American Science & Surplus has a 18 volt @ 2.5 (Approx. 45VA) amp transformer for 1$. Would these be suitable for a GainClone PSU, if three were wired in paralell? (I'm using the PCB from chipamp.com).
Also, is the listed 18v voltage before or after rectification?
It's the third down on the page:
http://www.sciplus.com/category.cfm?subsection=13&category=138
Also, is the listed 18v voltage before or after rectification?
It's the third down on the page:
http://www.sciplus.com/category.cfm?subsection=13&category=138
hi 'teapot,
I think you need 4 at a bare minimum. Don't forget you need 18-0-18. That's 2 for each channel, 18-0-18 @ 90VA. I'd think about paralleling all 4 to give 180VA. A lot of wiring, but they are cheap. The 18 volts is before rectification, so after 18 x 1.4 is approx. 25 volts.
Good luck.
I think you need 4 at a bare minimum. Don't forget you need 18-0-18. That's 2 for each channel, 18-0-18 @ 90VA. I'd think about paralleling all 4 to give 180VA. A lot of wiring, but they are cheap. The 18 volts is before rectification, so after 18 x 1.4 is approx. 25 volts.
Good luck.
Spasticteapot said:
You are correct, it just has been badly explained to you.
An 18V AC transformer gives an RMS value of 18V's. When rectified (converted from AC to pseudo-DC) it is 'unRMS-ed' by multiplying the RMS voltage with 2^0.5 (About 1.4) to give 25V. Now there is a DIODE voltage drop in a rectifier of about 0.7V, but overall, the voltage seems to increase, but thats only because its been converted from RMS AC Volts to DC Volts.
This then goes through the CAP bank which smooths out the 'bumps' in the signal. Then optionally, it goes through regulation, which you can think of as just 'chopping' of the top of the voltage to get rid of any 'ripple' that occurs when the PSU is under load.
Spasticteapot said:
Hi 'teapot,
I should have mentioned, it seems to be a default that we use full wave bridge rectification using 4 diodes and this does increase the voltage. There is also half wave with 1 diode and full wave with 2 diodes rectification that produce different and from memory lower output voltages and different current capabilities.
So we were all right.
BTW: The voltage reading I mentioned, 25v, will only occur after the smoothing capacitors. Without the caps, and measuring at the output of the diode bridge with a DMM you will not get a 25 volt reading.
regards
Thanks for all the help.
It looks like these are an acceptable option, and the price is hard to beat. (4$ for the lot!) However, they're obviously rather cheaply made, as well. How much would they negatively impact sound quality?
Also, ApexJR has a toroidial transformer for 25$ that looks good. However, they did'nt list the amperage, and I can only afford one for the both of them. It's got 2 20v outputs.
Item #: Basler 16-16431
It looks like these are an acceptable option, and the price is hard to beat. (4$ for the lot!) However, they're obviously rather cheaply made, as well. How much would they negatively impact sound quality?
Also, ApexJR has a toroidial transformer for 25$ that looks good. However, they did'nt list the amperage, and I can only afford one for the both of them. It's got 2 20v outputs.
Item #: Basler 16-16431
They won't have impact on sound quality , but may not be good(hum,high no-load current,etc).
Recently i purchased three little cheap ~2 W transformers.They consume 30 mA of current without a load , thats ~7 watts and heat a lot.
Toroid transformers usually produce less hum , what is one of consideration factors.
The power supply should be about twice as powerful as your amp's output.
Recently i purchased three little cheap ~2 W transformers.They consume 30 mA of current without a load , thats ~7 watts and heat a lot.
Toroid transformers usually produce less hum , what is one of consideration factors.
The power supply should be about twice as powerful as your amp's output.
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