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Double Bass Preamp/Amp Volume Controls

B

BobKay

Supporting Member
Nov 5, 2012
1,364
1,343
Estero, Florida; USA
#1
Is there a generally accepted practice for how to adjust the volume controls between preamp and amp?

For example, I have an EDB 2 going into the effects return on an AI Clarus head (in either a Coda or Ten 2 EX). Both have an input gain and a master volume for the channel.
AI recommends a starting point for the amp of setting the master at 12:00 and then using the input gain to control the overall output volume. I want to use the volume control on the EDB 2 at my mic stand. I'm having a problem with the Tex 2 EX of overdriving the speaker, at least at one specific frequency. The volume controls on the EDB seem to be very sensitive, i.e. it's easy to go from no volume at all to way too much.

Any suggestions on how to approach the overall settings on the two devices?
 
#2
There are basically two schools of thought here: doing what is technically correct, and doing what sounds good to you. I tend to use gain/volume controls on musical instrument amplifiers as an additional set of tone controls to get the sound I want. Don't be afraid to experiment. Try setting the gain controls relative to each other to see what sounds best to you. Have fun!
 
#3
For DB, I tend to use as little gain as possible and use the master for volume. For BG, I use as much gain as possible without clipping and use a whole lot less master. That's what my ears tell me to do. It isn't right or wrong, but it's what I do in general. That doesn't mean I don't do something else when the room or something else dictates.
 
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#4
Pre-amp and power-amp (master) gain controls are best used in a fashion that minimizes overload and maximizes signal-to-noise ratio (S/N). This is achieved by adjusting the pre-amp level control as high as possible without producing overload and then using the master to adjust the desired level. Keep in mind that, for the vast majority of circuits, the level controls are merely adjustable resistors that sit in front of each stage. Now, suppose one has achieved that optimum balance. What is the effect of reducing the pre-amp gain and increasing the power-amp gain? It would be to reduce S/N. "Opening up" the power-amp gain leads to higher levels of noise as does operating the pre-amp closer to its noise floor. What would be the effect of increasing the pre-amp gain and reducing the power-amp gain? It would be to invite distortion at the "front end" (the pre-amp) as a result of overload. The truth is that there is a range over which the two controls can be adjusted or "traded" to achieve a given desired overall level that will yield basically no overload and very acceptable S/N. It's not critcal. Gain is gain. Assuming no overload, different combinations of the controls will yield the exact same gain and, unless something is amiss with the circuit, those different combinations will not produce different tonal characteristics at all.
 
#5
Scientifically and logically, that absolutely makes sense. It's why I tend to use as much preamp gain as I can with BG, so long as there's no distortion. I hate distortion unless it's on purpose and isn't my amp. For DB, I have found that keeping preamp gain down and controlling volume with the master makes it easier to control feedback. I don't know why that would be, because logically, it shouldn't matter. But that's been my experience unless it's all in my head. It's not so much a sound thing as a feedback thing.
 
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#6
Gaolee said:
Scientifically and logically, that absolutely makes sense. It's why I tend to use as much preamp gain as I can with BG, so long as there's no distortion. I hate distortion unless it's on purpose and isn't my amp. For DB, I have found that keeping preamp gain down and controlling volume with the master makes it easier to control feedback. I don't know why that would be, because logically, it shouldn't matter. But that's been my experience unless it's all in my head. It's not so much a sound thing as a feedback thing.
Click to expand...
It makes sense scientifically and logically because it is absolutely true. Overload aside, unless there is some malfunction, tonal balance and feedback will not be affected by how a specific level of gain is realized. You may be responding to different control tapers or ranges, so that it seems as if using the master avoids feedback better than if you use the pre-amp control. I'd bet a box of cookies that it's not actually the case. :)
 
#7
drurb said:
It makes sense scientifically and logically because it is absolutely true. Overload aside, unless there is some malfunction, tonal balance and feedback will not be affected by how a specific level of gain is realized. You may be responding to different control tapers or ranges, so that it seems as if using the master avoids feedback better than if you use the pre-amp control. I'd bet a box of cookies that it's not actually the case. :)
Click to expand...
That I'm responding to different control tapers? Is that what we are betting a box of cookies on? Or that it's in my head! If it's control tapers, then I might win the box of cookies if that's the bet. I don't know for sure which side of that bet you are on. If it's that it's in my head, after your explanation, you win the box of cookies. That's most likely for sure. Time to do some experimenting.

One other thing I'm not sure of is whether the piezo in my DB sends a less compressed signal than the magnetic pickups in the BG.
 
#8
BobKay said:
I have an EDB 2 going into the effects return on an AI Clarus head (in either a Coda or Ten 2 EX). Both have an input gain and a master volume for the channel.
AI recommends a starting point for the amp of setting the master at 12:00 and then using the input gain to control the overall output volume.
Click to expand...

If the bass is plugged into the EDB2 and then into the return (as opposed to using the EDB in the send/return loop) the input gain on the AI doesn't even matter. The return jack plugs straight into the power amp of the AI, the only controls that do anything are the return level, master volume, mute button and pre/post EQ DI button.

I would set the master volume of the amp all the way up and control volume from the EDB unless you find that you run the master on the EDB below 9:00 all the time.
 
#9
Brian,
Thanks for the suggestion. My bass is plugged into the EDB2, the EDB2 is then plugged into the "return" jack on the effects panel. I then turn the effects gain knob to 12:00, and the master level to 12:00. Then I have to figure out where to set the "input gain" and "master" volume on the EDB. Four knobs in all to figure out.
 
#10
drurb said:
Pre-amp and power-amp (master) gain controls are best used in a fashion that minimizes overload and maximizes signal-to-noise ratio (S/N). This is achieved by adjusting the pre-amp level control as high as possible without producing overload and then using the master to adjust the desired level. Keep in mind that, for the vast majority of circuits, the level controls are merely adjustable resistors that sit in front of each stage. Now, suppose one has achieved that optimum balance. What is the effect of reducing the pre-amp gain and increasing the power-amp gain? It would be to reduce S/N. "Opening up" the power-amp gain leads to higher levels of noise as does operating the pre-amp closer to its noise floor. What would be the effect of increasing the pre-amp gain and reducing the power-amp gain? It would be to invite distortion at the "front end" (the pre-amp) as a result of overload. The truth is that there is a range over which the two controls can be adjusted or "traded" to achieve a given desired overall level that will yield basically no overload and very acceptable S/N. It's not critcal. Gain is gain. Assuming no overload, different combinations of the controls will yield the exact same gain and, unless something is amiss with the circuit, those different combinations will not produce different tonal characteristics at all.
Click to expand...
Les,
If I follow your explanation I would turn up the input gain on the EDB, and use the "master volume" on the EDB to control overall volume from the AI speaker, right? Is my strategy of setting both volumes (the effects gain and the master) on the AI to 12:00 a good approach?
 
#12
brianrost said:
If the bass is plugged into the EDB2 and then into the return (as opposed to using the EDB in the send/return loop) the input gain on the AI doesn't even matter. The return jack plugs straight into the power amp of the AI, the only controls that do anything are the return level, master volume, mute button and pre/post EQ DI button.

I would set the master volume of the amp all the way up and control volume from the EDB unless you find that you run the master on the EDB below 9:00 all the time.
Click to expand...
I agree overall, except that I wouldn't start with the master all the way up. S/N issues aside, that can be dangerous in the event that one accidentally swaps cables while things are "live."

Gaolee said:
That I'm responding to different control tapers? Is that what we are betting a box of cookies on? Or that it's in my head! If it's control tapers, then I might win the box of cookies if that's the bet. I don't know for sure which side of that bet you are on. If it's that it's in my head, after your explanation, you win the box of cookies. That's most likely for sure. Time to do some experimenting.

One other thing I'm not sure of is whether the piezo in my DB sends a less compressed signal than the magnetic pickups in the BG.
Click to expand...

Hahaha... I was betting that the different controls do not have different effects on feedback. :)
 
#13
shwashwa said:
yes, you have 4 knobs to figure out, and my experience with the ten 2 is that its easy to over drive the input and make it clip. with that amp i have had the best success sending it a low signal from the external preamp and getting your volume from the master
Click to expand...
That helps a lot. In my first use of the Ten2 I did overdrive it. So I'll turn down the pre amp, get close to the volume I want using the amps two controls, and fine tune from there.
 
#14
BobKay said:
That helps a lot. In my first use of the Ten2 I did overdrive it. So I'll turn down the pre amp, get close to the volume I want using the amps two controls, and fine tune from there.
Click to expand...
...or just turn down the pre-amp input level on the Ten 2. The idea is to avoid overdriving that stage and shwashwa's note that it's easy to overdrive is valuable information. Again, it's not critical. Avoid overdriving and maintain a good S/N. There are many positions of the knobs that will do that reasonably. It doesn't have to be optimum, especially because once the music starts, it's likely that no one will hear the noise floor of your amp.
 
#15
drurb said:
...or just turn down the pre-amp input level on the Ten 2. The idea is to avoid overdriving that stage and shwashwa's note that it's easy to overdrive is valuable information. Again, it's not critical. Avoid overdriving and maintain a good S/N. There are many positions of the knobs that will do that reasonably. It doesn't have to be optimum, especially because once the music starts, it's likely that no one will hear the noise floor of your amp.
Click to expand...
i understand what you are saying, but what im saying is that regardless where the preamp input knob is on the ten 2, if you send it a hot signal it will not like it. at least on the series 3. maybe thats why they came out with a series 4 so quickly...
i actually thought i was having speaker distortion or something for a while there because the signal you send it doesnt have to be all that hot to cause this, but when i turned down the output of my external pre the problem went away, and i messed with all kinds of gain staging options.
 
#16
In case of a high impedance input stage, there must be an active stage before the gain pot, that could be overdriven if it not only enhances the possible current loading (like that the HPFpre and a lot of the simpler impedance buffers like the mint box do) but also does voltage amplification (like OP-amps with an JFET input stage often do, depending on the external feedback construction that determine the voltage amplification factor).

Since the OP-amps amplification factor only depends on the value of a few resistors, this could be changed by swapping them against resistors with different values. I have read here on Talkbass several times, that the manufacturer of the AI amps did modify his amps on request for stronger signal inputs.

Overloading can happen using a JFET impedance buffer, but in this case either the signal is very strong, the supply voltage is rather low (by intention or by drained battery) or the balancing resistors are badly chosen to this very unique JFET sample. But the JFET is rather graceful, so the kind distortion it produces is not very disturbing, you rather detect a really weak signal output than any kind of audible distortion.
On the JFET-OP-amp, the amplification stage following the JFET input stage would produce the audible distortion (or the circuits following the OP-amp that get overloaded by the higher voltage signal).
 
#17
shwashwa said:
i understand what you are saying, but what im saying is that regardless where the preamp input knob is on the ten 2, if you send it a hot signal it will not like it. at least on the series 3. maybe thats why they came out with a series 4 so quickly...
i actually thought i was having speaker distortion or something for a while there because the signal you send it doesnt have to be all that hot to cause this, but when i turned down the output of my external pre the problem went away, and i messed with all kinds of gain staging options.
Click to expand...

In that case, then, as DoubleMidi points out, there must be an active stage before the level control that is being overloaded. In such a case, one must, indeed, reduce the level before the input. DoubleMidi claims that high-impedance input stages must have an active stage before the gain pot but I don't believe that "must" applies. It does if the pot is controlling the gain of an op-amp.
 
#18
Wow - thanks to all for your responses. This has gotten way over my head and beyond my limited ability to understand. I'll try the various suggestions and will hopefully find the right spots for all four knobs that result in the volume I want without overdriving the speakers. Again, thanks.
 
#20
It's more about not overdriving the electronics at any stage. Again, short of that, you have plenty of leeway. The apparent danger is overthinking it.:)
 

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