Ampeg B15 preamp: Drive balanced transformer from PI?

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Bigwan
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Joined: Thu Sep 14, 2006 8:30 am

Ampeg B15 preamp: Drive balanced transformer from PI?

Post by Bigwan »

I'd like to build a bass preamp for recording purposes. Loads of options, but the style of amp that appeals to me most is the Ampeg B15 portaflex/fliptop. A lot of info on the web suggests that much of the B15 "magic" happens in the phase inverter section. Any suggestions as to the best method of deriving a balanced output from the phase inverter of the B15? I had considered going down the "small power section into dummy load" avenue and tapping off the dummy load, but that seems a little excessive if I can do it from the PI instead (although a low power practice amp would be kind of cool too!)

Thanks in advance folks!
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Dr-Joned
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Location: The Great South, USA

Re: Ampeg B15 preamp: Drive balanced transformer from PI?

Post by Dr-Joned »

If you take a look at the schematic, you have a complete balanced setup before the power tubes. The 1k resistors feeding the grids on the power tubes would be the output. This would require "padding" the preamp level down a bit. I am not sure of the actual output voltage wise, but a coupling transformer could be used to drop the output impedance to a low impedance.
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Dr-Joned
Posts: 224
Joined: Thu Dec 13, 2007 9:43 pm
Location: The Great South, USA

Re: Ampeg B15 preamp: Drive balanced transformer from PI?

Post by Dr-Joned »

Here's a hint.............
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I Think I Think Too Much !
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