Aguilar OBP-1 preamp voltage

meanjd · #1 04-12-2007, 07:17 AM

Folks,

Aguilar state that 2 x 9v batteries are required to run their OBP-1 Preamp. The reason for this,they say,is to allow for more headroom. I can't see why it wouldn't work with 1 x 9v battery as their OBP-2 & 3 work fine with 1 or 2 batteries. Has any one used it with one battery. I want to put it into a '78 Jazz, so I'll have enough trouble getting one battery in without having to route out a cavity for a second battery - which is out of the question.

Regards,
meanjd.

meanjd · #2 04-12-2007, 07:24 AM

PS -
- Fishman used to make a Voltage Doubler, which would be ideal for my predicament, but sadly they no longer make them. If anyone knows where I can get one or something similar I would be most grateful.

Regards,
meanjd.

20db pad · #3 04-12-2007, 07:38 AM

I wote an email to Aguilar a while back - they say the OBP 1 will work with a single 9v battery, but the internal bias will change. I never ended up buying an onboard version - I bought the Aguilar outboard instead, which is the OPB-1 in a metal box. It uses two 9v batteries.

Buying and using the outboard version of this preamp might be a better idea than routing out holes in a potentially valuable bass like a '78 Jazz.

meanjd · #4 04-12-2007, 03:42 PM

20db,

Thanks for your reply.

I already use the DB 924 which I find extremely good. However, there is a substantial impedance mismatch between the output of the bass(high) and the output of the 924(low). The onboard version would give me low impedance directly from the bass to a bass head. This does make a difference to the overall sound which is partly lost between my passive bass and the 924 - even with a short quality instrument cable.
What do Aguilar mean when they say it changes the bias?

Regards,
meanjd.

fishtx · #5 04-12-2007, 05:11 PM

I think Spector is using a voltage doubler in their basses with the OBP-3, so it only requires a single 9v.

basey · #6 04-12-2007, 07:16 PM

It will work with 9volts (if its the newer, smaller one)
Take a extra battery clip and wire the black and red together.
Then use that as the second battery to see how you like it.
It's not that big of a difference. Not in my experience anyway.

A9X · #7 04-13-2007, 12:28 AM

Quote:

Originally Posted by meanjd

I already use the DB 924 which I find extremely good. However, there is a substantial impedance mismatch between the output of the bass(high) and the output of the 924(low). The onboard version would give me low impedance directly from the bass to a bass head. This does make a difference to the overall sound which is partly lost between my passive bass and the 924 - even with a short quality instrument cable.

What? The 924 will presumably still have the same 1M input impedance that the OBP1 has, so I don't beleive for a second that 1' of cable will make any difference. The 924 will similarly have a low output impedance to the amplifier (head or rack etc).

Quote:

Originally Posted by meanjd

What do Aguilar mean when they say it changes the bias?

Internally there will be a small part of the circuitry that sets the voltage and current that run through the FET(s) used for amplification at idle (when there is no signal present). If the bias is set to a different point from that which the designer wants it, because he designed the circuit expecting there to be 18V available, then low gain and/or excessive distortion, especially with the bass boosted, may result.

bongomania · #8 04-13-2007, 01:37 AM

Quote:

Originally Posted by meanjd

However, there is a substantial impedance mismatch between the output of the bass(high) and the output of the 924(low).

I'm surprised A9X didn't call this out: there is no such thing as a mismatch between the output of one device and the output of the next device in line.

The output of the Aguilar will be more or less the same z out regardless of whether it is onboard or in a box.

A9X · #9 04-13-2007, 01:59 AM

Quote:

Originally Posted by bongomania

I'm surprised A9X didn't call this out: there is no such thing as a mismatch between the output of one device and the output of the next device in line.

The output of the Aguilar will be more or less the same z out regardless of whether it is onboard or in a box.

LOL. I should have stated it more clearly. Mustn't talk on the phone and type posts at the same time.

meanjd · #10 04-16-2007, 07:00 AM

I'm going back to school!

meanjd.

cybersnyder · #11 04-16-2007, 07:44 AM

I have the older OBP-1 (larger size) and it sounds fine with a single 9V.

meanjd · #12 04-17-2007, 07:06 AM

[quote=A9X;4070255]What? The 924 will presumably still have the same 1M input impedance that the OBP1 has, so I don't beleive for a second that 1' of cable will make any difference. The 924 will similarly have a low output impedance to the amplifier (head or rack etc).

Believe me,it does make a difference. Lets forget the physics for a moment. Hearing is believing and I've heard.
The difference between the two set ups is audible. The signal from a passive bass travelling down a cable is met with resistance.The longer the cable the more resistance The more resistence the more passive and less top end from the sound. If your were to use an active cable (which would have little or no resistance as would an onboard preamp ) between the bass and the 924 as oppose to a stansard cable you would see what I mean.

Regards,
meanjd.

A9X · #13 04-17-2007, 08:01 AM

Quote:

Originally Posted by A9X

What? The 924 will presumably still have the same 1M input impedance that the OBP1 has, so I don't beleive for a second that 1' of cable will make any difference. The 924 will similarly have a low output impedance to the amplifier (head or rack etc).

Quote:

Originally Posted by meanjd

Believe me,it does make a difference. Lets forget the physics for a moment. Hearing is believing and I've heard.

I cannot tell you what you think you've heard, but I've done hundreds of similar audio comparisons and the measurements to back them up, and I don't beleive there is a difference, merely that you thought you heard one.

Quote:

Originally Posted by meanjd

The difference between the two set ups is audible. The signal from a passive bass travelling down a cable is met with resistance.The longer the cable the more resistance

The resistance of a couple of connectors, contact resistance and 1' of cable is trivial. Under an ohm. From the Mogami 2524 dtatsheet, its 0.01 ohm/foot. In the context of `2-5k output from a passive bass and a 1M input into the amplifier, it's sort of insignificant, no?

Quote:

Originally Posted by meanjd

The more resistence the more passive and less top end from the sound.

Capacitance is the reason for the loss of top end response predominantly. Again, 1' of lead might be 50pF (my favoured Mogami 2524 if 40pF/ft). Not particularly significant in the light of the average 20' lead and passive bass. A significant difference in load may affect the resonant peak of the passive circuit but an ohm won't.

Quote:

Originally Posted by meanjd

If your were to use an active cable (which would have little or no resistance as would an onboard preamp ) between the bass and the 924 as oppose to a stansard cable you would see what I mean.

What is an 'active cable'? If you mean the low output impedance of the active stage affecting the signal loss at high frequencies because of it's ability to effectively drive the capacitance of the cable, then that was never in question and I stated so before. What I do dispute is that an OBP1 wired inside a bass, or an OBP1 inside a case on your belt at the end of 2' of lead will measure and/or sound any different.