Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ncusack on February 02, 2011, 03:15:26 pm

Title: Help with a new build
Post by: ncusack on February 02, 2011, 03:15:26 pm

So i've been trying to work up a simple but versatile build idea for a set of transformers I have lying around. Specifically they are a hammond 1750E and 272DX. I've built a 5E3 before and im looking to try something a bit different. Attached is a copy of the schematic i've draw up and would like it if a few people could weigh in on the idea.

This is basically a version of the archived Cal Dreamer project from ax84. I've added in an effects loop but im not sure if thats the right way to approach it. Ive also added in some tonal and gain options to the first gain stage. In this design i plan to use a 12ay7 in place of the 12ax7 in V1 for a little more clean on the dial and Ill use the effect loop and in line pedals to attain overdrive.

If anyone can suggest changes or even a better project idea for the iron let me know.

Title: Re: Help with a new build
Post by: PRR on February 02, 2011, 11:15:49 pm

Many FXes will be unhappy about the +200V DC coming out the to-FX jack. Maybe a blocking cap?

Signal level at this FX loop is over 1V, pretty high for guitar-level FX. OTOH the output impedance is 39K, so typical rack-FX will load it down considerably.

Your string of B+ nodes will usually have resistors between cap-nodes.

Other-side of wall-cord, ground on B+ caps not shown.... I assume you know how this goes.

Title: Re: Help with a new build
Post by: ncusack on February 03, 2011, 01:19:18 pm

Yeah that was a quick schem done at work there should be 2 dropping resistors on the B+ rail. I have attached a new schematic.

Would you suggest moving the FX Loop to just before the second gain stage instead of after?

In the case of using a blocking cap what value would you suggest?

Title: Re: Help with a new build
Post by: tubenit on February 04, 2011, 05:07:50 am

Quote

In the case of using a blocking cap what value would you suggest?

Try .02-.047 range.

I would consider changing the .1 coupling caps post LTPI to .047 or.033 value. However, that is just a personal taste thing.

With respect, Tubenit

Title: Re: Help with a new build
Post by: ncusack on February 05, 2011, 07:33:28 am

Ok so here is an updates schematic with adjusted values and using the blocking cap plan. Let me know if it makes sense. I also threw in a trim pot for the send if that makes sense here.