Cute little preamp inspired by JBoz/F5

[yggdrasil]

This week I finished a little complementary preamp. Schematics attached.

It started out as a complementary JBoz. After it looked ok on the simulations I removed the cap's and replaced them with resistors. This configuration needs higher voltage rails than the version with capacitors.

I was rather anxious about the DC offset befor the build. After a few minutes warmup the DC offset wandered +-5mV. The DC offset was actually mostly influenced by the volume pot.

After it was up and running I run a test using RMAA 5.5 and a Creative Soundblaster live 24 bit USB. Both output and input volume was set to 75% on the computer. Then the volume pot was used to set correct level for the test. The same procedure was used when testing the JBoz this winter, and these results are used for comparison.

Sound: What can I say? I like it! I took myself in playing louder than usual, and I needed a SPL meter to beware of it.

I have attached schematics, pcb top and bottom, mirrored pcb top and bottom.

Pictures will follow when I locate the camera cable tomorrow.

 

[yggdrasil]

The test results 1

 

[yggdrasil]

The test results part #2

 

[chinsettawong]

Nice work!

🙂

 

[apassgear]

Nice work...

Output impedance of your Pre?

 

[yggdrasil]

The output impedance should be ~2K6 (R14, R21).

The amp got it's new home inside an old Pioneer integrated amp. Removed everything except the input selector and volume pot.

BTW the amp is point to point soldered. Used the PCB layout only as a guide.

 

[yggdrasil]

Front view, open top.

 

[Tolu]

How about a sound comparison between JBOZ and PreSE?

 

[Nelson Pass]

Very original.

 

[Tolu]

But what original? 😉

 

[Nelson Pass]

Very Original is one of the highest compliments.

In this case, the circuit accomplishes level-shifting from the DC
voltages required to bias the JFETs to the output at 0 DC.

Here is a possibly better way that you might want to explore:

 

[yggdrasil]

How about a sound comparison between JBOZ and PreSE?

They are very similar in sound. With the PreSE I get more space around each instrument.

Here is a possibly better way that you might want to explore:

Thanks a lot. I'll look into it.

...but first I need a couple of new poweramps(F5, Zen9).

 

[Tolu]

Have you tried it with less than 30V? E.g. 18V (2x9V blocks)?

 

[carpenter]

Here is a possibly better way that you might want to explore:

Am I on the right track?

 

[yggdrasil]

Have you tried it with less than 30V? E.g. 18V (2x9V blocks)?

No, I have only built the circuit from post 1. The R's to output eats some of the gain, so you want some extra voltage to make it work.

If you want to go with 18V rails you'll have to look into Nelson's suggestion, or this one.

 

[yggdrasil]

Am I on the right track?

Or even easier...

 

[yggdrasil]

Or maybe:

 

[Nelson Pass]

Am I on the right track?

R9 and R10 make it into something different yet, I think.

 

[Nelson Pass]

I all these case, I suggest that you build it, measure it, listen
to it, and see what you think.

 

[Tolu]

Or maybe:

Electrolytic caps in the signal way? 😕