Hi. I'm planning to buy an old Technics amp. I used to listen to a friends' model (can't recall which, but it was a class AA) and it was fantastic. I found a SU-V450 unit from 1990 in very good condition for about 100€, and I tried googling about opinions/reviews of it with no luck. The specs seem to be:

· Class AA, VC-4 (whatever that means)
· 2x50W @ 8 Ohms
· 20-20.000 Hz < 0,007% THD
· 100dB SNR

I will be using with my CD player and PC (music mainly). My speakers are a pair of Infinity 11MKII, rated 100W @ 8 Ohms. My current amplifier is a Yamaha AX-392.


Do you think it's worth the price? Is there a specifically good unit to search from this era (late 80's - 90's)?

Thanks in advance.


PD: i also found this, a SU-Z1 unit from 1980, 2x25W @ 8 Ohms, 20-20,000 Hz < 0,08% THD. No more specs unfortunately. What do you think?

The Technics Class A amps were pretty damn good (personal opinion). There's some well thought out and very neat circuitry in there and they were made to a good standard of construction. I have a SU-V3 from c1981 that still sounds excellent, although it's beginning to fail in the switching area (especially the input-selector, which has been cleaned several times in its life).

Before you buy, be aware that things like volume/balance etc controls could be noisy. They're easy enough to change and not expensive if you are a dab-hand at electronics but I'd imagine a professional replacement could work out expensive. Switching is an area where replacements might be hard to get, however, and cleaning would be less successful and harder to do.

Thanks for the tip.

I have found that my speakers are not 100W @ 8 ohms as I first thought, but 75W @ 6 ohms. With an amplifier that outputs 2x50W @ 8 ohms, will I have the risk of damaging my speakers/amp?

You will not be sending enough power to your speakers. The result could eventually - when you want to crank it up - be clipping which means blown tweeters. Always get amps which deliver more power than you need, not the other way around. The ohms mismatch should not be a really big deal.

Really? I read somewhere that due to the smaller impedance of the speaker, the amplifier would have to send it more current, and that could damage the amplifier. Is that wrong?

Amps are usually made to handle speaker from 4 to 8 ohm. On 4 ohms they will give out more power, but most of them really can handle it, and a bit more. What could hapen, IIRC (it has been a while), is that when an amp is too low on power, the feedback current from speakers could ruin an amp, but I can't remember how. I had to make AB class amp for graduation.

Of course, we all know hat happens if amp is too powerful - but you can drive 50W speakers with 500W amp - you just don't turn it up louder than speakers can handle

And I seriously doubt if anyone has driven an 50W amp to it's full power - do you know how loud is 50W? at parties, maybe, I have driven my 90W amp to more than half power, and it was damn loud. More than that caused pain to everyone

@Anacondo: I'd buy it - I had it for one period of life, and I was satisfied with sound. But then I listened music vith bass and treble to full, and loudness now I have Yamaha AX-390.

Ivan.

@ Anacondo
You are right! The situation is quite the opposite of what boojum is saying. The impedance of a speaker should ALWAYS be equal to or greater than the impedance of the amplifier.
It is just like you have read: the amp has to produce more current and when it exceeds the maximum current it will get overheated or might even be blown.

The same goes for the power specs. The power of the speaker should preferably be greater than the output power of the amplifier. If there is a significant mismatch then the loudspeaker might be damaged.

With Tube amps maybe, but I see no way how could this happen with a transistor amp.

J.M.

Absolutley not true, unless you know one hell of a lot more than JBL loudspeakers. Check out their site on underpowered amps. Clipping = square waves = blown tweeters. Please check out what JBL says on this subject before you reply. I blew a JBL tweeter and they replaced it under warranty and enclosed the little booklet about using too little power. Please check their site on this before you reply. Thanks.

Under- and over-power is bad. Underpower is supposed to be easy to notice however. But if you overpower speakers you may not notice that you are doing so. However in either case you have probably deafened yourself already, so the problem may be moot.

JBL says far and away the problem is underpowered amps being overdriven to clipping.

The info is here. Please read it. http://www.jblpro.com/pub/technote/lowpower.pdf

@ boojum

I have read the JBL info you linked to. Unfortunately I must say that nowhere in this manual I could find that the impedance or handling power of the loudspeaker should be lower than the amplifier specs.

It is correct that the output power of an amplifier is related to the impedance. When JBL is talking about low power it is about the electrical output power required by the musical energy in the audio signal. Hence it is related to the input signal and not to the output signal.

What the info does say is:
1. Purchase an amplifier that provides more power than you will need. The advice here is that your amp should be able to produce the output power that is required by the transients in the input audio signal before harmonic distortions come in. If the volume of the amplifier is cranked up these transients will cause audible distortion in the output signal and eventually clipping. This is what JBL means with 'low power' on amps.
2. Do not drive the amp into clipping. Clipping sounds occur on loud passages when the system is played at loud volume levels.

The JBL info doesn't say anything about the impact of the loudspeaker on the amplifier. To shine a little light on that I would say the following.

The impedance of an electrical device is the electrical resistance in the AC domain (AC = alternating current). It is a rather complex phenomenon which is a.o. relative to frequency and phase. But to keep it simple it is in essence an electrical resistance.
If you connect a loudspeaker with lower impedance than is required by the amplifier, you create too low electrical resistance on the output of the amplifier. This will cause the amplifier to produce higher output currents and might also drive the amp into clipping. If the mismatch is too big this will act as an electrical shortcut and the amp will be blown.

I hope this helps.

Cheers!

Any amp you buy will have a rated minimum impedence for speakers connected to it. Some amplifiers will support a range (say 4-16 ohms) and some a single value (8 ohms). Attaching a speaker with a higher impedence than rated will not be a problem - the amp just won't be able to put out rated power (this is different with tube amps, for a number of reasons). Attaching a speaker with a lower than rated impedence will draw more current (Amps) from the amp then it was designed for - some amps don't mind, some will respond by dying and some will respond by producing distortion of several tens of percent.

As for power rating - there are two factors in play.

If the amp is lower powered than the speakers you won't be able to play the speakers as loud as they can go. In an attempt to do this, you will likely drive the amp into clipping. Clipping kills tweeters for one of two reasons. Read Rod Elliot's excellent article on the matter for more information. What this means is if you turn the volume knob all the way up your tweeters might die/

If the amp is higher powered than the speakers, it will be able to play the speakers more loudly than they were designed for. That means if you turn the volume all the way up your speakers will die. However, if you practice some restraint with the knob it won't be a problem. Another bonus of a higher powered amp is that it won't clip on sharp transients. If you like listening to really dynamic must (classical, largely) then this will be good for you.

In short - you want the amp and speaker power to be similarly rated (not 10W speakers and 500W amp) but with more power on the amp.

Well, thanks all for your responses. A friend of mine advised me against buying 20 year-old gear, and I finally bought a brand new NAD C325BEE amplifier; I couldn't be happier with my decision. I miss the fancy VU meters, though.

I learned a lot from this topic, so thanks again.