Modified SCA-80 with Transcendence 2

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dmtparker

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Modified SCA-80 with Transcendence 2
« on: 14 Feb 2015, 08:23 pm »
OK, so I've had this SCA-80 that I bought on ebay several years ago and I finally decided to "look under the lid." To my surprise, it is not a Dynaco at all. It is a Transendence 2. A sticker on the amp says "Custom built by Jensen Stereo Shop" with the date "2/9/83." It has 4 preamp boards labelled "Transcendence 2" which appear to be the same circuit, but are stuffed and wired differently - I presume phono and line level preamps. The amp module is also labelled "Transcendence 2"  The output transistors (?Mosfets?) are labelled "K135" & "J50" The power supply is obviously also different though it looks like the original board was used. There is a "dynamite" stack of 4 caps replacing C-9 + 11. The balance and volume controls are stepped and the Bass/Treble controls are disconnected.
So, what have I got? I cannot find anything on the site referring to this model. Obviously it was an early 80's mod, apparently done by the Jensen Stereo Shop (the old name for Audio by Van Alstine's) Any further info such a circuit diagrams or articles about it would be greatly appreciated.

avahifi

Re: Modified SCA-80 with Transcendence 2
« Reply #1 on: 16 Feb 2015, 04:10 pm »
Congratulations, you have an AVA Transcendence Two Control Amplifier built in an old Dyna SCA-80 chassis.

Assuming it is working properly, it should be a great sounding unit.  If the original single ended Dyna power transformer was used, it will make about 25W/Ch very cleanly.

If it has a replacement center tapped toroid power transformer, it could be 100W channel or thereabouts.  Once built, the transformers are not interchangeable as different circuit designs were required for each version.

It was built so long ago that I don't even remember much about it.  The T2 preamp circuits were discrete transistor designs but were very expensive to make and did not stay in production very long.  However the unit was very durable.  The output devices are indeed Hitachi power mos-fets.  Their voltage and power ratings are overkill for this circuit and they should be nearly impossible to break.  The design pre-dated our computer records here and any detailed info about the circuits are long buried in our archived paper records.

Any issues with it are likely to be dirty switches and controls.  Spraying everything that can move inside with Caig Labs Deoxit D-5 spray contact cleaner (available from Parts Express) will likely restore any non functional switches back to good working order.

I hope it is giving your great musical service.

Frank Van Alstine

dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #2 on: 16 Feb 2015, 09:38 pm »
Actually, the preamp boards for both phono and line use dip ICs in sockets. I was wondering about replacing them with more 'modern' ICs, but as you say, it sounds so good that I may just leave well enough alone.

dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #3 on: 23 Oct 2017, 11:24 pm »
OK, now I DO need help. One channel died. Like 0, no sound whatsoever. Because it was easy, I replaced the output MOSFETs to no avail. Since I am (sadly) not using the phono stage and all 4 ICs were the same, I tried swapping them around to no effect. I tried further troubleshooting (without a schematic) by swapping the single wire from the line level boards to the output boards.  I figured that would at least tell me if the problem was with the line level or the output circuit. The results are very strange and I cannot explain them. I'll try to summarize schematically:
L pre > L out > good sound // R pre > R out > no sound (this is where I started)
L pre > R out > no sound // R pre > L out >good sound, but only very softly with volume at max!
From the first set, I would assume the L out is good and the R out is bad; but why on the other side is the volume so low with  R pre > L out ??

Any ideas? It was such a great amp, I hate to give up on it.

dB Cooper

Re: Modified SCA-80 with Transcendence 2
« Reply #4 on: 24 Oct 2017, 04:10 am »
dmtparker, wondering if this looks like your amp? Mine is (as the sticker says) a 'MosFet CA-80' although you will notice that the boards themselves are labeled 'Transcendence PC-7A' in the power section and 'Transcendence PC-2A' for the phono and line boards. Note the row of diodes in the lower left corner of the PC-7A; I believe they are all connected in series from my recollection of the schematic. I actually used to have schematics (do AVA amps still come with those?) but lost them years ago. I believe this is the absolute first generation of the 'MosFet' series although sounds like yours was '83 not '84.

I built the original Dynaco-circuit version when I was 15 with lawnmowing money and can't bear to part with it. Some time back, Frank told me he could probably make it sing again (the electrolytics are shot; it hums badly) but I don't know if it would be worth the expenditure (Round trip shipping alone would probably be $100).

Anyway, behold 'Old Faithful'.











dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #5 on: 24 Oct 2017, 12:35 pm »
Yes, pictures are very close. All pc boards look the same. My power caps are 4 instead of 3 tied together and the output caps are 2 newer/smaller (physical) size instead of the big blue dyna caps (though that could have been a later mod). Mine does not have a serial number, but has the date 2/9/83 and initials 'FVA' with the words 'Mosfet control amplifier' hand written on the blue Jensen Audio sticker.
What are your plans for yours? Without a schematic, I'm somewhat stymied trying to trouble shoot, but if you wanted to sell any of your boards, I could be interested.

Mark Korda

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    • Dawkus
Re: Modified SCA-80 with Transcendence 2
« Reply #6 on: 24 Oct 2017, 01:18 pm »
Hi DMT,
   I had that amp. I loved it but was forced to sell it to a friend when I had to few coins in my pocket. I'd put the year at 86 when I sent it to Frank VanAlstine to get modified. I still have the sales literature from Franks. I never throw anything about Hi-fi away. I'll dig it out tonight and when I do I'll get you a copy and FVA too.
    Mine was a unique amp that Frank might not even realized. It was a SCA-80(Q) which had the built in Hafler circuit for Dyna quad, you might of seen those Dyna Quadapters before, this was built into my amp. Therefore I might have had one of the first (surround sound) amps, in a way. As I remember you had to match the speakers in the back as it lacked a level control.
     At one time in the Eagles Nest, my lone studio 3rd floor apt. over an upolstery shop I had Dynaco A-40XL's in front with the A-10's in back listening and watching Top Gun or Predator on a stereo VCR by Magnavox, no DVD's yet.
    I know this really wasn't what surround sound is or was, sans Dolby too, but it sure showed off what that amp could do.
     I'm not on talking terms with the friend who has that amp now because of who we voted for president months ago. Even politics has effected Hi-fi...I'll dig out that info tonight after work....Mark Korda.

dB Cooper

Re: Modified SCA-80 with Transcendence 2
« Reply #7 on: 24 Oct 2017, 03:13 pm »
dmtparker... Here is a photo lifted from Frank's 'Audio Basics' 1988 back issue set, showing an 80 from that time. I notice that the layout of the caps in the back is different than mine or your description of yours, but it still has the original Dyna 'soup can' output caps, making me think that the ones in your amp were substituted at some point.

Mark, if you turn up that schematic, I wouldn't mind a copy myself.




Here is my front panel label. Yours being handwritten  and labeled 83 makes me wonder if it was early production or prototype. We apparently both have 'MOSFET CA-80' amps. I never heard about the 100wpc version; I would have done that. Even with 25wpc, it drove my inefficient Allisons quite well in a moderately sized room.





Mark Korda

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Re: Modified SCA-80 with Transcendence 2
« Reply #8 on: 24 Oct 2017, 05:30 pm »
Hi DB,
    I don't think I have a schematic but I have the catalog or sales info. I'll get any useful or informative info to you also....Mark...PS...I have that catalog you showed but it might of been well after my amp was modded.

dB Cooper

Re: Modified SCA-80 with Transcendence 2
« Reply #9 on: 24 Oct 2017, 05:46 pm »

What are your plans for yours? Without a schematic, I'm somewhat stymied trying to trouble shoot, but if you wanted to sell any of your boards, I could be interested.

I keep telling myself I'm going to send it to AVA and get it re-capped but never seem to get around to it. Don't know what a fair price would be. Maybe if you have an offer I'd mull it over. Not sure I can let it go though; there's a lot of nostalgia in it for me... Had it since I was a teenager (pre-AVA rebuild). But Maybe it's time...

Mark Korda

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Re: Modified SCA-80 with Transcendence 2
« Reply #10 on: 24 Oct 2017, 06:18 pm »
Hi Guys,
  Without a scanner anymore I will have to type this out. I hope Frank does not mind, I'm just trying to help. There is no schematic but some of this might help you in your repair if your going the DIY route; here goes.....April 1,1981.
   The MOS-FET control amplifier SCA-80 is a combination of the MOS-FET 80C circuits and Super FET PAT-4 Series 2 preamp circuits built into either a SCA-80 or SCA-80Q integrated amplifier chassis, complete with precision volume and balance controls and a new power supply.
   The new PC cards contain a simple, but eloquent three transistor Class A voltage amplifier circuit of all new design. Each devise has an independent current regulator for outstanding power supply rejection, the front end cannot overload or slew limit on any signal slope( the amplifier has an infinate slew factor). Each channel has trim pots for adjusting bias current and DC centerline for maximum power and symetrical clipping. Gain set and pole determining components are installed in matched pairs for exact channel balance.
      The current amp is a complementary pair of Hitachi 2SK133 and 2SJ48 power MOS-FET devices. They are each rated at 100 watts, 120 volts, and 7 amps and thus cannot be over driven in this circuit. Because the current amp has high input impedence, no driver transistors are required. V1 limiting, thermal bias tracking,and output coils are unnecessary and are not used.
    The power supply is a stiff unregulated 70 volt DC supply, with a seperate supply for the voltage amplifiers, and additional decoupling and regulation at the cards.
    Well thats all I can dig up for right now. It's above me but I hope might be of some use to you guys. I loved that amp....Mark Korda.

rlee8394

Re: Modified SCA-80 with Transcendence 2
« Reply #11 on: 24 Oct 2017, 07:08 pm »
Man, what a sweet integrated. I'd love to have one of these! I would recap the output caps and inductors with replacements from Updatemydynaco.com or other sources. There are lots around on the bay. Also would check the power supply caps. I also have the new Exicon Mos-Fet devices that I would install in place of the Hitachi transistors. If Frank isn't able to service your unit due to either age or current commitments, I'll check it out for you for a reasonable fee (you decide) plus parts.

-Ron

dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #12 on: 24 Oct 2017, 08:37 pm »
   The new PC cards contain a simple, but eloquent three transistor Class A voltage amplifier circuit of all new design. Each devise has an independent current regulator for outstanding power supply rejection, the front end cannot overload or slew limit on any signal slope( the amplifier has an infinate slew factor). Each channel has trim pots for adjusting bias current and DC centerline for maximum power and symetrical clipping. Gain set and pole determining components are installed in matched pairs for exact channel balance.
      The current amp is a complementary pair of Hitachi 2SK133 and 2SJ48 power MOS-FET devices. They are each rated at 100 watts, 120 volts, and 7 amps and thus cannot be over driven in this circuit. Because the current amp has high input impedance, no driver transistors are required. V1 limiting, thermal bias tracking,and output coils are unnecessary and are not used.
   
Slight differences here. Both of the pre-amp (phono & line) use an IC instead of discrete transistors the IC is marked: "214C    LF    356N"  The output Mosfets are marked "K135 & J50". The power supply has 4 x 4700uF caps, wired 3 for C9 and 1 for C11.

Without a schematic, pretty hard to troubleshoot.

dB Cooper

Re: Modified SCA-80 with Transcendence 2
« Reply #13 on: 25 Oct 2017, 02:41 am »
If Frank isn't able to service your unit due to either age or current commitments, I'll check it out for you for a reasonable fee (you decide) plus parts.

-Ron

I'll keep that in mind rlee. You're in Western MD, correct? Save a lot on shipping compared to MN. (This thing is heavy, plus I think there's an upper limit to what it makes sense to sink into it.)

avahifi

Re: Modified SCA-80 with Transcendence 2
« Reply #14 on: 25 Oct 2017, 09:59 pm »
We can still service this amplifier but of course we will need to see it.  It is a very durable and musical little amp and almost always worth fixing.

Not many audio companies still willing to service 35 year old models.

Your issue may be just a dirty switch contact.  Clean them all with Craig Labs Deoxit D5 spray contact cleaner available for about $10 from Partsexpress.com. Spray into all pots, switches, and jacks. Exercise them all at least 50 times each.

If all else fails, Ship it to us via insured UPS packed to survive being kicked down a flight of stairs.

Been out of commission for past few days due to cataract surgery. 

Frank

dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #15 on: 25 Oct 2017, 11:55 pm »
I agree that is a great offer. Not many companies are even around 35 years later! Unfortunately, I am in Panama and getting the amp back and forth from here would cost a small fortune. IF you have any recommendations for testing I could do to narrow things down to where I might be able to buy some replacement parts from you, I'd be very grateful. It was one sweet amp and the thought of converting it to an LM3386 with something from Update my Dynaco does not really appeal.

dB Cooper

Re: Modified SCA-80 with Transcendence 2
« Reply #16 on: 26 Oct 2017, 04:16 am »

Not many audio companies still willing to service 35 year old models.


Frank

Just one of a number of things that make AVA unusual in the industry. If you flipped through a Stereophile or TAS from then, how many of the glowing-review manufacturers would you still recognize?

rlee8394

Re: Modified SCA-80 with Transcendence 2
« Reply #17 on: 26 Oct 2017, 02:55 pm »
What Frank said. Try the cleaning first. If he is willing to service the amp, he would be my first choice if I were you.

dmtparker

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Re: Modified SCA-80 with Transcendence 2
« Reply #18 on: 26 Oct 2017, 02:59 pm »
What Frank said. Try the cleaning first. If he is willing to service the amp, he would be my first choice if I were you.
I assume this is in reference to db Cooper. I cannot imagine cleaning fixing a dead channel.

Brett Buck

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Re: Modified SCA-80 with Transcendence 2
« Reply #19 on: 26 Oct 2017, 04:28 pm »
I assume this is in reference to db Cooper. I cannot imagine cleaning fixing a dead channel.

    ???  I am not sure exactly what you are referring to, but certainly, by far the most likely failure mode is that some of the switch contacts in one channel are dirty or corroded  and not making contact. Electronic failures are rare, not unheard of, but certainly not on par with mechanical switches.

     Brett