chriswareham Posted December 19, 2015 Share Posted December 19, 2015 Hi folks! I've just acquired an Acoustic Control Corporation 140 amp from the States. It's currently winging its way to me, and I plan on initially using it with a step down transformer. Longer term, I want to replace the internal transformer to work directly from UK mains voltage. Does anyone know how difficult it is to do this properly? I wonder if this is complicated by the difference in frequency (50hz versus 60hz) as well, which I guess is particularly important for audio gear. Not going to attempt any conversion myself, as I don't go near mains level voltages, but would appreciate any advice from those who have converted stuff themselves or has someone do it for them. Quote Link to comment Share on other sites More sharing options...
sunburstjazz1967 Posted December 19, 2015 Share Posted December 19, 2015 It might already have a suitable transformer inside with a tapping for 230V but you wont know until you open it up, the Hz mainly affects motors but most fan motors in amps etc are computer style ones rated 50-60Hz as are most electronic components. Quote Link to comment Share on other sites More sharing options...
Woodinblack Posted December 19, 2015 Share Posted December 19, 2015 It may be difficult or easy, depending on how it was originally made. As said above, the frequency doesn't matter, so if it has a transformer that can do 240 it is easy, if it is a common transformer it is harder, if it has something custom it depends on if something the same size can be found. As you are not doing it yourself, you would have to ask the person doing it to tell you, and they wouldn't really know until they opened it up. You are going to need a heavy step down transformer to use it! Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 19, 2015 Share Posted December 19, 2015 [quote name='chriswareham' timestamp='1450514363' post='2933443'] Hi folks! I've just acquired an Acoustic Control Corporation 140 amp from the States. It's currently winging its way to me, and I plan on initially using it with a step down transformer. Longer term, I want to replace the internal transformer to work directly from UK mains voltage. Does anyone know how difficult it is to do this properly? I wonder if this is complicated by the difference in frequency (50hz versus 60hz) as well, which I guess is particularly important for audio gear. Not going to attempt any conversion myself, as I don't go near mains level voltages, but would appreciate any advice from those who have converted stuff themselves or has someone do it for them. [/quote] If the PSU is a "standard" one i.e. isolating transformer driving a bridge rectifier then it should be replaceable with a 240v equivalent that has the same output voltage, the frequency difference shouldn't matter because the PSU output is DC. As previous poster said you might get lucky and already have a transformer with a 240v input tap. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted December 19, 2015 Share Posted December 19, 2015 With an amp that old chances are the primary is 110v only. You'll need a schematic to determine the requirements to swap in a 220v primary. Quote Link to comment Share on other sites More sharing options...
3below Posted December 19, 2015 Share Posted December 19, 2015 Schematic available here [url="http://www.ampix.org/albums/userpics/10075/Acoustic_140.pdf"]http://www.ampix.org/albums/userpics/10075/Acoustic_140.pdf[/url] It appears that you need 75V output, There is also a resistor R401 wich is 47M for 120V, the value is stated for for 240V but I can not read it clearly , my guess is 100M (2 x value for 120V). Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 19, 2015 Share Posted December 19, 2015 (edited) [quote name='3below' timestamp='1450534562' post='2933724'] Schematic available here [url="http://www.ampix.org/albums/userpics/10075/Acoustic_140.pdf"]http://www.ampix.org...coustic_140.pdf[/url] It appears that you need 75V output, There is also a resistor R401 wich is 47M for 120V, the value is stated for for 240V but I can not read it clearly , my guess is 100M (2 x value for 120V). [/quote] Good find, the schematic actually shows the transformer rewiring necessary for 240v although its unclear whether its actually the same transformer, its possible that it is and all you are doing is running the primary coils in series rather than parallel. It also gives the resistor value change required for the power LED which as you surmised is 100Mohm. [i]Edit - looks like it needs a 500VA transformer not a 1000VA as I originally thought.[/i] Generally good news though as it looks like its easy to mod, what with having a bog standard PSU design. Edited December 19, 2015 by bassman7755 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted December 19, 2015 Share Posted December 19, 2015 [quote name='bassman7755' timestamp='1450535524' post='2933730'] Good find, the schematic actually shows the transformer rewiring necessary for 240v [/quote]It shows that for the export model, but it probably wouldn't be the export model if it's coming from the US. Considering the age I'd replace the filter cap, and upgrade it to at least 4700uF/100v. It's been a very long time since I've done power supplies, but I do recall that the transformer secondary voltage isn't the same as the voltage once rectified and filtered, so it will take some research to find out the required secondary voltage. Quote Link to comment Share on other sites More sharing options...
3below Posted December 19, 2015 Share Posted December 19, 2015 (edited) [quote name='Bill Fitzmaurice' timestamp='1450540863' post='2933784'] It shows that for the export model, but it probably wouldn't be the export model if it's coming from the US. Considering the age I'd replace the filter cap, and upgrade it to at least 4700uF/100v. It's been a very long time since I've done power supplies, but I do recall that the transformer secondary voltage isn't the same as the voltage once rectified and filtered, so it will take some research to find out the required secondary voltage. [/quote] Good points about power supply and capacitors, as Bill notes the 75V is after rectification and filtering (I am so full of cold at the moment I am not capable of much coherent thought). Hammnond provide this useful design sheet [url="http://www.hammondmfg.com/pdf/5c007.pdf"]http://www.hammondmf...m/pdf/5c007.pdf[/url] The pragmatic way would be power up with 110V (yellow power tool transformer?) and measure the ac voltage output on the transformer with no load. If you are lucky the transformer will have manufacturer markings which will allow the output voltages and power capacity to be identified. As you noted you are not going the DIY (destroy it yourself) route. Just let a good technician sort it and enjoy real transistor Watts (rather than D type Watts). How did we ever gig with 100W transistor heads? Edited December 19, 2015 by 3below Quote Link to comment Share on other sites More sharing options...
chriswareham Posted December 19, 2015 Author Share Posted December 19, 2015 Many thanks to you all for pitching in with advice, and 3below in particular for finding the schematic. I'll see if the guy who customised my Sound City is up for doing the conversion (Theo Argiriadis http://www.tube-electronics.co.uk/). Quote Link to comment Share on other sites More sharing options...
DBerriff Posted December 19, 2015 Share Posted December 19, 2015 (edited) Deleted on review of OP. Edited December 19, 2015 by DBerriff Quote Link to comment Share on other sites More sharing options...
chriswareham Posted December 19, 2015 Author Share Posted December 19, 2015 [quote name='3below' timestamp='1450541338' post='2933786'] Just let a good technician sort it and enjoy real transistor Watts (rather than D type Watts). How did we ever gig with 100W transistor heads? [/quote] :-) I've read that Acoustic rated their amps according to what is nowadays referred to as "program" levels rather than the "peak" levels of most manufacturers. So when an Acoustic 140 is officially rated for 125W, it's comparatively more powerful than most transistor amps with that rating. At least that's what I've read, but it would explain why so many people find Acoustic amps surprisingly loud. Quote Link to comment Share on other sites More sharing options...
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