Ahh..ok..now I read you. Even if you have something made custom ($$$), it would probably require a bigger case...more $$$$. Those trafos are rated pretty high for their size!
I'll stick to the minor mods for my 535. The thing that spurred me to do this is that I think the caps are not performing to spec because the last few years the amp started to sound closed in and lifeless. At first I thought it was my hearing, but listening via headphones on my other equipment, I can hear with great clarity.
After the mods, I'll check the bias and everything should be much better.
I'll stick to the minor mods for my 535. The thing that spurred me to do this is that I think the caps are not performing to spec because the last few years the amp started to sound closed in and lifeless. At first I thought it was my hearing, but listening via headphones on my other equipment, I can hear with great clarity.
After the mods, I'll check the bias and everything should be much better.
Interesting that a lot of the 555 suggested mods were stock on the 555II (better input jacks, no electrolytics in the signal path - I believe it also has a CCS in the input stage).
Anyway, I've got a 555ii and I find it to be quite a good amp. It had a couple of shorted predrivers when I got it and the fuse holders were trashed... I replaced the fuse holders, a few small EL's and all 2SA1210's and 2SC2912's, and it's been running great ever since (been on and in use for most of the past six months).
One mod I saw in a unit that was being sold on eBay looked interesting. Basically, the owner had pulled the stock transformer and replaced it with a stacked pair of 800VA unpotted toroidals. I would guess they were something like the Avels available from Parts Express. Anyway, quick conversion to dual mono, since the rectifiers and filters are already in place for it.
Anyone here done a dual mono conversion like this? If so, how'd it work out?
Thanks,
Paul
Anyway, I've got a 555ii and I find it to be quite a good amp. It had a couple of shorted predrivers when I got it and the fuse holders were trashed... I replaced the fuse holders, a few small EL's and all 2SA1210's and 2SC2912's, and it's been running great ever since (been on and in use for most of the past six months).
One mod I saw in a unit that was being sold on eBay looked interesting. Basically, the owner had pulled the stock transformer and replaced it with a stacked pair of 800VA unpotted toroidals. I would guess they were something like the Avels available from Parts Express. Anyway, quick conversion to dual mono, since the rectifiers and filters are already in place for it.
Anyone here done a dual mono conversion like this? If so, how'd it work out?
Thanks,
Paul
Are the original 555's noisy, then? Were they always noisy or is it just that many of them have now become noisy?
I just checked my 555II, and, while I am measuring 6mV of noise at the outputs, it looks to all be out of band +/- 100KHz. Sitting right next to the speaker, I can't hear any noise, not even any difference when connecting and disconnecting the wires to the speaker.
I just checked my 555II, and, while I am measuring 6mV of noise at the outputs, it looks to all be out of band +/- 100KHz. Sitting right next to the speaker, I can't hear any noise, not even any difference when connecting and disconnecting the wires to the speaker.
The later versions have a potted transformer? That seems like a great idea, should silence the MF.
I really should do something about these amps of mine, a proper overhaul. New caps, a silent transformer. They are worth it!
The sound is just great, not sterile, still very good resolution, broad soundstage, plenty of oomph for rock and roll. Listen for hours without fatigue.
I really would like to get a pair of 555IIs as these are supposed to be sonically superior to the 535Is, has anyone had a chance to do this comparison?
Best regards,
Jarno.
I really should do something about these amps of mine, a proper overhaul. New caps, a silent transformer. They are worth it!
The sound is just great, not sterile, still very good resolution, broad soundstage, plenty of oomph for rock and roll. Listen for hours without fatigue.
I really would like to get a pair of 555IIs as these are supposed to be sonically superior to the 535Is, has anyone had a chance to do this comparison?
Best regards,
Jarno.
Jarno,
Yes, the 535s are good little amps. I don't have any experience with the 555s. I just remember seeing them in the demo rooms and thinking how a starving student like me could afford one.
I'll post my impressions as I make each mod to my 535. I replaced the fuses with ceramic types, but I didn't hear much of a change. I think that is when the thought entered my mind that the caps needed to be replaced.
If I'm not mistaken, Nelson Pass said he designed the first amp for each 5xx series.
I'm definitely targeting the feedback resistor. I'll see if that makes a difference. I understand by upping the resistance value just a bit (I think its 22k), the amp sounds sweeter.
Yes, the 535s are good little amps. I don't have any experience with the 555s. I just remember seeing them in the demo rooms and thinking how a starving student like me could afford one.
I'll post my impressions as I make each mod to my 535. I replaced the fuses with ceramic types, but I didn't hear much of a change. I think that is when the thought entered my mind that the caps needed to be replaced.
If I'm not mistaken, Nelson Pass said he designed the first amp for each 5xx series.
I'm definitely targeting the feedback resistor. I'll see if that makes a difference. I understand by upping the resistance value just a bit (I think its 22k), the amp sounds sweeter.
Well, I'm sure glad I read this thread a couple of weeks ago. I opened up the Adcom this afternoon to look a little closer now that I have the service manual. How this is still working, I don't know, but I've got brown gunk underneath some of the caps. Plus, the lids on the 3 of the 4 caps are bulging slightly. 
I also measured the stock caps and it looks like I have to go with Panasonic TSHAs in the same value. Otherwise, I have to shoehorn bigger caps in the case. There just isn't that much room.
I also took a look at the stock RCA inputs and they look like little bits of plastic are about to come loose that hold the center pins of my interconnects. Since I'm trying to go as cheaply as possible, I have Parts Express Dayton jacks and they fit fairly well. I'll probably pull the stock cable. I've got plenty of nice wire laying around, twist of a couple of pairs and call it done.
I'll probably pull some of that extra wiring running around inside, remove the B switch and the B outputs. I'm not going crazy on this because my wife likes to keep our toddler entertained with her favorite CDs, so quick and easy is the order of the day.
I also measured the stock caps and it looks like I have to go with Panasonic TSHAs in the same value. Otherwise, I have to shoehorn bigger caps in the case. There just isn't that much room.
I also took a look at the stock RCA inputs and they look like little bits of plastic are about to come loose that hold the center pins of my interconnects. Since I'm trying to go as cheaply as possible, I have Parts Express Dayton jacks and they fit fairly well. I'll probably pull the stock cable. I've got plenty of nice wire laying around, twist of a couple of pairs and call it done.
I'll probably pull some of that extra wiring running around inside, remove the B switch and the B outputs. I'm not going crazy on this because my wife likes to keep our toddler entertained with her favorite CDs, so quick and easy is the order of the day.
Jarno said:
Hi Jarno,
I have not listened to 535I's but I own a 555II for the last 16 years, and found it reliable and easy to use. While you asked for 535/555 comparison I thought another comparison would be helpful.
I replaced the 555II at various times with tube amps (<35 w/ch) and have not listened to it for several years now.
To my ears it sounds good in the low end, but does not provide the dynamics (slam) of my EICO HF-87 for example. Higher frequencies, about 6k and higher, sound harsher and more astringent to me. I also feel the 555II does not provide the sense of realism and sound stage of the EICO ST70, to stick to one tube amp comparison.
Of course my tube amp produce max 35 watts vs. ~200 for 555II, but for my listening habits I don't need much power and found the EICO HF-87 more enjoyable
I have always felt the 555III could be improved/rebuilt to a very fine amp, but I have not seen a good DIY effort of this sort.
Francois
Finally dug into the 535 and removed the psu board. Wouldn't you know it - the caps are not snap-in types. They are radials with 3 leads (the extra pin is not soldered to the board and no trace is connected to it). Also, their diameter is smaller than a 6800 uF 63V snap-in cap. There isn't an easy way to populate the board with new caps...real estate is too tight in there.
So, plan B - taking out the awful speaker connectors opens up some space on the PSU. I'm going to lay out a new PSU board to allow snap-in caps up to 30 mm in diameter. Also, I can get some more real estate by removing the traces for the "B" speaker connectors.
I found some binding posts on ebay for $14 shipped which will be a close fit to the speaker wire connectors in the 535.
I think this will be worth it because now I can easily remove caps and roll new ones if I get the urge to experiment.
I'll probably have an extra board left over when I'm done, so if anyone is interested, please let me know. This is for the 535, not the 535II.
So, plan B - taking out the awful speaker connectors opens up some space on the PSU. I'm going to lay out a new PSU board to allow snap-in caps up to 30 mm in diameter. Also, I can get some more real estate by removing the traces for the "B" speaker connectors.
I found some binding posts on ebay for $14 shipped which will be a close fit to the speaker wire connectors in the 535.
I think this will be worth it because now I can easily remove caps and roll new ones if I get the urge to experiment.
I'll probably have an extra board left over when I'm done, so if anyone is interested, please let me know. This is for the 535, not the 535II.
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