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Old 26th November 2005, 04:20 PM   #1
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Join Date: Jul 2004
Location: ottawa
Default Help for newbie building Toccata preamp


I building Thorsten's Toccata preamp ( and I have a newbie question about the power supply (schematic attached below). I've breadboarded the 9V filament supply and in a no-load situation I am getting 14.5 VDC across the outputs after the caps as opoosed to the 9V on the schematic. The 9-0-9 transformer is putting out about 10-0-10 so some of the over-voltage comes from that. I've checked the cap ciruit about a hundred times so I don't understand what could be wrong. This isn't my first project (I build a JELabs 300B) but admitedly I am very inexperienced about circuit theroy. What am I doing wrong?


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Old 26th November 2005, 06:36 PM   #2
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Join Date: Feb 2002
You will get far less voltage under load, most likely. Filaments draw a lot of current.

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Old 26th November 2005, 06:41 PM   #3
moamps is offline moamps  Croatia
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Join Date: Oct 2002
Location: Croatia
It's just fine. The caps are charged to the peak voltage; Vp=1.4*Vrms.
The voltage will drop when you load power supply with the current sources and the filaments.

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Old 26th November 2005, 07:33 PM   #4
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Thank you so much. I will sleep much better tonight.

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