Hiss generally comes from using a cheap op-amp in the first stage. That's pretty unlikely in a fully solid-state amp.
Vox pathfinder 15r headphone jack series#
Quote from: BigPolishJimmyI wonder if these will develop the hiss problems that the valvetronix series had? reducing preamp hiss lower than the inherent hiss of the power amp is pointless. most hiss originates in the first stage
If you can't hear it fully cranked with your ear against the speaker then making it 20dB quieter is pretty pointless. there are lower noise op-amps than the 4550's, but you soon strike the law of diminishing returns and that you won't notice the difference between modern cheapies like LM833's, TL07x-series etc, and das zupervundendorfer's at $$$$ each. Getting the mains off the PCB and well insulated is a very good idea, particularly if you want to tinker inside. Trade spouse in on one that is a) deaf or b) mad for RnR.
Vox pathfinder 15r headphone jack code#
These days the only way to be sure is the test I mentioned, but I'll be surprised if you don't find that whatever the code letter, it's already a log taper. A fairly orderly system in the 1960's has been well corrupted by everybody baking their own cake. You can't assume anything from the taper code letter. A germanium diode will clip around 0.1V so you may have a problem getting enough signal into the output stage. The LED's that are in there are clipping around +/- 2-3 volts. The trick with clipping diodes is to make them different, that's what gives you 2nd harmonic. I've a Vox AC30 Amplug and all I hear (with gain >2) is hiss. I'm going to try to reduce the noise level as much as possible so that if I don't do the speaker out mod, I can use headphones without the hiss. Putting in sockets for the op-amps to try out the lower noise ones These boards include power rectifier and amp. Remove all the original audio amp components and use one of those PSU+AMP TDA2030 boards from Eb*y. This will make removing the PCB easier for tweaks.Ģ. Will mean drilling a hole in the chassis. Move the AC circuit from the main PCB and use a fuse holder instead. My problem is that of too much volume (hearing sensitive spouse and all that)ġ. An alternative to replacing it (since it's probably hard to get an exact physical replacement) is to replace R18 with a large value. The volume control pot is a B50K which I assume means that it's linear as opposed to audio taper. There's a blog article where someone used a pair of 1N34As.
I'll look into replacing the leds, either with a single one of different color or with a couple of germanium diodes. Roly, thanks for the suggestions and the schematic. That should work, although you could always mount another socket somewhere for an external speaker and retain the headphone/Line Out option.
Quote- Remove/short the headphone resistors and use the headphone jack as a speaker out jack Quote- Zeners to "control" the supply voltage for the op-ampsĭo you have a reason/problem? If you don't actually have a problem then I wouldn't bother, most op-amps have about 120dB of power supply rejection. If it's a linear taper then it will be about 25k to each end, but if it's quite different then it's already a log pot. Set it to 5/10 and measure the resistance from the wiper to each end. Quote- Use an analog taper pot for volumeĪll pots are by their nature analog - I think you mean "audio" taper or log pot, which the volume control should already be. You may find some tonal advantage in playing around with one of these LED's trying one with a different forward voltage (generally a different colour) with will give you asymmetric clipping of +ve and and -ve parts of the signal, which can produce a nice 2nd harmonic. The overdrive from this stage is clipped by the following back-to-back red LED's. Quote- Change the gain resistor of the second stage to reduce the gain when the drive switch is on A six inch speaker is worth replacing just because it's six inch, and a buzzy six inch speaker.
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