Hi,
I picked up a Yamaha XH150 which you guessed it is an high impedance amplifier, and I'm looking to see if you can mod it to an low impedance amplifier?
(I saw in another thread it was possible on a different 100v amp link)
I've attached the service manual that also has schematics.
Any help will be greatly appreciated?
Thank you!
I picked up a Yamaha XH150 which you guessed it is an high impedance amplifier, and I'm looking to see if you can mod it to an low impedance amplifier?
(I saw in another thread it was possible on a different 100v amp link)
I've attached the service manual that also has schematics.
Any help will be greatly appreciated?
Thank you!
Sadly I think you can´t.
Different from the other 100V amp (and 99.9% of all out there), it has NO output transformers , neither autotrafos nor push pull, but it was straight built as an SS amp with incredibly high rail voltages which can provide 100V RMS on its own.
Never before saw that.
So output impedance is 200 ohm or 63 ohm (100V - 70V) and that´s it.
Rails must be between 150 and 170VDC ... each 😱
It is technically possible to use a 200/63 ohm primary, 4/8 ohm secondary transformer to use normal speakers, not sure about the economic convenience.
My practical solution would be to try a 110/120V primary 24V secondary 150-200VA power transformer, to adapt the 100V line to a 4 ohm speaker, almost perfect matching and sound would be "acceptable".
In any case, that amplifier is designed from day 1 to drive transformers, won´t know (or care) about the difference between a single large one or a lot of tiny ones, as long as impedance is reasonably close, which it will be.
Different from the other 100V amp (and 99.9% of all out there), it has NO output transformers , neither autotrafos nor push pull, but it was straight built as an SS amp with incredibly high rail voltages which can provide 100V RMS on its own.
Never before saw that.
So output impedance is 200 ohm or 63 ohm (100V - 70V) and that´s it.
Rails must be between 150 and 170VDC ... each 😱
It is technically possible to use a 200/63 ohm primary, 4/8 ohm secondary transformer to use normal speakers, not sure about the economic convenience.
My practical solution would be to try a 110/120V primary 24V secondary 150-200VA power transformer, to adapt the 100V line to a 4 ohm speaker, almost perfect matching and sound would be "acceptable".
In any case, that amplifier is designed from day 1 to drive transformers, won´t know (or care) about the difference between a single large one or a lot of tiny ones, as long as impedance is reasonably close, which it will be.
My practical solution would be like what Bogen did. They took a plain SS amp with 8 ohm output rating and put a 70v transformer on the output. Just as you would normally do at each speaker on a 70v or 100v line. They put the transformer there to step UP the "regular" output, but it works in reverse just as well.
Cool 🙂
Didn´t expect to find an over the counter 100V to 8 ohm 150W transformer, unlike common 5-10-15W ones but since at least one model is available, then by all means go for it.
https://www.adiglobaldistribution.us/Product/JF-MTC300T15
https://www.fullcompass.com/prod/08...mer-for-70v-or-100v-distributed-speaker-lines
Didn´t consider an OEM type such as the one in Bogen or any other similar PA amp because those are custom wound for a given manufacturer, but hey, JBL offers them, so ....
Or are those surplus sales?
Didn´t expect to find an over the counter 100V to 8 ohm 150W transformer, unlike common 5-10-15W ones but since at least one model is available, then by all means go for it.
https://www.adiglobaldistribution.us/Product/JF-MTC300T15
https://www.fullcompass.com/prod/08...mer-for-70v-or-100v-distributed-speaker-lines
Didn´t consider an OEM type such as the one in Bogen or any other similar PA amp because those are custom wound for a given manufacturer, but hey, JBL offers them, so ....
Or are those surplus sales?
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I did a jukebox installation where they wanted more than teh amp in the box provided. SO I got an SAE amplifier - at the time it was a happenin' brand - And bought a pair of EV 70v transformers to slap on its output. Those drove a series of speakers around the club.
https://www.proacousticsusa.com/com...sformers/toa-mt-200-matching-transformer.html
https://www.proacousticsusa.com/com...sformers/toa-mt-200-matching-transformer.html
That JBL is $106. Drop in the bucket for an installer, who will turn around and charge the customer $424 plus tax (well, maybe only $318) as a line item on the bill. Most wouldn’t know enough to complain about it. But ****, I can go to a pawn shop and buy an amplifier for that. And have money left over for a new set of power supply capacitors. What to look for? 300 watts per channel at 4 ohms, preferably one that is “2 ohm capable” for safety margin. Old QSC USA900, RMX850, or even an old Model 41. Bridge it, and directly drive a 70V line. If one channel fails, simply hook to the good channel and continue running at reduced power. QSCs are nice in this regard since a single channel failure doesn’t take the other out. And if you run (load) it down with only 150 watts it will be like running a 16 ohm speaker which means it will run forever.