old altec amps

[dnparadice]

Hello All, Im Jayson and I work for Davis Audio Visual. Im young so I never experienced Altec in there prime. I just get stuck fixing all the aging Altec equipment that has never been turned off since the 70s and 80s when it was installed. I respect any amp that can be turned on and left on for 20+ years with no major problems. That being said all the in house audio was originally Altec; mixers, signal processing amps and speakers with custom room combining components in the larger conference rooms built and installed by LVW. The amps used are 99% 2280A 8ch modular power amps. No one ever had the mind to ever open them up and clean them out before me so when I opened them up for the first time some of them were literally chocked with 20 years of dust and the fans were completely frozen in place. Its amazing they worked at all, and did not catch on fire. Since the hotel we work at does not want to replace the system I have started to repair the old components. The amp cards in the 2280As are easy enough to repair, some only had a single capacitor that needed to be replaced others are a little too far gone. I am handy with a soldering iron but some of the cards have literally toasted and are too brittle to repair. So this brings me to my question. Does any one know where to get cards for old altec amps. I checked out the Great Plains Audio but it looks like they focus on speaker components (my next project). Any help would be great!

-Jayson

[Todd W. White]

IraTec Pro Audio Repair has them, and can fix them.

Call Ira at (405) 324-5311.

Tell him I sent you.

[dnparadice]

Thank you, I called Ira and he is great! We will be sending out some amp cards to be repaired very soon .

thank you again

-Jayson

[Rob 515]

Hello, I have several questions about an altec 2280A Amplifier. It is a mainframe that I have set up with the 8 amplifier modules paralleled into a 1 channel at 600+ watts @ 8 ohms.One of my Questions is since this is a 70 volt amplifier and I have it set up into 1 channel @ 8 ohms is it still 70 volt output? The reason I ask is when I measure the voltage on the speaker output connections it reads no voltage with the volume (on a connected preamp) set at zero and as I increase the volume the voltage on the output goes up. So if I have the volume at say 9 O'clock then the voltage is at about 10 volts or so and as I increase the volume the voltage increases. So I would have to set the volume at 12 O'clock to get 35 volts or so and all the way up to actually read 70 volts on my volt meter at the output.Is this the normal way a 70 volt amplifier works? Or is the output supposed to be 70 volts at all times? I know I am supposed to connect a step down transformer at the speaker end and it steps the voltage back down and makes it into 8 ohms for the speaker. But the manual for the amplifier says if all 8 of the amps are paralleled then it is 8 ohms, so do I need the step down transformer at the speaker when set up as parelleled? How much voltage does it take to damage an 8 ohm speaker? Like if I didn't use a step down transformer and just connected directly to the speaker and never cranked the volume over 9 o'clock or so then only 10 volts or less would reach the speaker. Is that enough voltage to damage a speaker? I'm wondering because I heard a step down transformer degraded the sound and would like to use it without a transformer. Anybody got any info on this? I have read the manual front to back and it says this amp is configurable to high power low impedance output and that's how I have it set up, so do I still need a step down transformer?
thanks for any help
rob

[Old Guy]

Don't do anything

600 watts at 8 ohms is about 70 volts, so i don't see why you think there is a problem?

No it doesn't put out 70 volts all the time, and as far as how much voltage damages an 8 ohm speaker it depends on the speaker.

Regardless from what you seem to be saying it is working fine...so why fix it?

[Rob 515]

Hi thanks! I'm not wanting to fix it, just wondering if I can use it at low volume without a step down transformer on the speaker end? I have 2 of these amps and I have a set of A7 speakers and a set of large JBL stage speakers (all 8 ohms input) and I am trying to set up a small movie theater for about 25 to 50 people. So I wanted to use these amps for that.
Anyway mainly what I need to know is if I need to use step down transformers on the speakers?
thanks
rob

[whitebroncoii]

A 70V system is not constantly 70V. The 70V system output looks just like any other power amplifier. 70V is the constant in calculating power taps.

70V speakers have transformers. Usually these transformers have four power "taps" or step-down windings.

1W transformer tap connected to 8 ohm speaker = 5000 ohms [(70.7V x 70.7V)/1W]
5W transformer tap connected to 8 ohm speaker = 1000 ohms [(70.7V x 70.7V)/5W]
30W transformer tap connected to 8 ohm speaker = 167 ohms [(70.7V x 70.7V)/30W]

70V loads (speakers with transformers) are paralleled to each other. Add the power taps and connect a 70V power amplifier 20% bigger (or more). It is perfectly OK to drive a single 5W load (loudspeaker with transformer tapped at 5W) with a power amp capable of 240W @ 70V. The amplifier does not care. It is not OK to connect ten loudspeakers tapped at 30W (300W total) to a power amp rated at 240W @ 70V.

one 2271 is rated at 75W into 66.6 ohms [(70.7V x 70.7V)/75W]
two 2271s are rated at 150W into 33.3 ohms [(70.7V x 70.7V)/150W]
three
four
five
six
seven
eight 2271s are rated at 600W into 8.3 ohms [(70.7V x 70.7V)/600W]

You could drive an 8 ohm loudspeaker, or a couple of loudspeakers wired for an 8 ohm load, with the full compliment of a 2280 (8 x 2271). However, there are lots of easier power amplifiers to use.

[Old Guy]

Hi thanks! I'm not wanting to fix it, just wondering if I can use it at low volume without a step down transformer on the speaker end? I have 2 of these amps and I have a set of A7 speakers and a set of large JBL stage speakers (all 8 ohms input) and I am trying to set up a small movie theater for about 25 to 50 people. So I wanted to use these amps for that.
Anyway mainly what I need to know is if I need to use step down transformers on the speakers?
thanks
rob

I still don't understand...if it is rated for an 8 ohm load, and you put an 8 ohm load on it, there is no reason to think you will need a transformer.

You also state you have sets of speakers rated 8 ohms...that is most likely EACH, which means a pair is 4. So no you cannot use the amp that way.

An amp rated 600 watts at 8 will run the 8 ohm load just fine, why would you think any different?

[Rob 515]

"A 70V system is not constantly 70V. The 70V system output looks just like any other power amplifier. 70V is the constant in calculating power taps."

This is the part that I seem to be having a hard time understanding.I didn't know that a 70V system output looks just like any other power amplifier. So if I connect just one 8 ohm load (one loudspeaker) to the one 600 watt 8 ohm output of the amp then I shouldn't need a step down / line matching transformer? Is this correct? Only if I want to connect more than one loudspeaker to one 8 ohm output of the amp , say two or more in parallel, then I will need the step down / line matching transformer?

"70V speakers have transformers. Usually these transformers have four power "taps" or step-down windings".

My speakers aren't 70 volt from the factory, but I do have some 80 watt 70 volt transformers I could use one for each speaker. But if I am using only one 8 ohm load (one 8 ohm speaker) on one 8 ohm output of the amp (eight 2271 combined) do I still need the transformer at the speaker?

1W transformer tap connected to 8 ohm speaker = 5000 ohms [(70.7V x 70.7V)/1W]
5W transformer tap connected to 8 ohm speaker = 1000 ohms [(70.7V x 70.7V)/5W]
30W transformer tap connected to 8 ohm speaker = 167 ohms [(70.7V x 70.7V)/30W]

"70V loads (speakers with transformers) are paralleled to each other. Add the power taps and connect a 70V power amplifier 20% bigger (or more). It is perfectly OK to drive a single 5W load (loudspeaker with transformer tapped at 5W) with a power amp capable of 240W @ 70V. The amplifier does not care. It is not OK to connect ten loudspeakers tapped at 30W (300W total) to a power amp rated at 240W @ 70V."

SO... if I'm not going to parallel several speakers onto one output of the amp then I shouldn't have to use the step down /line matching transformer? correct?

one 2271 is rated at 75W into 66.6 ohms [(70.7V x 70.7V)/75W]
two 2271s are rated at 150W into 33.3 ohms [(70.7V x 70.7V)/150W]
three
four
five
six
seven
eight 2271s are rated at 600W into 8.3 ohms [(70.7V x 70.7V)/600W]

You could drive an 8 ohm loudspeaker, or a couple of loudspeakers wired for an 8 ohm load, with the full compliment of a 2280 (8 x 2271). However, there are lots of easier power amplifiers to use.

The reason I have all amps (8 x 2271) paralleled is so the output is 8 ohm, because if I split the amp into 2 channel of 300 watts ( 4 x 2271) + (4 x 2271) then the outputs would be 16 ohms and my speakers are 8 ohms.

I have 2 of these amps 2280A and each is set for 600 watts (8 x 2271) so if I connect one 2280A to one speaker and the other 2280A to the other speaker and connect left channel of preamp into one 2280A and right channel of preamp into the other 2280A then I should be able to connect one speaker 8 ohm with no transformer to each 2280A. Is this correct?

I think I get what you are saying about overkill and I guess if a person is not going to connect a string of speakers in parallel then he probably don't need this type of amp or this many watts.

thanks for your help

ooo

[Rob 515]

I still don't understand...if it is rated for an 8 ohm load, and you put an 8 ohm load on it, there is no reason to think you will need a transformer.

You also state you have sets of speakers rated 8 ohms...that is most likely EACH, which means a pair is 4. So no you cannot use the amp that way.

An amp rated 600 watts at 8 will run the 8 ohm load just fine, why would you think any different?

Yes each speaker is rated 8 ohms. My altecs each have one 299-8A and one 515-GHP and one 8 ohm crossover.

The part that was confusing me was since this is a 70.7 volt PA amplifier, I was thinking I had to use a step down / line matching transformer on each speaker.

Confusing for me!

thanks