Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: panhead on October 19, 2011, 12:00:29 pm

Title: Extra preamp stage a good idea here?
Post by: panhead on October 19, 2011, 12:00:29 pm

I drew up a schematic for a simple push pull amp with a paraphase inverter. I have two preamp stages before the PI, thinking that I can have a sort of boost stage. Attached is the schematic. Please feel free to comment.
PS...This is very preliminary.
Thanks

Panhead

Title: Re: Extra preamp stage a good idea here?
Post by: JayB on October 19, 2011, 05:58:58 pm

Hell yeah, why not?

If you get any blocking distortion, just lower the gain some with grid blockers or voltage dividers.

Title: Re: Extra preamp stage a good idea here?
Post by: panhead on October 19, 2011, 08:24:33 pm

I'm considering using a 12AT7 for V1 mostly because I have a few hanging around. It's an easy enough swap, but I'm not sold on the tone of the 12AT7 for a preamp. I also will probably use EL34's and big enough iron for the output, plus higher voltages than indicated on the schematic for more headroom. I don't think lack of distortion will be an issue. I'm more interested in the quality of the distortion. I've wanted to build somethig with a paraphase PI for a while, since some old Ampegs were the coolest sounding amps I've owned. The extra gain plus the PI should get me out of the Fender world, where most of my amps have been.

Title: Re: Extra preamp stage a good idea here?
Post by: plexi50 on October 19, 2011, 08:52:28 pm

Im getting a little burned out always using 12AX7 tubes. I love using the Octal 6SN7 & 6SL7 preamp tubes

Roughly the same gain but smoother transition. Great sounding tubes

Title: Re: Extra preamp stage a good idea here?
Post by: panhead on October 19, 2011, 09:47:03 pm

I really like tone of the 6SL7 and 6SN7. The 6N9P (Chinese knock off of a Russian military tube) is a less microphonic version of the 6SL7 that has close to the same tonal color (and is cheap money).

I've built a few 5E3 type amps for people lately, and I do like the grittiness a lot, but I want to try for a warmer and fatter tone. I thought I'd start with a typical tweed Fender preamp and single knob tone control and then fatten it up a bit. I figure the paraphase inverter will give me some harmonics (probably from crossover distortion) and the .1uF coupling caps will pass a lot of mids. Hopefully I'll like it. I don't know how much the second V1 triode will overdrive the PI or if that's even desirable. This is an experimental amp for me, rather than a commissioned build, and I have enough extra parts accumulated that I can play around a little.