GA5T preamp layout

[RLBJR65]

Yeah, I know these amp fet emulations have pretty much run their coarse... but it sounds so good as a pre amp for a 386 amp that I thought I would post it anyway. Based on a Gibson Skylark Tremolo amp model GA5T. Still working on the Tremolo portion of the circuit.

Vero layout is untested! I will post the perf layout I used soon.

http://aronnelson.com/gallery/Richard-Boop-RLBJR65/GA5T_Preamp?full=1

The Layout was done with bancika's DIY layout creator. What a wonderfull program! If you have not tried it out yet take a look. Here is the thread, it's getting quite long.
http://www.diystompboxes.com/smfforum/index.php?topic=44838.0;topicseen
Download the program from bancika's web page. http://www.storm-software.co.yu/diy/index.php?project=layouts

Richard

[MartyMart]

Looks great Richard, couldn't it use a "master volume" at the output ?
A standard 100k log should work as an overall vol control.
cheers and thanks for the time/effort

Marty

[MartyMart]

Just quickly built this, sounds very "tasty" and I like the fact that it's a lower "gainer"
It has a lovely "sparkle" to it and certainly has it's own "voice"

Works fine, though the tone pot seems to be backwards 
I used 2k7's off both gates and a 4u7 cap off Q1/22uf off Q2, so I have a bit more
gain at the top end ,,,,,,,,, ( running out of parts badly !! )

Added a 1M pull down resistor at input and a 1N4001 protection diode/100uf/100nf PS filter cap.

Also added the 100k master volume pot at the back, works perfectly.

Cheers,

Marty.

[RLBJR65]

Thanks Marty. Your discription is right on. I sometimes have a hard time telling others what I hear.
Can't remeber if the tone worked backwards on mine. I'll have to take a look when I get home.
BTW Here is the original schematic I was working off of. http://www.schematicheaven.com/gibsonamps/skylarkga5t.pdf

I liked the "sparkle" and lower gain. It cleans up my 386 amp at lower volume. I have not tried it with a Ruby but suspect it would have the same effect. Some guys may want a little more gain though. I'll add your mods to the layout.

Great Idea adding a master volume pot! Why didn't I think of that?

I've got alot going on right now, not much time to build but I hope to get the tremolo working to some day.

Richard

[MartyMart]

Sounds great into both valve/SS amps, also nice direct through a speaker sim
Look forward to the trem section ...... 

MM.

[RLBJR65]

Never got a chance this weekend to take a look at it. Helped my neighbor pour and finish 18 yards of concrete, eeeyuck. Then helped my nephew put together a play yard club house thing for the kids. The play yard was supposed to take 10 hours, yeah right Maybe with a 4 man crew Also installed 2 air conditioners, mowed the yard, took the dog to the vet and put together my Fathersday gift. It was a hammock BTW and I actually got to try it out. Just long enough to drink a beer though! Sometimes weekends like that make me look forward to all the traveling I have to do during the week.

Anyway... maybe the tone pot should have lugs 3 & 2 connected to C3 and lug 1 to ground instead? The schematic just shows a variable resistor to ground. Or maybe it should be a reverse rotation pot.

Did you add any roll off caps or anything? I thought it sounded really good as is so I didn't bother trying.

I had the lfo working by itself just subbing a fet for the tube but it did not work (no trem) in the circuit. I'm thinking that another transistor needs added something like ROG's EA trem. Or maybe I just screwed something up the first time. Anyway it needs a depth pot so I'll have to add some stuff and play around with it. Maybe I'll get a few minutes with the bread board this weekend.

As always your input is appreciated. If you have any more ideas or suggestions please let me know.

Richard

[MartyMart]

Sounds like a busy weekend !!
I spent mine travelling and working ( concert in Dortmund )

I didn't add the double freq roll off section, seemed to sound fine without it, perhaps that's
what gave it the "sparkle" !
Dont sweat over the trem section, there's plenty of simple and good trems around ( Kay/EA etc .. )

MM.