2 parallel Sansamps blended into the same power amp - Is this possible?

gibsualdo · #1 01-08-2009, 09:45 AM

I want to split my signal into 2 channels, then run each into seperate Sansamp VT Bass preamp/pedals, and then blend the two together and then run a single cable into the effects loop return of my amp (bypassing the preamp). Problem is, I'm not sure what to use to blend the two.

I have a Boss LS-2, I could put a VT Bass in each loop, then connect the output of the LS-2 to the effects loop return, but will the LS-2 defeat the VT Bass' low Z signal rendering it unfit to send direct to the power amp section of my amp?

If this is the case, does anyone have any suggestions as to what I could replace my LS-2 with? I have a DOD 240 Resistance Mixer I could use, if this will help but being a passive mixer, I don't know if it's adequate for the job or not.

Should I just get myself a small powered mixer?

bongomania · #2 01-08-2009, 09:58 AM

Interesting question! I've never tried to blend line level signals with either a passive mixer or an LS-2, so I don't know what the results would be. I almost think the passive mixer might work better in this case, as the outputs of the VT Bass should not be too badly affected by loading, although feedback is still a big concern. I just wonder if the LS-2 would be clipped by line-level inputs.

Since you already have both of those, and since the worst that can happen is some distortion or feedback, I'd say try both and let us know how they sound. After you've done that experimentation then you could look into small powered mixers if necessary.

gibsualdo · #3 01-08-2009, 10:10 AM

Cheers bongo, that's my mine concern with the LS-2. I've got rehersal later tonight, so I'll get a chance to try it then, provided I can find my 240 which has been hiding somewhere in the depths of the band room for a while now. If not, I'll at least be able to report how the LS-2 fares.

SteveMcB · #4 01-08-2009, 12:04 PM

By all means, try the solutions you already have, you're exceptionally unlikely to do any damage. I've had trouble with signal/tone loss using passive resistance mixers in the past - significant tone colouration may result. I'd suggest using a (very) small active mixer, which can be had very cheap, like the Behringer MX400, which is a 4-in 1-out active mixer, costs only about $25US IIRC. I have one on my board when I biamp effects but use one amp (processing the highs only), and it works well. It's reasonably rugged, very cheap, and doesn't noticably colour the tone.

Steve

P.S. "Powered mixer" usually denotes one with a power amp built in, which I'm pretty sure is not what you want.

AndyLES · #5 01-08-2009, 02:03 PM

Be warned - some FX units flip phase. In other words, say you mix the two paths (VT Bass path #1 + effect with VT Bass path #2 + no effect).

The effect on one path may flip the phase of the signal, leading to weird hZ cancellations.

cheapbasslovin · #6 01-08-2009, 07:00 PM

Quote:

Originally Posted by AndyLES

Be warned - some FX units flip phase. In other words, say you mix the two paths (VT Bass path #1 + effect with VT Bass path #2 + no effect).

The effect on one path may flip the phase of the signal, leading to weird hZ cancellations.

It seems unlikely that two identical pedals would cause phase issues, but I've been wrong about stuff before.

I thought the LS-2 was capable of a +20 db boost for each channel. Is that not enough required to reach power amp driving levels?

bongomania · #7 01-08-2009, 07:06 PM

A couple of mix-ups there. 20dB is just an amount of gain, not a signal level. I find that it takes in the neighborhood of 50 dB gain to bring a passive jazz bass output up to +4dBu line level. The VT can supposedly reach line level on its own (I haven't tested that personally to confirm) so additional gain is not needed. I can see though what you might be suggesting, that the VT's are set to a lower output level in order to avoid clipping, and then the LS-2 adds boost to achieve line level... that could work, worth a try. Two identical pedals can certainly cause phase problems, especially if one of them is 'engaged' and flipping the phase 180 deg. and the other is not engaged, not flipping the phase.

cheapbasslovin · #8 01-08-2009, 07:19 PM

Quote:

Originally Posted by bongomania

Two identical pedals can certainly cause phase problems, especially if one of them is 'engaged' and flipping the phase 180 deg. and the other is not engaged, not flipping the phase.

I was under the impression that he was going to use them as an A+B all the time. I may have read too much into the OP.

AndyLES · #9 01-08-2009, 10:53 PM

Even if he runs both VTs at the same time, the minute he puts on an effect in one of the two signal paths, and not both at the same time, there can very well be a phase problem.

cheapbasslovin · #10 01-08-2009, 11:12 PM

Quote:

Originally Posted by AndyLES

Even if he runs both VTs at the same time, the minute he puts on an effect in one of the two signal paths, and not both at the same time, there can very well be a phase problem.

I get what you're saying, I just misread the intentions of the OP.

gibsualdo · #11 01-09-2009, 03:08 AM

Thanks for the suggestions folks, I didn't bother digging out my passive mixer in the end, but experimenting with the LS-2 was a success!

I didn't try putting any effects before one of the Sansamps, I'll try that next rehersal on Sunday. I'll be leaving both Sansamps on all the time, so hopefully there'll be no phase issues with effects infront of them.

I should add, that even with the preamp bypassed on my Ashdown ABM, the output volume still functions as normal on my amp. I'm not sure if this is normal, Sansamp manuals say that when using the effects loops return, the master volume should be disabled but this isn't the case with my ABM. Anyhow, it sounded pretty damn awesome to my ears with plenty of volume, and I'll certainly be sticking with this set up for the foreseeable future.

Another method I tried, which didn't appear to sound any different, was running one Sansamp straight into the effects loop return, and the other straight into my ABM's line in. I'll probaly stick with the LS-2 mehtod above though, since patch cables are cheaper than 20ft instrument cables

I'll report back again, once I've had a chance to try things out with my DOD 240.

**DosiYanarchy** · #12 01-09-2009, 03:38 AM

The Volume control works on my Ashdown Mag 300, even when I plug straight into the effects loop, I think this is quite common, but i've played a few amps where that hasnt been the case.

Im glad its worked out for you with the LS2 and the VTbasses, I suppose the other options would be:
1. genuine clean boost after the LS2 to bring it up to line level
2. plug into the Ashdown preamp, and bypass the EQ (im sure yours has the little EQ on/off switch as mine has) you can still boost the level from the Gain control and the Volume

although this is irrelevant as the master volume works with the effects loop

I always plug into my effects loop, bypassing the Ashdown pre, and never need to boost past instrument level.