Impedence matching on my preamp?

[KikkyMonk]

I have an Entwistle Ashdown Pre-amp which is very similar to the RPM-1. Anywho, I also have a lakland skyline bass with bartolini pickups and on-board electronics. I have been, for years, using the LOW input (10k Ohms) which is for active basses. I assume my bass is active because it takes a battery and when I pull on the volume knob it goes into passive mode.

 

I have always had an issue driving the VU gauge to a good level even with my bass at 100% and the input at 100% and a fresh battery.

 

On a whim I plugged into the HIGH input (3.9M Ohms) and it is noticeably louder and I have no trouble driving the amp to a good level. I was finally able to turn down the input a bit. Also the sound sounded much thicker as well (probably from the increased output of my amp).

 

Can some smart person tell me what is going on here and which input to use?

 

Thank you,

Dave

[alexclaber]

In my experience only VERY loud active basses need to go in the active/high(when referring to input levels)/low(when referring to input impedance or gain) input. (Aren't they confusingly named?!)

 

So in 95% of cases I'd say the passive/low(input level)/high(gain or impedance) input is the one to use. If you find your bass distorts the input on loud notes then switch to the active input, otherwise leave it be.

 

In your case you have a passive mode on your bass which means that the pickups will struggle to drive an active input when the preamp is bypassed, especially as Bartolinis tend to be quite low output.

 

I'd be curious to know what the Ashdown manual says - the one with my old SWR Grand Prix was very clear about which input to use but that was a very well written manual.

 

Alex

 

P.S. Just dug up the SWR manual online:

 

"PASSIVE/ACTIVE INPUT JACK

This input can and should be used if your instrument has passive electronics (no built-in preamp). Some pickups such as EMG, Fishman, etc. employ batteries for operation and will work perfectly using the Passive/Active input. Technically speaking, this input should be used if your instrument has an output voltage of 1 volt RMS or less. Consult your owners manual or ask the manufacturer if you are unsure. Preamps made by Bartolini, Sadowsky and Rick Turner make a perfect marriage with this input.

 

 

ACTIVE INPUT JACK

The Active Input jack should be used with instruments having a built-in (on-board) preamp that will produce signals over 1 volt RMS. Known basses that should use the Active input are Kubicki X-Factor and some early Ovation Electrics. Some really "hot" pickups installed in your instrument may find this input more compatible. The best judge is your own ears. Keyboards, drum machines, etc., should use the Active Input jack.

 

NOTE: Using the Active input with passive basses may result in a loss in high end transients. Players who roll off their high end starting at about 2K to 3KHz or prefer a "darker" sound may find this input more to their liking.

 

If you hear some distortion on your active bass and are using the Active input, CHECK YOUR BATTERY!! This will save you and a service technician a lot of aggravation."

 

[KikkyMonk]

The manual says the HIGH input is high sensitivity and also high impedance to suit the output from PASSIVE basses. The LOW input is low sensitivity and lower impedance to suit the output from ACTIVE basses.

 

Like I said I have been using the LOW input for years but never could get enough level to get the tube preamp to distort. I switched to the HIGH input and everything is perfect now.

 

I did write Lakland an email asking about the output impedance but they have yet to get back to me (1 week and counting).

 

Maybe the fact that they Bartolinis are low output accounts for the fact of not being able to get a good level into my preamp. I figured since there way on-board electronics and a battery that should juice up the level enough. For a long time I just figured something was wrong.

 

Between what your saying and what my ears (and bandmate's ears) are telling me I'll just stick with the HIGH input and be perfectly content with my newfound tone.

 

Thanks for the nice post Alex.

[alexclaber]

Quite a lot of onboard preamps are unity gain, so if your pickups are low output then your preamp output will be low. I believe Bartolini preamps have adjustable gain to fit better with their preamps. Aguilar ones are unity gain AFAIK.

 

Alex

[TimR]

My Trace Elliot manual says pretty much the same. I think that explanation is spot on. My Ibanez has the Bartiloni active preamp but I have to run the amp with the active/passive button set to passive. I have to turn the gain to 8 to get the clip light to show. Whereas my passive Charvel will light the clip at 6/7.

 

DavidM also informs me his Ibanez 1005 doesn't have as much output as his Spektor.

 

I've always thought that the Active always meant that the tone controls were active, not that there was any amplification going on inside the bass. IE you can Boost Low/Mid/High on an active where as only cut tone on a passive.

[DavidMPires]

I used to plug my Ibanez on my Ampeg with the passive mode of the amp on so i could be heard by my fellow band mates. I reckon that maybe with a new preamp you could change it.

 

I don't do it anymore co's i'm afraid of damage my Ampeg.

[DavidMPires]

I've just made a simple test with my Warwick blue cab 30, and my Ibanez. Taking into consideration that I don't have gain to adjust and there is no light to clip. Pluging my bass on the passive input gives me about twice the volume/output comparing with the active input, this may be due to the low volume of the built in pre of the Ibanez.

 

I shall try this with my ampeg tomorrow or so, and will try it again next monday on studio with really high volumes. I will let you know how it goes.

[DavidMPires]

Kikky not trying to steal your thread:

 

it hurts if you plug an active bass into an active input?

[TimR]

I'm not sure of your question, do you mean can you damage the amp?

 

No, my understanding of it is that the Active setting has buffers to protect the amplifier from high outputs from the more powerful active basses. Whereas the passive input is for passive basses, and lower power active basses.

[DavidMPires]

Yeah using an active bass on the passive input, but controling the preamp light, does it damage the amp?

[Audere]

You can not hurt your power amp with an active bass plugged into the passive input.

Normally the only circuit change is a resistor divider is connected to the jack when you plug into the active input or push the switch to change modes etc.

 

The first series resistor will already limit the current in all reasonable cases with or without the 2nd R to ground.

You might get some distortion but not much probability of damage with an overload condition.

 

If by the preamp light you mean the peak light on many Ampegs then this is the level at which a clean sin wave will exit the preamp stage with about 1% of the 3rd harmonic distortion added - this level of distortion is noticeable but will not damage anything. FYI - I have only tested 3 of the Ampegs with tube front ends but they were all very similar. I assume the SS preamps behave the same way.

[rumpelstiltskin.]

Normally the only circuit change is a resistor divider is connected to the jack when you plug into the active input or push the switch to change modes etc.

 

this is often referred to as a "pad". it offers some level of signal attenuation -- lower signal level -- on the order of -6dB to -10dB. usually. every manufacturer has a different approach. like the SWR manual says, unless you know your bass to have very hot output, or unless you're hearing distortion at every gain setting (meaning the input signal is overdriving the preamp, even when the gain is low), you should use the passive 0dB (unity gain) input instead of the active attenuated (padded) input.

 

this post was meant to clear up confusion, but if it's total greek, i can explain it in more words that will hopefully show you how it all works.

 

robb.

[Rocky McDougall]

.

I've always thought that the Active always meant that the tone controls were active, not that there was any amplification going on inside the bass.

 

 

Electronics is my weak spot in Bass knowledge. I always thought the on board pre-amp amplified the complete signal to the amp not just the tone controls.

 

Rocky

[DavidMPires]

I though the asme as you Rocky

[rumpelstiltskin.]

sometimes it does and sometimes it doesn't. there is too much variation in pickups to consider anything in the preamp a standard.

 

for example, bartolini preamps have a small pot inside the cavity that alters overall gain. with the preamp set flat and the volume contol at full, you can increase or decrease from unity gain.

 

robb.

[DavidMPires]

I shall check that out