This is my first thread on diy Audio posting. Hoping to learn something new!
I am trying to figure out if this salvaged Executone AMPT-60 PA receiver is in working order. It powers up fine, but I don't know how the correct way to connect speakers to the the unit. I can't find any schematics on it. There are 1/4" connectors on the back, and also 10 terminals. They are labeled {COM, 20V, 70V}, (-), +DC, A, E, F1, F2, BUSY. The first three are all in a specifically marked box for grouping.
The unit seems to be a 60W amplifier.
I hope to connect this to speakers and see if the radio works.
Thanks for your help everyone!
I am trying to figure out if this salvaged Executone AMPT-60 PA receiver is in working order. It powers up fine, but I don't know how the correct way to connect speakers to the the unit. I can't find any schematics on it. There are 1/4" connectors on the back, and also 10 terminals. They are labeled {COM, 20V, 70V}, (-), +DC, A, E, F1, F2, BUSY. The first three are all in a specifically marked box for grouping.
The unit seems to be a 60W amplifier.
I hope to connect this to speakers and see if the radio works.
Thanks for your help everyone!
Attachments
This is a PA amplifier designed for use in a factory or warehouse to power 70V line speakers, thus minimising the power loss over large distances.
https://cie-group.com/how-to-av/videos-and-blogs/tappings
It may not have the facility for connecting ordinary hi-fi speakers.
The four left hand jack sockets are inputs for microphones and an aux socket. The fifth one at the right says "tuner output" - tell us what the rest of the writing on that output says.
This will be a mono amplifier.
Ask for help by posting the details in the 'PA Systems' forum.
https://cie-group.com/how-to-av/videos-and-blogs/tappings
It may not have the facility for connecting ordinary hi-fi speakers.
The four left hand jack sockets are inputs for microphones and an aux socket. The fifth one at the right says "tuner output" - tell us what the rest of the writing on that output says.
This will be a mono amplifier.
Ask for help by posting the details in the 'PA Systems' forum.
Sorry for posting this in the wrong Forum. I'm not sure if i can edit this post to change where it is stored.
Simply make a new post in the 'PA Systems' forum. You can cut and paste your information into the new post if required.
Ask if it is possible to modify this PA amp to drive an ordinary 4 to 8 ohm speaker.
P.S. The tuner output is not for connecting to an ordinary speaker, but to an additional amplifier.
Ask if it is possible to modify this PA amp to drive an ordinary 4 to 8 ohm speaker.
P.S. The tuner output is not for connecting to an ordinary speaker, but to an additional amplifier.
FYI A PA amplifier like this has a step-up voltage transformer at the output - see diagram.
Sometimes there is an internal, unused tap for 4 or 8 ohm which close internal inspection may reveal. Post photos.
P.S. I'm asking the moderators to transfer this thread to 'PA Systems'.
Sometimes there is an internal, unused tap for 4 or 8 ohm which close internal inspection may reveal. Post photos.
P.S. I'm asking the moderators to transfer this thread to 'PA Systems'.
Moved to PA Systems.
It is possible there is no voltage step-up transformer in the amplifier and that the output circuit drives the 25 V or 70 V line directly.
In that case, an 8 ohm speaker would require the addition of a step-down transformer.
simon7000 says that you "should" be able to connect an 8 ohm speaker direct to the 25 V line, but I should like to be convinced of that.
EDIT: Of course if you have an old disposable 8 ohm speaker you can always try it!
In that case, an 8 ohm speaker would require the addition of a step-down transformer.
simon7000 says that you "should" be able to connect an 8 ohm speaker direct to the 25 V line, but I should like to be convinced of that.
EDIT: Of course if you have an old disposable 8 ohm speaker you can always try it!
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It is a 60 W amplifier.
Taking V = 25 V and P = 60 W, we can use R = V^2/P to discover that we have a 10.4 ohm line.
By that measure, simon7000's suggestion should indeed work.
Taking V = 25 V and P = 60 W, we can use R = V^2/P to discover that we have a 10.4 ohm line.
By that measure, simon7000's suggestion should indeed work.
I think it should be mentioned you can add a 100/70V audio transformer to any regular speaker if it doesn't fit any of the output voltages or level you're dealing with. For HIFI use it's also worth mentioning you won't find any stereo 100/70V amplifiers since you will not have any stereo perception while moving through a high voltage PA sound reinforced areas. It's made to have very low power loss over very long distances, which makes the requirements of very high power (most of which will be wasted over the long distances lines resistance) and make the long distance cables a lot less expensive. Think about big buildings, ski piste or large area covering PA (stadiums, exposure events, sport events etc).
Or in other words, an average guy doesn't have the need for a 70/100V amplifier. It's very specialized and doesn't meet the most requirements of a HiFi enthusiast.
Or in other words, an average guy doesn't have the need for a 70/100V amplifier. It's very specialized and doesn't meet the most requirements of a HiFi enthusiast.
Yes, 70 V in the OP's case. Like this one for $6 : https://www.parts-express.com/70V-10W-Line-Matching-Transformer-300-040?quantity=1
Good enough for his ambition to see if the radio works.
After losjng my CS800s, PV-4c amps & 2200 LP & 200 CD to theft, I bought a couple of MMA-875t for $25 and $40. 75 watt warehouse amps. <0.5% THD 20-20000 hz. They work fine on the 25 v output into 8 ohms. $5 the pair 3 way speakers (6" woofer) replaced the SP2-XT psir & 1210 pair that were hauled off in a Jeep Cherokee. One amp for LP & CD in the music room, one for the HDTV and PC sound in the dining room. WIth the RCA jack mixer cards, they can mix stereo down to monaural. One cool feature, if you do use the output transformer, an output transistor meltdown can never damage your $3 speaker.
Unlike the PA amps I rebuilt from shorted out hulks, the PA amps arrived working. Good thing, since all tools were stolen (~$30000) and about 200 lb of electronics parts including ON semi TO3 transistors were hauled off to the steel scrapyard.
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The meltdown just takes out the $50 transformer, sending the amp back to the scrap heap.
I would much rather throw away an amp I paid $40 with the freight, than a $600 list price , 1 day in a car +$400 actual price, speaker. These warehouse amps are cheap, sound good, and usually come working but very dusty. Disadvantage, since they are monaural, for stereo you have to turn two of them on & off with a power strip. Another advantage, with a mute switch you can turn the sound off of commercials on the television. The TV remote does not mute the TOSLINK output of sound.
I’d rather not throw away an amplifier I paid $40 for. One still needs a DC protect AHEAD of the transformer because its not any more expendable than a good speaker. ($3 speakers are.) If it’s a conventional amplifier ahead of that trafo the solution is simple : One capacitor (Or two, to make an NP). Bass response isn’t uber critical and the trafos arent good below 50 Hz so a pair of 2200’s is all that’s needed. A push pull driven off a center tap (which was common in the 70’s and early 80’s for 20-100W commercial amps) requires a bit of attention. You feed the two sides of the primary into an integrator and trip a relay which interrupts the center fed B+. Dirt simple, and better amps would have this built in.
Series to speaker minus to minus e-capacitors sound like **** on low volume. Been there, tried that. I listen to classical piano a lot which requires accuracy on the higher frequencies. Two series 5600 uf caps sounded funny. My $400 used speakers are Peavey SP2(2004) with a -25 db HarmonicDistortion spec at 5 watts. The SP2 are -20 db down below 54 hz.
Relays require testing to qualify for DC service. Cheapest way to buy two suitable for DC service is a blown up Crown or Peavey PA amp. About $60 minimum with the freight.
I'm running a naked transistor output Peavey M-2600 amp on the SP2's now. A bit risky. Perhaps will correct this winter. Those $10 ebay/aliexpress/amazon protection circuits with the AC rated metal contact relays strike me as snake oil. Nobody seems to be selling nfet circuit pcbs. A series polyprophylene 3300 uf capacitor would be ~$1100 per channel. https://www.parts-express.com/Solen-200uF-400V-Polypropylene-Capacitor-027-630
Relays require testing to qualify for DC service. Cheapest way to buy two suitable for DC service is a blown up Crown or Peavey PA amp. About $60 minimum with the freight.
I'm running a naked transistor output Peavey M-2600 amp on the SP2's now. A bit risky. Perhaps will correct this winter. Those $10 ebay/aliexpress/amazon protection circuits with the AC rated metal contact relays strike me as snake oil. Nobody seems to be selling nfet circuit pcbs. A series polyprophylene 3300 uf capacitor would be ~$1100 per channel. https://www.parts-express.com/Solen-200uF-400V-Polypropylene-Capacitor-027-630
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If it’s one of those center fed push pull that directly drives the primary, the power supply voltage isn’t very high, typically 28V no load, 24V full load. So it can be used with a battery supply in absence of AC. You can use relays or 32V fuses to interrupt the DC on those. GJ’s amplifier has -/+DC terminals, and its probably for the DC backup. Ive seen many 20-60 watt amps where they are. If it runs off that low supply voltage, the center fed transformer trick is the easiest way to get step up. More “modern” designs often use a more conventional amplifier, but forget about DC backup at anywhere near full power.
MMA-875t and MMA-8150t rail supplies are +-42v. transistors drive an output transformer except 4 ohm is direct connect. M-2600 rail voltages are the same. No transformer in M-2600. All three so silent without a fan.
Digikey had a 200 uf 450 v polyprophylene capacitor for $18, so 3300 uf (1 ohm at 50 hz) would be 17 of them. Only $306 per channel. About same price as a 1508-KADT woofer in SP2.. However, digikey only had 5 200 uf in stock.
Digikey had a 200 uf 450 v polyprophylene capacitor for $18, so 3300 uf (1 ohm at 50 hz) would be 17 of them. Only $306 per channel. About same price as a 1508-KADT woofer in SP2.. However, digikey only had 5 200 uf in stock.