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Stingray aftermarket 2 band pre

#521
MagicMan_841 said:
Well I just finished my version in pedal form and it sounds really good! However, it does clip a little when I run my P/J bass through it... I'm guessing that this is caused by a different (higher?) pickup impedance than on a Ray with a single pickup. Is there something that can be done to give the circuit more headroom?
Click to expand...

You can run with a second battery but 18V is right on the redline for the LM4250. Stick a couple of 1N4001 diodes in series with the +ve rail to bring it down a touch and you should be fine.
 
#523
MagicMan_841 said:
Thanks for the quick reply, sir!
Click to expand...

You're welcome :)

MagicMan_841 said:
Would it be possible to feed 18V through it but use a resistor to lower the voltage to, say, 15-16V?
Click to expand...

Yes, a resistor should work but diodes would give a more stable voltage. The drop from a resistor varies with current consumption. The drop from a diode is less variable.

Note that given the ultra-low current consumption of this circuit you may need up to 4 diodes to drop down to 16V. Use a meter to check.
 
#524
Sounds good. I'm going to get me some diodes and try that!

Thanks!

Also, is it normal that at full volume on the preamp circuit I don't get a volume boost when running a passive bass through it? At full volume I have unity, just like I would get with a passive volume control (which I am guessing it is, as a matter of fact).
 
#531
MagicMan_841 said:
Since my circuit is housed in a pedal, I'm using a 9V powersupply (Fuel Tank Jr.)... that's pretty consistent voltage-wise, I guess :D
Click to expand...

I wonder if the fact that you are using it as a pedal, and have a set of controls before the preamp, is causing the reduction in gain?

You could probably reduce the value of the 220K resistor at the input, or maybe increase the value of the 100K resistor in the feedback loop, though that might alter the way the bass control works. But that would set the gain.
 
#534
I played around with it again some more last night and... it now sounds dead quiet, no clipping, no hiss... may just be a grounding problem after all! I'm using the pedal case to ground the components, which may not be the most reliable idea... I'm going to add individual ground wires to the bodies of the pots.
 
#536
Rokoko said:
... Has anybody tried feeding the preamp power from a pedal board psu. Shouldnt that hive me a steady 9v? But are there problems by doing this?
Click to expand...

That should work fine. You can also wire up a regular stereo jack to switch the battery on. I don't know why MM switched the (+) lead of the battery when they could have done it the usual way. Saves on getting a fancy switching jack too.

But even if you choose to use it battery powered, this op amp draws very little current, which is why the original Stingray didn't even turn the battery off when you unplugged it!

Of course if you try different op amps they will use more juice.
 
#537
Rokoko said:
... Has anybody tried feeding the preamp power from a pedal board psu. Shouldnt that hive me a steady 9v? But are there problems by doing this?
Click to expand...

My brother's Line 6 guitar works that way. You plug a stereo cable from the guitar to a box that sends the power up one side of the cable to the guitar and sends the audio signal down the other side and through the box to the amp. I don't think it would be hard to wire up any typical preamp to work that way. I've always wanted to try this, but as others have said, the battery lasts so long in the 2-band preamp that it's easy enough to replace the battery once or twice a year.
 
#538
So, I've been building these for a while now, and felt that it wasn't delivering enough gain. I started looking at the parts list, and noticed a discrepancy in the parts list... A resistor listed as 1.5M on his schematic, was 1.2 in the parts list here.... so that got me to looking at the schematic, and then I compared it against another hand drawn one I had. There was some major part values differences.

So I have here a vintage Sabre 2 preamp, and since it's pretty much the same circuit, I started combing though it and found the mistakes. The Sabre matched the two hand drawn schematics I have.

So... first, the 100K resistor in the feedback loop between pins 2 and 6 should be 220K. This will increase the gain. It sounds much better with this change.

Then there are no 1.5 or 1.2M resistors in the real MM preamp. The resistor from pin 8 should be 2.2M. That sets the quiescent current, or how much current the op amp is drawing when it's idle. That should reduce current draw.
 
#539
SGD Lutherie said:
So, I've been building these for a while now, and felt that it wasn't delivering enough gain. I started looking at the parts list, and noticed a discrepancy in the parts list... A resistor listed as 1.5M on his schematic, was 1.2 in the parts list here.... so that got me to looking at the schematic, and then I compared it against another hand drawn one I had. There was some major part values differences.

So I have here a vintage Sabre 2 preamp, and since it's pretty much the same circuit, I started combing though it and found the mistakes. The Sabre matched the two hand drawn schematics I have.

So... first, the 100K resistor in the feedback loop between pins 2 and 6 should be 220K. This will increase the gain. It sounds much better with this change.

Then there are no 1.5 or 1.2M resistors in the real MM preamp. The resistor from pin 8 should be 2.2M. That sets the quiescent current, or how much current the op amp is drawing when it's idle. That should reduce current draw.
Click to expand...

Very interesting. Thank you for digging in to that.

Could you post an updated schematic here and in the freestompboxes thread?
 
#540
SGD Lutherie said:
So, I've been building these for a while now, and felt that it wasn't delivering enough gain. I started looking at the parts list, and noticed a discrepancy in the parts list... A resistor listed as 1.5M on his schematic, was 1.2 in the parts list here.... so that got me to looking at the schematic, and then I compared it against another hand drawn one I had. There was some major part values differences.

So I have here a vintage Sabre 2 preamp, and since it's pretty much the same circuit, I started combing though it and found the mistakes. The Sabre matched the two hand drawn schematics I have.

So... first, the 100K resistor in the feedback loop between pins 2 and 6 should be 220K. This will increase the gain. It sounds much better with this change.

Then there are no 1.5 or 1.2M resistors in the real MM preamp. The resistor from pin 8 should be 2.2M. That sets the quiescent current, or how much current the op amp is drawing when it's idle. That should reduce current draw.
Click to expand...

hmmm.. since you have an authentic Sabre preamp in front of you there is no dispute in the values. The Sabre abd Stingray preamps I built have enough gain and sound great with the 100K in the feedback loop. I noticed the Sabre guitar schematic has a 220K in the loop. I'll swap it for a 220K and see if it sounds better. Since I use LT chips I always left pin 8 empty. Thats what I love about being a DIY'er, I can tweak and modify the builds as I go along.
thanks for the info :hyper:
 

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