Post Number: 211
|Posted on Sunday, March 11, 2007 - 5:26 am: |
Here's my setup. Alembic MK Signature > F1-X > QSC 1850HD > Acme Low B2
The F1-X is run full range to the QSC 1850HD using the direct out so no rear outputs are used.
Here's what's going on. On a volume setting below 4 on my F1-X everything is fine. When I begin to approach a volume of 5 a pop/clip shows up when playing my E string. All volumes greater than 5 continue to pop/clip more and more until total distortion at around 9.
I have my QSC 1850HD power amp turned down so the input clipping signal light never comes on so I know its in the signal before the amp.
Since the pops/clips don't happen under a volume of 4 on the F1-X then the problem shouldn't be my bass (batteries, something else) since I'm not changing any settings on my bass. The only adjustment that I'm making is with the F1-X volume. I also tried using both input 1 and input 2. The problem still happens when using the padded input but it just begins to show up at a volume of 6 instead of 5.
I had an extra tube so I swapped it out. With the second tube in the unit the pops/clips still started at around a volume of 5 but there were more pops/clips sooner. (i.e. the second tube at a volume of 5 had the pops/clips of the first tube at a volume of around 7)
The pops/clips appear to be directly related to lower frequencies. The more bass I add on the F1-X the greater the problem.
Here is how I normally have my F1-X set ...
Direct Out Post and Ground
Any ideas? Suggestions? Herbal remedies? Chicken bones?
Post Number: 506
|Posted on Monday, March 12, 2007 - 1:44 am: |
I took the liberty of referring your query to Andy Lewis at Acme his response is somewhat counter intuitive but give it a go:
"This is the key:
I have my QSC 1850HD power amp turned down so the input clipping signal
light never comes on so I know its in the signal before the amp.
He needs to turn his amp up. All the way. Then he can turn down the other gain stages, and eliminate the clip."
Post Number: 212
|Posted on Monday, March 12, 2007 - 4:30 am: |
Thanks David. I appreciate you checking in with Andy for me. I had thought about calling him but since I felt this was an issue with the F1-X I didn't want to bother him.
I am actually running everything just like Andy suggested. At first I just thought that maybe I wasn't putting enough power into the Low B2 so I did try running with the power amp maxed.
Andy is correct that running my power amp maxed allows for me to not turn the F1-X volume up as loud which gets around the problem of the popping/clipping. That is actually how I have been running it. Unfortunately that does not solve the problem of why the F1-X is popping/clipping at what I perceive to be so low of a level. For some reason the F1-X is introducing this popping/clipping into the signal but yet I am nowhere near the point of clipping the input to the power amp. With the power amp volume maxed the power amp input can still handle more signal because the clipping light isn't ever coming on. So even with the power amp maxed I am not driving the power amp input as hard it can be driven safely.
With the power amp volume maxed the F1-X begins to pop/clip before the power amp input begins to clip so the power amp input could still be driven harder it's just that the F1-X is introducing the pop/clip problem before that point. There's still plenty of power left to go in the power amp; I'm just not getting it because the F1-X pops/clips prior to reaching the point of clipping the power amp input.
With every pre-amp / power amp combo that I've ever played through the power amp input clips way before the pre-amp reaches a point of clipping because the pre-amp is designed to have plenty of headroom. People wouldn't want a pre-amp that begins to clip before producing an output signal level sufficient enough to fully drive the input of a normal power amp.
That's why I'm thinking that something has maybe burned out or is in the process of going south in my F1-X.
Post Number: 757
|Posted on Monday, March 12, 2007 - 5:05 am: |
Have you tried exercising the effects send and return jacks? I seem to remember these could get a buildup of corrosion that can be removed by plugging and unplugging several times (20 or so). This would be similar to rotating the knobs on your instrument to clean out scratchy pots.
Post Number: 213
|Posted on Monday, March 12, 2007 - 5:29 am: |
Thanks for the suggestion Mike but I'm not running anything through the effects loop. Your suggestion did get me thinking though. I'm wondering if maybe something is up with my direct out (which is how I'm connected to the power amp).
When I get home I'm going to switch from using the direct out to using the full range out and see if it makes a difference.
Post Number: 1318
|Posted on Monday, March 12, 2007 - 5:33 am: |
The direct out will carry a line signal - so what type of input on the power amp are you plugging into?
I seem to remember some people had a -20 dB pad added to bring down the output signal.
Post Number: 214
|Posted on Monday, March 12, 2007 - 5:55 am: |
The power amp has a normal balanced XLR input for each channel and I'm running the F1-X direct out into the channel 1 XLR power amp input. I don't think the signal would be too hot though since I'm not seeing any input clipping at the power amp.
The direct out in the F1-X itself sounds suspect to me. I guess I'll know for sure once I change it from using the direct out to using the full range out.
Post Number: 232
|Posted on Monday, March 12, 2007 - 5:28 pm: |
I think the problem you're having is due to using the direct out instead of the back panel preamp outs!
There are a lot of different signal levels in the amplifier chain, and you need to feed the next guy in the chain with the proper level for the best results. The lowest level is the instrument level, then line level which your F1-X produces at the effects and direct out. The next highest level is preamp out which is produced at the rear panel jacks, then finally speaker levels, at the output of the power amp.
The max preamp level is probably around 4x the line level outputs (something like 3VAC RMS at full tilt, vs slightly less than 1VAC for a very hot line level output). The lower signal level from the direct out is why you can't drive your power amp to full output. Switch to the back panel output and you're probably going to have to deal with too much of a good thing (e.g. output).
Did you use the direct out because of the XLR connector? The manufacturer provides that for sound reinforcement applications where there's a long snake run from the house mixer to the amp stacks near the speakers. You want to have a balanced connection there to reduce hum. In your case, you want to use the unbalanced phone plug input (in the middle of the amp's XLR connectors) to deliver the preamp out signal to your amp. If the run is less than 20' there won't be any loss of quality or noise issues. You use a regular shielded cable there, like between your instrument and the preamp.
Once you've wired up, then you want to set levels from end to end again. I'd start full up on the bass, pretty high on on the preamp gain (maybe 7-8), then tweak the power amp gain so you see the input clipping lights. You might need to drop them quite a bit. I normally would set up with my preamp lower (to keep things clean) and run the power amp a little higher so I don't need to tweak two knobs to control the max output level.
Hope this helps,
Post Number: 215
|Posted on Monday, March 12, 2007 - 6:10 pm: |
"Did you use the direct out because of the XLR connector?"
Yes, that's exactly what I did. I viewed it as "balanced is better than unbalanced" and plugged it up that way. I normally play at a very low volume so I had never noticed the pop/clip before.
"If the run is less than 20' there won't be any loss of quality or noise issues."
That's a juicy tidbit of information that I was not aware of. I was thinking of it like "I'll run balanced instead of unbalanced because I don't want even a hint of buzz/hiss in my signal" all the while not knowing that I may be underpowering the input signal to the power amp.
I still haven't had a chance to test everything out using the normal full range unbalanced out instead of the direct out (18 month old children and all, don't ya know) but I'll give it a go tomorrow hopefully.
It's too eary to officially say "problem solved" but I'll definitely say "lesson learned" and I'll rewire my rig tomorrow.
(Message edited by lothartu on March 12, 2007)
Post Number: 216
|Posted on Tuesday, March 13, 2007 - 11:50 am: |
Well I'm a happy camper. As soon as I ran the full range out to the power amp instead of the direct out all the pop/clips went away.
For the first time I am now able to hear what my rig actually sounds like. Yippee!
Thanks again to everyone for their help and input.
(the happy one)
Post Number: 4864
|Posted on Tuesday, March 13, 2007 - 8:03 pm: |
Congrats! I learned something new from this thread; so I'm happy too!