Hello DIY'ers,
I am the new and proud (but 3000 euro lighter) owner of a pair of SA-2's with optical bias
After reading the thread by BrianEno I noticed that Mr Pass stated there was a more perfect front end designed, but "management" at the time did not go with it...
Would it be possible to modify the front end of these optical bias version SA-2's to that / a more perfect version?
The seller also owned a pair of SA-11M thresholds which, according to him sounded better on voices; he also stated they were specificly designed for the german market...
My amplifiers seem to work fine (they are almost spot on as far as heatsink temperature is concerned), an sound great except indeed for the highs, which could be a bit sweeter, would this be because of the front end used?
One amplifier does give a bigger "thud" on the woofer when switching on and off, the second only when switching on. I read here Mr Pass recommends replacing electrolytic capacitors. Could I start with just those small ones in the front end, anyone recommendations for specific good sounding brands?
As the amplifiers are working fine (except for the thud, and a little treble harshness) I would not like to take unnecessary risks, I am not an engineer, just a hifi enthousiast with some solduring skills and a multimeter but I am willing to try with some help of you guys!
I am the new and proud (but 3000 euro lighter) owner of a pair of SA-2's with optical bias
After reading the thread by BrianEno I noticed that Mr Pass stated there was a more perfect front end designed, but "management" at the time did not go with it...
Would it be possible to modify the front end of these optical bias version SA-2's to that / a more perfect version?
The seller also owned a pair of SA-11M thresholds which, according to him sounded better on voices; he also stated they were specificly designed for the german market...
My amplifiers seem to work fine (they are almost spot on as far as heatsink temperature is concerned), an sound great except indeed for the highs, which could be a bit sweeter, would this be because of the front end used?
One amplifier does give a bigger "thud" on the woofer when switching on and off, the second only when switching on. I read here Mr Pass recommends replacing electrolytic capacitors. Could I start with just those small ones in the front end, anyone recommendations for specific good sounding brands?
As the amplifiers are working fine (except for the thud, and a little treble harshness) I would not like to take unnecessary risks, I am not an engineer, just a hifi enthousiast with some solduring skills and a multimeter
but I am willing to try with some help of you guys!
I noticed an SA/2e for sale recently, there was a sticker on it, it was upgraded to the e series. Can anyone, or maybe Mr Pass, please tell me what to do to upgrade my SA2 too? It would be interesting to know if it is just some components I have to change (and by what I have to replace them with) or if it is a totally different front end board alltogether.
Thanks in advance for help!
Thanks in advance for help!
I would leave it as it is.
You have already the last SA/2 Series 'optical bias'.
The only thing you could consider is an update of the electrolytics.
I would not tamper with a 'Nelson Pass' Original.
The DC problem that you have is probably a failed transistor you have to isolate.
I had one in my SA/1's and I discoverd it because it had a much higher biasvoltage then the other ones. I replaced the faulty one, don't worry for matching because that's not necessary with all the parallel devices and the emmitterresistors that will balance the load.
You need some tools of cause like a Variac, DMM, dummyload and preferably a Scope.
These guys here can help you out I'm for sure.
You said you bought it for 3000 Euro's and that's a lot of money for a not working set of SA/2's
The seller should refund you the money if you did not already knew before that they had problems.
I sold mine for only a thousand more and they were perfect, had all the electrolytics updated and were SA/1's.
The seller should solve your problem for that amount you payed!
You have already the last SA/2 Series 'optical bias'.
The only thing you could consider is an update of the electrolytics.
I would not tamper with a 'Nelson Pass' Original.
The DC problem that you have is probably a failed transistor you have to isolate.
I had one in my SA/1's and I discoverd it because it had a much higher biasvoltage then the other ones. I replaced the faulty one, don't worry for matching because that's not necessary with all the parallel devices and the emmitterresistors that will balance the load.
You need some tools of cause like a Variac, DMM, dummyload and preferably a Scope.
These guys here can help you out I'm for sure.
You said you bought it for 3000 Euro's and that's a lot of money for a not working set of SA/2's
The seller should refund you the money if you did not already knew before that they had problems.
I sold mine for only a thousand more and they were perfect, had all the electrolytics updated and were SA/1's.
The seller should solve your problem for that amount you payed!
unknown frontend
Hello all,
recently got a S/500. It had DC offset 3 V in one channel and distortions at higher levels.
Found defective device 2N5566. Have ordered replacement already, hope it will work...
I noticed that these both previously posted schematics (Thanks, Nelson!) doesn't match with the PCB in my S/500. A matching schematic would have been very helpful. So I had to find the defective device by swapping with the good channel...
Does anybody (Nelson?) have knowledge of this specific version? Seems to be an early version (or stripped down)?
Here is a picture:
Thanks
Hello all,
recently got a S/500. It had DC offset 3 V in one channel and distortions at higher levels.
Found defective device 2N5566. Have ordered replacement already, hope it will work...
I noticed that these both previously posted schematics (Thanks, Nelson!) doesn't match with the PCB in my S/500. A matching schematic would have been very helpful. So I had to find the defective device by swapping with the good channel...
Does anybody (Nelson?) have knowledge of this specific version? Seems to be an early version (or stripped down)?
Here is a picture:
Thanks
Attachments
Hello Nelson,
thanks for the quick reply!
The schematic doesn't match, unfortunately. On the other hand it was pretty helpful as it's similar, input stage is identical (I suppose..).
The board has an opto coupler 4N37 plus one transistor PN 4250A not contained in the drawing and I can see only one thermistor.
Any idea?
Cheers, Gerhard
thanks for the quick reply!
The schematic doesn't match, unfortunately. On the other hand it was pretty helpful as it's similar, input stage is identical (I suppose..).
The board has an opto coupler 4N37 plus one transistor PN 4250A not contained in the drawing and I can see only one thermistor.
Any idea?
Cheers, Gerhard
Gentlemen, I have upgraded the big power supply caps on my SA-2's so far. I wanted as well to update the rectifiers but am challenged as to what the best solution here should be. Fast, slow - and with the upgraded capacitance in the power supply would anyone have experience with a specific model of rectifier? Thanks in advance
Nelson prefers the slow ones.
I've upgraded my SA/1's from the stock 29,000 uF Mallory's to 68,000 uF CDE's.
The rectifiers are attached to the bottomplate so I reckoned they cool down enough so I kept the ones that were already in. I did not encounter any problems with them as far as I know.
It looks like the optical bias version to me because there's a blue thermister that pokes into your heatsink. The black one is for the thermal shutdown provision.
The last Schematic Nelson supplied is from the Series II versions.
The first one he supplied is the most correct one because it has the IC's and thermistors on them.
I will also attach a frontendboard from a SA/1 optical bias version which seems the same to me as your version.
Attachments
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Ok, so I am enamoured with capacitors these days having just finished updating the cross-overs on my speakers for a second time. This time using Mundorf and Obbligato capacitors instead of the basic generic caps that can be had at one of my local speaker parts stores. I could not be more surprised and pleased at the results of replacing the caps of these speakers which for the mid 80's were considered to be upper echelon in quality. This makes me wonder how much of an improvement can be had by updating the front end caps on my SA/2 with a couple of today's "Supercaps" like a V-Cap or a Dueland.
My question then is this. Which of the front end caps would be sensible to replace. The silver pF caps I would think should stay. The tantalum seems like it would be eligible as would the Mylar and Polyfilm caps. The 47uF aluminum also seems a good candidate likely where a Blackgate would have gone, but has anyone tried to shoehorn a film cap here?
I am looking for bang for the buck here, so if a single change makes a big sonic difference then this would be a place to invest as opposed to changing all.
Lastly has anyone added bypass caps to the main big cans and if so what would experience recommend?
Thanks!
Marketprice Threshold Stasis Series
Based on my 30 year experience with Threshold gear buying and selling this would be my best estimation for near mint Threshold Stasis designs.
I have not much experience with the last 'e' Series (SA/3.9 ~ SA/12 and S/450 ~ S/1600) so I did not provide listings for these ones.
The once graced with meters (Stasis 1, S/1000 and SA/1 are particurlary wanted)
The Stasis 1 is pretty rare and the only offering in the US I ever saw was from Nelson's long time associate Joe Sammuth.
My favorites: SA/3 (because Nelson likes it so much) the S/500 and the SA/1.
Upgrades are for 90 percent in the frontend section.
When ever I bought a Threshold I immediately swapped all the lytics (big cans also) and I would start a so called stowed away or not used for a long time with a Variac. Nelson did not employ any sofstart relays with these models in so far I know so you won't burn out the rushincurrent limiting resistors.
- Stasis 3: $700.00
- Stasis 2: $1000.00
- Stasis 1: $5000.00 (pair)
- S/150: $450.00
- S/200 Series II: $600.00
- S/200 optical bias: $700.00
- S/300: $700.00
- S/300 Series II: $800.00
- S/300 optical bias: $900.00
- SA/3: $900.00
- SA/3 optical bias: $1000.00
- S/500: $1000.00
- S/500 Series II: $1150.00
- S/500 optical bias: $1350.00
- SA/2: $2250.00 (pair)
- SA/2 optical bias: $2500.00 (pair)
- S/1000: $3500.00 (pair)
- S/1000 Series II: $4000.00 (pair)
- SA/1: $4500.00 (pair)
- SA/1 optical bias: $5000.00 (pair)
Based on my 30 year experience with Threshold gear buying and selling this would be my best estimation for near mint Threshold Stasis designs.
I have not much experience with the last 'e' Series (SA/3.9 ~ SA/12 and S/450 ~ S/1600) so I did not provide listings for these ones.
The once graced with meters (Stasis 1, S/1000 and SA/1 are particurlary wanted)
The Stasis 1 is pretty rare and the only offering in the US I ever saw was from Nelson's long time associate Joe Sammuth.
My favorites: SA/3 (because Nelson likes it so much
) the S/500 and the SA/1.Upgrades are for 90 percent in the frontend section.
When ever I bought a Threshold I immediately swapped all the lytics (big cans also) and I would start a so called stowed away or not used for a long time with a Variac. Nelson did not employ any sofstart relays with these models in so far I know so you won't burn out the rushincurrent limiting resistors.
- Stasis 3: $700.00
- Stasis 2: $1000.00
- Stasis 1: $5000.00 (pair)
- S/150: $450.00
- S/200 Series II: $600.00
- S/200 optical bias: $700.00
- S/300: $700.00
- S/300 Series II: $800.00
- S/300 optical bias: $900.00
- SA/3: $900.00
- SA/3 optical bias: $1000.00
- S/500: $1000.00
- S/500 Series II: $1150.00
- S/500 optical bias: $1350.00
- SA/2: $2250.00 (pair)
- SA/2 optical bias: $2500.00 (pair)
- S/1000: $3500.00 (pair)
- S/1000 Series II: $4000.00 (pair)
- SA/1: $4500.00 (pair)
- SA/1 optical bias: $5000.00 (pair)
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