Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Effects => Topic started by: fluzo18 on May 08, 2009, 05:19:57 am

Title: Hotbox without EQ
Post by: fluzo18 on May 08, 2009, 05:19:57 am

Hello,

This is my first post here, this forum is a great place to learn. I'm building a pedal preamp à la Hoffman I have a question regarding the schematic.
Can you please take a look at the schematic and let me know how do I attach the last triode?

This is the schematic:
http://img7.imageshack.us/img7/4031/hotboxsch.gif

Thank you for your help!

Title: Re: Hotbox without EQ
Post by: PRR on May 09, 2009, 03:08:19 am

> the 470K resistor junction

You don't want to stop there. V2A does the major distortion.

And you DO need the OUTPUT pot, and probably a Treble-cut pot, as well as the GAIN pot. Otherwise it is a 180 horsepower motorcycle with no throttle.

You want to bypass the tonestack, you will need roughly another 10:1 loss in the same place to keep the same gain/overload structure. It already has a ~~10:1 loss-network, the 1Meg+100K between the tonestack and the OUTPUT control. Change that to 100:1. Either make the 1Meg a 10Meg, or make the 100K a 10K. Either will work, but I'm more likely to have a 10K than a 10Meg handy.

Leave the 10K where you can swap it. Depending on musical style, amplifier, and supply voltage, it may want to be 5K or 20K.

Actually, you can omit V2B. The 100:1 loss allows a reasonable input impedance with a low output impedance. That won't save any bottles, but does avoid the tediousness of V2B cathode-stuff wiring.

Title: Re: Hotbox without EQ
Post by: fluzo18 on May 09, 2009, 04:49:41 am

Thanks PRR for your reply.

I'll try what you suggest, or maybe I should buy a bigger box and build the circuit as is...