DIY Stingray 3EQ Preamp

[RobbieK]

I tried without C5 cap and difference is huge, like new set of strings . It is more hi fi sound,

Yes. Without that cap, the pre will have a very flat response with the three tone pots set in the centre. Much more like a modern preamp.

I tried it with 1nf and 100pf.

Having a cap right across the pickup like this, will always create a big resonant peak. By changing the cap, you are simply moving that peak around in frequency. To experiment I'd recommend halving and halving again etc. 1n, 470p, 220p, 100p, 47p. Once you have the treble in the region you like the sound of, then you should try taming that peak by adding a resistor in line with the input. I'd think something around 10k will audibly lower the magnitude of that peak. I'd temporarily use a pot, perhaps 100K linear, to find the treble response you like, then put in a fixed resistor. If you can't mount it on the board, solder it to the pickup hot wire, then run another wire to the input of the pre. Put heatshrink over the resistor and both solder joints. Another option would be to install a trimpot somewhere.

If you find the bass too "hifi" sounding without that cap, another way to alter the treble response is to significantly lower the input impedance of the pre. This is simply done by using a lower resistor where that cap was. I'd think around 100k will start to give you an audible rolloff of high treble, and a more fatter, warmer tone. Again, I'd experiment with a pot there to find the z you like. Or have a switch with a couple of impedances - like Audere does.

I wonder what will happen if I put 2.2m resistor instead that cap?

This won't effect the treble response you have with that cap removed. It is only necessary if you decided to use an active-passive true-bypass switch with the pre. For this you'll need to have the volume pot before the preamp (100K or 250K audio taper would be ideal), and you'll also need a resistor across the output, where the original volume pot was earthing the negative side of the output cap. Without these resistors, the bypass switch will pop.

I just took a quick look in my LTspice model. That sub would make an absolutely huge difference in treble voicing.

PW, you would know well, the effect of placing a cap right across a pickup like this. It really is a strange design choice, right? And it will have a very different resonant peak depending on the pickup spec.

With this cap you can make more suitable for some other kind of basses and pickups.

Absolutely. I read a guy on another forum was trying to use this pre with a P pickup. A 2n2 cap across a typical P pickup will sound very strange indeed. I'd think the resonant peak will be around 1Khz. Very nasal tone with such a boost in the upper mids...

Will 30k volume alter sound of preamp?

No. In this situation, where the pot directly follows an opamp, anything from 5K to 50K will be fine.

 

[Petebass]

Absolutely. I read a guy on another forum was trying to use this pre with a P pickup. A 2n2 cap across a typical P pickup will sound very strange indeed. I'd think the resonant peak will be around 1Khz. Very nasal tone with such a boost in the upper mids....

That would be me. I don't notice anything unusual or honky at 1K. I used a Nordstrand pickup and to my ears there was initially too much treble (4k-6K), which is weird considering this 2n2 cap is supposed to be a LPF. I fixed it by adding a separate LPF to the P pickup only. I also had to add a HPF at 60HZ in order to balance out the extra lows from the P. The net result is actually quite awesome

 

[AphekGreg]

I've just been alerted to this thread. I'm someone who doesn't love the stock 3 band eq and prefers the 2 band. The stock 3 band is too scratchy for my tastes and a little thin in the upper mids.

I've has a 2 band in my Ray for a while, but have been wanting to see about modifying the 3 band eq, as there are elements of it I really like.

Having made some mods, I think I now prefer the 3 band!

The most significant thing I did, was increasing the value of the LPF cap on the input. I've captured some frequency plots as I've gone on, so I can see what's happening, as well as hearing it.

Pretty rough way of doing it, but I've just played the open strings each time, letting them ring out. The meter is set to peak hold.

This is the stock preamp flat.

This one has a 3.3n cap replacing the 2.2n LPF.

This is with the LPF cap removed. This is everything I don't like about the stock preamp, multiplied by about 10. Sounds truly awful. Thin and scratchy.

Last is a 2.7n LPF cap and a 15n replacing the 8.2 HPF at the input.

I've also been experimenting with the Treb and Mid freqs, which I'm liking better too.

Resonant peaks are very common in audio. A lot of classic studio eqs have them on their LPFs. Modern digital eqs, often allow you to vary the size of the peak.

I installed a Wal style John East (I think) preamp for a friend last year. It's eq is a variable LPF, with a second control to vary the size of the resonant peak at the cut off freq.

Of course we all have different tastes and what works for one person, won't for another, so take this as you will.

 

[Passinwind]

PW, you would know well, the effect of placing a cap right across a pickup like this. It really is a strange design choice, right? And it will have a very different resonant peak depending on the pickup spec.

Indeed. But even though I have zero experience with this preamp, my immediate inclination is: if it ain't broke, fix it anyway.

 

[EricssonB]

...all the stuff that he said...

Dude yeah now I want to put in a 5-way selector switch to lemme pick between capacitors, and probably with a blend knob. Oh noes.

 

[AphekGreg]

Dude yeah now I want to put in a 5-way selector switch to lemme pick between capacitors, and probably with a blend knob. Oh noes.

Ha! I've been thinking of a 3 way toggle to select mid frequencies. I already have a toggle between the mid and bass knobs for parallel/single/series pickup wiring.

 

[RobbieK]

That would be me. I don't notice anything unusual or honky at 1K. I used a Nordstrand pickup and to my ears there was initially too much treble (4k-6K), which is weird considering this 2n2 cap is supposed to be a LPF. I fixed it by adding a separate LPF to the P pickup only.

G'day Pete. Sorry man I thought you had put this pre in a P bass. If you watch my vid on building a multi-cap tone control for my P, you'll see the effect of caps around that 2nF range across a P pickup. But with a P, the height of that resonance is far lower because there's still a volume pot, plus cable capacitance etc. But even a 5-6dB peak sounded pretty nasal to me, and I had to tame the middle 5 or 6 caps with a resistor. This is starting to get OT, but the idea of a multi-cap switch for that 2n2 cap on this 80's 3-band stingray pre would be pretty cool. As I mentioned on obf, in my stingray, I have an active filter with a sweepable resonance. (This started as an idea from a thread with Passinwind and one or two others a couple of years ago.) But I think something sort of similar could be obtained by switching through different resonance caps at the front end of this pre...

 

[razormeister]

Group,

I just stumble onto this thread and what incredible timing. I'm about to build a Stingray from scratch and wanted to build the preamp as well.

I am planning on trying out a different wiring scheme to the preamp.


This is a Nordstrand scheme that I bought and am using in a Fender P/J bass that I absolutely love.

The knob configuration is:
Pot 1 - Stacked Volume/Volume
Pot 2 - Active/Passive Push/Pull and Passive Tone Control that works in Active and Passive mode
Pot 3 - Stacked Active Treble/Bass
Pot 4 - Active Mid with Push/Pull Band Selector ( I would only use the Active Mid, not the Push/Pull Band Selector

To replicate this, I will have to put Pot 1 and Pot 2 running into the input of the Stingray Preamp and run the output of the Stingray preamp to the output jack instead of the volume control as in the standard wiring of the Stingray preamp.

I am not sure how loading the front end of the preamp with the pots from the stacked volume controls and passive tone filter is going to work with this preamp, so I am going to have to build it and test it.

I'll post when I have done that.

If anybody can see something wrong with adding the volume controls and passive tone filter to the front end I'd appreciate any information - thanks!

 

[RobbieK]

I am not sure how loading the front end of the preamp with the pots from the stacked volume controls and passive tone filter is going to work with this preamp, so I am going to have to build it and test it.

A typical guitar cable has 500p of capacitance (although this varies a fair bit). So if you leave that 2n2 cap across the front of the stingray 3-band, you have to imagine there being a very very long (18m!) cable between the pickups and the pre. That cap is fine with a low inductance, low impedance stingray pickup. But with a PJ set up and three pots between them and the pre, I think you'll lose quite a bit of treble with that cap there.

The other problem that you'll have is that both the classic stingray preamps aren't designed for active-passive switching, so I'd put a 1Meg resistor where that 2n2 cap was, across the input. The voltage on the preamp side of that 8n2 coupling cap is 4.5V, and the resistor will keep the other side of it at zero volts, so it doesn't pop when switched.

run the output of the Stingray preamp to the output jack

Actually, the output will go to your active-passive switch first, before the jack. And you'll have the same problem on the output when you remove the volume pot, because it's doing the same job with the 10uF coupling cap. So, put a fixed resistor there to earth so the output coupling cap doesn't pop either. Anything 22K to say, 220K should be fine.

As for switching the centre freq of the mid control, I'm not sure I'd bother as it has a very low q (works on a very broad audio range), but if you do, it's a good idea to have your switch add caps in parallel to the existing ones. This is also in the interests of quiet switching.

Best of luck man. Keep us informed!...

 

[razormeister]

Thank you Robbie for the input it’s greatly appreciated.

Time for abuild and test.

 

[razormeister]

Also Robbie, I am using 2 Seymour Duncan ceramic MM pickups. I don’t absolutely need to have the Active/Passive switching, or the passive tone control for that matter. The benefit for my P/J is that in passive mode, I basically have a Jazz Bass configuration. And I’m not planning on putting in anything but the Mid potentiometer, no Q select.

What I do want out of this whole circuit is to move the volume control to the front end with the stacked Volume/Volume configuration.

I saw a few posts back that someone added a pan pot to the front end for a two pickup blend. But in that circuit, they left the volume on the output of the preamp.

So I appreciate your suggestions and will play with them.

The big thing for me is that I want to avoid a pickup selector switch. I don’t want to have to route open up the back of the bass to add the selector switch, and then put a cover plate on the back.

 

[RobbieK]

Cool. Well with MM pickups (wired in parallel) you should be OK. If you put a VV up front, you may want to play around with that 2n2 cap, or even, as I mentioned, replace it with a resistor. Not just to earth the coupling cap, but to adjust the input impedance. But trust your ears. You may be totally happy with it just as it is. That's cool.

IMHO, the MM 3-band is a strange choice for a DIY build. Its quirks are confusing for beginners that's for sure! Instead of a typical buffer, the input stage is a sallen-key HPF for starters. Then there's that 2n2 cap. I've often wondered about that cap. I'd love to meet someone who worked at EB in the late 80's. It has really defined that 3-band stingray sound I guess over the years.

I've had a few Stingray pickup basses over the years with passive option. I've ended up modding dual gang vol pot so in passive it's a 250K, and in active it's a post-pre 25k. A passive MM pickup is definitely a usable tone. I've recorded with it a few times, but personally I found it a bit bland for live gigs.

 

[enterx]

Very Cool Sound.
with old Stock some part.
Run at 9-18V Super Sound.

 

[DangaDanga]

Anyone attempt stingray special mods?

 

[deepestend]

I came across a board in cleaning up for a move. Message me for it...free.

 

[deepestend]

I came across a board in cleaning up for a move. Message me for it...free.

Had some responses... this is a blank PCB, so message me if you can do the build. All I have is the blank PCB.

 

[enterx]

New Year Modify Add Gain

 

[Hclafkir]

Thought I might toss this wiring diagram up for a blend pot addition. Cool preamp!

View attachment 2820787

Hey everybody, how would an active/passive toggle switch be added to this?

 

[Maxwell55]

I have a question and I'm interested in building this and etching my own board, how and where do the pickup(s) connect on here? the sterling wiring diagram shows 2 IC's, possibly the second IC is used for buffering the PU's ? anyone would know, I'd like to possibly wire either to 1 or 2 PU's, schematic would be nice. thank you

 

[Gabriel_cwb]

Hello guys,

I've got this handmade 3 EQ preamp, based on the Dominic's schematics (actually it was made exactly like the schematics). The preamp wasn't built by me, it was build by a luthier, in which I ordered it from (picture attached).

I've been using it for a year and I'm very happy, no problem at all.
This week I take it off my because I'm gonna to install it in another bass, so I decided to run some tests to check the frequencies of each knob.

Attached is a graph of 2 measures, red one is all flat, and the green curve is bass knob at 100%, mid and treble at 0. So, I think the decrease below 50hz is very weird... It's supposed to be flat since 20hz, right? Is there something wrong with my preamp?