Spectro Acoustics

[Ingot worx]

the 202

[onanparts]

Looks like the long overdue facelift on my 500-SR is getting moved up.... Condition pictured is how I received it about 10 years ago. It saw a lot of road miles by the previous owner. Small band going from town to town and not much care in how it was handled. Electrically it has held up fine to all the abuse.

[Ingot worx]

Looks like the long overdue facelift on my 500-SR is getting moved up.... Condition pictured is how I received it about 10 years ago. It saw a lot of road miles by the previous owner. Small band going from town to town and not much care in how it was handled. Electrically it has held up fine to all the abuse.

Wow! I remember  seeing that model in night club AV racks in the 80's. Always looked really impressive with 8  or so of those things all racked with the LED's all reading in tandem. That was the BGW era.. Crest was there too. I remember the guy that sold me my Spectro amp (it was a plain faced rack mount 200 series) He referred to it as " poor man's Bugwa (BGW).  What I realized about the 202 that I am rebuilding is that the amp channels can be removed with just a couple of screws and then "pop" just disconnect the whole channel from the Molex connector. So "modular design"  this would have been advantageous in touring situations / live situations where a backstage tech could quickly swap out a channel during a show. Designed for high duty cycles and physical abuse. These things really set the standard for what was required in the pro audio industry which was evolving quickly with greater demands and SPL requirements being asked for.

The fact that these amps are still ticking is a testament to their build quality and design. Other than failing caps and some semiconductors that are getting tired, the core of the amp could conceivably last forever.

[Ingot worx]

I have finished re capping my 202. I also replaced the RCA connectors and the bridge rectifier. I kept the original RCA output transistors because they all work fine, but I also replaced the.33Ohm 2 watt resistors with film resistors. I tried to use good electrolytics like Panasonic where I could find them, and polypropylene wherever possible. All of the driver transistors were OK, but I picked up some spares. having the schematic really helped..Thanks much for that! The Power caps were replaced with 1800uf caps, and I had to drill out new mounting holes for the housings. All in all, I'm very happy with the sound of the amplfier. It's really crisp and nuanced. I'm going to experiment with some of the cap changes from new to older versions from the schematic, but I really intend to make some new looking faceplates for it and the 217.

[gavbruno]

Hello all,

I've been enjoying catching up on some of the Spectro history while researching my latest find. I recently purchased a rack that included the following:

Kenwood KD-2055 turntable
Denon dvd player (forgot the model number)
SA 500SR amp
SA 217R preamp
SA 210R eq
SA 220R fm tuner
KLH DNF1201A dynamic noise filter
KLH TNE7000A transient noise eliminator
KLH Model-1 speakers w analog  bass computer

The left channel was a bit scratchy when testing the setup so I figured all it'd need is a good cleaning. The 500sr amp ended up blowing the speaker fuses, main fuse and blew a test speaker. Afterwards the left channel was obviously completely out, no leds worked. I thought it could be some blown transistors so I had it taken in to a local shop and the guy replaced the problematic transistors. There is still some fuzziness/scratchiness in the left channel (the problematic channel). I've used different speakers and the problem persists. Is this an indication of more transistor troubles, are others failing? I must admit I don't know much about repairing these devices. I've been looking around as much as possible to identify the problems so I don't get taken advantage of with further repairs. I'm also interested in potentially working on this myself.

Any suggestions would be a huge help. Also if anyone has any paperwork or diagrams on any of these pieces that would great. I did manage to get the manuals for all these units which I plan on scanning and uploading for all later this weekend. I'll also upload pictures of the setup later.

Thanks for the stories and input!

[Robin]

Bob probably has the schematic for the 500. If he has it, I will ask him to post it. The noise may be filter caps. One amplifier channel may just be better at hiding it than the other channel?

[Robin]

Boy are we ever in luck! I found something right above my desk. I spent an hour or so and turned all this good stuff into a pdf, but it is 5 megs, so Bob will post a link to where to get it. What I found is not only schematics, but parts lists, circuit description and test procedure. For a bunch of 20 something year olds that spent way too much time at the bar, we actually did some good work back then. I also found a schematic for the 200 SR. There is a hand written test procedure for the tuner, but nothing else?
Hope this helps.
Robin

[gavbruno]

Thanks for the quick reply. Man, that would be great to get my hands on those. Hopefully they'll help shed some light on the matter. I'm taking the unit back to the tech on Monday as I have some warranty on the repair. I'll run some of this by him. I'll certainly keep my eyes peeled for the location of the PDF from Bob.

Well I'm a 20 something year old that probably spends too much time at the bar and listening/fiddling with this gear. It is really some amazing stuff and I can't wait to get it sorted out. I've been looking all over to get as much info on the Spectro Acoustics line as possible. Thanks again for the feedback. Pictures and scans are still on their way, crazy work schedule as of now!

[Robin]

OK, Bob hasn't placed a link to the document yet and I don't know how to do large documents, so e-mail me for Spectro Acoustics 500 watt amp documentation. I also have a 200SR schematic.
robin@midnitesolar.com

[boB]

Here it is !

http://k7iq.midnitesolar.com/spectro%20500%20test.pdf

boB

[gavbruno]

Thanks for throwing that link up, Bob! The schematics definitely came in handy for the tech. However, not handy enough apparently. Just got the amp back and still distortion in the left channel. This time he said he found more transistors that looked to be on their last leg, some resistors, and he adjusted the bias. I'll suggest the filter caps when I take it back tomorrow. Any other suggestions before I take it back tomorrow? The distortion seems to occur during dialogue or segments of low volume. Thanks again for any suggestions.

[Robin]

Transistors do not typically have a last leg. They let you know they are unhappy by blowing up. I would be very suspect of filter caps. There certainly can be other things causing the distortion, but it probably is not a power transistor. Might be smaller ones or leaky capacitors?
If worse comes to worse, maybe we can have bob look at it. Bob is very busy here though and may not have enough time although he would really enjoy it.
I would like to find a Spectro 500 for sale someday. We might use it here at the plant.

[gavbruno]

Just got the amp back and the tech said the bias was off. I hooked the amp back up and finally the distortion was gone and everything sounded great. I ran the thing for about 30 mins before the amp popped, killing the left channel and frying my good speaker. The left grill on the back of the amp couldn't be touched it was so hot. Obviously I'm getting very discouraged with this whole thing. Im beginning to think taking it back to the same tech would be useless.

[Robin]

The tech turned the bias up too far!!!

[1ajs]

random question does anyone know where i could find a replacement fuse holder mine fell out of my 500sr when i was bringing it home.

havent had anyluck at all finding one :S

my 500sr was paird with a nad but i sold that today and think im gunna run it paird with a dynaco pas3 tube pre witch sounds and way nicer then a st70 oddly