Altec pro amp, for home use ?

[SirPaulGerman]

I found a nice altec lansing 9442a anniversary edition, for around $150, those amps were designed for the pro market.
I am going to use for home audio

Can you guys comment on the design and specs ?

I noticed 2 UPC4574 op amps
and 2 10000ug 63v power capacitors
transistors 2SA1302 / 2SC3281

The brochure give spec for TIM noise, less than 0.1

 

[academia50]

Works ? What are those tennis balls hiding?😵

 

[SirPaulGerman]

Those pics are from the web, that the only pics from the inside I was able to find

 

[blazemaster83]

Ah the rare tennis ball model. I have always been a big fan of these amps, but they are starting to get old.

 

[indianajo]

Looked at the schematic. It has 2 TA7317 protection circuits which have been on snipe hunt agendas for years. The UPC4574 op amp is available at digikey only in the cut leg version for soldering direct to pcb. On the plus side, no dual transistors in the input which are no longer available.

 

[SirPaulGerman]

Do you like the design and specs ?

 

[wg_ski]

It’s a fairly common design that usually works well. The SOA protection circuits are optimized for bulletproofing, so if your speakers impedance get crazy low or highly reactive it may go into limit on you. It limits at 12 amps peak and 2.6 amps reactive. It will fully protect things if you run it shorted. I have some speakers it might have trouble driving (and others it won’t). The tendency nowadays is to relax the protection to get better sound, and live with the reliability risks.

 

[SirPaulGerman]

Any mods besides a complete recap ?

 

[huggygood]

The SOA protection circuits are optimized for ballproofing,

The guy who took the photo of his amp must have wanted to try 🤣 🤣

 

[EdGr]

The SOA protection circuits are optimized for bulletproofing, so if your speakers impedance get crazy low or highly reactive it may go into limit on you. It limits at 12 amps peak and 2.6 amps reactive.

Agreed. The foldback current limiting is severe. The manufacturer knew that and provided space for R65 and R66.
Ed

 

[wg_ski]

Any mods besides a complete recap ?

Likely be safe for home use with R65, 66 = 680 ohms, which will raise the short circuit (or reactive load instantaneous current) to about 4.5A. That will be within SOA at 50C which will be about as hot as you’ll ever run it. Any normal speaker (even an MTMWW which tend to dip to 3 ohms and have multiple phase excursions in the low midrange) would be fine with that. I wouldn’t drop them lower than 470 ohms in any case. That would still be safe for someone touching the speaker wires together for a moment while it’s running.

Don’t try to run 2 ohms on this. On this voltage I use 4 pairs of of outputs for that (and an EF3 with 150W drivers).

I would only recap what needs to go. If I measured 200 W/ 4 ohms at clip out of it I’d even leave the 10,000 uF ones.