When I built the Threhold SA/1 copies with the original power supply it all fit in a 16" long chassis and didn't weigh too much. When I rebuild with a 2.4kva toroid and 8 76,000uf caps with a 8mh inductor in a CLC configuration I had to extend the chassis to 24" long. If I did it again I would use two chassis, a seperate chassis for the power supply with the softstart. Moving the one 24" HEAVY chassis now is a challege, good thing it doesn't move around much. 
Mr Pass. I appreciate all of the avenues that you have opened up for the DIY community. Building and playing around with your designs, I haven't broken anything yet so that says something! Thank you
John, That makes a lot of sense. This should be about as heavy as the stock amp. I am still (somewhat) young and I also don't move the amp around very much. My thought was two fold. Reduce heat in the chassis and get the transformers away from the rest of the amp. I think I will try to build it in the amp first and see how that goes. I can't imagine lifting one of your amps. I can grab a new piece of aluminum and mount everything to that. Put some new rubber feet on it too and just set the stock stuff aside.
John, That makes a lot of sense. This should be about as heavy as the stock amp. I am still (somewhat) young and I also don't move the amp around very much. My thought was two fold. Reduce heat in the chassis and get the transformers away from the rest of the amp. I think I will try to build it in the amp first and see how that goes. I can't imagine lifting one of your amps. I can grab a new piece of aluminum and mount everything to that. Put some new rubber feet on it too and just set the stock stuff aside.
I am making progress. The amp is much more stable at 40v. I hooked up one channel to a test speaker and I got tones and music so off to a good start. I put the stock value resistors in there and bias was good. However, DC offset was not within the range of the potentiometer. I increased R5 from 100ohm to 221ohm which gives just enough adjustment at operating temperature for the DC offset. I think maybe a 1k pot in P1 would solve the problem or maybe running a 300 ohm resistor in R5.
I then swapped all of the active devices to the stock ones suggested in post #1, and swapped out the KSC2690 and KSA1220 with some new ones just to have a fresh start. I had everything already on hand. I will need to get some more ZTX450's though. I left the LSK170s. Those cost money... The DCoffset acted the same. It is pretty stable and can set to float between -+2mv of 0 no problem. I am sure in the chassis it will be even more stable.
I will build out the DIYaudio PS boards and start testing the amp for oscillation so I can set the oscillation cap (C4). Then I can start fenagling everything into the Threshold chassis, and match my work on the other channel.
I then swapped all of the active devices to the stock ones suggested in post #1, and swapped out the KSC2690 and KSA1220 with some new ones just to have a fresh start. I had everything already on hand. I will need to get some more ZTX450's though. I left the LSK170s. Those cost money... The DCoffset acted the same. It is pretty stable and can set to float between -+2mv of 0 no problem. I am sure in the chassis it will be even more stable.
I will build out the DIYaudio PS boards and start testing the amp for oscillation so I can set the oscillation cap (C4). Then I can start fenagling everything into the Threshold chassis, and match my work on the other channel.
John, between -2 and 2, thereabouts so pretty good. I just put the channel in the amp with the new power supply. Wow, this thing is dead silent now! Very nice in that regard. Right now, the room is a bit cold so I have it biased higher than I thought it would be. I am probably between 40-45 degrees and sitting at around 225mv. A significant jump up from the 50mv-70mv that I would run with the 80v rails.
So I have taken a little time to listen to the single channel. So far, it sounds much more balanced with a much smoother sound. The treble on the 80v rails was a bit off. It sounded good, just not quite where I thought it was supposed to be having heard Pass's stuff. I don't want to come to any real conclusions until I get it all together. I have a Focusrite 2i2 sound card and want to learn how to do distortion measurements. Maybe this amp should be the guinea pig.
I ordered a bunch of ZTX450's which should be here soon. Then I can do a little matching and assemble the other channel.
What is a post without pictures:
So I have taken a little time to listen to the single channel. So far, it sounds much more balanced with a much smoother sound. The treble on the 80v rails was a bit off. It sounded good, just not quite where I thought it was supposed to be having heard Pass's stuff. I don't want to come to any real conclusions until I get it all together. I have a Focusrite 2i2 sound card and want to learn how to do distortion measurements. Maybe this amp should be the guinea pig.
I ordered a bunch of ZTX450's which should be here soon. Then I can do a little matching and assemble the other channel.
What is a post without pictures:
Thank you Zen Mod. Mr Pass's efforts have done a lot for a lot of people. He is a great guy. Can't say enough good things.
Okay, so I have the amp back together. I have a few things to touch up but I brought the bias up and watched how things behaved. both channels are good. Cover on to cover off bias doesn't shift as it did before so that is a big improvement. I haven't even played with C5 yet. That will come soon. However, I got impatient and hooked it up to my speakers. My initial impressions are that the bass has so much more control now which you wouldn't think considering I reduced the wattage by quite a bit. Also, more detail and the highs are better now.
Here is a pic of it put together. I will let it burn-in for a while then I can take some time to sit with it and see how she sounds. So far so good
Okay, so I have the amp back together. I have a few things to touch up but I brought the bias up and watched how things behaved. both channels are good. Cover on to cover off bias doesn't shift as it did before so that is a big improvement. I haven't even played with C5 yet. That will come soon. However, I got impatient and hooked it up to my speakers. My initial impressions are that the bass has so much more control now which you wouldn't think considering I reduced the wattage by quite a bit. Also, more detail and the highs are better now.
Here is a pic of it put together. I will let it burn-in for a while then I can take some time to sit with it and see how she sounds. So far so good
Attachments
Any news ? great work btw !Thank you Zen Mod. Mr Pass's efforts have done a lot for a lot of people. He is a great guy. Can't say enough good things.
Okay, so I have the amp back together. I have a few things to touch up but I brought the bias up and watched how things behaved. both channels are good. Cover on to cover off bias doesn't shift as it did before so that is a big improvement. I haven't even played with C5 yet. That will come soon. However, I got impatient and hooked it up to my speakers. My initial impressions are that the bass has so much more control now which you wouldn't think considering I reduced the wattage by quite a bit. Also, more detail and the highs are better now.
Here is a pic of it put together. I will let it burn-in for a while then I can take some time to sit with it and see how she sounds. So far so good
View attachment 1106189
Yes! Thank you. I spent a decent amount of time listening to the amp with the new setup. It sounds a lot better. This combo of lower voltage and the new front end design seems to be working great. I am running it at about 180mv across the 1 ohm source resistors and around 48 degrees in a 70 degree room. Would likely need to lower it for summer.
Listening impressions:
Treble:
The treble isn't too sparkly or airy. However, when you intently listen to the treble, it is much more detailed and does a great job of blending with the mids. These amps have a reputation by todays standards for lacking in detail on treble. Songs with a lot of high frequency content don't tend to be as absurd sounding. Songs that are mastered well on the high frequencies are present themselves well.
Mids:
The mids are clearer, lush and full acoustic instrument with a lot of harmonic woody tones sound great. Voices are great and clear. You can hear when the singers open their lips at the beginning of a song to start singing. I could hear some singers take breaths before but now a bit more detail. Whole sound is a lot smoother. The mids really pull you in now.
Bass:
The bass carries weight... A lot of it! It is more tactile. Bass drums hit better. The bass was good before as that is one of the things these old Stasis amps were known for during their time. Now it is better. More control.
Imaging:
The imaging on this amp is pretty good. More precise. I noticed that center image isn't always in the center. Sometimes a little left, a little right sometimes dead center. The L, R, L&R outside the speakers is also great. The presence of the singer or instrument is there but not so much so that it pulls to many things to the center.
Soundstage:
The soundstage is very large. The amp has the warm characteristics that it had originally. I assume the large soundstage has something to do with the richness of the mids and the weight that the bass carries. That is one of the best features of this amp.
So all in all a worthy upgrade. I may keep my eye out for a damaged Stasis amp and build it out with new boards etc. Just another itch to scratch. In the meantime, I have plenty of amp projects thanks to this bad influence. I think Mr. Pass has learned a thing or two over the years.
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Power supply:
-22000uf caps on two DIYaudio boards.
-Antek 500va 30v transformers.
-If you decide to do a single power supply, get a 1000va or larger if you want. I believe the stock was 1000va.
Attached are a few pictures:
-One of the output stage
-The clearance to the front end heatsink to the source resistors
-A shot of the channel with the new front end attached
-The amp stock
On the outside, it just looks like a stock S/500. It is a big amp and only 70-80 or so watts, I will have to test people to see how many watts it is after hearing it...
If you guys want any pictures in particular, I will be happy to take them. The only thing that I replaced on the outside are the RCA jacks for a new pair.
Listening impressions:
Treble:
The treble isn't too sparkly or airy. However, when you intently listen to the treble, it is much more detailed and does a great job of blending with the mids. These amps have a reputation by todays standards for lacking in detail on treble. Songs with a lot of high frequency content don't tend to be as absurd sounding. Songs that are mastered well on the high frequencies are present themselves well.
Mids:
The mids are clearer, lush and full acoustic instrument with a lot of harmonic woody tones sound great. Voices are great and clear. You can hear when the singers open their lips at the beginning of a song to start singing. I could hear some singers take breaths before but now a bit more detail. Whole sound is a lot smoother. The mids really pull you in now.
Bass:
The bass carries weight... A lot of it! It is more tactile. Bass drums hit better. The bass was good before as that is one of the things these old Stasis amps were known for during their time. Now it is better.
More control.Imaging:
The imaging on this amp is pretty good. More precise. I noticed that center image isn't always in the center. Sometimes a little left, a little right sometimes dead center. The L, R, L&R outside the speakers is also great. The presence of the singer or instrument is there but not so much so that it pulls to many things to the center.
Soundstage:
The soundstage is very large. The amp has the warm characteristics that it had originally. I assume the large soundstage has something to do with the richness of the mids and the weight that the bass carries. That is one of the best features of this amp.
So all in all a worthy upgrade. I may keep my eye out for a damaged Stasis amp and build it out with new boards etc. Just another itch to scratch. In the meantime, I have plenty of amp projects thanks to this bad influence. I think Mr. Pass has learned a thing or two over the years.
----------------------------------------------
Power supply:
-22000uf caps on two DIYaudio boards.
-Antek 500va 30v transformers.
-If you decide to do a single power supply, get a 1000va or larger if you want. I believe the stock was 1000va.
Attached are a few pictures:
-One of the output stage
-The clearance to the front end heatsink to the source resistors
-A shot of the channel with the new front end attached
-The amp stock
On the outside, it just looks like a stock S/500. It is a big amp and only 70-80 or so watts, I will have to test people to see how many watts it is after hearing it...
If you guys want any pictures in particular, I will be happy to take them. The only thing that I replaced on the outside are the RCA jacks for a new pair.
Attachments
Dear sirs.
With restoration in mind, I am currently working on a board-layout that hopefully end up being a drop-in replacement for my Threshold amps. I do this because it is important to me that the amps look factory when you look inside. (Makes me sleep better at night).
I have access to an early S150, an S200 Optical and a pair of SA2's.
All of 'my' amps have a bit of audible hum in the speakers at all times. With the S200 in can be heard from the listening position. With the SA2's you have to get very close to the speakers to notice it. All amps have been recapped (no change before/after), biased to 48 degrees, and sound as expected in every way, so I suspect it is simply a combination of sensitive speakers and the 'raw' nature of the power-supply.
I recently built an ACA with a transformer/rectifier/single beer-can-cap supply. This too had audible hum in the speakers, but adding a small R/C filter right before the LSK170, made it completely silent.
Would it make sense/be possible to add some local R/C filtering to the new FE, for when using it as replacement in the original Threshold-amps?
Thank you.
With restoration in mind, I am currently working on a board-layout that hopefully end up being a drop-in replacement for my Threshold amps. I do this because it is important to me that the amps look factory when you look inside. (Makes me sleep better at night).
I have access to an early S150, an S200 Optical and a pair of SA2's.
All of 'my' amps have a bit of audible hum in the speakers at all times. With the S200 in can be heard from the listening position. With the SA2's you have to get very close to the speakers to notice it. All amps have been recapped (no change before/after), biased to 48 degrees, and sound as expected in every way, so I suspect it is simply a combination of sensitive speakers and the 'raw' nature of the power-supply.
I recently built an ACA with a transformer/rectifier/single beer-can-cap supply. This too had audible hum in the speakers, but adding a small R/C filter right before the LSK170, made it completely silent.
Would it make sense/be possible to add some local R/C filtering to the new FE, for when using it as replacement in the original Threshold-amps?
Thank you.