Acurus A250 and starground

[Fsatsil]

Thanks guys! I mainly went with the 47u/100v caps because I had a bunch of them on hand from my Adcom gfa5400 rebuild. I noticed my 200X3 seems to be a bit of a Frankenstein. Two of the channels have matching parts with black film caps and black Toshiba output transistors but the third channel has all red Wima film caps and four green Toshiba outputs. Is this common with these amps?

 

[Fsatsil]

 

[KNielsen]

I think Mondialfan may have seen this before, or could answer your question....

One could think that this amp is produced as one of the last amplifiers before Mondial switched to GEN2 models..? But I don't know

Right now I have 3 A250's, and it's fun to see how Mondial development their amplifiers over the years. Non of the 3 has identical components at the output circuit (each individual amp has the same components though, not like the one you pictured), and the inputground is also changed in later production.

 

[Fsatsil]

This is my first Acurus amp and I really love how easy it is to disassemble! Looking at the PCBs the traces/pads do look a bit delicate. How careful do I need to be when desoldering parts from these boards?

 

[KNielsen]

This is my first Acurus amp and I really love how easy it is to disassemble! Looking at the PCBs the traces/pads do look a bit delicate. How careful do I need to be when desoldering parts from these boards?

I only had one board that cursed some problems. But actually I don't find them that fragile, as long as you do not force the components out, there should be no damages...

 

[Fsatsil]

That’s good news KNielsen! I just pulled the amp apart this evening and had a better look at the mismatched channels. They seem to be identical besides the black caps and green output transistors. Luckily two out of the three channels are perfect matches and I only need two channels so I have one channel for spare parts. Now I need to do some soldering and get the post fuse cap mod done! Thanks for your help.

I only had one board that cursed some problems. But actually I don't find them that fragile, as long as you do not force the components out, there should be no damages...

 

[mondialfan]

Its common to find different manufacturer parts in a lot of the boards, especially in the early gen 1 stuff. Mondial seemed to have a deep parts bin. I've found that the boards with the black film coupling caps are generally the earlier ones, however the fact that you have all black packaged Toshiba outputs on those says that they're later. Toshiba switched from the green/black transistors to all black packages sometime in the mid-90's from what I can tell.

Although the traces are small they're not that fragile actually. I've found that they stand up to resoldering quite well.

 

[Fsatsil]

I wonder if it was like this from the factory or a board or two was replaced over its lifetime? I had a little free time to do some mods this evening, I replaced all the black polyester caps with same size Wima MKP, small Electrolytics were replaced with Nichicon Muse BP, and added 47uf/100v caps on the V+/- rails after the fuse. The amp is back together and sounding great! Thanks for the help guys

 

[KNielsen]

I wonder if it was like this from the factory or a board or two was replaced over its lifetime? I had a little free time to do some mods this evening, I replaced all the black polyester caps with same size Wima MKP, small Electrolytics were replaced with Nichicon Muse BP, and added 47uf/100v caps on the V+/- rails after the fuse. The amp is back together and sounding great! Thanks for the help guys

A small size bypass cap like 1uf/250vdc across your 47uf post-fuse-mod would be top notch.
Great job though

 

[Fsatsil]

Thanks! Last night when I was doing the mod I was going to add a .47uf Wima MKP to the post fuse caps but It was late and I had a few beers and I completely forgot about it and put the amp back together before I realized I had forgotten. I’m sure I’ll have the amp again someday and I’ll add the bypass caps but for now the amp is sounding great! I set the bias to 10mv and the dc offset was nice and low at 1mv/4mv. Now I just need to think about upgrading the power supply.

 

[KNielsen]

I set the bias to 10mv and the dc offset was nice and low at 1mv/4mv. Now I just need to think about upgrading the power supply.

A set of new e.caps will improve the sound. The original blue once are not that good in my opinion.
I personally prefer Kemet at this location.

God day

 

[Fsatsil]

Have you had issues with Cornell Dubilier capacitors? The ones in my amp are still testing like new and I’ve always considered these larger made in the USA caps to be high quality parts. Those Kemet caps seem to be similar if not the same as the old BHC Aerovox caps, very very high quality and made in the UK if I recall. I don’t know what series you used but they used to make an audio grade “slit foil” capacitor that a bunch of the higher end British companies used in their amps. I actually have a quad of 10000uf/63v “slit foil” caps that I’m saving for a future diy amp. But anyways, I started to price out what it would cost to add a second bridge rectifier and use a pair of 15000-18000uf/100v caps per channel and it gets expensive real fast. I think I’m going to stick with the stock capacitors for now. Do you have any opinion on adding a big film bypass capacitor across the power supply caps? The amp was all stock except for a pair of big 8uf/200v RelCap PPMF polypropylene film bypasses across the power supply caps and I’m not sure if I should keep them or remove them?

 

[KNielsen]

Have you had issues with Cornell Dubilier capacitors? The ones in my amp are still testing like new and I’ve always considered these larger made in the USA caps to be high quality parts. Those Kemet caps seem to be similar if not the same as the old BHC Aerovox caps, very very high quality and made in the UK if I recall. I don’t know what series you used but they used to make an audio grade “slit foil” capacitor that a bunch of the higher end British companies used in their amps. I actually have a quad of 10000uf/63v “slit foil” caps that I’m saving for a future diy amp. But anyways, I started to price out what it would cost to add a second bridge rectifier and use a pair of 15000-18000uf/100v caps per channel and it gets expensive real fast. I think I’m going to stick with the stock capacitors for now. Do you have any opinion on adding a big film bypass capacitor across the power supply caps? The amp was all stock except for a pair of big 8uf/200v RelCap PPMF polypropylene film bypasses across the power supply caps and I’m not sure if I should keep them or remove them?

I'm not a nerd here, but..

I have seen 2 A250's with dead Ecaps... One of them was my own. I use Kemet as they are god value for the money, and a great lifespan, typically 16-19.000hours on them.

In the old days I use to prefer RIFA, now owned by Kemet with their name on it, the white Ecaps in their aluminium cap series... but pricey
Ecaps is really a matter of taste.. The ripple on the caps selected will change the way the bass behave.
I have 8x13.000/100vdc, total of 104.000uf in my own A250, all with bypass caps (Panasonic ECWF(a) 1uf/250vdc). It gives a very neutral bass and and the bypass caps added some hights. The stock supply I do for others is normally boosted to 2x36.000/100vdc without bypass caps, it gives little more pronounced bass vs. my 8x-cap-setup and the standard A200x3/A250 powersupply.

Regards

 

[KNielsen]

Do you have any opinion on adding a big film bypass capacitor across the power supply caps? The amp was all stock except for a pair of big 8uf/200v RelCap PPMF polypropylene film bypasses across the power supply caps and I’m not sure if I should keep them or remove them?

If you mean audio type big foil cap.... I wouldn't do it. Chances are they will act like big antennas. If you are going with the big ones, then be aware that the outer foil should be coupled to -, as this will make a better screen for interference. Noise..
But still, I wouldn't do it without equipment to measure befor, under and after the change

 

[Fsatsil]

The bypass caps that came with the amp are 8uf/200v RelCap PPMF which is a metallized polypropylene film cap which I’ve actually used in speaker crossovers! I removed them when I first opened up the amp, I saw no point in having them and figured I could always use them in a future project.

 

[KNielsen]

Well.. couldn't sleep so went up early.. A good sip of coffee, and then ahead putting this amp together before breakfast with the family.
It's not my own amplifier but, still gives that great satisfaction when a project is finished

 

[mondialfan]

If you mean audio type big foil cap.... I wouldn't do it. Chances are they will act like big antennas. If you are going with the big ones, then be aware that the outer foil should be coupled to -, as this will make a better screen for interference. Noise..
But still, I wouldn't do it without equipment to measure befor, under and after the change

If they are going across the main storage caps to be used as bypass caps then it would be fine to use them, but don't even think about using them for input coupling caps. In that position the large bodied caps can be problematic as Knielsen suggests.

If you didn't install post fuse bypass caps then adding them across the main storage caps is the next best thing. I typically use something physically smaller than the caps you're describing. I like to use 1 - 2 uF polypropylene films like the radial panasonic ECW series.

 

[KNielsen]

It should be mentioned that I just removed my bypass caps today on the powersupply.. I can't really figure out if they create to much "shizzle" in the top end... The post-fuse mod does a really good job on its own! So the bypass caps been on/off for for some month now...

And off-topic: I removed all the red and blue heat-shrink tubing, replaced it all with black tubing. So it's now officially "Edition Black"!!
Looks awesome in the box.

I'll post a pic later

 

[Fsatsil]

Nice job on that amp KNeilsen it looks very clean. Which power supply capacitors did you use?

 

[KNielsen]

Nice job on that amp KNeilsen it looks very clean. Which power supply capacitors did you use?

Panasonic ECWF(a).. 1uf/250vdc.. I have roughly 8mm of free space from ecap to the lid, so there is not much to those from although if I had space I would save some money for the new Jantzen Amber.
I am using same Panasonic's on my two bridge rectifier though, just 8x 100nf/250vdc.

Edit: think I answered my own amp... The correct answer is on next page