Tom's Stereo 120 Upgrade


ST120 upgrade complete. No issues. Assembly manuals very accurate and very helpful. PS tested at exactly 72 volts (on my old Heathkit VTVM). The amps tested fine.

For me the improvement was dramatic. Although the amp was functioning before the upgrade, there was a lot going on that needed attention. Particularly a fluttering sound in the background and only fair high frequency response.

Result of the upgrade: No background noise; dramatically improved highs and really solid clear bass. I really think the amp is now much better than the speakers. Still on the lookout for a pair of A25's!



Still some hum. Assuming PAT-4 upgrade will help with that!

Thanks once again for an excellent product and outstanding service! I will be ordering PAT-4 stuff soon.


Updating of Dynaco PAT4 and Dynaco Stereo 120, as told by Graham from Leicestershire, England

"My hi-fi system is composed of a Dynaco PAT-4, Dynaco Stereo 120, Marantz CD player, Dual record player and a pair of AR 2ax speakers. I built the Dynaco amps from kits in 1968 and they have been in continuous use ever since.

Out of curiosity I googled 'Dynaco' and found Dan's 'updatemydynaco' website.. that set the ball rolling! I decided that this might be the opportunity to replace some of those 46 year old components. Dan guided me through the ordering process and I ordered the kits and updated both amps.

The PAT-4 now has the phono upgrade kit, the distortion reduction kit and regulated power supply, (plus new line stage mods). The Stereo 120 has the full works (total rebuild) including Dan's AMP 101 modules and super heat sinks.

I did have a background hiss in one channel which had been there before I did the updates and Dan diagnosed it as probably a defective resistor in the PAT-4. After changing the resistor I had more pops and bangs from the same channel. After a number of 'question and answer' e-mails and after various tests Dan not only diagnosed the problem but also put together a kit of parts to fix it. (He may produce the parts as a line stage component replacement kit P4LSRC).

My system is now sounding better than ever, and I am hearing detail that I haven't heard before. well worth the update effort. Dan's Dynaco updates, detailed instruction manuals, hints, tips and general advice are first class. It is reassuring to know that a dedicated audio/electronics expert is only an e-mail away.

I would recommend anyone who has Dynaco amps to take a look at Dan's website, contact Dan and have the satisfaction of updating their amps, and be rewarded with truly exceptional sound."

Thanks again,


Leicestershire, England

Two Stereo 120 re-builds in Belgium. Marc comments thusly:

The longer I listen to both my amps, I can only have the highest admiration for your design. The sound of this amplifier exceeds its price range by an extremely large margin. I would describe the sound as "neutral/warm". No trace of hashness anywhere. Very musical and addicting. Sound makes one think of tubes.....

I've mentioned to you that I have other amplifiers, but I could easily live with only this one and be perfectly happy. (Although I might just hold on to my other Dynaco, a VTA-ST-120 tube amp by Bob Latino.) The only thing that did not really work out was the bi-amping on my 91 dbW/m Tannoy Glenair 10's. This is a speaker issue however, the cross-over frequency being 2,1 kHz..... above which there is not much energy on most recordings. As a result, the extra amp did not really matter.

I'll have to find another way to put it at work.. :-))

I had the time of my life building these and could'nt be more pleased with the result ! THANKS.

All the best,


Pictures from Marc's First Amp Conversion


Pictures from Marc's Second Amp Conversion


About PAT4 Upgrades, Nick says:

Not long ago I ordered as a package from Updatemydynaco (Dan) the PAT-4 distortion kit, the tone control bypass switch and the power supply.
As a start my PAT-4 had been completely re-capped and sounded pretty good. I was also one of those folks who did the "lots of microfarad" upgrades to the old power supply cap yet the prospect of the regulated design was just too hard to resist. For anyone with basic soldering and wiring skills, these three updgrades should be easy and it took me only a couple of hours from start to finish. The instructions are excellent and clear, and to boot Dan included two C16 caps in my package. I also followed the instructions and dropped the gain by about 7dB (3.7kOhm resistors). All assembled and buttoned up, I looked at the output on an oscilloscope and already the improvement was obvious in the reduced noise "fuzz" at the output.

But what was really a treat was the sound: Listening through a van alstine built Super Fet Dynaco 150 I got off e-bay and a set of EPI speakers, two things were obvious immediately. First, the reduced noise resulted in music that seemed to be set against a quiet, "black" background and second it was far more detailed than before. Small nuances like the rub of fingers on guitar strings, voices, or small taps on cymbals were far more vivid. The sound is very pleasing indeed. Without question this is one of the best investments that you can make into your PAT-4!

Oh, and Dan is also a great communicator - knowledgeable, friendly and helpful.


About the Full Monte Stereo 120 Upgrade, Dan from Kansas City writes:

I recently came across an ST 120 and wanted to give it a tune-up as a couple transistors on the right channel did not look stock and 3 of the output transistors as well. I am a believer in refreshing old capacitors and resistors so I did some poking around. That is where I met Dan from Updatemydynaco. He asked me what my goal was with the amp and even helped me figure out whether the amp was in immediate need of attention. It turns out all its vital signs were normal and the amp was in running operation as it stood. So I listened to the amp for a couple days to get an idea of how it sounded while my order was filled and sent. I would have been happy to listen to the amp longer but everything arrived in THREE days from my order date. Unbelievably quick shipping mated with very patient and educational telephone discussions already had this project off to a good start. Basically I ordered the whole nine yards.... Amplifier Modules, Updated Power Supply Kit, Power Supply Capacitors, and The Dynamite Capacitor.

I started with the Amplifier Modules. They were a breeze, the instructions were bulletproof and the components looked fantastic. I simply followed the directions and installed the modules. It was that easy. The first sonic improvement I noticed was that the amp lost some of its haziness. It was easier to imagine space between instruments and more of the source material was available to the speakers. I was excited about this, but I was still hopeful for even better performance.

Next I stuffed the Power Supply Kit board, again, the board was hassle free. It was very to easy install as well. The fit and finish of the Amp Modules and the Power Supply are top shelf. Once I had the Power Supply installed, I became instantly aware of how much "garbage" the original board had been feeding the amp modules. Now everything was incredibly clear. Detail was present in everything from fast attacks on acoustic instruments to rosin drenched Cello. There is a cry in The Gunners Dream that could finally take proper affect. The amp was now congestion free. Somehow, I still had an incredibly small sonic desire that was not fulfilled.

In comes the Power Supply capacitors and The Dynamite Capacitor. I opted to chance C9 and C11 to the offered 3900uf caps and replace C12 as well. For me, this was the most fulfilling part of the modifying process. All mods done previously were great steps in bringing this amplifier up to par with great amps of today. But bringing in the weight of the massively increased capacitance in the power supply was precisely what I needed. All of the clarity, all of the tonality, the quickness and detail were now backed by an undeniable increase in bottom end. Talking Drums could actually talk. I finally found out why people would comment on the capabilities of the KLH Six. All of my AR gear had enough behind them to show their true potential. The amp had come together now- brilliant clarity and substance that could make all of my speakers play louder than I needed.

I do not know what my ST 120 sounded like back when it was born, 1965. But I cannot think it sounded better than it sounds right now. Better capacitors, much better resistors, great diodes, and those transistors... Add the security of Mosfet circuitry to the mix and you can't go wrong. I certainly do not have the end all, be all of amplification- but with my new ST 120, I have more than I need. Well recorded offerings are so indulging that I end up listing too late into the night. I did not expect this level of musicality from this solid state amplifier. All things considered, I could not be happier.

Thank you Dan, Thank you for your unbelievably great products,
I am a believer
Daniel from Kansas city

For the knowing, Up-stream is a dynaco Pas-3(updated), and "The Turntable" by Acoustic Research/Teledyne. If needed, Sony DVP S9000es for digital playback.

About the Sound

Rob from Oregon:

"...the next track utilized is from Genius Loves Company (Concord CCD-2248-2). Fever (Track 5), with Natalie Cole, was recorded just prior to the passing of Ray Charles. There is nothing particularly smooth about Ray's voice at this point in his life, and the track provides a wonderful counterpoint to the ethereal quality of Ms. Cole. Think of is as sandpaper vs. butter. The updatemydynaco mod effortlessly captures the essence of this contrast of vocal age, style and timbre...In the final analysis- any piece of equipment should at best never call attention to itself, but in an unobtrusive way draw you into the music. Does the updated ST-120 accomplish such a rare feat? In a word, yes..."

Mark says:

"Your amp boards sound great.
I have ordered some other parts a little while ago.
Looking forward to replacing the PS sections.
I have a bunch of 120's I got from my Dad (he worked at dynaco).
These never were very good sounding.
Your updates made my day.
They sound really good.
nice job"

Dan from Vancouver:

"Happily my units are working well and I remain well pleased with these. Absolutely a 'worth doing' upgrade.. thank you. Surprised that your products aren't of large common knowledge... they should be, as they are both good and affordable. A rare combination these days."

A pro's comments about the Stereo 120 and PAT-4 Upgrades

"I just wanted to let you know I did your kit today for the 120. I have rebuilt several hundred 120's over the last 15 years. I usually have 4 or 5 of them setting here awaiting a break in the action of my tube audio restoration business. I have a few really ugly chassis and transformers from some parts units and sent them out to get powder coated.

When they got back, I remembered that I had bought a pair of your kits to try. I have built many 3886 and 3875 chip amps and while they sound a lot better than they should, I haven't been that impressed. I built your boards today and installed them in the new chassis with an Audio by Van Alstine power supply board mod. (commercial interruption by Dan - I think the PSUG Kit would make it sound even better!)

Been listening to it for a couple of hours, heat sinks are just warm, and it sounds very good! I can certainly recommend your kit to anyone who doesn't want to try to fix the original Dyna boards. Most repairs done on those boards don't last long, because most people don't really fix them, they just replace a blown transistor and fire it back up. They work for a while, then blow same one......

I also recently put some of the DRD4 PAT-4 Distortion Reducer Kits I got from you for the PAT 4. I also mod PAT-4's, and mine sound substantially better than a stock one ever did, but your kit makes a huge difference, even after my film cap rebuild.

Thanks and keep up the great stuff..."

Bruce Brown
Vintage Tube Audio

About Building the Kit

Chuck from New York:

"...I put both of the new boards together yesterday, and enjoyed it very much - the boards are really nicely done, and stuffing them is quite simple the way it's laid out. Hard to make a mistake..."

Rick, who has updated two Stereo 120's, says:

"You have a very nice product. The assembly instructions are excellent. Building the kit was easy. Take your time. Follow the instructions. Read them again if you don't understand the first time. The information one needs is there. Your timely answers to my emails were very helpful. The finished amplifier is better than the original. It was a fun project."

Bill from Florida:

"...What an easy kit to put together. Your manual is perfect! I have done a ton of kits in my life and this one was the easiest I have done in awhile. I may end up getting the power supply retrofit in the future, but, so far, everything is running fine and cool. No hums, hissing, buzzing.....nothing but music!!
Thanks again for your help and advice.

About the Overall Experience

"It started when I discovered that one channel of my Dynaco audio system was inoperative. Seeking a solution, I came upon Dan's web site via a Google search of “dynaco". After disassembling the stereo 120 amplifier, and many emails to and from Dan, I (we) discovered that several components in the power supply had failed, resulting in 96 vdc frying one of the audio boards. Dan's super heat sink, updated board seemed the ideal solution for me, a diy-er and hobbyist, especially since I had assembled the amplifier, PAT~4 pre-amp and FM-3 tuner from kits back in 1968. The materials included in Dan's ki t are first class; the board is of excellent quality and design, with plated-through holes for components, and the silk screen circuit and component diagram is sharp and clear. With Dan's excellent instruction manual guiding every step, it's very difficult for ANYONE to make a mistake. The cost at $109.00, including shipping, for the super heat sink version is more than reasonable - at $89.00 for the non-super heat sink kit, it's a steal, especially compared to other rebuild offerings on EBay. Finally, the quality of the sound coming from my “new” audio system is superb- I think it's better than the original."
Chuck Golden
New York

Phil reports:

"...Thank you for making this kit available. I have already built the kits and installed them... I love this old amp again!"

Feedback from Ebay

About the Music

Chuck reports:

"I took the new "Dynaco-Akitika Stereo 120" for a "road test" yesterday - played Saint-Saens Organ Symphony (CD) at about max listening volume for about 40 minutes - the house shook, wall hangings were vibrating, but the amp didn't even work hard. It got a bit warm around the heat sinks, but not so warm that I couldn't keep my fingers on it. Amazing......just thought you'd like to know this. Bravo!"

Paul, on the DRD-4 Distortion Reducer for the PAT4:

WOW!!! WOW!!! WOW!!! That's all I can say about the Distortion Reducing Upgrade for my PAT-4. I also replaced all of the electrolytics over the past few weeks. But the DRD4 was the top. I finally got it up and running this Sat., July 14, 2012. The first record I played was George Benson and I can't stop. Everything sounds so perfect.

I have been messing around with phono's and amplifiers since Christmas 1955 when Santa left a 1 tube childs' record player. It was soon apart and separated in sort of a component setup way before anyone could spell component. I haven't stopped since. I've had a few amps. but this is something I have never heard before. My turntable is a home brew made of an old 1956 Rek-o-kut motor and platter. I use various MM cartridges always looking for the magic cartridge that sounds the best. It's not the cartridge, it's all of the above. Preamp, amp, speakers, cartridge, turntable and so on. Now I have an old Audio Technica something or other. The tonearm is also homebrew parts of an old arm I bought on ebay for $4.00. So much for now. Gotta go and listen more.


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