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ptrapp 29th September 2001 11:31 PM

I have a shielded E+I transformer that delivers a total of +- 180VA, 35V per rail. My intentions were to use it in one of the amps described at the ESP pages, but after thorough examination he didn't seem to be suited.

Does anybody know a 'modest' amp project this tranformer may be usefull for?


Philip Trappeniers

Thoth 30th September 2001 03:22 AM

Unfortunately, 180VA at +/-35V is marginal for most amplifier projects. It doesn't stand a chance for any Class-A amp, as the current draw would be too high.

If you're dead set on using this transformer on a project, you should look into a preamp, a DAC, or a similar, low power project. The current drawn by low power projects is usually low enough that your transformer should handle it.

Due to the E/I construction, your transformer will have a tendancy to induce a line-frequency hum in any unshielded wires or traces that are nearby. Placing the power supply in an external case will help.


djk 30th September 2001 08:25 AM

When you say 35V per rail is that AC or DC? +/- 35VDC would be fine for a pair of the ESP 3A boards and would give about 50W per channel at 8 ohms with a 180VA transformer.If it is 70VCT AC then it would be fine for powering a mono 100W at 8 ohms for a subwoofer or center channel.Use one pair of MJ21193/21194 if you need 100W at 8 ohms from the ESP 3A.You could drive a 4 ohm load with some cooling(a small fan for both the outputs and transformer).

ptrapp 30th September 2001 10:50 AM

That is 35V AC per rail.


Petter 30th September 2001 09:02 PM

180 VA is rather low for good power amp, but excellent for a very nice preamp. How about using the X-series input stage (other thread in solid state forum) or build a Pass clone -- often discussed here or go to the source


paulb 1st October 2001 12:48 AM

Rod's project pages seem to be down right now, but I think your transformer could power 2 channels of the DeathOfZen amplifier (almost hate to mention it with this crowd...). Use a full-wave Centre Tap arrangement and you should get about 50 Volts DC, single-ended. You could then chop down the 10 volts with his "Capacitance Multiplier", except put a 39V zener from the transistor's base to ground (check if the resistors Rod suggests will give enough idle current for the zener). This should give you what the DoZ requires.
A 180 VA transformer should be able to give you enough DC power.

[Edited by paulb on 09-30-2001 at 07:53 PM]

paulb 1st October 2001 01:40 PM

Another idea is to build something based on the LM3876/3886 series, but using a single supply. 50 volts DC would be fine for one of these ICs. Unfortunately, Rod's PCBs are based on the dual supply circuit, but you may be able to kluge something up by adding here, snipping there, etc.

djk 2nd October 2001 07:56 AM

"That is 35V AC per rail. Philip"
I read this to be 35-0-35AC or 70VCT AC so rectified and filtered that would be +/- 50VDC .One more time.What have we got here?

paulb 2nd October 2001 01:23 PM

djk, I think you have it right. 35-0-35 AC, +/- 50 VDC with a full wave bridge, or +50 VDC with a full wave CT. Correct, Philip?

ptrapp 2nd October 2001 04:28 PM

Thanks for all the replies!

I had to be more clear with specifying my transformer:

It is a 35V-20V-0-20V-35V (AC voltages) transformer, rated at 180VA.

Perhaps there exists a possibility in using the 20V taps. However, I think this will result in even less power available.


Philip Trappeniers

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