How the heck would you wire that? Not that I'm planning to since the cavity on my P Lyte won't allow for it, but how do you make that happen?
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18v vs 9v ?
- Thread starter The Unit
- Start date
You could basically run a voltage divider the same way youd have a Vcc (18) and a Vbias (9) for op amps, and use the Vbias as the Vcc for the pickups, i believe
Im not sure how this works because i have never looked into the guts of specifically active PICKUPS, but most circuits don't increase gain just by increasing the Vcc eh? Could be being stupid after the Saints just embarrassed themselves
with respect, this makes no sense, and is incorrect. I've never seen a circuit where the gain is controlled by the voltage rails.
The extra headroom you get from 18V is useful to the designer. No, increasing the voltage does not increase the gain of a circuit automatically but it does allow the designer to use higher gain if he/she wishes. I can't say that I have seen that personally, not that I study active bass designs for a hobby, but I have seen the Fender designers use higher output pickups when they use 18V.
I have a Deluxe Active Jazz (9V), a Reggie Hamilton Standard Jazz (18V), and a Standard Jazz Fretless (passive). Typical hard pluck output of the DAJ is 800 mVp-p, the RHSJ is 2.8 Vp-p, and the SJF is 2.2 Vp-p. The two active basses have up to 12 dB of bass boost so the preamp will have to handle four times the pickup voltage at max boost which is 3.2 Vp-p for the DAJ and 11.2 Vp-p for the RHSJ. The Reggie has about the same output as the passive Standard Fretless but the Deluxe Active is a quiet bass, as many owners have noticed.
But this makes sense when you consider the realities of opamps and batteries. A fresh 9V battery is over 9V but as it discharges its voltage will drop considerably. Obviously even a fresh 9v battery cannot supply enough headroom for an 11.2V signal so 18V is required if you want to run full boost on a standard (for Fender anyway) passive pickup. The reality is that if you want to get the full rated output of any alkaline battery you have to discharge it to 0.8V per cell because that is the end of life voltage that the battery industry uses to measure battery capacity. A 9V battery has 6 cells in series inside its case so the end of life voltage for a 9V battery is 4.8V.
You can see then what is going on with the DAJ preamp and pickup design. The low output pickup signal will be 3.2 Vp-p at max boost, the single 9V battery supplies 4.8V even at the end of its life, and that leaves 1.6V of headroom for the opamp. That is a reasonable number, the opamp output transistors might need a few hundred mV each so this setup allows the bass to get the full rated battery capacity from the 9V battery you put in it. Some people complain about the low output though.
So the 18V RHSJ runs typical pickup output levels and with fresh batteries it has no problems with full boost. Now you cannot run full boost without distortion once the batteries have dropped to about 6V each so the 18V system will not run distortion free down to the 9.6 V you get from two batteries in series at end of life. However the pickup waveform is only 2.8 Vp-p on the very first cycle after you pluck the string, on the second and following cycles it is only 1.6Vp-p or less. After boost that is still only 6.4Vp-p and two 9V batteries in series will provide that plus some headroom even when fully discharged. So the 18V bass will only distort on the first cycle after a hard pluck even on dead batteries and that may not be too noticeable.
So basically 18V will let you run considerable boost on normal output level pickups even when the batteries are dead while 9V will either give you a lot of distortion or force you to use low output pickups.
I have a Deluxe Active Jazz (9V), a Reggie Hamilton Standard Jazz (18V), and a Standard Jazz Fretless (passive). Typical hard pluck output of the DAJ is 800 mVp-p, the RHSJ is 2.8 Vp-p, and the SJF is 2.2 Vp-p. The two active basses have up to 12 dB of bass boost so the preamp will have to handle four times the pickup voltage at max boost which is 3.2 Vp-p for the DAJ and 11.2 Vp-p for the RHSJ. The Reggie has about the same output as the passive Standard Fretless but the Deluxe Active is a quiet bass, as many owners have noticed.
But this makes sense when you consider the realities of opamps and batteries. A fresh 9V battery is over 9V but as it discharges its voltage will drop considerably. Obviously even a fresh 9v battery cannot supply enough headroom for an 11.2V signal so 18V is required if you want to run full boost on a standard (for Fender anyway) passive pickup. The reality is that if you want to get the full rated output of any alkaline battery you have to discharge it to 0.8V per cell because that is the end of life voltage that the battery industry uses to measure battery capacity. A 9V battery has 6 cells in series inside its case so the end of life voltage for a 9V battery is 4.8V.
You can see then what is going on with the DAJ preamp and pickup design. The low output pickup signal will be 3.2 Vp-p at max boost, the single 9V battery supplies 4.8V even at the end of its life, and that leaves 1.6V of headroom for the opamp. That is a reasonable number, the opamp output transistors might need a few hundred mV each so this setup allows the bass to get the full rated battery capacity from the 9V battery you put in it. Some people complain about the low output though.
So the 18V RHSJ runs typical pickup output levels and with fresh batteries it has no problems with full boost. Now you cannot run full boost without distortion once the batteries have dropped to about 6V each so the 18V system will not run distortion free down to the 9.6 V you get from two batteries in series at end of life. However the pickup waveform is only 2.8 Vp-p on the very first cycle after you pluck the string, on the second and following cycles it is only 1.6Vp-p or less. After boost that is still only 6.4Vp-p and two 9V batteries in series will provide that plus some headroom even when fully discharged. So the 18V bass will only distort on the first cycle after a hard pluck even on dead batteries and that may not be too noticeable.
So basically 18V will let you run considerable boost on normal output level pickups even when the batteries are dead while 9V will either give you a lot of distortion or force you to use low output pickups.
A long time ago when I played only EMGs, I called them and asked if I should run 18v. They said yeah, I should do it if I could. That was the extent of the conversation. Good enough for me. I could, so I did.
The EMG-81 Active pickup and the original Music Man Stingray use LM4250 opamps. The LM4250 opamps can output signals to within 0.9V of each rail with a 3V supply and to within 3V with a 30V supply.
The Barcus-Barry 3000A preamp uses a TL062 opamp. The 062 has a typical maximum output to 1.5V of the supply rails. With a minimum to 5V of the supply rails.
The Bartolini NTMB preamp uses a MC33178 opamp. The 33178 has a typical maximum output to approx 1V of the supply rails. With a minimum to 2V of the supply rails.
So if we use 9V supply:
The LM4250 can output a maximum signal of approximately 7Vp-p (estimating the output swing from the graph on the data sheet)
The TL062 can output a maximum signal of 6Vp-p for the best case and if you have a 062 on the low side of the specs you may have no signal output at all. (Although the worst case 062 I have ever seen was only 3V from one rail in a 9V circuit. So that one would have been limited to 3Vp-p.)
The MC33178 can output a maximum signal of 7Vp-p for the best case and 5Vp-p for the worst case.
So the amount of headroom of a preamp is dependent on the supply voltage and the opamps. If a designer is looking to maximize the headroom of a given circuit they would design with rail-to-rail opamps to use the entire range of supply voltage for the signal.
-Frank
The Barcus-Barry 3000A preamp uses a TL062 opamp. The 062 has a typical maximum output to 1.5V of the supply rails. With a minimum to 5V of the supply rails.
The Bartolini NTMB preamp uses a MC33178 opamp. The 33178 has a typical maximum output to approx 1V of the supply rails. With a minimum to 2V of the supply rails.
So if we use 9V supply:
The LM4250 can output a maximum signal of approximately 7Vp-p (estimating the output swing from the graph on the data sheet)
The TL062 can output a maximum signal of 6Vp-p for the best case and if you have a 062 on the low side of the specs you may have no signal output at all. (Although the worst case 062 I have ever seen was only 3V from one rail in a 9V circuit. So that one would have been limited to 3Vp-p.)
The MC33178 can output a maximum signal of 7Vp-p for the best case and 5Vp-p for the worst case.
So the amount of headroom of a preamp is dependent on the supply voltage and the opamps. If a designer is looking to maximize the headroom of a given circuit they would design with rail-to-rail opamps to use the entire range of supply voltage for the signal.
-Frank
Thanx RobbieK, so that system won't work like that if wired up? I don't know much about electronics... What was explained to me made sense at the time and in theory but I don't know the actual physical restrictions etc involved in the electronics of it, so if you tell me it can't work i'd believe you
Out of interest I did also find this: Invalid Link Removed
yes you could certainly wire a 9/18v system if you like, but I see no need for it. Any bass boost or filtering on an emg active pickup pre is set. You can't change it. The actual headroom required has nothing to do with the voltage rails available. It's all to do with how hard you play and how close the pickup is to the strings. If you find your bass is distorting too quickly after a new battery, then I would bypass your bass/treb pre and listen to make sure it's not also the pickup pres. If these are distorting, then you need to drop the pickups, get better batteries, play softer or increase the voltage, provided the manufacturer says it's ok. If your active pickups aren't distorting on their own but then distort with the bass/treb pre added, you need to try playing softer, lowering the pickups, get better batteries, wire the vol at the input of the pre instead of the output and turn it down a bit, try an attenuator here instead, run less bass boost at your axe, and a little more at the amp, or, yep, run an 18v system.
As I mentioned, if you listen very carefully, the tone of an opamp circuit changes ever so slightly as the voltage rail drops. This is especially so with those 80's and 90's opamps that were mostly designed for hifis. And were optimised for bipolar 15-18v supplies. (30-36v). Boomertech mentioned the TL062 and the mc33178. IME, these both suffer from this, (although if you get to know this slightly choked tone, you can detect when the batteries will soon need replacing). So I have a feeling that the improved tone that people often hear when they increase the Vcc is more to do with the response of the opamps in their pre and not actually the extra headroom.
I'd be surprised if designers still used these old opamps for 9v circuits. They probably aren't even available in surface mount form factors anyway. Onboard basses, car stereo, boom boxes, are really the only place audio circuits seem to get 9-12v. All the digital stuff is 5-6v and the newer rail-to-rail opamps are the go here these days. And mixing desks, hifi, studio gear, solidstate pres still use 30-36v.
The musicman pre opamp is famous and even older. I've never used it - really before my time - so I can't really comment on it, but OTOH, there is something quite magic about that original 2 band pre, especially with those big parallel-wired humbuckers. If memory serves, that opamp has a pin that allows you to programme its current draw and hence its slew rate etc etc.
Looks like McKeen is a fan of slap bass and bass boost and playing the bass
. As I mentioned in my first post, I recommend 18v for this type of stuff as well.
The TL0xx opamps and their variants like the TLE20xx are still greatly used in 9V circuits. Us older engineers that have been designing with them for so many years know their limitations and quirks intimately, and are very comfortable with using them. They are still produced in through-hole DIP and SMD packages.
The MC33178 as of three months ago is no longer available in a through-hole DIP package, but the SMD package is still in production. Its a really nice low current audio amplifier.
The LM4250 is still in production with both through-hole DIP and SMD packages. The beauty of this opamp is its extremely low idle current <1mA, making it ideal for battery operated circuits. The one thing that is totally missing from the data sheet is its distortion specifications/measurements (data sheet is from Aug 2000). When distortion data is missing, there is a reason why maybe that is part of the MM tone?
-Frank
The MC33178 as of three months ago is no longer available in a through-hole DIP package, but the SMD package is still in production. Its a really nice low current audio amplifier.
The LM4250 is still in production with both through-hole DIP and SMD packages. The beauty of this opamp is its extremely low idle current <1mA, making it ideal for battery operated circuits. The one thing that is totally missing from the data sheet is its distortion specifications/measurements (data sheet is from Aug 2000). When distortion data is missing, there is a reason why maybe that is part of the MM tone?
-Frank
If you work in the studio world they are always going in about how they have modeled these new plugins on old famous studio gear and have gone into great detail to recreate the way the opamps etc interact in the hardware version
Do you think they are getting anywhere close with these digital versions of these old units?
Do you think they are getting anywhere close with these digital versions of these old units?
Yes it's very nice. I can see why Bill Bartolini uses this. He has a great ear. His pickups have always been voiced very well too.
Yeah true! Amongst us bassists, it's got that TS808/JRC4558 mystique for sure. I think it's also nice because there's just one opamp there, no separate buffer. This forces that low input Z which is a big part of the stingray tone - loading that parallel humbucker. Notice the vol is on the output. Years ago I wired a "bright" switch in an 80's stingray that was just a hiZ fet buffer between the pickup and the pre with a tru bypass. In the modern bass cabs this really makes it sound like a modern boutique bass. I have a feeling that in 5-10 years time, with everyone using lightweight neo speakers with their super smooth midrange, more and more bassists will be searching for something to pop the mids. Some pres on the market already have an adjustable input Z, and I think this is why. It's a bit like all the valve and tape gear coming back into studios after people realised how much the digital gear lacked that certain something (harmonic distortion!).
Well I don't do tonnes of sessions these days, but most of the guys with good small studios have a mixture of nice analogue gear and nice plug-ins. I'm afraid personally I do only ocassional producing gigs so my ears aren't that tuned in, but from my friends who produce all the time, I get the feeling that the expensive plug-ins these days are pretty darn impressive. I'm mixing an album right now, but I'll hand it back to the original producer for final touches and mastering, I think....
okcrum
in your chest
I was surprised myself when I found the first one (Korean-made) in a TBC. The battery life was quite good, and I imagine the newer on chip charge pumps are even more efficient.
