. Also ran into some other small problems with the copper on the same board(!!). The other channel everything went smoothly and no repairs were done at all

 

[mondialfan]

Stock board on top upgraded on bottom. Notice the addition of two film and e-cap pairs.

On mine the caps attach to the DC rail trace on one side with the other side having a wire attached that goes back to circuit common.

 

[KNielsen]

Stock board on top upgraded on bottom. Notice the addition of two film and e-cap pairs.

On mine the caps attach to the DC rail trace on one side with the other side having a wire attached that goes back to circuit common.
View attachment 1459722

Nice with a closeup Mondiallfan although I'm finished for now .. next time (my other A250) I place my postmod caps like your pic shows, would have been alot easier... And much less wire to attach..

I see you only changed R1 and R2. Are these the most important on the circuit?

Also, the power transistors.. in both my A250's there are 4 green/4 black.. are the once we are looking at new?? Or did Mondial source their transistors from different companies since they are all black (maybe a noob question) ?

Regards

 

[Jdk07]

Stock board on top upgraded on bottom. Notice the addition of two film and e-cap pairs.

On mine the caps attach to the DC rail trace on one side with the other side having a wire attached that goes back to circuit common.
View attachment 1459722

Thank you Mondialfan
To drill the 4 holes for the film and e-cap pair 2 of them should be right next to the DC rail trace then solder one side of the two caps to the DC rail trace on the soldering side of the board and attach a wire to the other side of the two caps to board ground. Is it Correct? Thank you for your help