I got a 100v Roland amplifier from Japan. Currently using a piggy back transformer but want to install something more permanent. Same plugs as Thailand so easy to forget the transformer and blow the thing up. the rating on the amp is 100 volt 70 watt (power input not speaker output)

 

Just wondering what size (wattage) I should get? Not sure if power is rated on the primary or secondary of a 220 / 100v transformer. I would need to get 100 watts on the 100 volt secondary side? Would rather go a tad bigger so it can handle the load comfortably but not too big as weight is a consideration. 

I'd go for a 150W x 100V transformer, a bit of headroom and these things are often rather "optimistically" rated.

 

Is your amp definitely 100V only? A lot of Japanese kit actually has universal (90-250V) power supplies, there will be a rating plate somewhere that tells you.

 

1 hour ago, Crossy said:

I'd go for a 150W x 100V transformer, a bit of headroom and these things are often rather "optimistically" rated.

 

Is your amp definitely 100V only? A lot of Japanese kit actually has universal (90-250V) power supplies, there will be a rating plate somewhere that tells you.

 

Definitely 100v, well that's on the specs plate. 100v 70w

Thanks Crossy 

A fair few 100V transformers on Lazada one of these (100V 100W) https://www.lazada.co.th/products/220-100v-220-110v-hitachi-i2507658906-s8880736605.html? would do the trick.

 

2 hours ago, Crossy said:

A fair few 100V transformers on Lazada one of these (100V 100W) https://www.lazada.co.th/products/220-100v-220-110v-hitachi-i2507658906-s8880736605.html? would do the trick.

 

I got a couple like that already mate but they're pretty heavy and a bit more expensive than a standalone open Trx. These ones already got plugs and outlets on them, which I guess easy enough to take out and hardwire. Also wasn't sure when they rate them 100 watt on the secondary / primary or both. I guess the P=EI equation changes per voltage?

2 minutes ago, Kenny202 said:

I guess the P=EI equation changes per voltage?

 

Transformers are pretty efficient, power out = power in (mostly).

 

V goes down I goes up, P remains the same.