"A little background hiss" - 2 Umble build reports

[zjokka]

I finished my second Umble today and it went so much smoother than anything I build before... on the DMM that is.
The first time around, I just couldn't get the last FET (I used J201) to bias right but adjusted that by ear. In that way I could dial out a bit of noise. I remembered that when boxing it up the noise level when down quite a bit.

Now with my second built all Ds baised right and easily at 4.5V but the noise again was incredible. Tone and sustain. I only tried it on a tiny practice amp, but could put the volume up anywhere near half unless I put the little amp under '1'.

Also, ROG article says there is some background hiss, but I don't hear that in the clip.


Could this noise come from

-having the pots mounted temporarily on a breadboard
-alligator clips galore
- long leads all around (5 pots (15 wires) in addition to in and out, + & -
- bad soldering if the circuit checks out ok on the values?
- not using metal film resistors? I did measure every resistor and put them some in series to have matching values. Is there really a sonic difference between a metal film 100k and two series carbon resistor that make up the same value

In the first build I succeeded in getting the noise and gain down somewhat by using a 2N5457 for Q1 (J201s for the others) but that was after I couldn't get 4 j201s to bias right.

I was also wondering whether anybody had ever tried running these amp simulations at higher voltages? would that help the noise or exactly the opposite?

thanks!
zj

[nordine]

check for bad caps.. electrolitic caps betray more than often

[lautmaschine]

If the caps are okay, I'd check the trimpots.  They can become quite noisy.  I recently replaced the four trims in my English Channel with fixed resistors and the noisefloor has dropped significantly.