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 Post subject: Re: Small tube amp
PostPosted: Jul Sat 06, 2019 4:46 am 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5692
Location: Vancouver Island, Canada
Most people find a phono input, usually going to the volume control, then to one audio stage (one tube such as 12SQ7) ahead of the power tube (50L6), is not loud enough. Turning the cellphone or MP3 volume to max causes distortion.
So you will find it needs another tube stage, or a step-up transformer on the input.
I was trying a different CD player today, had distortion, realized volume was up to max, turned device down, radio up, sounded clean.

A 1:10 step-up transformer works well, easier than adding a tube stage, the device volume can be left at mid volume, and the transformer blocks DC voltage.
(For an input on a cheap AA5, I just use the transformer from a 12 volt wall wart in reverse, but have been told umpteen times that is not an audio transformer, not HiFi, even tho to my ear it works very well.)
So shop around for an audio transformer. Also, combine L and R channels from the earphone jack with a 1K resistor on each, combined to give the transformer a mono signal. Search here for 'auxiliary input' info.

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