Bass preamp (mm114/ Haz)

[Warwick]

Hello , is anyone have the kindness to draw me this layout (with only one imput for a box).

[Sergio]

Hallo, this is an spector preamp? But does it has 2 inputs? I thought by the youtube videos these were onboard preamps, direct from the pick ups, so no way to choose between 2 inputs. Have you tried other preamps, musicaman ? Sadowsky? I play a warwick fortress 5 and im curious about the preamps, despite most of the times I play it passive.

[Sergio]

I ll answer myself seems like vr1 and vr2 are the Blend control and people find it works right passive or active pu switching. Vr3 is volume and the other two vr's. Are  highs and lows. So maybe taking the input direct to vr3 would be best for box mounting.

[Warwick]

Yes, it is the Spector preamp (kramer,Tobias,Cort). I already built the Sadowsky and the Musicman (3 bands): they work very well!
By cons i do not know how to drow the layout...If someone could do it would be nice!

[Sergio]

It should not be difficult, only problem could be shrink it to the max. If noones willing i can give it a try. By the way, which basses have you tried or have had best sounds with your built pres?

[Warwick]

I have 9 bass...
Jazz bass sounds good with Sadowsky, Precision bass and Warwick Dolphin Pro 1 with Musicman preamp .In fact it depends on the sound you searched for...It is necessary to vary the pleasure...
I have bass also with onboard preamp so I do not couple them with box preamp (Status bass).
Thank you in advance if you can draw it! (The size of the drawing is not too important for me:it's for a box)

[Sergio]

Ugly very ugly, standing resistors, capacitor soldered direct through external pot pins, strange output spot, probably others can make it a lot better,  but i think this couldl work. if you give it a try and it sounds good let us know!

[Warwick]

Thank you very much Sergio! I will build the preamp.
I shall inform you dice that I shall have ended.

[Warwick]

There is no error on a resistor? I see 12k. It shouldn't be 1.2K?

[Sergio]

Exactly, you are right the 12 k next to the output spot should be 1k2. My fault i copied resistors and forget to change value after paste. My apologies, wont be able to change it until tomorrow. I supposed that part of the preamp magic will be in the picofarads cap being accurate, with metal resistors is much easier , i mean not that they are 223 exactly, but if you can measure them, better 200 than going to 100 pf or 300pf

[Warwick]

Thank you!

[j-pee]

is it, after all, verified? :)

[bigsnack]

Hello!  This was discussed in further detail on another forum.  I made an update to the file based on some of the cap values needing to be corrected.  Two folks in that thread have built and confirmed that this works.  Enjoy!

[Warwick]

I had built the
preamp but without success. Now I understand better.
Sorry but I haven't had time to come here since and give an answer ...

Well, I just have to order the components now. Thank you!

[bigsnack]

You're welcome!

The issue was that the schematic was likely built using the labels of the components, instead of the actual values.  Those labels include the cap value, plus a third digit which signifies the "multiplier".  The corrections below were made:

222p = 22*(10^2) = 22*100p = 2200pF capacitor
223p = 22*(10^3) = 22*1000p = .022uF capacitor
473p = 47*(10^3) = 47*1000p = .047uF capacitor
682p = 68*(10^2) = 68*100p = 6800pF capacitor

I'm waiting for my parts to arrive as well, and then I will be building one.  This was verified by a builder already though, so it should work!  Let me know how it goes!

[Warwick]

Thank!
 For the moment I am in confinement mode. So I will have to wait a little longer ...
But I will answer you

[nekkz]

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...

Turns out,
 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.