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Old 4th May 2011, 12:09 PM   #11
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I have experimented a bit with using power xformers as OPT's. The short version is: it'll work for low-power push-pull, but it's never going to be hi-fi. Some observations:
- Typically, about a 20:1 turns ratio gives decent impedance matching for a pair of smallish output tubes to an 8R speaker. Since sound quality isn't really a strict requirement (otherwise you'd use proper OPT's), exact impedance matching is not really a requirement. You'll loose some power, but it'll work. I've had fairly good results with 2x115V-9V transformers. I'm not sure where the 2:1 ratio Tajzmaj talks about comes from; that would reflect 4x8=32Ohms to the primary side with an 8R speaker connected; I think you're probably shooting at something like 5k-10k on the primary side, which means you need about a 1000:1 impedance ratio (8K:8R), so a voltage ratio of something between 20:1 and 40:1. Assuming you're looking at transformers with a 230V center-tapped primary, anything with a secondary of 6V to 12V should be usable.
- Core saturation tends to become a significant problem below 50Hz. This is visible on a scope and tends to look pretty bad, but may not be audible. Don't expect much output power below 35Hz.
- I've never gotten a power transformer to keep up with frequencies above about 5KHz - 8KHz. I'm currently using a stereo amp with a pair of 6AQ5's in triode mode in each channel, and its frequency response is maybe -3dB @ 8KHz and keeps dropping rapidly above that. On the low end, the -3dB point is somewhere around 55Hz if memory serves.
- Anything smaller than about 20VA is probably going to give an even worse frequency response.

I think you could build a low-powered guitar amp using a power transformer. Maybe bass as well, but you might have to be a bit more picky regarding the transformer. For hi-fi it's a no go, but the drawbacks can be completely acceptable for an instrument amp that is not intended for completely accurate reproduction but rather for having an own, unique sound.

/Edit: Sorry, I thought this was posted in the Valves section, that's how I ended up with the turns ratios mentioned above. I was thinking of tube OPT's.
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Old 4th May 2011, 12:21 PM   #12
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guitars have a frequency of 82.4 to a few k or even less. So it should not be a problem
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Old 5th May 2011, 10:17 AM   #13
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Hey mastodon do you know what it would aproximately be if you were using solid state at line level and what power transformers you would consider using from your experience with them thanks for the great info that was interesting
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Old 5th May 2011, 04:11 PM   #14
Tajzmaj is offline Tajzmaj  Slovenia
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Hi Mastodon
This 2:1 ratio comes because Seedseed need transformer for comperssor with solid state output......Because I read that thread I know what he was asking........so here comes this misunderstanding. He don't need tube amp output transformer like here was proposed ....... Uh 2:1 with tubes? Maybe with few of 6c33 in parallel......
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Taj
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Old 6th May 2011, 07:17 AM   #15
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There was no suggestion of the compressor being solid state in the original post.
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Old 6th May 2011, 07:06 PM   #16
Tajzmaj is offline Tajzmaj  Slovenia
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He asked if 1176 compressor can work without output transformer.......and1176 is solid state....
Regards
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Old 7th May 2011, 07:55 AM   #17
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Quote:
Originally Posted by Tajzmaj View Post
He asked if 1176 compressor can work without output transformer.......and1176 is solid state....
Regards
with not without .
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Old 7th May 2011, 01:48 PM   #18
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No mention of 1176 in OP.
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Old 7th May 2011, 06:52 PM   #19
Tajzmaj is offline Tajzmaj  Slovenia
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1176 compressor output transformer alternative
Maybe I was wrong. I noticed this 1176 thread from seedseed.....
Best regards
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