I just swapped the LM4250 for LT1128. Tonally they seem to be pretty close to me ears. The LT1128 is slightly hotter and seems to have slightly less highs. Other than that, it's hard for me to tell them apart.
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Stingray aftermarket 2 band pre
- Thread starter blmeier7
- Start date
I noticed a huge difference. are you running it at 18V? I swapped the 2M2 resistors for 220K's as instructed in previous threads. The LT1128 is a lot hotter and there is a bump in the hi-mids. a more growly tone without the clanky high overkill
Yes, it's running at 18V. I definitely noticed a small dip in hi-mids compared to the LM4250. I recorded both so I could A-B the recordings. I can post them if anybody's interested.
I also tried the LT1028. It had more highs. I guess thats my preference, I like a growly sound. It really growls when only the front coil is on.
I haven't seen the previous threads you referred to. What's the purpose of swapping the 2M2 resistors for 220K resistors? I haven't done this so that's probably the difference.
Some op-amps have higher input current than the one originally specified. Dropping the resistors down to 220k makes the circuit more tolerant of variation in input current but increases the supply current slightly.
The engineer Jim Williams said to try out the LT1351 and they say the LT1115 is pretty good for bass. Jim has been designing preamps since the 70's for pro musicians. I have both but haven't popped them in yet. LT1351 is around 390uA and the LT1115 is 13mA. since they are free samples, nothing to lose, tone to gain
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I was wondering about the volume pot value. Even though it works in this circuit 25K is still an odd value for a volume pot. what would happen if I bumped it up to 50K or 100K? would it be detrimental to the circuit or tone?
As far as I can tell, it's not wired in the same way as normal volume pot so it'll behave differently in the circuit.
As it is, it sets the output impedance of the amp and the higher it gets the higher the potential for noise problems. Can't hurt to experiment though.
As it is, it sets the output impedance of the amp and the higher it gets the higher the potential for noise problems. Can't hurt to experiment though.
gonna try a 100K and see what I get. also I think the 220K pickup input resistor can be bumped up. gonna try a variable resistor to see what it sounds like at different values - 324K, 500K, 750K, 1M
tweaked the box preamp first. swapped 25K volume pot for a 250K and the sound really opened up. more clarity in the highs and mids. it sounded muffled before. I noticed the higher the value the pickup input resistor the more attenuation. So I dropped it from 220K to 47K and the sound opened up even more. sounds really great with the Strat and piccolo bass. didn't notice any noise from the tweaks, mV output didn't change. I'll try a 100K pot and a 100K resistor for the onboard bass preamp.
chnaged the onboard volume pot to a 100K linear and a lot more signal is coming through. didn't notice any noise, might be due to the LT opamps I'm using. the signal is VERY hot. found a nice spot on the volume and it reads 35K on the DMM. anything above that would be way too much signal. decided to leave the 220K pickup input alone to keep the original design. sounds great!
the original owner's manual is interesting. It suggested not to turn the volume past halfway if you want a clean signal. that must have been the days before padded amp inputs
chnaged the onboard volume pot to a 100K linear and a lot more signal is coming through. didn't notice any noise, might be due to the LT opamps I'm using. the signal is VERY hot. found a nice spot on the volume and it reads 35K on the DMM. anything above that would be way too much signal. decided to leave the 220K pickup input alone to keep the original design. sounds great!
It's funny that this literature and Sterling Ball say that the bass EQ is boost/cut but it's never seemed that way to me at least on my Pre-EBMM Stingray.
I wondered about this too. With the stringray preamp I built, the bass definitely seems to be boost/cut. I have a preamp bypass switch so it's really easy to compare the preamp to the the passive tone. The active tone sounds most similar to the passive mode when the bass pot is at about 50%.
I found this interesting tidbit from Barry Klein who was an ET at Music Man and helped Leo develop the preamp. He used the same workbench as Leo. It makes me appreciate the design even more
Leo and Tommy are deceased but they left behind a great design. I think Barry works at Western Digital.
Barry Klein:
You guys talk about the preamp and who designed it. I worked at Music Man in the 70's as Leo Fender's and Tom Walker's electronic technician. I worked in both the Music Man and CLF facilities. Leo was using an LM4250 op amp in a way it was not really intended for - but it did the job. He designed it by plugging in parts and strumming the 6 strings of his test bed neck. He spend DAYS doing that, driving everyone nuts.
It was never portrayed to me that Tom did the original preamp designs - but it would make sense as I could not believe Leo was designing with an op amp. But I suspect that Tom designed the ORIGINAL preamp, as since I started with Leo who was the one tweaking the guitar/bass preamps - not Tom. The use of the LM4250 for that preamp was kind of mindblowing too - everyone thought it was junk and not worthy of an instrument preamp. And God - he was using tantalum capacitors in the audio circuit!
Leo knew that circuit better than anyone, knew what component did what and tweaked that damn circuit until both Tom and I just about went nuts. Tom sent me over there to work with Leo to try and finalize a design one time. I tried to suggest a totally different circuit. He didn't like it much. Leo didn't hear too well (after years of playing "ding dong ding" full blast in his closed lab) and he boosted treble to really high levels. Leo wasn't very current at that time. That is why the Strat is so bright and the stingray guitars ungodly bright. I would not get all religious with the LM4250 op amp that Leo used. It has really lousy specs other than supply current. the op amp was replaced with an LF441 later on - which has much better specs. Maybe there is even something better available now... I haven't kept track of op amp improvements. I would think that the boost in slew rate with the LF441 would result in a better sound with less distortion artifacts. Even when we were just starting out guys would replace the opamp circuit with a JFET circuit that someone was selling at the time.
Leo and Tommy are deceased but they left behind a great design. I think Barry works at Western Digital.
Finally got around to building one of these guys and it came out pretty good. I stuck it in an OLP to test it out and it sounds great.
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Looks like a nice clean build. Glad to hear it worked, and thanks for posting the pic - I enjoy seeing the boards come to life
- Aug 21, 2008
- 10,386
- 253
- 68
- Disclosures
- Owner, SGD Music Products
- Aug 21, 2008
- 10,386
- 253
- 68
- Disclosures
- Owner, SGD Music Products
