I'm trying to build this preamp. I have a Spector Euro 5
made in 2003, she didn't have the TonePump preamp circuit. I bought her used for 800$ 10 years ago from a guy working for Goddin... Well, it was the deal of my life, and I never realised until recently.
The problem is, she doesn't sound as good as the version with TonePump. As I like doing things myself and to learn from that, I looked up for a TonePump schematic and found this thread. It's even better, it's the old HAZ circuit. Great!
I'll share my works, because, because, this thread exists and deserves to go into the verified section of the board.
So the first contribution, I fixed the schematics, as someone noticed, these cap values didn't make any sense. Also, I'm pretty sure the 100p and 330p ones are 10p and 33p. I ran several simulations of the circuit and it gave me a dirtier signal with lower values (which was to be expected)... As I don't know if it sounds good, I'll wait for the prototype to be built before correcting these values as well. The output signal is quite interesting and displays very interresting distortions in it. I'm not electrical engineer, to me, this circuit is complex to analyse so I don't know if it's correct or not, but that smells very good. Can't wait to build the PCB prototype.
My bass has 4 knobs, not 5, so 2 knobs need to be grouped together... I had two choices :
1. Use a A25k blend pot as analog pickup select.
2. Use a dual concentric stacked pot B100k for Tone control...
1. Finding quality
A25k log blend pots is very hard, not even Mouser or Digikey have these. EMG produces one called ABC, but it has descrete logic on it and is very expensive (79$), and furthermore backorder almost everywhere.
2. Dual concentric B100k pots don't exist.
I had to go with choice 1 and combine the pickup volumes (RV1 and RV2) into an audio blend pot. This is one of the current designs for the NS-USA. I could only find cheap chinese 3$ audio blend pot which will collect dust and make a scratchy noise in 4 months and break my lovely SWR amp crossover. It's quite boring. If you have suggestions, or hints on this aspect, I'd welcome them.
Finally, I have a PCB design for it, but I'll try it and experiment with it before posting the design with the part listing I'm using, probably in KiKad format as Open Hardware license. I'll probably have it in the next month, shipping companies are flooded at the moment with the pandemic.