How much current does your bass preamp use

[bongomania]

Re the semantics and what a calculator does: when I took chemistry classes, they required us to program our calculators to obey sig fig rules. When I took calculus and physics classes, they had no such requirement. In guitar electronics, the tolerances are typically so wide, and the signal waves (and corresponding power usage) so ever-changing, that the potential precision of sig figs is pretty much irrelevant.

By way of example, I have measured the capacitance of a guitar cable 10 times in a row, using good-quality test gear, and gotten a slightly different measurement each time. All the pots, caps, etc. that someone might buy for a bass are imprecise and variable. So why use sig figs?

[ctmullins]

Because it's fun to be pedantic!!!

[Smilodon]

I think I just broke this thread...

[khutch]

My Fender Active Jazz actually draws 593 uA but as much as 50 uA of that is in the battery monitor circuit that I put in. My Ibanez SR505 draws 770 uA.

Ken

[WRBass]

Originally Posted by ctmullins

Stupid question - how do you measure this? I'm thinking I can insert a stereo cord, then put an ammeter between the ring and sleeve on the other end - would that work?

Originally Posted by SGD Lutherie

Yes.

Is this how everyone is measuring the current? IMO, the best way is to measure the current coming directly from the battery.

[WRBass]

Originally Posted by WRBass

Is this how everyone is measuring the current? IMO, the best way is to measure the current coming directly from the battery.

Never mind! I think I get it now.

[khutch]

Yes, as you have realized this is a wonderfully convenient way to measure the current flow in the battery. Now you can measure battery voltage this way too but you will be measuring the voltage through the off impedance of your preamp and that could be fairly large compared even to the input impedance of a DVM. When I do this on my Fender I lose about half a volt but this number would have to be calibrated for each individual bass since it could vary a lot and possibly vary a lot among different samples of the exact same preamp. If you take the time to measure the battery voltage directly and then through the output jack you will have the calibration factor for your bass and this is a convenient way to measure the battery voltage on any bass but especially on those whose battery cover is screwed on.

Ken

[mrbaloo]

Updated list:

• Peavey Cirrus 5 FL (Made in USA): 11.21 mA
• Peavey Cirrus 5 (Made in USA): 10.10 mA
• Peavey DynaBass type preamps (Dyna, Sarzo, TL-5): 7.5 mA
• Peavey Cirrus 5 BXP: 4.72 mA
• EMG BTC with two OPA1611s draws: 3.6 mA
• Dean Edge 4: 2.01 mA
• Audere JZ3 preamp: 1.66 mA
• Ibanez SR2010 Ashula Bass: 0.79 mA
• Ibanez SR505: 0.77 mA
• Ibanez SR505: 0.75 mA
• Ibanez SR305m (EMG BQC preamp): 0.74 mA
• Fender Active Jazz including a 0.05 mA battery monitor: 0.593 mA
• Fender MIM Deluxe Jazz: 0.55 mA
• Musicman Stingray (3-band EQ): 0.36 mA / ZZZ h
• Vintage MM 2-band preamp with LM4250 op amp: 0.25 mA
• G&L L2000 Tribute: 0.17 mA

[mech]

Originally Posted by khutch

.... on my Fender I lose about half a volt but this number would have to be calibrated for each individual bass since it could vary a lot and possibly vary a lot among different samples of the exact same preamp. If you take the time to measure the battery voltage directly and then through the output jack you will have the calibration factor for your bass and this is a convenient way to measure the battery voltage on any bass but especially on those whose battery cover is screwed on.

Ken

Any battery operated circuit should have an isolation diode in series with one of the battery connections. This will prevent letting the smoke out if a battery is touched to the terminals the wrong way. The voltage drop you see by using a cable to check voltage would be caused by the drop across the diode, .3-.6 volts.

mech

[khutch]

That is entirely possible but not every circuit needs a series diode and I have no idea if the Fender preamp uses one or not. At the tiny current drain a DVM input represents the drop across the diode is unlikely to be as high as 0.5 V, but it depends on the diode. When you try to power up a opamp from 0.5 V it will not really be on and so its impedance could easily explain the half volt drop. Or there are probably a couple of power supply splitting resistors in series across the whole thing and they could be large enough to produce the half volt drop. There are many possibilities, choose the one that seems best to you or reverse engineer all the preamps in the world to establish the truth in each case. My only point is that while an output jack current measurement is completely accurate, an output jack voltage measurement will have some error and if you know the error for your bass you can make a useful battery voltage measurement at the output jack.

Ken

[ctmullins]

Kinda late to this party, but here is what I measured on my own instruments:

Aguilar OBP-1 at 18V - 1484 μA (published not found)
Bartolini NTBT-918 at 18V - 1183 μA (published 1000)
EMG BTC at 18V - 428 μA (published 740)
Cafe Walter PZP-1 (piezo pickup buffer) at 9V - 219 μA (published 250)

(using the aforementioned "stereo cable; measure ring to sleeve" method)

I can't swear that the Aguilar and Cafe Walter have completely fresh batteries, so their values may be a bit low. The odd thing is that the BTC is definitely running on fresh batteries, but my reading is considerably lower than published. ???

[mrbaloo]

Originally Posted by ctmullins

Kinda late to this party, but here is what I measured on my own instruments:

Aguilar OBP-1 at 18V - 1484 μA (published not found)
Bartolini NTBT-918 at 18V - 1183 μA (published 1000)
EMG BTC at 18V - 428 μA (published 740)
Cafe Walter PZP-1 (piezo pickup buffer) at 9V - 219 μA (published 250)

(using the aforementioned "stereo cable; measure ring to sleeve" method)

I can't swear that the Aguilar and Cafe Walter have completely fresh batteries, so their values may be a bit low. The odd thing is that the BTC is definitely running on fresh batteries, but my reading is considerably lower than published. ???

You are always invited to this party. Thank you for your measurement data. Here is the updated list:

• Peavey Cirrus 5 FL (Made in USA): 11.21 mA
• Peavey Cirrus 5 (Made in USA): 10.10 mA
• Peavey DynaBass type preamps (Dyna, Sarzo, TL-5): 7.5 mA
• Peavey Cirrus 5 BXP: 4.72 mA
• EMG BTS with two OPA1641s draws: 3.16 mA
• Dean Edge 4: 2.01 mA
• Audere JZ3 preamp: 1.66 mA
• Aguilar OBP-1: 1.484 mA
• Bartolini NTBT-918: 1.183 mA
• Ibanez SR2010 Ashula Bass: 0.79 mA
• Ibanez SR505: 0.77 mA
• Ibanez SR505: 0.75 mA
• Ibanez SR305m (EMG BQC preamp): 0.74 mA
• Fender Active Jazz including a 0.05 mA battery monitor: 0.593 mA
• Fender MIM Deluxe Jazz: 0.55 mA
• EMG BTC: 0.428 mA
• Musicman Stingray (3-band EQ): 0.36 mA
• Vintage MM 2-band preamp with LM4250 op amp: 0.25 mA
• Cafe Walter PZP-1 (piezo pickup buffer): 0.219 mA
• G&L L2000 Tribute: 0.17 mA

The reader may note that the two EMG BTC measurements are very different.

BTW, the stereo-cable-measurement-trick is used by the McMillen Batt-O-Meter unit as well. But I have measured my basses using a digital multimeter in series with the battery/-ies.

/mrbaloo

[mcnach]

Originally Posted by line6man

Lower-case u is a commonly accepted substitute for lower-case Mu on this forum. I've probably done it a thousand times, and no one has ever pointed it out before.

Not only on this forum, it's been widely use for as long as I can remember... nowadays it's easy to type the mu letter for micro... Not so much years ago, and u was and is still used.
I work with microlitres and micrograms all day long... that's commonly ul and ug.

[mcnach]

Originally Posted by Johnny Crab

Power supply says 9 VAC @ 2000 mA via a transformer.
Line 6 BassPodXTLive. Never amp-clamped the line in to verify exact amount since it is so small.
NOTE: Undervoltage will COOK the transformer. Been there, done that, no T-shirt.

What the power supply can supply does not indicate what the preamp actually draws. You can use another supply capable of a million amps, and your preamp will still only draw the few mA it needs, regardless.

[12bass]

I made a mistake earlier. I have an EMG BTS, not a BTC, in my Hamer Chaparral 12 which currently has two OPA1641s, not two OPA1611s. I just made a proper measurement with a multimeter and it draws 3.16 mA. Not sure what EMG is using currently, however, my BTS came with an LF442 which normally uses ~ 400-500 μA. I'm using the OPA1641s because they sound better - a bit quieter and more open sounding. Also measured a Bartolini NTBT (9V) at ~ 1 mA.

[mcnach]

Originally Posted by Munjibunga

This thread is fully infested with pedants.

I'm accessing the forum through my phone... can that infect my android OS, or should I worry only when using a PC?

[12bass]

BTW, the EMG BTC and BTS are basically the same circuit, except the BTC uses a single concentric potentiometer for bass/treble, while the BTS has two separate pots. Electrically they are the same. Also, FWIW, generally speaking I've found that the very low quiescent current op amps tend not to sound as good as the ones that draw a bit more current.

[mrbaloo]

Originally Posted by 12bass

...I've found that the very low quiescent current op amps tend not to sound as good as the ones that draw a bit more current.

Ok, I think Peavey may have thought about that to get a good sounding bass. No bass else seems to draw that amount of current.

[mech]

Originally Posted by 12bass

Also, FWIW, generally speaking I've found that the very low quiescent current op amps tend not to sound as good as the ones that draw a bit more current.

This has been my experience, also. It's due to the output of the PU being able to overdrive the input of the first stage and I've seen it more with passive PUs. They are capable of pretty large spikes when the string is hit hard. Low impedance active PUs are less likely to overdrive a properly designed input stage but add their own current draw. If the input voltage to the first stage is reduced enough to prevent distortion then an additional gain stage is necessary to recover the loss and will lead to more noise in the system. Low current devices have been traditionally higher noise anyway. It's basically a tradeoff between headroom vs power consumption and why most designers have gone to 18V systems. As a disclaimer, I'm not familiar with all the devices that are currently on the market.

mech

[mizu]

I've just measured the current draw on my Cirrus and Millennium Plus.
Both USA made, both have same preamps with sweepable mid.

Cirrus: 9.8 mA
Millennium Plus: 1.2 mA

Looks like those VFL pickups are real power hogs