Ampeg Portabass Input Impedance

[DaBeat]

Hey guys,

does anybody knows the input impedance of the Ampeg Portabss line (Ampeg PB 250 / PB 800)? The answer is important for connecting piezo pickups. There is no information worldwide.

Ampeg says it is for electric AND double bass. But there are no specs.

Thanx DaBeat

 

[Jeff Scott]

I used to have the PB250; IIRC, the input inpedance is around 500KΩ, too low to work well with a piezo pickup without a buffer preamp in line.

 

[DaBeat]

Thank you Jeff,

your answer is more than helpful! It might be that i need to get an extra preamp.

 

[Jerrold Tiers]

Yes, about 500K is exactly right.

 

[Jim Carr]

These all would work...

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[DaBeat]

Thanks for your suggestions.

If it is only 500k: Why did they proclaim it as an amp for doublebass? Sorry, but that´s a little weird.

From a customer´s point of view, you don´t buy an expensive amp for 1000 bucks all-knowing that you need to get an extra preamp. Just a thought.

 

[Jerrold Tiers]

Thanks for your suggestions.

If it is only 500k: Why did they proclaim it as an amp for doublebass? Sorry, but that´s a little weird.

From a customer´s point of view, you don´t buy an expensive amp for 1000 bucks all-knowing that you need to get an extra preamp. Just a thought.

Well, because you DON'T "need" an extra preamp........

It depends on your pickups. I am blaming the whole Porta-Bass fiasco on one guy, and he IS an amplified acoustic guy..... well, sort-of, because it isn't his fault, but he was used as THE example.

I don't know what he used for pickups, but he had no problems. I am quite sure that the matter was investigated, and the input was accepted as good. It would be simple to increase it if needed, at least to double, it is just one resistor, and the circuit has virtually no loading aside from that resistor.

And it isn't as if there was some confusion about pickups, we made some other amps that were specifically for acoustic, and they had special super-high impedance for straight piezo acoustic guitar pickups. SLM distributed acoustic instruments, guitars and also a full line of orchestral string instruments, violins, basses, etc.

While that particular end of things I wasn't involved with, it should not have been an issue.

 

[billfitzmaurice]

Thanks for your suggestions.

If it is only 500k: Why did they proclaim it as an amp for doublebass? Sorry, but that´s a little weird.

From a customer´s point of view, you don´t buy an expensive amp for 1000 bucks all-knowing that you need to get an extra preamp. Just a thought.

The fault doesn't lie in the amp, it lies in the pickups. That amp input impedance standard dates to the 1930s, so when the piezo pickup came along 40 odd years later it should have been engineered to work with that existing standard. Piezos being what they are that's very difficult, so a pre is pretty much a necessity. If the piezo pickup manufacturer doesn't say so upfront shame on them.