Cute little preamp inspired by JBoz/F5

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.
 

Attachments

  • prese2.pdf
    71.1 KB · Views: 1,055
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.
 

Attachments

  • 148_4868.jpg
    148_4868.jpg
    95.8 KB · Views: 1,402
The one and only
Joined 2001
Paid Member
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:
 

Attachments

  • comp jfet boz.jpg
    comp jfet boz.jpg
    29.9 KB · Views: 1,035
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.