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Old 11th August 2008, 03:53 AM   #1
smile44 is offline smile44  France
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Default Audio transformer

Hi,

I'm building a small solid state guitar amp, based on the audio stage of an old Philips turntable. It's a push-pull circuit, with a driver transformer and an output transformer. I have found the driver transformer I was looking for, but I have difficulties with the output transformer.

Here is what I'm looking for :

Impedance primary : between 500 and 1000 ohms
Impedance secondary : 4 or 8 ohms
Max output power : between 0.75W and 1W, but not more or not less than that (I want distorsion from this amp, but enough power too).

I'm looking for something rather cheap (15 or 20 $, but not more).
Does anybody know if and where I could find such a transformer ?

If it's not possible, I'm willing to try to build/modify one myself. Is it possible to do that ?
I haven't found any tutorial on that subject : does someone know a good website that could help me ?


Thanks a lot !

Manuel
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Old 11th August 2008, 05:06 AM   #2
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This one is close: http://edcorusa.com/products/transfo...sm10k-150.html

and so is this one: http://edcorusa.com/products/transfo...sm10k-150.html

but neither meets your wattage spec.

Your project sounds so outlandish I fear that either you are trolling and have caught me or are one unique guy!
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Old 11th August 2008, 12:21 PM   #3
smile44 is offline smile44  France
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Hi,

thanks for your answer. Unfortunately, the output impedance wouldn't match my needs either (4 or 8 ohms).
The primary also needs to be center tapped (which is probably the case on the transformers you showed me).

This project is very serious, and I would like to post here some pictures and soundfiles to show you what I'm looking for.

First of all, some salvaged audio section of Philips turntables :

Click the image to open in full size.
Click the image to open in full size.

and here is how it sounds, with a treble booster in front of it :

Sound Sample 1

Sound Sample 2

Sounds good ?

The salvaged audio section I have are pretty good but the output transformer has too much power (2W... !), and the result is not enough distorsion. I have found some acceptable output transformers from Mouser, but with 300mW, they distort too quickly and too much. I need something in between !!

Looking at your answer, I guess I should go the DIY way for this audio output transformer.


Do you think it is possible to make my own output transformer myself ? Any tip/website to help me ?

Thanks a lot !

Manuel
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Old 11th August 2008, 12:21 PM   #4
smile44 is offline smile44  France
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Sorry, links didn't work for the soundfiles :

here they are :

Sound sample 1
Sound sample 2
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Old 11th August 2008, 01:13 PM   #5
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perhaps Edcor (or another transformer company) could wind something custom? Wouldn't hurt to check out.
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Old 11th August 2008, 04:26 PM   #6
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Quote:
Originally posted by smile44
thanks for your answer. Unfortunately, the output impedance wouldn't match my needs either (4 or 8 ohms).
The primary also needs to be center tapped (which is probably the case on the transformers you showed me).
Yes they would work. The impedance ratio of the 10K:150 transformer is 67:1, so a 8 ohm secondary load results in a 533 ohm impedance on the primary. The primaries are center tapped.

Sure you can get them custom made, but there goes your $20 budget!
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