Volume after preamp... good, bad or otherwise?

[rojo412]

If one were to put the volume control AFTER the preamp in the signal chain
(pickups -> pan -> preamp -> volume -> Jack)
what would the result be?

If this is a workable idea, what change would be made to the pot values?

Just askin'... bored today.

 

[line6man]

It would work a bit better than having it before the preamp.

The downside is, you can't have an active/passive switch.

As far as the pot value, the impedance of the signal is lower at the output of the preamp than it is before the input, so you will want to use a 25K or 50K pot.

 

[rojo412]

No prob a/p. This is for an EMG equipped bass, so it wouldn't need it.

 

[Rob22315]

Some preamps are designed with the volume pot as the last thing before the jack. See the internet reverse engineering of the Bart NTMB on the for example. I think they BYOC confidence booster is the same. It's a simple way to control the preamp output but could allow the cable impedance to affect the output a little bit because you now have an R-C circuit between the last active element in the preamp and the input to the amplifier. I haven't run the calcs to see where typical values for cable capacitance, preamp output impedance, and amplifier input impedance might place a roll-off frequency. It could reasonably well out of the audible frequency range, or not. Most times, the resistor used at the output of an active preamp is around 50k. Passive volume pots are 250-500K.

Since it's a common practice, you should give it a try and see if you like it. If not, it's easily reversible.

I added a small JFET buffer to my frankenbass mostly to try it out. The buffer was the last thing before the jack so I'm using the existing v/v/t pots that came with the passive bass. Sounds good to me but I can't say whether or not putting the volume after the buffer would have been better for that application because I haven't tried it.

 

[rojo412]

My exact use for this would be running the preamp out of a Squier Deluxe Active Jazz in a Schecter bass with active EMGs.

I actually think that the SDAJ preamp may use the vol after the pre, as it looks like the volume control is a 25k pot, the blend is a 500k blend, and the tone controls are 100k (linear, I assume). The pickups are passive, and may even be humbuckers. Here's the diagram:

Invalid Link Removed

Just a wacky question, while I'm at it... would I be able to use the 100k pots on that system with the OBP-3, which is rated for 50k linears? I only ask because the Squier has the stacked b/t pot.