Dynaco SCA-80 Stereo?

Oerets

Oerets

AK Subscriber
Subscriber
Ran into a Dynaco SCA-80 integrated amplifier that is a non "Q" model. On the back it shows main and remote speaker connections.

Any info on this compared to the SCA-80Q. Figure it to be about the same just not as common.


Barney
 
Thanks, but mine is a SCA-80 no "Q". Will only play one pair of speakers at a time it looks like.


Just says Dynaco Amplifier on front panel.



Barney
 
The SCA-80 was Dynaco's first solid-state integrated amp. It combined most of the PAT-4's preamp circuitry with the Stereo 80 power amp circuit. The SCA-80Q added passive ambience extraction to the SCA-80 -- a slightly simplified version of the QD-1 Quadaptor circuit. If memory serves, the main circuit differences between the two models were in the wiring of the speaker selector switch and the inclusion of a power resistor in the common feed to the rear channels on the SCA-80Q. That power resistor is located on the inside of the rear panel and performs the ambience extraction.
 
The only difference is the -Q had most of a Quadapter built in. I got mine just as the Q version was released and the dealer gave me a separate Quadapter, which had a rear level control that the SCA-80Q didn't have.
 
Apparently the SCA80Q like to blow up. I've got a blown one on my bench right now with one channel out, and it's not the first time. I've had it apart for a while, waiting to come up with a .47 ohm resistor. I finally got two 1 ohm resistors to parallel, so it's time to get back to work on it. These are not built for easy access when something needs to be replaced.
 
Agreed...I just had one in where the output power was down on one channel. The bootstrap cap had shorted. The amount of disassembly I had to do to replace it was truly annoying. I have yet to put it back together!
 
I've just buttoned mine up for now. The balance control needs to be fixed first. Until then it will sit.


Barney
 
I've got one of these arriving from that auction site in a week or so. I wanted something appropriate to match the Dynaco A25 speakers that I'm nearly finished rebuilding. I know I should replace the rectifier diodes with 400 PIV rated pieces, and all the electrolytic caps, but wonder if replacing the old 5% carbon resistors with 1% metal film parts is a worthwhile effort? I'm planning a complete disassembly of the unit so I don't think physical access to the components will be an issue. Finally, are there any transistor substitutions that will greatly benefit the sound?
 
Typically, the old carbon comp resistors will have drifted a bunch, usually upward in value. The circuits were pretty non-critical, so it's typically not a big deal.

More interesting is the excess noise generated by carbon comp resistors. That is, they make more than the predicted noise with DC current running through them. R26, R31, R33, and R36 are most likely to make a difference.

C11 often goes bad...the 3 section cap that filters the preamp and the driver stage of the power amp. I make a nice kit that replaces it with regulators that drop in nicely.

http://updatemydynaco.com/storeindex.html#SCA80C11
 
Thanks, I knew the old carbon composite resistors were bad for drift/noise. I really appreciate your knowledge of which are most critical to the sound quality. And I'll definitely be replacing/upgrading all of the electrolytics including that C11 multi-section cap.
 
Unless you love to experiment, do not dump a whole lot of time and money into this thing as at best it will never sound that good. The PAT-4 preamp was about the worst preamp ever. I had a pair of the ASCA80s, a Q and a non-Q back when the units were not that old and it made scratching nails across a chaulk sound like Mozart in comparison. You may want to pull the ST80 manual and using it to mod the SCA to bypass the preamp section. The ST80 is (cough, cough) not too bad an amp but still one of the worst capacitive output amps I have heard.
 
(I'd like to have one too, tell you the truth...) ;-)
They're always too 'spensive at eBAY... maybe I should just adopt a PAT-4...

Good luck, have fun, and keep us posted!
 
Unless you love to experiment, do not dump a whole lot of time and money into this thing as at best it will never sound that good. The PAT-4 preamp was about the worst preamp ever. I had a pair of the ASCA80s, a Q and a non-Q back when the units were not that old and it made scratching nails across a chaulk sound like Mozart in comparison. You may want to pull the ST80 manual and using it to mod the SCA to bypass the preamp section. The ST80 is (cough, cough) not too bad an amp but still one of the worst capacitive output amps I have heard.
Click to expand...



And on the other hand, I have heard a number of systems with the PAT4 and both the owners and I thought they sounded fine.

I sugest getting it operational if you can do the work yourself and then maing your own decision.

If it takes a paid tech to do it, then investing the $50 to $100 per hour they are likely to charge is not worth it, these units don't have enough intrinsic value to justify spending that much money on repairs and upgrades.

Shelly_D
 
I'm reasonably skilled with a soldering iron and there's nothing in this vintage amplifier that's terribly difficult. If it keeps me busy at night for several weeks and plays nicely with the A25 speakers after the rebuild, then it's all good.
 
You must log in or register to reply here.

Similar threads

S
Under appreciated: Dynaco SCA-80
Replies
4
Views
4K
bare
B
S
Dynaco SCA-80Q upgrade
Replies
6
Views
2K
Catmanboo
Catmanboo
S
Dynaco SCA-80Q with pushbuttons?
Replies
2
Views
1K
oldenuff
oldenuff
kerrytat2
dynaco sca 80q
Replies
5
Views
3K
ARRAY
ARRAY
Z4N5H1N
Dynaco SCA-80Q...worth picking up?
Replies
3
Views
1K
anden
A
Back
Top Bottom