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Old 14th December 2011, 08:57 AM   #1
Bone is offline Bone  United Kingdom
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Default Using Mains Transformers as Outputs

Many mains transformers have the right ratios to use as push-pull output transformers. (eg 120+120:6v)
The iron used in these transformers is not audio grade however.
What effect will this have on the frequency response?
Are Toroidal transformers any different?

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Old 14th December 2011, 09:21 AM   #2
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Find a winder and ask him to make a toroidail transformer for you with multiple windings.
I have read a few post about toroital mains was used as an opt. The opinions were mixed. Try it if it's cheap.
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Old 14th December 2011, 10:56 AM   #3
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A lot of info in The Net.
For instance: Valves & Tubes. What use are they?. IF I wanted to build such an amp I would rather go towards parallel feed output (no magnetising current in a core).
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Old 14th December 2011, 01:37 PM   #4
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Most mains transformers will not go to 20 KHz. Some will, but testing is the only way to find out. If the amp in question is a guitar amp, then it may just work since HiFi response to 20 KHz is not needed. When I was young and didn't know better I made quite a few guitar amps using mains transformers for output.

Now that I know better.....the last cost guitar amp I made uses a mains transformers for output. The transformer is an Antek 50 VA toroid and the amp cranks out 20 watts of good sound with a pair of UL84's.

A mains transformer will not work for SE but may be OK for P-P. Generally a toroid will have a better chance of handling the high frequencies but requires a more careful balance in DC current between the two halves of the P-P amp.
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Old 14th December 2011, 01:39 PM   #5
Magz is offline Magz  United States
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My commercial preamp used small toroidal power transformers as outputs. They were OK, but replacing them with Lundahl LL1674 amorphous cobalt core transformers was a big improvement.
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Old 14th December 2011, 01:46 PM   #6
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Another thought. For your torridal PP output, use a tube with a low RP to get as high a frequency response as possible. 6080 for example comes to mind, and would work great for a class A 5watt PP amp.

You can use a mains transformer in SE, but you need a parafeed(choke or resistor) output with no DC in the output transformer.
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Old 14th December 2011, 02:29 PM   #7
DF96 is offline DF96  England
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There is more to an audio transformer than turns ratio and core material. Winding interleaving, for example.
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Old 14th December 2011, 02:42 PM   #8
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Old 14th December 2011, 02:52 PM   #9
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Here's an example of a SE amp using a cheap Antek mains transformer. It sounds quite good, despite costing less than $200 for parts.
6V6 Lumiere
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Old 14th December 2011, 11:36 PM   #10
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Yes, Shoog is an expert in this. I myself built a differential output stage(my phono and line stages are differential) with 6s19p driven by 6e6p as a cheap experiment. I used a 50VA toroidal with the 6V secondaries wired in parallel. The cathodes were AC coupled and the 4 triple cascode CCS's LED biased and made of 2 BC549's and 1 MJE340 were retuned to a negative supply of about 20V. I was lucky first time as all the sinks were matched to better than 0.5 mA. It was very easy, cost peanuts and to my delight considerably outperformed my commercial 300B SE. I would mention that I mostly listen to classical music which doesn't need much power in the bass.
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