Concern about safely connecting two sets of speakers to one amp

printboy

Wondering if anyone could answer an ohm question for me as there is lots of confusing info on the web. Plus I just cant seem to get a grasp of this stuff.

I am considering to buy a completely restored (cleaned, recapped...) mid 1970s Realistic SA-1500 integrated amp. Below are the specs on the amp. However the amp states on back to use 8 or 16 ohm speakers only.

At present, I run both Polk 4As @ 6 ohms and Polk S4s 8 @ ohms as main fronts as I like the combined sound. (Dave Shirly @westmassguy recently upgraded both XOs with dramatic effect).

I connect the speakers to a speaker selector box, with impedance protection switch off, which is then connected to my NAD 7020e receiver. The volume knob on my receiver is set at and never exceeds the 9 o'clock position as I use a Niles Line Level volume control as the output on my Tjoeb 99 Cd player and a number of songs on my iPod is louder than say my Nakamichi tape deck. I never play music extremely loud.

So would it be safe for both the speakers and the amp I am looking to buy if I stayed with this speaker connection/arrangement?


Thanks in advance for thoughts or advice on the matter.
Quin

Realistic SA-1500
Power output: 35 watts per channel into 8Ω (stereo)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 1%
Input sensitivity: 3mV (MM), 160mV (line)
Signal to noise ratio: 65dB (MM), 75dB (line)
Speaker load impedance: 4Ω to 16Ω

F1nut

IMO, you'd be much better off getting one pair of better speakers. You'd have less gear and connections for a cleaner signal path combined with the better speakers will result in 'mo better sound.

mhardy6647

I have no idea how well the nominal impedance values of those two loudspeakers actually represent their frequency-dependent impedance curves. I don't really know how robustly designed that R/S amplifier (which, I believe, was made by Hitachi) is, either.

All things considered, prudence would dictate not trying to run both at the same time on that amplifier. This is assuming that the "A+B" speaker connection made in the amplifier via its speaker selector switch connects the A and B speakers of each channel in parallel, thus:




There are two caveats.

1) It is possible (though not likely) that the R/S amplifier would connect "A+B" speakers in series rather than parallel. In that case, the load impedance would be additive (i.e., A+B would be higher than A or B separately). This is a rare condition in solid state amplifiers. It can be tested (carefully!!!!) by connecting one pair of speakers to "A" and then selecting "A+B". If there is still sound from the "A" speakers, the connection is parallel. If there is no sound from the "A" speakers when "A+B" is connected (and no speakers are connected to "B"), then the connection inside the amplifer is series.

2) You could connect the two pairs of speakers in series yourself, bypassing the use of the A + B switch. If you do, the load should be safe for the amp, but you will always have all four speakers playing.

FWIW, here's what a series connection of two pairs of speakers looks like, schematically.

mhardy6647

Not to complicate matters, but are you sure about the model number of the R/S amplifier? I remember the SA-1000 and SA-2000 (ca. 1976-77) and the somewhat later SA-1001 and SA-2001, but I don't remember the SA-1500... and a quick perusal of www.radioshackcatalogs.com didn't turn it up

Is it, perhaps a Canadian or "ex-US" (e.g., European) model, perhaps?

EDIT: Well, found it, sort of:
https://www.hifiengine.com/manual_library/realistic/sa-1500.shtml

It does look like a model intermediate to the SA-1000(A) and SA-2000... but I've never seen one before. OM is multi-lingual, so it appears to be a Euro-model. Cosmetics do suggest same OEM as those two amps, though... which, as I posted before, I do believe was Hitachi.

SA-1000/SA-2000


source: www.radishackcatalogs.com (1977)

SA-1500



(image from www.hifiengine.com)

printboy

Wow! Mhardy didnt mean for you to do that much work! Was just hoping for a short answer at most. Thanks.

For my present system I just wire the speaker selection box to the NAD A terminals only so all four speakers are playing at the same time. This is what I want. I can turn on and off the various sets of speakers via the speaker selector switch if needed.

To answer your question yes the SA-1500 is a Canadian model. Have an opportunity to buy it for a very nice price all restored and recapped. Read some nice things about this amp from vintage dealers outside the US and that it was probably manufactured by Foster Electronics in Japan. Wanna get back into 70's silver face equipment after all these years but need to do it on a budget. So no Pioneer, Sansui.... Dont listen to radio so dont need another receiver. Have a very nice Realistic 31-2009 12 band equalizer as well. I used to poo-poo Realistic stuff back in the day, I now think they made quite decent stuff before the 80s that can be now bought at a decent price.

Again thanks for your input on the matter... pun intended.

Quin

mhardy6647

It could be Foster OEM, but I think most of the integrateds from that period sold by RS were Hitachi made. The tuners definitely were, as were many of the cassette decks (not all) and perhaps even the better 8-track decks.


If you have an impedance-protected speaker switch, I'd recommend using that with the amp.

As an aside, I would also imagine that the faceplate on that amp is kind of "champagne" or gold-ish colored, not silver (if that matters to you, i.e., the OP). The SA-1000 and SA-2000 certainly were -- although the later integrated amps were in fact silver.

F1nut

The moral of the story, those that don't know, don't know they don't know.

mhardy6647

oh -- I don't know about that.

mhardy6647

I will say I am not a big fan of the stacking speakers craze, though (referring to @F1nut's earlier post to this thread).

printboy

thanks Mhardy I dont mind champagne color... Dont need to be color co-ordinated. just using silver face as a term for an era in audio. Thanks for all your help. much appreciated.

F1 why the negatives waves? I admit I dont know a lot about audio and was asking help for those that do. Isnt that the purpose of any forum? You have not contributed any positive here. Just criticism and shown yourself as an elitist.

F1nut

printboy wrote: »

thanks Mhardy I dont mind champagne color... Dont need to be color co-ordinated. just using silver face as a term for an era in audio. Thanks for all your help. much appreciated.

F1 why the negatives waves? I admit I dont know a lot about audio and was asking help for those that do. Isnt that the purpose of any forum? You have not contributed any positive here. Just criticism and shown yourself as an elitist.

Just the opposite, what I offered was nothing but pointing you in the right direction, a positive. Enjoy your bad sound.