I picked up this amp about a year ago and I need some advice on how to convert it from 220 to 120. I live in United States and my wall current is 118V AC. Please see attached pictures for more information.
I'm assuming I need to :
- get a transformer 120V AC to 18V DC output.
- change the power connectors(can I user the same mains wire?)
- switch issue(can I use the same on/off switch?)
- change the fuse specifications(what type of fuse do I need?)
I would just change the transformer for a 120v version and the mains plug for the correct type. You can use the same cable.
I would also increase the fuse to 2 amp rating.
Stick a label over the Input Power rating with the new details on it.
I wouldn't use the same cable. I would change to 3 wire ground. Also the European cable may use a lighter guage thane needed as the voltage was higher. I'd use 3 conductor 18 for this amp. Cutting up an old computer cord would do. Make sure the switch fuse etc is on the Right wire (as you look at it when plugged in) (so it is polarized properly).
The fuse also as said will have to double due to lower voltage for same watts.
I think I'll get an IEC 14 connector and mount it on the chassis somewhere close to the power supply. Should I runt the ground wire to an area in the chassis next to the power transformer?
What's the best way to cut a hole for the IEC connector in this type of chassis?
Can anyone suggest a power transformer that would work for this amplifier? 120V - > 18V (2X what does this mean ?). I see some 18V transformers that don't say anything about 2X 18V sceondary. Would I need 2 of those to make this work?
Thanks
looking at your photo:
The cable comes in with brown hot blue neutral, brown to the fuse. then to the switch. Neutral appears to also be switched using DP switch. Then both leads go to the primary side of the transformer. There are 3 wires from the secondary It appears to be a +18 -18 with the black (center tap) going to the ground side of the power supply filter caps.
So that would mean an +18 -18 volt power supply... PLEASE Try to verify this with a schematic I'm looking at this with a photo and bad vision . or have a tech check it that can verify this with the higher European mains' voltage.
This picture should help clear things up a bit. Thanks for your help. I just need to get a 2X18 DC transformer right? What numbers am I looking for in watts and amperage? I can't find any information about the current transformer.
last post might be misleading with the + - as it's still AC at this point. I think what you have is 18 volts from each blue wire to the black which I believe is the center tap
Let me try this again. I think you need a transformer described as 18-0-18 or 36v CT. for 110 volt primary.
I can' t find a schematic or cross reference on your current transformer.
Try looking at Hammond In the low voltage section. I think they have one and two amp transformers in this range I'm more familiar with the high voltage ones.
Bear in mind physical size is going to be different.
Antek has 18 -0 -18 Volt transformers too... but torroidal and you would probably need to add a current/onrush limiter
So am I looking for a transformer that has " dual secondaries " ?
"18Vx2" does the x2 mean dual secondaries ?
Does "18Vx2" mean the same thing as : 18-0-18 ?
Is there a way for me to determine the wattage or amperage requirements ?
Sorry about so many questions on this. My concern is that I want to hook it up right the first time. I don't have any replacement channels for parts so if I fry it I'll just have to gut the cabinet. I also have to order over the internet because I don't have any supply channels around here for this kind of stuff.
18 v X 2 is not always the same as 18 0 18. There could be 18 V 0 18V 0 wires with separate windings. However your picture shows 2 aqua secondary wires and a black. This leads me to believe that you have a Center tappped Transformer. In the US here that would usually show in a parts catalog as 36VCT
As far as current needs. that is somewhat of an estimate without specs of your amp and transformer. Somewhere on your amp should be a plate saying watts. Volts X amps = watts so without data you would need to take that formula and figure how many amps your amplifier is expected to draw and buy a transformer accordingly.
I've looked EVERYWHERE on the amp and don't see any wattage numbers. At first I was assuming it's a 30 (only because of the name GA-30 ) watt amp but really have no idea.
Their web site sucks. www.castley.it I see the amp in some weird tilting flash thing under products but there's no information about ANY of their amps. Just pictures. I don't see any way to email them either. Anyone on the board live in Italy that might be able to contact them for me and ask about the power transformer requirements for the GA-30?
Their telephone # is : +36 071 7825422
Incidentally, (assuming it's a 30 watt amp) and using this formula : Volts X amps = watts . Do I use 18V or 36V for the voltage value ?
Thanks
You can look at what the output transistors are an make a guess. Just as a WAG the total power consumption of that amp is probably < 50 watts. Mouser has Hammond transformers of 54VA that would probably work. Solder terminal ones though. The have others listed...but that's in stock. To get one with leads you would probably need to buy an 80VA hammond which is most likely overkill AND would probably not fit in your amp.
I THINK your "TBA" transformer was made in china although I can't find any more.
If you don't want to wag it you could take it to a tech who could put it on a step/up transformer and test it and make a recommendation.
personally I'd put about a 50 or 60 VA transformer in it or even a little larger if it fit and then make sure the voltage at the power transistors wasn't too high and call it done.
Hi Zappacat.
I suggest you provide links to pages where you can order transformers , whatever's convenient to you, and we help you choose one from all those which appear there.
I forgot: post the measures of the iron core, that´s to say the height,width and thickness of the packed sheet iron "E" and "I".
Or: what size is the rectangle where the label is glued?
Quote from: J M Fahey on May 11, 2010, 10:57:16 PM
Hi Zappacat.
I suggest you provide links to pages where you can order transformers , whatever's convenient to you, and we help you choose one from all those which appear there.
I forgot: post the measures of the iron core, that´s to say the height,width and thickness of the packed sheet iron "E" and "I".
Or: what size is the rectangle where the label is glued?
Measurements for rectangle where label is glued : 60mm X 27mm = 2.3" X 1"
Links :
http://www.mouser.com/Power/Transformers/_/N-5gc5/
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=786735
right now the transformers I'm looking at are based on going to the transformer area at the digikey site and specifying ONLY the following as filter elements :
TYPE : single primary
MAXIMUM POWER : 35VA
PRIMARY WINDINGS : single
SECONDARY WINDINGS : dual, center tap
Assuming the above are correct, what should I be specifying in terms of "Series Output Voltage @ Current" ?
Thank you very much. I'm guessing the amp should at least be interesting to mess with.
Personally I would try to go a little higher on the VA rating and check to see if transistor and cap voltages were not exceeded but...
using your criteria the closest I see in Digikey is the Hammond 166J36 @36VA single primary 36 V single secondary center tapped
unless I'm missing something that should work.
I didn't check Physical size and fit though
There are other ballpark ones LISTED but not stocked.
I thought it had to have dual secondaries?
Quote from: bry melvin on May 13, 2010, 03:10:27 PM
Personally I would try to go a little higher on the VA rating and check to see if transistor and cap voltages were not exceeded but...
using your criteria the closest I see in Digikey is the Hammond 166J36 @36VA single primary 36 V single secondary center tapped
unless I'm missing something that should work.
I didn't check Physical size and fit though
There are other ballpark ones LISTED but not stocked.
Hi zappacat. That measurement you made was *very* useful.
The transformer is smaller than I think.
The (approximate ) Math: rectangle 6 x 2.7 cm; compatible with a core of 1.9 x 2.54 cm (3/4" x 1")= 4.826 cm square ; good for about the square of that in V.A.= 23.3 VA.
So, earlier guesses of 30 or 35 VA ratings were quite on the spot.
It would mean a 18+18V or 36V c.t. @ 1 ampere.
Any current or VA rating above that is not a waste, but a security margin.
After rectification and filtering it provides around +/-24V DC.
A real world amplifier will provide around 14V RMS (tops) into an 8 ohm load, around 24W RMS. Call it 20W RMS and we are set.
Some suggestions:
http://www.mouser.com/ProductDetail/Hammond/164J36/?qs=sGAEpiMZZMv4oUrzpPKU3G%2fRTSrPlrIuSG7DBMfNh7M%3d
http://www.mouser.com/ProductDetail/Hammond/162J36/?qs=sGAEpiMZZMv4oUrzpPKU3Gl9uzeWkd1%252bV%252bIZXWKOO%252b4%3d
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=185D36-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A41-43-36L-ND
I think that's enough.
Good luck.
EDIT: Bry Melvin's suggestion is just on spot; I suggestewd a slightly larger trasnsformer to play it even safer, you de$ide.