I want to know the output impedance value of Ibanez active circuit.

[NakajimaYusuke]

Hi, I am using Ibanez SRFF 806.
[Invalid or Expired Link Removed]
I want to know the output impedance of this bass.
I have asked to Ibanez about this. But they did not answer.

So, I searched the Internet for the example of output impedance of the active circuit for bass. (Built-in preamp for bass)
But, there seems to be no theory in the value of the output impedance of the bass active circuit.
The value varies from manufacturer to manufacturer.

But I noticed a certain tendency.
If the manufacturers are the same, the output impedance values are often the same even if the model is different.
So, If I could get to know the output impedance of an Ibanez's active circuit, the value is probably the same as my model.
I hope so.

Please let me know if you know an example of output impedance value of Ibanez active bass. Thank you.

The following is an example of the output impedance of the active circuit of other manufacturers.

PIKE AMPLIFICATION Shapeshifter Blue 100 Ohm
Noll electronic ONBOARD PREAMP TCM 2 <10K Ohm
DELANO SONAR 3MS 100 Ohm
AGUILAR OBP-2 100 Ohm
ROVIDENCE VZ-B1 470 Ohm

 

[RobbieK]

There are ways to measure this, or if you have a schematic, it can be closely estimated. Do you mind me asking why you need to know?

If you need to plug it in to a particularly low z input, perhaps a passive DI, or a line-in on an old desk, or some vintage valve gear, TBH anything below 10K is usually fine.

If the bass has an active/passive switch it almost certainly means the volume pot is on the input side of the preamp, which means the output comes straight from an opamp, through a series resistor, usually 100 - 1000 ohms, so will pretty much be the value of that resistor.

If the bass has its volume pot between the pre output and the jack, then the bass's output z will vary depending on where the volume pot is set. If you are getting problems in this situation, (tonal change as you turn down, or even abrupt volume sweep) then you could try replacing the pot with a smaller value, or buffering the pot, or even relocating it to the front end of the pre. (But that too will usually dull the tone a little.)

 

[NakajimaYusuke]

Thank you. My "Necessity to know output impedance" is exactly the input from bass to low-z equipment.
In particular, I want to connect the bassto the "Mic In" in mic preamp.
As an experiment, I did it the other day.
Of course, I understand that this usage is not normal.
But the sound was good for me. It was not a terrible sound.

As a general theory of impedance matching,
the output impedance of the bass must be lower than the input impedance of the mic preamp in such a case.
I would like to confirm that this connection is a reasonable connection as impedance matching.

The input impedance of my mic preamp is 330 ohm.
So, I would like to know whether output impedance of my bass is higher or lower than 330 ohms.

If it is higher than 330 ohm, it means that there is a problem with impedance matching but there is no problem with sound.
If it is lower than 330 ohm, it means that there is no problem with impedance matching and also there is no problem with sound.
In either case I will try recording on this connection,
but I would like to know whether this connection is correct from the perspective of impedance matching.


I could not find the schematic of my bass circuit. However, I found a similar wiring diagram.
SOLD - Prewired Ibanez EQB-IIISC on-board 3-band preamps from Ibanez Premium basses
Although the detailed specification is different, I feel the basic structure is the same.
Volume pot is on the input side of the preamp.

 

[megafiddle]

Impedance matching is important when transfering power, or when using line matching transformers. But impedance matching is not important here. You are trying to transfer a signal voltage level without attenuation or frequency loss.

This is typically done by making the load impedance many times greater than the source impedance. For example, active circuit outputs are in the range of a few hundred ohms, while inputs for active circuits are in the range of about 50K ohm, or about 100 times greater. For another example, Hi Fi line signals are about 10 to 100 ohms output impedance, while the input impedances are 100K ohm, or about 1000 times greater.

With such a low input impedance of the mic preamp, you are at the least losing some signal level. On the other hand, the mic preamp provides extra gain over an active level input, so it likely more than makes up for the signal level loss.

You may or may not be losing some frequency response.

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[NakajimaYusuke]

I'm sorry. I misunderstood the meaning of the word "impedance matching".
"Impedance matching" means "output impedance = input impedance".
So, "output impedance < input impedance" is not called impedance matching.
This is what today I learned.

In my previous post I wrote "impedance matching", but that was wrong word.
What I wanted to say is equipment connection manners that "output impedance is low" and "input impedance is high".

I know that it is not necessary to align "the output impedance of the bass" and "the input impedance of the mic preamp" in this case.
It is OK if the output impedance of the bass is lower than the input impedance of the mic preamp.

 

[megafiddle]

I'm sorry. I misunderstood the meaning of the word "impedance matching".
"Impedance matching" means "output impedance = input impedance".
So, "output impedance < input impedance" is not called impedance matching.
This is what today I learned.

In my previous post I wrote "impedance matching", but that was wrong word.
What I wanted to say is equipment connection manners that "output impedance is low" and "input impedance is high".

I know that it is not necessary to align "the output impedance of the bass" and "the input impedance of the mic preamp" in this case.
It is OK if the output impedance of the bass is lower than the input impedance of the mic preamp.

The mic input is still low impedance though.

So a 470 ohm preamp driving a 330 ohm mic preamp is improper.
But a 100 ohm preamp driving a 330 ohm mic preamp is also improper.

When a preamp is designed, it is expected to be used with a high impedance input, about 50K ohm or greater. This guarantees that the preamp output signal is unaffected by the input impedance.

If you could watch your preamp signal while connecting it to the mic input, you would see it change. The level would change and possibly the frequency response would change. It might work ok with this preamp, but it might not work ok with a different one.

-

 

[RobbieK]

The input impedance of my mic preamp is 330 ohm.

That's very low. They are usually at least 1.5K. What sort of pre is it?

As a rule of thumb, the input z should be at least 10 times greater than the output z of the source.

 

[NakajimaYusuke]

Thank you for information. I learned a lot.
My mic preamp is dbx386.
dbx 386
I also felt that the 330 ohms is too low as an input impedance. Even if it is MIC IN.

If I imagine that the input impedance of the mic preamp should be more than 10 times the output impedance of the bass,
In my case, the output impedance of the my bass must be less than 33 ohms. This is too low. Not be possible.
Therefore, as long as I connect my bass to 330 ohms MIC IN, I guess that impedance problems always occur.

I usually use line-in when connecting bass to this dbx 386 preamp,
However, the sound that connected the bass to MIC IN was also good for me.



I may use this 330 ohms MIC IN in the future,
but I note that it is an incorrect connection from the perspective of impedance.