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  1. #1
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    Dynaco ST-120 Replacements?

    Back in the early 70s I purchased two Dyanco A-50s, a PAT-4 preamp, and a ST-120 amplifier. A year or so later I purchased another set of A-50s, a second PAT-4 and a second ST-120 thinking I would try the quad sound. Quad didn't do much for me so I ended up making it simple stereo system with one PAT-4 feeding the second with two speakers per side, one on top of the other. I have used this set up for over 35 years and never had a problem it with and liked the way it sounded. Recently one of the ST-120s died. While I was looking around for parts to fix it, I found all the mods that could be done to improve it. I also found a number of reviews that said the Dyanco ST-120 was a poor early transistor design and that just about anything today would be better. Now I am on the fence. Would the money put toward fixing the one and making the mods to both be better spent on two new amps? I was always happy with the ST-120s but perhaps ignorance is bliss and if I heard a newer amplifier I would be surprised at how much better it sounds over the ST-120. Does anyone have an opinion on what they might do in a similar situation? Do you have any recommendations on what would be good simple amplifier with no controls, only inputs and outputs, to replace both ST-120s without breaking the bank? As you may have guessed it has been a while since I have considered new gear and I donít even know the good brands anymore.

  2. #2
    Man of the People Forums Moderator bobsticks's Avatar
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    35 years is pretty long and succesful relationship. And, of course, the commentary begs the question, "Compared to what?". I mean if their talkin' 7k Mac amps or 18k Pass Labs monoblocks, well that's great but hardly feasible.

    It might be more helpful if you mentioned what kind of price ranges you've heard for a reconditioned and modded unit. If it's low enough that may well be the way to go, especially since you can be confident you'll like the results.

  3. #3
    Shostakovich fan Feanor's Avatar
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    Back in the day

    Quote Originally Posted by dynaco_user
    Back in the early 70s I purchased two Dyanco A-50s, a PAT-4 preamp, and a ST-120 amplifier. A year or so later I purchased another set of A-50s, a second PAT-4 and a second ST-120 thinking I would try the quad sound. Quad didn't do much for me so I ended up making it simple stereo system with one PAT-4 feeding the second with two speakers per side, one on top of the other. I have used this set up for over 35 years and never had a problem it with and liked the way it sounded. Recently one of the ST-120s died. While I was looking around for parts to fix it, I found all the mods that could be done to improve it. I also found a number of reviews that said the Dyanco ST-120 was a poor early transistor design and that just about anything today would be better. Now I am on the fence. Would the money put toward fixing the one and making the mods to both be better spent on two new amps?...
    I owned a Dynaco ST-80 back in the day; it was an OK but hardly sensational amp. I've been told, though, that of the ST-80 was perhaps a slightly better sounding amp than the ST-120 -- believe that if you will.

    If you are a DIY type and willing to repair and upgrade for the price of parts, then it might be worthwhile. Otherwise I would say definitely not. You can buy better, used amps for less money no doubt. One I'd recommend having owned it in the recent past, is the Adcom GFA-555II.

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    Quote Originally Posted by bobsticks
    35 years is pretty long and succesful relationship. And, of course, the commentary begs the question, "Compared to what?". I mean if their talkin' 7k Mac amps or 18k Pass Labs monoblocks, well that's great but hardly feasible.
    Most of the negative comments did not compare it to any specific piece of equipment. They only say that it was an early design with many short comings that newer designs do not have.


    Quote Originally Posted by bobsticks
    It might be more helpful if you mentioned what kind of price ranges you've heard for a reconditioned and modded unit. If it's low enough that may well be the way to go, especially since you can be confident you'll like the results.
    I don't plan on buying another ST120 if that is what your are suggesting. I would buy the parts and do the mods and repairs myself. I must admit however that although I am comfortable with doing the actual hands on work, I am not that comfortable with trying to come up with my own transistor substitutions. It appears that even the modifications are now old enough that some of the parts are no longer readily available.

  5. #5
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    I sold many Dynaco ST-120's when they were current models, and they sounded pretty good - back in 1967. Many newer amps do sound much better, and I'm sure that by replacing those amps with something newer and better will yield very satisfactory results.

    Without going into the stratosphere, I'd suggest looking for something like a used Rotel RB-980BX amp which puts out 150 watts per channel - more than twice that which one ST-120 did - and is a whole helluva lot better sounding too.

    The speakers mentioned aren't quite "state of the art," so shelling out big bucks for a really super amp is something that won't be noticed, but a better amp than a ST-120 will definitely be an improvement, and there's no need to break the bank to get one.

    I'm sure there are plenty of other power amps that other members here might recommend, but there's no denying the value and quality of a used Rotel RB-908BX (whch usually goes for around $300) . I use an Adcom GFA-5800, which is often available used for around $700 - $800, but at 250 watts per channel at 8 ohms, it's a bit of overkill for A-50 speakers.

  6. #6
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    Quote Originally Posted by Feanor
    I owned a Dynaco ST-80 back in the day; it was an OK but hardly sensational amp. I've been told, though, that of the ST-80 was perhaps a slightly better sounding amp than the ST-120 -- believe that if you will.

    If you are a DIY type and willing to repair and upgrade for the price of parts, then it might be worthwhile. Otherwise I would say definitely not. You can buy better, used amps for less money no doubt. One I'd recommend having owned it in the recent past, is the Adcom GFA-555II.
    Thanks for the recommendation. I will give it some thought. I have not priced all the parts to do both amps but from what i have seen so far it should be about $100. The GFA-555II on the other hand is apparently only available used and there is quite a variation in price. Even the lowest priced ones however are more then redoing the ST-120s. Of course that is only the case if I am successful, and the performance difference might make it worth while to change to Adcom even if it is a more expensive approach. Plenty to muddle over. Thanks again for your help.

  7. #7
    Shostakovich fan Feanor's Avatar
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    Quote Originally Posted by dynaco_user
    Thanks for the recommendation. I will give it some thought. I have not priced all the parts to do both amps but from what i have seen so far it should be about $100. The GFA-555II on the other hand is apparently only available used and there is quite a variation in price. Even the lowest priced ones however are more then redoing the ST-120s. Of course that is only the case if I am successful, and the performance difference might make it worth while to change to Adcom even if it is a more expensive approach. Plenty to muddle over. Thanks again for your help.
    Good luck if you upgrade -- I definitely wish I had that sort of skill. As a matter of interest, Adcom 555II's run about $400 on eBay, etc.

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    More Questions

    First, I thank everyone who has taken the time to respond. It is appreciated.

    I have been thinking about this and looking around and two ideas come to mind. One idea is that I might purchase two Onkyo M-282s to replace the two ST-120s. They are not top of the line for sure but the specs. actually seem a little better than the ST-120s. They are on sale for $199 each so two of them would not break the bank and I could still put some money toward the ST-120s at my leisure but not feel bad if it turned out to be a bust and I ended up scrapping one. The other idea is that I noted that newer amps are often rated with 4 ohms of impedance and it occurs to me that the A-50s as I recall are 8 ohms. Perhaps I could hookup two A50s to a side in parallel and only buy one amp. That would mean I could put the same amount of money for two amps toward a single amp, or perhaps even a little more, and have much better sounding amp. Based on this I have two follow up questions.

    1. I know that M-282s are a step or two below what most of you might consider useful but considering that I am used to the ST-120s can you think of any reason why they would not be an acceptable purchase? I read one user review that indicated he noted some 60 cycle hum in the outputs, but most of the other user reviews I found indicated it was a decent amp for the price.

    2. Is there any reason why I would not hook up two A-50s in parallel to an amplifier rated for 4 ohm service as long as I kept them phased properly? I know the A50s are no longer state of the art but they donít have ferrofluid in them so they have aged very well. They still sound as good to me as the day I purchased them. Of course it might also be that my hearing is not what it used to be but I can still hear the high pitched chirps of humming birds at a distance which is more than my wife can say ;-).

  9. #9
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by dynaco_user
    I was always happy with the ST-120s but perhaps ignorance is bliss and if I heard a newer amplifier I would be surprised at how much better it sounds over the ST-120. Does anyone have an opinion on what they might do in a similar situation? Do you have any recommendations on what would be good simple amplifier with no controls, only inputs and outputs, to replace both ST-120s without breaking the bank?
    There really is some good news here, but understand that I will be giving my candid opinion. Let me start by saying I have built and owned several Dynaco components over the years. Unquestionably, they represented an incredible value in the 60s and 70s when they were most popular. I've built the FM-5 tuner, PAS-3x preamp, and PAT-5 preamp and owned a factory built ST-120. I later ('76) had the PAT-5 modified by Frank Van Alstine at Jensen's Stereo Shop (now AV Hi Fi). They still have upgrades to Dynaco gear, but all they use of the ST-120 is the chassis. Everything else is changed.

    Honestly, far better sound exists today than the PAT-4/ST-120 at a modest price. If it were me, I would retire at least one of the PAT-4/ST-120 pairs and buy what I think is the modern incarnation of the Dynaco value concept: NAD. While they may not have much sex 'n sizzle, NAD makes some very good sounding integrated amps that offer great value. In that power range, either the C320BEE or the C325BEE would be a wonderful replacement. For $300 new, you can buy the 325 which offers 50 solid watts per channel. In the used market, you can find 320s in the mid to low $200 range. These amps are more dynamic and are free of the high frequency grain audible in the forty year old Dynaco designs.

    Some folks have expressed concern with reliability. I understand that some of the older units were less than stellar in that respect. I own one of their AV receivers and know a couple of other guys who own current NAD gear and have experienced no trouble.

    Highly recommended. Here is their website: NAD and here's a link to a popular internet based audio classified site called Audiogon. just search for NAD. Good luck!

    rw
    Last edited by E-Stat; 08-21-2008 at 11:08 AM.

  10. #10
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by dynaco_user
    1. I know that M-282s are a step or two below what most of you might consider useful but considering that I am used to the ST-120s can you think of any reason why they would not be an acceptable purchase?
    Well, it would not improve the overall sound very much because quite frankly the PAT-4 is still a limiting factor. I really think you need to consider replacing both the amp and preamp with a modern integrated to meet your budget.

    Quote Originally Posted by dynaco_user
    2. Is there any reason why I would not hook up two A-50s in parallel to an amplifier rated for 4 ohm service as long as I kept them phased properly?
    Actually, stacking multiple speakers was done quite a bit back then. In my vintage system, I use double New Advents in that arrangement. Stacking them provides a larger, more realistic sounding image size and increases efficiency by 6 db. That would be same thing as quadrupling the power of your amp. Make sure you invert the upper pair so that the tweeters are closest together. Based upon my earlier suggestion, a C325BEE driving your double A50s would work very well. The NAD design has no trouble driving such a load and would provide more than adequate output.

    rw

  11. #11
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    Problem Solved I Think

    Quote Originally Posted by E-Stat
    Well, it would not improve the overall sound very much because quite frankly the PAT-4 is still a limiting factor. I really think you need to consider replacing both the amp and preamp with a modern integrated to meet your budget.
    Thanks for the advice. I suspect you are probably right about the PAT-4s. They have served me well but it is time to retire them. Based on your brand recommendation, I have looked at the selections on the NAD site and have decided to purchase the C355. It might be overkill for the A-50s but I like the fact that you can hook two sets of speakers to it and turn them on and off independently. It might also save me from having to upgrade the amp later if I really get the bug and decided to replace the A50s as well down the road. Thanks again your patience and help.


    Quote Originally Posted by E-Stat
    Make sure you invert the upper pair so that the tweeters are closest together.
    For 35 years I have been stacking them with the same orientation. It never occurred to me to do otherwise. I will have to give inverting the top one a try.
    I wonder what I will learn tomorrow!

  12. #12
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    Quote Originally Posted by dynaco_user
    Based on your brand recommendation, I have looked at the selections on the NAD site and have decided to purchase the C355. It might be overkill for the A-50s but I like the fact that you can hook two sets of speakers to it and turn them on and off independently. It might also save me from having to upgrade the amp later if I really get the bug and decided to replace the A50s as well down the road. Thanks again your patience and help.
    Well, you can never really have too much power - that's just more headroom. It also has two sets of pre-outs so you could drive a different and/or an additional amplifier. Or powered subwoofers. You're welcome. I think you'll find a lot more "focus* with the NAD amp over the venerable Dynaco combination.

    Quote Originally Posted by dynaco_user
    For 35 years I have been stacking them with the same orientation. It never occurred to me to do otherwise. I will have to give inverting the top one a try.
    What you are doing is roughly emulating a taller line source. Putting the tweeters together should improve the imaging. You can find any number of multi-driver towers today that use what is called an "M-T-M" approach. That stands for midrange tweeter midrange and describes the notion of centering the tweeter(s) between lower range drivers. Like this, for example:

    MTM/D'Appolito design

    rw

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    Update

    As a followup, I have had the C355 for over a week now. At first I was mildly disappointed. When compared with the two PAT-4/ST-120s the highs seemed less pronounced, the mid frequencies did not seem as distinct, and the bass exaggerated. Moving the base and treble controls from the center positions helped a lot but I missed my Dynaco equipment. Then I happened to play some newer New Age CDs I have that were made in the late 90s and they sounded fantastic. Most of my CDs were made when CDs first came out and they were probably made from analog masters used for making LPs. In fact some of my CDs are indeed direct replacements for LPs that I had listened to a lot and were showing their age and wear when CDs first appeared on the scene. Since they are some of my favorites, they are what I listened to first and resulted in my first impression. Perhaps the response of the Dynaco equipment was not as flat as the new NDA unit or the older music was not produced flat. In any case with newer recordings
    it does sound as good, if not better than the Dynaco equipment and I would certainly recommend the C355. Of course, a month ago I might have recommended the Dynaco equipment so my recommendation does not count for a lot.

    My only complaint now is that the remote control does not provide enough variation in volume. It is motor driven, perhaps with a stepper motor as as the settings are very repeatable, and one setting is too low for listening while the next one up is not where I would put it for comfortable conversation. I find I have to set it where I want between the two steps using the volume control on the unit. Perhaps with less efficient speakers than the A50s the steps would not seem so large but with them each step produces a significant change in volume.

    As an aside, I pulled the grills off the A50s to see how the tweeters were oriented so I could stack them as you suggested and found they were not all the same. On three of them the two woofers were in the upper half with the tweeter directly above them right at the top edge. On the fourth one the woofers were in the same location in the top half but the tweeter was mounted directly below them so it was near the center of the speaker. I
    definitely purchased them as pairs direct from Dynaco (an employee purchase - a friend worked at Tyco Labs) so the only thing I can figure is they had a production change for some reason but I have no idea which style is the newer and supposedly better version. I did however turn the top units over on both sides even though on one side it does not move the tweeters that much closer together. I am not sure I hear an improvement from doing that, but it certainly didn't hurt.

    Thanks again for your help and to all that responded.

  14. #14
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by dynaco_user
    As a followup, I have had the C355 for over a week now. At first I was mildly disappointed. When compared with the two PAT-4/ST-120s the highs seemed less pronounced, the mid frequencies did not seem as distinct, and the bass exaggerated.
    Keep listening and I think you'll find that you will be discovering subtle details in your musical collection you haven't heard before.

    Quote Originally Posted by dynaco_user
    As an aside, I pulled the grills off the A50s to see how the tweeters were oriented so I could stack them as you suggested and found they were not all the same.
    Do any look like this?



    In a sense, they already are a quasi-MTM design having two woofers and the roughly centered tweeter. Getting the drivers closer will minimize comb effects.

    rw

  15. #15
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    Quote Originally Posted by E-Stat
    Keep listening and I think you'll find that you will be discovering subtle details in your musical collection you haven't heard before.
    Yes, but with my old music will that be a good thing? ;-)


    Quote Originally Posted by E-Stat
    Do any look like this?

    rw

    Three of the them do but one does not. On one of them the right woofer is the one that is up high in the corner and the left one is down a bit and the tweeter is below the right one, not above it.

    Is your representation considered to be the last configuration produced?

  16. #16
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by dynaco_user
    Yes, but with my old music will that be a good thing? ;-)
    Overall, I've found the answer to be yes but indeed higher resolution systems do reveal any limitations found with the source. With vinyl, you sometimes hear the pre echo found in some disks. Flat recordings sound, well flat. One does get a better appreciation, however, of what really good recordings can do.

    Quote Originally Posted by dynaco_user
    Is your representation considered to be the last configuration produced?
    I really don't know. That was the first pic I found.

    Keep playing the amp pretty solidly for the next couple of weeks as there are likely some break in effects.

    rw

  17. #17
    Audio Enthusiast Valkilm's Avatar
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    Hello,

    This might seem kind of "late" and "out of date" for you, but before yesterday I bought a NAD C355BEE amplifier, so I would like to exchange some ideas with you, please e-mail me at: valkilm@hotmail.com and we will discuss on our NAD's
    Val

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