My little project ST120R...........

[garage1217]

Project ST120R

Sitting on the couch last night, I was bumming out as I was thin on funds and not able to complete my chip amp project.. bummed to the point of selling it. Browsing ebay I came across a very COOL idea. A guy had gutted an old Dynaco St120 and replaced the parts with modern chip amps. Bingo! I had an St120 sitting on a shelf for years! This is perfect as the new monoblocks that I built "Peter Daniels LM4780 kits run in parellel" produce 60wpc just like the old dynaco. The goal is to totally refurb the old st120 with modern parts and dual monoblocks bringing it up to modern specifications which is why I named it "ST120R for Stereo 120 reconditioned"

In the spirit of the st120 which was one of the first modern high power transistor power amplifiers featuring capacitive output coupling and a regulated power supply "taken from notes found online about the st120" I figured I would do the 42 year old design justice. I would implement the most modern amplifier technology IMO which are gain clone "chip amps". IMO if Dynaco was building kits today, no doubt they would also choose chip amps keeping up with bang for the buck cutting edge technology that any joe can build and afford and sound fantastic.
Here are some photos of the original dirty dusty 42 year old solid state wonder......




Here are some photos of the chip amps themselves....


Tonight I gutted the st120 and layed out the new parts. One thing that 2008 parts have in common with 1966 parts is weight! The new torrids weight as much as all of the st120 guts if not more.
This photo shows 1966 solid state technology that produced 60wpc


This photo shows 2008 solid state technology that also produces 60wpc


Here are photos of the parts layed out inside the new chassis....





The chip amps parts list is as follows...
LM4780 kit with blue boards $68
Premium resistors upgrade (4 x 220R Caddock, 4 x 680R Riken, 8 x 22k
Caddock) $60
4 x BG N 100/50 $52
4 x BG STD 1000/50 $64
2 x Plitron 300VA toroids $160

Items needed to order and things to do....
- order in iec plug, fuse & switch
- order in binding posts
- order in RCA connectors
- order in new mounting feet
- order in heatsinks
- order in or build standoff's for boards
- order in all stainless steel hardware.
- Have a 1/4" aluminum plate cut to cover the entire bottom of the chassis. The chassis is flimsy and I want to give all the parts a solid mount
- Have bottom of chassis powdercoated... Still undecided on color but the bottom of the amp will be silver or black
- Have top cage powdercoated gloss or matt black & keep original dynaco logo & factory build serial number tag

Will keep this post updated on the progress..... Hopefully I have somthing to show in a week or so progress wise...

[garage1217]

Well did one visual mod tonight *LOL* Even thought I used high end caps, I really do not care about any ohhs and ahhhs from anyone reading the name brands.. and I thought the red shrink was just UGLY and would not match the theme I had planned visually. So I sliced off the shrink on all caps and spent a few hours polishing the aluminum. Going to spend more time on the polish but they are looking great.

[tangmonster]

This all looks ver cool.

Are you going to try and reuse the old heatsinks?

Maybe Swop the new inners 90 degrees to the right so that you have a simetrical view from the front.

Enjoy!!

[garage1217]

Tried to lay it out that way, but with the amps connections at each end, it would be a mess wireing. I am VERY detailed in my electrical, that will soon show and this layout will be the best for what I plan to do.

[tangmonster]

hehe

you are right , the wiring is going to be very important with the "show it all design" I'll wait for more pictures.

[garage1217]

Binding posts, rca jacks and rubber feet ordered in today.... Did not want any gold terminals on this amp Was a pain to find these. Still looking for a good IEC chassis connector for the power cord. I saw one with fuse & power switch built in... trying to locate one of those!

Dayton audio binding posts....


Unknown silver plate over copper core RCA chassis jacks...


And 1 1/8" x 1/2" rubber mounting feet as I do not beleive in spikes on ss amps *LOL* Just tear up my rack.

[Conrad Hoffman]

IMO, it looks great, and is the best possible fate for a Stereo 120. The Stereo 120 is arguably the "Plan 9" of amplifier designs.

[garage1217]

Not sure what plan 9 is *LOL* Is that in reference to the 50's alien horror movie?

Anyways yeah... I bought it thinking.. I could refurb it and just have an old turd to sit on the garage shelf and power some cheapy speakers. Once I got it, I went through the parts list to replace everything with new components hahahaha. Was like $300 in parts, I about died. So scrapped the idea and was just going to sell it off, then it hit me. I could use the chassis woohoo!

Just wait until that baby is stripped and powdercoated / reinforced. Going to look GREAT!

[Conrad Hoffman]

Yup, Plan 9 from Outer Space, directed by Ed Wood! Voted the worst director and film of all time. I do highly recommend the movie Ed Wood done by Tim Burton (I think). Long ago I saw an amplifier critique discussing poor design decisions, and the 120 was used as the shining example. Slow outputs, and winding the output inductors around the caps, and the caps themselves, amongst other things. I haven't looked at the circuit in years, but thank goodness we know better today! Just to give it a couple good words, back in college we built lots of Dynaco stuff, and the 120 certainly offered good bang for our limited bucks. Those Stereo 70, PAS-3x, PAT-4, and various solid state amp kits taught us a lot, and I wish I had stashed away a dozen Stereo 70s or MKIIIs, given their selling prices today.

[garage1217]

Hear ya on that! They go for the price of gold now. I have heard some modified st70's that I did not mind but the original.... ugh... I do give credit to the st120 as being one of the first ss amps to ever be built that sounded decent. But at the same time, compared to todays standards it is a waste of shelf space which is why I gutted it! Nice open chassis with lots of venting is great!