sunray Posted June 18, 2018 Share Posted June 18, 2018 I need to replace a lost 100V to 0dB unit (left on a job at rip out), I'd intended to use one of my plethora of speaker transformers and a simple resistor/pot attenuator, but having looked inside a commercial unit I see bridge rec and smoothing from 100V, dc to dc convertor, 3 op-amps and associated parts, o/p transformer. Anyone have intimate experience of these units? Link to comment Share on other sites More sharing options...
sandall Posted June 18, 2018 Share Posted June 18, 2018 Sounds incredibly complicated. I'm sure the old Philips one I "inherited" is just a transformer with a jack plug. Link to comment Share on other sites More sharing options...
sunray Posted June 18, 2018 Author Share Posted June 18, 2018 The one I left behind was an ABS box with 1/2 of choc block poking out of both ends, I'd say it was only just big enough to take the transformer and a resistor or two. I did a refit a couple of years back and there were 3 built into small boxes with jack plug one end and a 3 pin Bulgin at the other as part of the strip out. I was going to make sure they went straight in my tool box but unfortunately they were missing before we started, along with the 2 mixer PSU's. Link to comment Share on other sites More sharing options...
sunray Posted July 6, 2018 Author Share Posted July 6, 2018 I constructed one using a 10W transformer tapped at 1W then a 2k2ohm resister to top of a 1Kohm pot and a 10uF cap from wiper to amp. Theoretically this gave me a maximum of 1V o/p. In practice the level was too low, more like 100mV. Replacing 2K2ohm with 1Kohm and 10uF with 1Kohm gives a max o/p of around 2V. Additionally I have added an 8R speaker and switch which I found really handy. I have now been able to look at a commercial box (currently on ebay between £80 and £130): 1W tap then 3k3ohm feeding 5Kohm pot then 470R in each leg feeding amp. Link to comment Share on other sites More sharing options...
Simon Lewis Posted July 7, 2018 Share Posted July 7, 2018 Or, Ampetronic have some ready made? 100V line adaptor Link to comment Share on other sites More sharing options...
sandall Posted July 7, 2018 Share Posted July 7, 2018 .......and a 10uF cap from wiper to amp. Is this necessary? Link to comment Share on other sites More sharing options...
sunray Posted July 7, 2018 Author Share Posted July 7, 2018 Or, Ampetronic have some ready made?Indeed and so do many others. My original (Eagle) at some 30 years old had been used about 4 times and I expect the replacement to have about the same usage. It cost about 1 hours labour to assemble from bits in hand, If it gets missed on the next rip-out I won't worry. .......and a 10uF cap from wiper to amp. Is this necessary?I usually put this in in case it gets plugged into a phantom powered input but it is currently bypassed by a 1Kohm resistor, I doubt I'll ever think about changing it now.It's not in the Monocor or Taski versions. Link to comment Share on other sites More sharing options...
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