Acurus A250 and starground
KNielsen
Well-Known Member
I repair them. A T3 diode will fit inside the switch, coupled with new wire with a diode and a resistor to one of the secondarys and starground. I think it's a 1N4004 I use with 150kohm outside the switch if I remember correctly with the current T3 I use. I don't like the LED to bright.
Be aware that the switch is easy to break, so take your time and a steady hand
KNielsen
Well-Known Member
Looking at my parts I think it's a 100Kohm/3w. But try what you'll find the best. A 56Kohm will be quite bright
KNielsen
Well-Known Member
For Acurus modifiers: My modded Vs a stock 4004 mk.l...
The mod A250 beats the 4004, no doubt.
Only thing the 4004 does better is a low-end that goes deeper, but one really feel that there is great room for improvement. The details in the mid and treble is far better in the A250.... For now that is!
The 4004 will be built according to mk.ll specs and the 8008 supply (or close to spec). It also suffers from hum, even though is has seen a new set of xformers, so alot of work before a new test between the two can be performed again.
I might order new power and driver transistors while the 4004 is here and install. I'll have to measure the amp first though to establish the condition.
The mod A250 beats the 4004, no doubt.
Only thing the 4004 does better is a low-end that goes deeper, but one really feel that there is great room for improvement. The details in the mid and treble is far better in the A250.... For now that is!
The 4004 will be built according to mk.ll specs and the 8008 supply (or close to spec). It also suffers from hum, even though is has seen a new set of xformers, so alot of work before a new test between the two can be performed again.
I might order new power and driver transistors while the 4004 is here and install. I'll have to measure the amp first though to establish the condition.
I'm interested in this "star ground" mod, but I haven't yet found any details on it, though I haven't made it through all 38 pages of this thread yet - it's all way over my head...
I have two A250s, one I bought new with the captured pigtail power cord, and the second I bought off USAudioMart a year ago that is slightly newer, with the removable power cord and steady/strong power LED. For as long as I can remember, my original has had a hum unless I use a "cheater plug" so the ground isn't connected to the wall - I'm hopeful that with the details of this star ground mod, a local repair shop could make it as quiet as the newer one.
I would be very grateful if anyone can put their hands on a drawing without too much trouble and post it here or send it my way.
Thanks!
Jim
I have two A250s, one I bought new with the captured pigtail power cord, and the second I bought off USAudioMart a year ago that is slightly newer, with the removable power cord and steady/strong power LED. For as long as I can remember, my original has had a hum unless I use a "cheater plug" so the ground isn't connected to the wall - I'm hopeful that with the details of this star ground mod, a local repair shop could make it as quiet as the newer one.
I would be very grateful if anyone can put their hands on a drawing without too much trouble and post it here or send it my way.
Thanks!
Jim
KNielsen
Well-Known Member
@Duck851 the headline "starground" should be altered to "mods", as this thread has evolved far beyond groundconnections 
When I first started this thread my idea was to seperat all grounds that flows around on the output circuit, and thereby having them meet at one common starground. Nevertheless as @mondialfan pointed out on page 1 if I'm correct, it's not necessarily a good idea messing with, and definitely not without good equipment to measure the results afterwards.
The ground at the big blue E.caps is the main ground, "starground" in all Mondial Acurus gear... What I found is that in some of the A250's, the input ground from RCA connects to speaker minus... In the later production and all A200-models, this connection is send directly to the ground at the E.caps instead of connecting via the speakergnd .. Changing this is all you need, if the amp at hand isn't build like this from factory.
Remember to keep the 10ohm and back-to-back diodes that's under some heatsink, these has to be in the new connection also... The rest is OK
Best regards
When I first started this thread my idea was to seperat all grounds that flows around on the output circuit, and thereby having them meet at one common starground. Nevertheless as @mondialfan pointed out on page 1 if I'm correct, it's not necessarily a good idea messing with, and definitely not without good equipment to measure the results afterwards.
The ground at the big blue E.caps is the main ground, "starground" in all Mondial Acurus gear... What I found is that in some of the A250's, the input ground from RCA connects to speaker minus... In the later production and all A200-models, this connection is send directly to the ground at the E.caps instead of connecting via the speakergnd .. Changing this is all you need, if the amp at hand isn't build like this from factory.
Remember to keep the 10ohm and back-to-back diodes that's under some heatsink, these has to be in the new connection also... The rest is OK
Best regards
KNielsen
Well-Known Member
Yes, the center screw is ground between the E.caps
I disconnected the thin negative input wire from the negative binding post and cut the ring terminal off to splice a length of wire to reach the screw on the plate between the big power supply caps. After I wiggled the caps out of their brackets I found that screw has leads back to the negative binding posts anyway. Am I in the wrong place?
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KNielsen
Well-Known Member
Picture of the RCA connection? Does it have a seperat groundwire directly to starground?
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This wire went to the negative binding post. Before I cut the ring terminal off I verified that there is a 10Ohm resistor in there with a meter. The wire coming from the binding post that runs along the bottom attaches to the screw in the middle of the plate that I thought was where I was supposed to connect the wire from the input. It seems to me that circuit then was alredy complete, right?
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KNielsen
Well-Known Member
If this wire is connected directly to starground, that's all you need to do... Some of the newer A250 came with this setup, and don't need this mod
Regards
KNielsen
Well-Known Member
Hum in your speakers or xformer?
Speakers. I'm in the US, I don't know if you have a grounded power wire where you are, but if I don't use a "cheater plug" that does NOT connect the ground pin on the amp's power cord to the wall socket, I get hum in the speakers.
Tonight I'll pull the cover off my newer one that doesn't hum and see if I can spot any difference in how that area is wired.
Tonight I'll pull the cover off my newer one that doesn't hum and see if I can spot any difference in how that area is wired.
The newer one that doesn’t hum is the same as far as I can tell, so it’s something else…
The power input looks completely different because of the removable cord but I don’t know how to find any circuit differences
The power input looks completely different because of the removable cord but I don’t know how to find any circuit differences
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mondialfan
Well-Known Member
There should be no circuit differences between the older A250 with the integrated AC cord and the later models. The later models did get a slightly larger transformer and they're capable of a few more watts of output.