So I'm nearly complete with the first of a few preamps that I'm building for me and my friend. Just about got this one done when I noticed that it seems to distort upon the power being applied, and then accumulate until you switch it off. My hunch is that it's in the power section.
Schematic that I came across on someone else's build:
My layout with a different power section added:
Soundcloud link if you need to hear it:
Audio clip with all pots on full. Downloads enabled in case you want the subtleties not provided by the audio stream.
Switched on at about 7 seconds. Just beyond the mid-point time warp that skips a minute you can hear how gated and distorted it gets. Not sure what that's about yet. Switched off for a bit then switched back on -- everything's okay.
Any takers?
Side note: this thing is pretty hot. May need to throttle it down a bit.
Unwanted Preamp Distortion
- blackbunny
- Resistor Ronker
3 things bother me in this circuit.
Firstly, the circuitry around the input seems unnecessarily complicated, and would likely result in a severely bandpassed frequency response with a prominent midrange hump.
What are you using this circuit to amplify? Single coil guitar pickups? Humbuckers? Passive bass pickups? The input could easily be redesigned to suit the source a lot better.
Secondly, I would change the power supply voltage dividing resistors from 2M2 to 100k to allow more bias current.
Thirdly, running a preamp and active tone controls - with about 15db of cut and boost available - from a 9v supply means that it will run out of headroom very easily when boosting the EQ unless you are amplifying very small input signals, such as a piezo pickup or very low output pickup. The TL07x and TL06x will latch up to the supply rail when the signal voltage swing exceeds +- 4.5v , causing serious distortion and oscillation when the tone controls are fully boosted.
Firstly, the circuitry around the input seems unnecessarily complicated, and would likely result in a severely bandpassed frequency response with a prominent midrange hump.
What are you using this circuit to amplify? Single coil guitar pickups? Humbuckers? Passive bass pickups? The input could easily be redesigned to suit the source a lot better.
Secondly, I would change the power supply voltage dividing resistors from 2M2 to 100k to allow more bias current.
Thirdly, running a preamp and active tone controls - with about 15db of cut and boost available - from a 9v supply means that it will run out of headroom very easily when boosting the EQ unless you are amplifying very small input signals, such as a piezo pickup or very low output pickup. The TL07x and TL06x will latch up to the supply rail when the signal voltage swing exceeds +- 4.5v , causing serious distortion and oscillation when the tone controls are fully boosted.