| Author | Message | ||
| smuprof
New Username: smuprof Post Number: 6 Registered: 12-2003 |
I've got an 83 Exploiter. Recently, the output seems to be much lower, particularly compared to other basses I own. Since I never really measured the output before, its hard to know for sure. I've changed the battery, and I know that I can adjust the pots for each pickup, but I'd like to make sure the preamp is working correctly. If I'm looking at the output with a scope or AC VOM, what would you typically expect the voltage output to be from plucking a string? Is there any simple way to check the output and determine if there's a problem that needs further work? Thanks in advance. | ||
| dfung60
Member Username: dfung60 Post Number: 61 Registered: 5-2002 |
If the output is low, things are probably not right. First make sure the easy stuff is taken care of - that the new battery really is new (a fresh alkaline 9V will read over 9.4 VDC), and have another bass around so you can really do a good A-B comparison of output level. I posted a while ago on a different topic about output levels, mostly for a Series bass. Set up to read AC voltage (you can just plug one end of a cord into your bass and touch the probes on the other end) in the <2V range. Hit an E or A pretty hard and wait for the multimeter reading to stabilize. I saw 0.08 VAC on a passive Fender, 0.11 VAC on a Modulus with EMGs, and 0.32 VAC on a Series bass on battery power. I suspect your Spoiler's output level should be in that 0.11-0.3 range too, depending on how you have the trimpot set. If your output level is low, then you'll need to take a similar reading directly off the pickup and find out from Alembic whether you have a pickup problem or preamp problem. Good luck, David Fung | ||
| dfung60
Member Username: dfung60 Post Number: 62 Registered: 5-2002 |
If the output is low, things are probably not right. First make sure the easy stuff is taken care of - that the new battery really is new (a fresh alkaline 9V will read over 9.4 VDC), and have another bass around so you can really do a good A-B comparison of output level. I posted a while ago on a different topic about output levels, mostly for a Series bass. Set up to read AC voltage (you can just plug one end of a cord into your bass and touch the probes on the other end) in the <2V range. Hit an E or A pretty hard and wait for the multimeter reading to stabilize. I saw 0.08 VAC on a passive Fender, 0.11 VAC on a Modulus with EMGs, and 0.32 VAC on a Series bass on battery power. I suspect your Spoiler's output level should be in that 0.11-0.3 range too, depending on how you have the trimpot set. If your output level is low, then you'll need to take a similar reading directly off the pickup and find out from Alembic whether you have a pickup problem or preamp problem. Good luck, David Fung | ||
| smuprof
New Username: smuprof Post Number: 7 Registered: 12-2003 |
Thanks, David. I'll give it a shot and post the results. John | ||
| smuprof
New Username: smuprof Post Number: 8 Registered: 12-2003 |
Okay, sorry for the delay, but here's what I've found so far: Exploiter is 0.035 - 0.05 VAC peak, quick decay to 0.01 as the note sustains. Peavey US Millennium (18v) produces 0.15 - 0.2 VAC peak, quick decay to 0.01 as note sustains. 1964 Jazz passive produces 0.001 - 0.002 VAC (1 - 2 millivolts). I also looked at the pickup alone from the Exploiter, and it produces levels similar to the passive Jazz - 1 - 2 millivolts. In summary, seems to be consistent across the 3 basses, (passive v 9v v 18v preamps), but they all seem a little low compared to what you were seeing. May a difference in set-up or scale (mine seem about 10% of yours)? Clearly the preamp is boosting the output of the pickups, and it seems to be higher than the old Jazz, but . . . Any additional thoughts Dave? Anyone? Can anyone confirm the 1 - 2 millivolt output of passive pickups? Or some readings from a similar vintage instrument? Thanks in advance. John | ||
| dfung60
Member Username: dfung60 Post Number: 68 Registered: 5-2002 |
Hmmm... Things definitely don't seem quite right here. We seem to be pretty close on a conventional active setup (my EMG Modulus at 110mv, your Peavey at 150mv). At 35mv, your Exploiter seems really low (I believe this would be a typical passive output level). Your old Jazz output seems too low too. Nominally, the passive input on an SWR amp would be expecting a signal up to 50mv (around 200mv on the active input). Perhaps this is a byproduct of how we are measuring the levels? I was just using a vanilla Fluke multimeter, so it's not fancy (no peak hold) but I'm pretty confident of the readings. David Fung | ||
| son_of_magni
Intermediate Member Username: son_of_magni Post Number: 166 Registered: 1-2004 |
You cannot get a valid measurement with a DMM. You need an oscilloscope. A DMM takes too long to determine the level and the sample rate is too slow. The only thing the DMM can do for you is to compare the levels of different instruments using the SAME DMM. In reality a passive bass can put out peaks way over 200mv, maybe over 2 volts. I have never used a scope to look at the signal from an Alembic, I might get a chance later this week if you want me to. But I don't think it will solve your problem. What is the internal gain adjustment set to? - SoM | ||
| smuprof
New Username: smuprof Post Number: 9 Registered: 12-2003 |
SoM - Internal gain is about 75% on both pickups. I thought about the scope, but it would take a bit to round one up, and I wanted to start just comparing information. I'm using a Fluke also, and it seems like we're getting similar numbers for more modern, higher powered outputs. I'd be curious what kind of numbers you might find if you get a chance to check with your scope. I'll try to round one up here as well. Thanks. Still baffling. | ||
| dfung60
Member Username: dfung60 Post Number: 69 Registered: 5-2002 |
I'd beg to differ with son_of_magni on this. If you want to read the peak transient levels (which can hit 100x the steady state level) then you need a scope that has peak capture capability. A regular scope won't show level, so you really need a digital storage oscilloscope (DSO). But the level that you perceive as the "volume" of the bass is pretty steady state and easily read with a DMM. Hit a note and there will be a quick transient at high output level followed by a steady state level that you can read for seconds before it fades out. That sustained level is directly comparable to the steady state sine waves that the amp manufacturer would be using to drive the amp when measuring specs. If the sustain level is 1/10 what a "regular" bass reads, that's -10dB which you will perceive as a very low output level bass indeed. If you have a storage scope you can actually see an interesting part of the behavior which is otherwise hard to see - the "headroom" of your electronics. The initial transient response is very, very high compared to the sustain level, I believe +10 to +20dB. If you capture the initial transient, you can see whether the waveform is squared off, which would be indicative of the electronics being unable to provide the dynamic response of the instrument. By the time things settle down in the sustain portion, pretty much any active electronics should be able to cleanly amplify the signal, but during the chaotic initiation of the note, a proper reproduction would be very hard. DSOs are designed to capture this sort of phenomena - you set them to trigger at a certain voltage level and they will start recording the input waveform. But it's hard to actually do this with a musical instrument since the transient time will be on the order of a 1/2 second or more - an eternity for a DSO that is capturing half a billion samples per second. David Fung |
