Update on my chip amp project now called "ST120R"

[desertheat 10+ year member]

Project ST120R

 

Sitting on the couch last night, I was bumming out as I was thin on funds and not able to complete project as the chassis were coming out to almost $500.00 custom built... 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 recondition the old st120 with modern parts and dual monoblocks bringing it up to modern specifications.

 

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.

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 toroids weigh 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

Premium resistors upgrade (4 x 220R Caddock, 4 x 680R Riken, 8 x 22k

Caddock)

4 x BG N 100/50

4 x BG STD 1000/50

2 x Plitron 300VA toroids

 

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 amp theme will be silver or black

- Have top cage powdercoated gloss or matt black.

 

Will keep this post updated on the progress.....

Click to read more...

 

[JimJ 5,000+ posts]

Very interesting...although if you had done that to an ST70 or MkIII I don't think I'd approve //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[desertheat 10+ year member]

*LOL* Yeah would have to dissaprove also //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Been gunning to build an st70 with modern parts and a new chassis as you can get anything for them brand new these days... Still looking for the st70 modern clone sound valves vta70i... Ticked I missed off on one of those in kit form. There mk3 reproduction was very cool as well. Not that I loved the sound of the st70 in particular... *LOL* But I love the artform, class and old school feel that tubes give.

 

[desertheat 10+ year member]

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.

 

[bose301s 5,000+ posts]

Those toroids look to be overkill for a 60wpch amp. Also I hope you plan on heatsinking the FETs or you're gonna fry it. Other than that it looks sweet, and nice Runycon caps, best out there pretty much.

 

[Mr T 10+ year member]

Those toroids look to be overkill for a 60wpch amp. Also I hope you plan on heatsinking the FETs or you're gonna fry it. Other than that it looks sweet, and nice Runycon caps, best out there pretty much.

Maybe slightly, but it doesn't hurt to have some headroom...
Nice build, but I hate you, this is EXACTLY what I want to make, but don't the money to do so //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[desertheat 10+ year member]

The transformers are 300VA, 2 x 22V AC units. which produce the required voltage, how do you feel the required voltage is overkill? Size does not = overkill. Also there are no FETS in the setup, if you are speaking about the 16 mur680 diodes, they do not need to be sinked. Only the lm4780 needs to be sinked which is on the order list above as I am searching for the "right" sink design for my application.

One of the features I like most about chip amps.. in total there are only 25 actual parts per amp including each circuit board.

 

[desertheat 10+ year member]

Binding posts, rca jacks and rubber feet ordered in today....

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.

 

[desertheat 10+ year member]

Finally found reasonable heatsinks. They are a tad on the small side so I plan to use a pair of small low speed fans and actually cnc an air tunnel through the chassis, up through the sinks "sinks will face eachother" and have the fan drawing air up through the top.... Hope that makes sence...

Sort of like [ ] Basically a duct from the bottom, ******* air through the sinks and out the top of the heavily vented chassis.

Sink dimensions...

21 fin, flat bottom 4-9/16" x 2-3/8" x 15/16"H. 4 - 1/8" corner mounting holes.

 

[Mr T 10+ year member]

Who needs 200-300? You can "snake" one in for under 100 dollars easily by making your own chassis out of scrap parts and finding some good deals....

 

[thylantyr 10+ year member]

Finally found reasonable heatsinks. They are a tad on the small side so I plan to use a pair of small low speed fans and actually cnc an air tunnel through the chassis, up through the sinks "sinks will face eachother" and have the fan drawing air up through the top.... Hope that makes sence...
Sort of like [ ] Basically a duct from the bottom, ******* air through the sinks and out the top of the heavily vented chassis.

Sink dimensions...

21 fin, flat bottom 4-9/16" x 2-3/8" x 15/16"H. 4 - 1/8" corner mounting holes.

This idea is nice if you have low profile fans.

http://ampguts.realmofexcursion.com/ADCOM_GFA_4302/inside1.jpg

 

[desertheat 10+ year member]

that pic is close, but I will be building more of a tunnel effect. so air will be forced through the sinks. I have a massive assortment of fan choices from vendors down here and I have spied some very nice 5/8" thick slim line ultra quiet units.

 

[thylantyr 10+ year member]

These fans might be 1 inch too big for your project. Neato.

http://www.bigassfans.com/

//content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[desertheat 10+ year member]

Update as of today 2-7-08 //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Well called in and cancelled the heatsink order just before it shipped haha. I decided to go with a LARGE CNC'ed block of aluminum that both chips will attach to. The other design was just to complicated after thinking it over. Simplicity = bliss. Will show more info on the custom sink block soon.

 

Today my Dayton audio binding posts came in from parts express. Top quality items! I had to drill out the old mounts and use a small diamond file to cut the keyway for the mounts. Turned out flawless and all binding posts are perfectly straight.

 

Along with the binding posts, the mounting feet came in from parts express. I am VERY dissapointed in the mounting feet. They are a VERY hard rubber with little grip. Seems like I might as well have solid plastic feet. Will see how they are when the chassis has weight in it but I cannot see how they will get better.

 

Last items, I received a LARGE qty of flush and button head 6/32 stainless hardware + stainless nylocks from work for free! Very happy about this! High quality hardware for free is rare. I went out to the garage to find a dual cutting edge erwin unibit to drill out the binding post mounts and sitting in the same drawer was a 1950's small tap set with a 6/32 tap that I aquired years ago that has never been opened! Score! Perfect for the new stainless hardware.

 

Here are the photo updates.

 

 

 

 

 

 

 

 

 

 

 

 

 

Cannot wait to get this chassis acid dipped and powdercoated! It is one ugly mother hahaha!

 

I made a decision to mount all the amplifier components on a seperate cnc'ed aluminum plate that will match the bottom of the amplifier footprint wise. It will be raised up about .40" to allow the wireing to be hidden. To make install easy / easy to replace a component of somthing ever happens, I will be adding in quick connects from the IEC - toroids - DC filter - Amplifier. I will not use the quick connects on the audio side of things.

 

The quick connects I am useing are simply the BEST I have ever used. They actually come from the RC car hobby. They are called "deans ultra" connectors. You have to be REALLY carefull when purchasing deans connectors as there is a TON of counterfiets on the market. The true deans have an amazing fit, finish and can handle a lot of amperage. Here is a pic of them...

 

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[desertheat 10+ year member]