Preamp (pedal) into a power amp

[Jim C]

I could see this with low ouput pedals.
Looks like all of my experiments were with pre's with adequate output.

 

[tech21nyc]

Since both brands mentioned have models with .775 inut sensitivity, why would they not work as good or better than a dedicated MI amplifier? I've found more problems using the effects return with an outboard pre with a MI amp.

The point I was making is that those amplifiers are not "designed" for musical instrument use, so don't get frustrated if you try to plug a 9 volt pedal in and can't get enough power out of the amplifier. If they were musical instrument amplifiers you could plug into them with a guitar or bass and there would be enough gain to work properly with the amplifier. Those types of amps are expecting a much higher signal level from a mixer. The gain controls on amps like that are not the same as the volume control on a guitar or bass amp. From Crown:

Should I have the level controls on my amplifier turned all the way up?
It depends on the system and how much gain you have prior to the amplifier. The level control can be thought of as an input attenuator. It does not limit the power available from the amplifier. With the level controls turned down the amplifier can still reach full rated output power, it just takes more drive level from your mixer to achieve it. Generally, you should set the mixer's individual channel fader and master gain to 0 dB, then adjust the amplifier level controls to the desired sound level.

This is not to say they can't be used for an electric guitar or bass application but it helps to have a better understanding of how those amps operate going in. In terms of sound, as long as you are getting the amount of output necessary to your speaker cabinet, there should not be much difference between a SS pro-audio amp or a SS power section of a guitar or bass amp. If we start talking tube power amps that's another discussion.

 

[DoctorZeus]

Our rack units will easily work with most power amps. If using one of our pedal DI's you are best off with a power amp that has a .775 volt input sensitivity. The type of power amps being discussed here (Crown, QSC etc) are designed for sound reinforcement applications. They are not musical instrument amplifiers.

Thank you for weighing in. Any Power amp suggestions?

 

[tech21nyc]

Any amp that has enough wattage for your speaker system and an ample amount of headroom. It depends what you are trying to do. You should make sure that the input specs of the amp will work with whatever preamp you are using.

 

[agedhorse]

While respecting the real world safe power handling g of the cabinet(s)

 

[BasturdBlaster]

As far as using a preamp pedal that doesn't provide the appropriate amount of output to feed a PA style amp, what would be the "best" way to increase the preamps output in order to work correctly?

 

[HelpImaRock]

As far as using a preamp pedal that doesn't provide the appropriate amount of output to feed a PA style amp, what would be the "best" way to increase the preamps output in order to work correctly?

Put your preamp into your preamp so you can preamp while you preamp. Or something.

 

[N. Kentucky Bass]

As far as using a preamp pedal that doesn't provide the appropriate amount of output to feed a PA style amp, what would be the "best" way to increase the preamps output in order to work correctly?

Sure. Or if you've got a really weak preamp, add a clean boost pedal for up to 20 more dB like the TC Electronic Spark Mini. Just make sure your speaker cabinet can handle the raw horsepower. And be sure to use a High Pass Filter!!

 

[agedhorse]

Sure. Or if you've got a really weak preamp, add a clean boost pedal for up to 20 more dB like the TC Electronic Spark Mini. Just make sure your speaker cabinet can handle the raw horsepower. And be sure to use a High Pass Filter!!

What's the maximum output level? It's not in any of the specs sheets.

 

[N. Kentucky Bass]

What's the maximum output level? It's not in any of the specs sheets.

Not sure how to respond! It says up to 20dB on the faceplate and that's what the marketing literature says. WAY louder than I need! Actually, I'm experimenting with the boost pedal on the input side of my Noble preamp. Theory is to saturate the all-tube circuit. We'll see how that goes.

 

[agedhorse]

Not sure how to respond! It says up to 20dB on the faceplate and that's what the marketing literature says. WAY louder than I need! Actually, I'm experimenting with the boost pedal on the input side of my Noble preamp. Theory is to saturate the all-tube circuit. We'll see how that goes.

That's not maximum output level, that's maximum gain.

The maximum output level is a critical spec to determine if the device can drive a power amp. Driving the input of a preamp is different, you would want to know the maximum output level of the preamp that's driving the power amp.

 

[N. Kentucky Bass]

FWIW, here is Jack Roan's comment in an email to me on the Noble preamp's maximum output level:

I don’t have a firm number for the maximum output level, but I think its around 30-35Vrms. Waaaay more than you would need to drive that [QSC PLX 3602] amp to full power. BUT it does depend on the strength of your input signal. With the EQ flat and volume all the way up, the Noble is adding around 20dB, so if that is not enough you can add some gain in front of the Noble. I think it should work fine though!

Jack

 

[Jim C]

As far as using a preamp pedal that doesn't provide the appropriate amount of output to feed a PA style amp, what would be the "best" way to increase the preamps output in order to work correctly?

I've had good luck with rack mountand a few pedal compressors for a gain boost.

 

[wolffire99]

Would a pedal with line level output like the hx stomp be adequate for 1.5 Vrms input sensitivity?

 

[agedhorse]

Would a pedal with line level output like the hx stomp be adequate for 1.5 Vrms input sensitivity?

Depends on the maximum output level.

I wasn’t able to find the spec. for maximum output level, therefore I can’t give you an accurate answer.

 

[N. Kentucky Bass]

This thread is the first time I've heard the concept of maximum output level. Some (many?) gear manufacturers don't even list it in the data sheet. As a lowly mortal non-engineer, I just asked Perplexity.ai for some Plain English guidance. This is helpful for me and might be of interest to some of you.

Define the "maximum output level" value for electric bass pedals and why it is important for driving an amplifier.
Answer
The "maximum output level" for electric bass pedals refers to the highest signal voltage that a pedal can produce before clipping or distorting the signal in an undesirable way. This value is important because it determines how much headroom the pedal has to drive an amplifier without overloading it. Amplifiers have a specific input sensitivity, typically around 2V RMS, which is the maximum signal level they can accept before clipping or distortion occurs. If a bass pedal's maximum output level exceeds this input sensitivity, it can cause the amplifier to distort or clip, resulting in an unpleasant and potentially damaging sound. To avoid this, the maximum output level of a bass pedal should be lower than the input sensitivity of the amplifier it is driving. A common guideline is for the maximum gain of the first stage (pedal) to be no more than 20 (26dB) for a solid-state preamp. This ensures that the pedal's output remains within the amplifier's input sensitivity range, allowing for a clean and undistorted signal. Maintaining an appropriate maximum output level is crucial for preserving signal integrity and preventing unwanted distortion or damage to the amplifier's components. It ensures that the bass signal can be amplified cleanly and accurately, resulting in a clear and well-defined tone.

what if the preamp is an all-tube circuit, not solid state?
Answer
If the preamp is an all-tube circuit, the considerations for maximum output level and driving an amplifier are slightly different compared to a solid-state preamp. Tube preamps typically have a lower maximum output voltage compared to solid-state designs, usually in the range of 1-3V RMS. This is because tube circuits operate on lower voltages and have a more limited dynamic range before distortion occurs. The key points regarding an all-tube preamp's output level are:

1. Tube preamps have an inherently higher output impedance (several kOhms) compared to solid-state designs. This higher source impedance can interact with the input impedance of the power amplifier, potentially causing frequency response variations.
2. The maximum undistorted output voltage before clipping is relatively low, around 1-3V RMS. Going beyond this level will cause the tube stages to distort.
3. Many vintage and modern tube power amps are designed to accept these lower input voltage levels, with an input sensitivity typically around 1V RMS for full output power.
4. If the tube preamp's maximum output exceeds the power amp's input sensitivity, an attenuator or passive volume control may be needed between them to avoid overdriving and distorting the power amp's input stage.
5. Driving the tube preamp into higher output levels can increase the "tube sound" characteristics like harmonic distortion and compression, which some listeners prefer. However, excessive overdrive will cause harsh clipping distortion.

So in summary, while tube preamps have a lower maximum output compared to solid-state, they are designed to properly interface with tube power amps expecting these voltage levels. Care must be taken to match levels, but some controlled overdrive can enhance the "tube sound" if desired.

 

[agedhorse]

This thread is the first time I've heard the concept of maximum output level. Some (many?) gear manufacturers don't even list it in the data sheet. As a lowly mortal non-engineer, I just asked Perplexity.ai for some Plain English guidance. This is helpful for me and might be of interest to some of you.

Define the "maximum output level" value for electric bass pedals and why it is important for driving an amplifier.
Answer
The "maximum output level" for electric bass pedals refers to the highest signal voltage that a pedal can produce before clipping or distorting the signal in an undesirable way. This value is important because it determines how much headroom the pedal has to drive an amplifier without overloading it. Amplifiers have a specific input sensitivity, typically around 2V RMS, which is the maximum signal level they can accept before clipping or distortion occurs. If a bass pedal's maximum output level exceeds this input sensitivity, it can cause the amplifier to distort or clip, resulting in an unpleasant and potentially damaging sound. To avoid this, the maximum output level of a bass pedal should be lower than the input sensitivity of the amplifier it is driving. A common guideline is for the maximum gain of the first stage (pedal) to be no more than 20 (26dB) for a solid-state preamp. This ensures that the pedal's output remains within the amplifier's input sensitivity range, allowing for a clean and undistorted signal. Maintaining an appropriate maximum output level is crucial for preserving signal integrity and preventing unwanted distortion or damage to the amplifier's components. It ensures that the bass signal can be amplified cleanly and accurately, resulting in a clear and well-defined tone.

what if the preamp is an all-tube circuit, not solid state?
Answer
If the preamp is an all-tube circuit, the considerations for maximum output level and driving an amplifier are slightly different compared to a solid-state preamp. Tube preamps typically have a lower maximum output voltage compared to solid-state designs, usually in the range of 1-3V RMS. This is because tube circuits operate on lower voltages and have a more limited dynamic range before distortion occurs. The key points regarding an all-tube preamp's output level are:

1. Tube preamps have an inherently higher output impedance (several kOhms) compared to solid-state designs. This higher source impedance can interact with the input impedance of the power amplifier, potentially causing frequency response variations.
2. The maximum undistorted output voltage before clipping is relatively low, around 1-3V RMS. Going beyond this level will cause the tube stages to distort.
3. Many vintage and modern tube power amps are designed to accept these lower input voltage levels, with an input sensitivity typically around 1V RMS for full output power.
4. If the tube preamp's maximum output exceeds the power amp's input sensitivity, an attenuator or passive volume control may be needed between them to avoid overdriving and distorting the power amp's input stage.
5. Driving the tube preamp into higher output levels can increase the "tube sound" characteristics like harmonic distortion and compression, which some listeners prefer. However, excessive overdrive will cause harsh clipping distortion.

So in summary, while tube preamps have a lower maximum output compared to solid-state, they are designed to properly interface with tube power amps expecting these voltage levels. Care must be taken to match levels, but some controlled overdrive can enhance the "tube sound" if desired.

Virtually everything in the above text is simply incorrect. Was this an AI generated response?

The maximum output level needs to be GREATER than the input sensitivity rating of the power amp, otherwise the preamp will clip before the power amp reaches rated power. Most power amps have limiting circuits as well, so you want to be able to drive at least 6dB beyond the sensitivity of the power amp. Also note that the sensitivity of a power amp is specified with the input level controls fully up.

It makes NO difference if the preamp is tube or solid state. The output levels and impedances can be very similar without any difficulty. There may be some outliers, but they are rare.

 

[N. Kentucky Bass]

Virtually everything in the above text is simply incorrect. Was this an AI generated response?

The maximum output level needs to be GREATER than the input sensitivity rating of the power amp, otherwise the preamp will clip before the power amp reaches rated power. Most power amps have limiting circuits as well, so you want to be able to drive at least 6dB beyond the sensitivity of the power amp. Also note that the sensitivity of a power amp is specified with the input level controls fully up.

It makes NO difference if the preamp is tube or solid state. The output levels and impedances can be very similar without any difficulty. There may be some outliers, but they are rare.

Your response is clear and makes sense. Thank you! Yes, Perplexity is one of the AI services, and this is the third error I have encountered this week -- all regarding bass gear, BTW. Obviously, large language model training does not know how to deal with music gear!

 

[agedhorse]

Your response is clear and makes sense. Thank you! Yes, Perplexity is one of the AI services, and this is the third error I have encountered this week -- all regarding bass gear, BTW. Obviously, large language model training does not know how to deal with music gear!

Actually, this serves as a GREAT example of why making decisions based on AI is so dangerous. I get amps in for repair where the user tried to fix their amp based on information provided by AI (and YouTube videos) and most of the time they further damage their amp to the point of some being damaged beyond economical repair. Those using AI to self diagnose medical conditions is another mind blowingly scary scenario, and results in some equally scary outcomes.

 

[N. Kentucky Bass]

Also note that the sensitivity of a power amp is specified with the input level controls fully up.

What advice do you have for controlling final output volume? To put the amplifier's attenuator in the max position and control volume with the preamp/device in front of the amp? Some mixture of the two?