Waddycall

I’m experimenting with giving up on bass specific amps and got a class a/b power amp to try with my bass pod. I feel very optimistic about it. No band practice til next Thursday so fingers crossed it’s  going to do what I think it will.

Thanks Phil,

it all makes sense. I understand ohms law but some posts have led me to believe that its more complicated than that. I was also unsure if there was additional risks from bridging caused by some kind of phase shifting or something else I might make up but if volts are volts bridged or not then its all good with me.

i enjoy tinkering with gear, experimenting with tone and like to understand the technical aspects hence the original post👍

Right, thanks folks - that wraps it up for me. Also had a look at a few more class d heads. Fender rumbles are also bridged at least the 150, 350 and 800 are.

If I’m looking for a power amp again in the future (which I may be) I’d be tempted to go small and put it in bridge mode. No point in paying for and carrying twice as much amp as you need.

Yeah but

🤣

24 minutes ago, Dad3353 said:

 

Take your tablets, like that nice doctor fellow said. Chill. Breath. Earl Grey, or camomile tea may help. Take a walk (not, not on the Wild Side..! D'oh..!).
For the purposes of the interogations you're torturing yourself with, there is no difference, none whatsoever, between what comes from one amp channel or two bridged amp channels. Whatever difference there may be is only of interest (and even then, not much...) to a lab technicien studying high-falluting stuff of purely academic use. Now, take those pills, go for a nice long walk and get back to practicing bass playing, there's a good chap. 

 

...

 

 

Ace - I’ll go with that until someone comes along and appears to contradict it! No mental torture here just genuine interest 🤪

just seems to be an automatic “don’t put it in bridge mode”  response to power amp stuff which I’m curious about especially as it seems some amps are supplied in bridge mode from the factory.

Thanks Bill. This is good stuff. I appreciate everyone’s comments on this but I’m still a bit confused. Maybe that’s because I’m going round in circles due to thinking about watts/power. 

So a given cab  at a given frequency can handle a certain amount of voltage swing before it suffers mechanical damage?

Is it feasible then that the two theoretical (one bridged one single channel) 300w rated amps  (however iffy the rating may be) could be able to put the same voltage swing onto the same cab? What I think I’m struggling with is the difference between a voltage swing of equal magnitude/amplitude from a single channel amp and a bridged amp. Does that make sense?

i.e, is voltage swing voltage swing or can it have different characteristics dependant on single channel or bridge mode?

im assuming higher power amps can generally put a higher voltage swing into a given load?

8 minutes ago, Bill Fitzmaurice said:

Quote

 

Yes. You're not considering impedance.

What if had said 300w into 8ohms? Am I still missing something relating to impedance?

That would suggest that if I wanted a an amp at say 300w (to move away slightly from the power concern issues) theres no difference between buying a single channel amp rated at 300w or buying a small two channel amp and bridging it to get the equivalent 300w which seems contradictory to the posts regarding voltage swing or am I missing the point? That would also suggest that anyone using one channel of a two channel power amp would have been better off getting a low power one and bridging it to get the same output.

And what does that mean to users of class d amps like the Ashdown RM that are bridged as standard? Are they more likely to blow speakers than users of single channel analogue amps of the same power rating?

1 minute ago, Dad3353 said:

 800w bridged and 800w per channel unbridged..? Seems odd to me.

Sorry what I should have said is that it sounds like there is a difference between using one channel of an amp that gives 800 W per channel and using both channels of a smaller amp bridged at 800 W. 

Ace. So it’s basically the combined push pull on the driver? 

And there is a difference between 800w bridged and 800w un-bridged.

Cool, so this is getting interesting! What’s the difference between power and voltage swing? Is it due to the fact that it’s not a simple dc voltage at a steady current?

Thanks, the bridge mode or not makes no difference makes  sense.

Something else  I can’t get my head round-

power amp manufacturers seem to recommend choosing an amp that’s twice the rated power of the cabs. I guess that makes sense for a fixed venue type installation but if I followed that advice I’d be connecting a 2.4kw amp to my 210!

apparently I also need clean headroom - how much is that?  I need to avoid clipping the amp as that will damage the cab but don’t want so much power I risk overpowering the cab. Where’s the balance?

by the way I’m not having any issues - just curious. My old Hartke Ha350 (250w into my cab) is plenty loud enough - my power amp is bridged to compensate for low input voltage. I’ve no intention of blowing anything up or deafening myself.

Recent threads including one about my new power amp have got me curious about bridge mode and it’s perils. I can understand the potential risk of having too much power but get an impression that it’s that power specifically delivered in bridge mode that can cause problems. Is this the case or is it as simple as too much power is bad, bridge mode or otherwise?

Also my old Ashdown RM800 evo II operated permanently in bridge mode with no indication of this other than in the manual (I think). Is it common for class d bass heads to run permanently in bridge mode (I think all the rm evos do)  If so are cabs connected to these amps at more risk than those connected to other amps of similar power?

my new power amp puts 830w into 4ohm. My old RM head  puts 800w into 4 ohms. My 8 ohm cab has a continuous power rating of 1200w. Other than the extra 30w is the power amp more likely to damage my cab than the RM?

id appreciate any comments in thicko speak.

26 minutes ago, Bunion said:

Have you looked at the volume settings in the XT they might need resetting 

Yep, all tweaked. I believe I’ve got it as good as I can get it without clipping and I’ve evened out the level of all the patches I’m using. The factory presets are a nightmare for differing levels!

Here’s what the manual has to say about the gain controls -

9 minutes ago, agedhorse said:

On the amp, the channel 1 input sensitivity control should be set all the way up (fully clockwise). 

Yeah, I keep hearing that and continue to fail to understand it. As it’s an input attenuator I don’t see the difference between turning that down and turning down the output attenuator of the bass pod other than doing it “wrong” saves chucking out 600w of scratchy pot noise (pod pot is noisy) through my cab. 

I also don’t understand how it differs from using the master volume pot on a standard bass amp as surely that is also an attenuator for the input into the power stage?

I’m interested in understanding this though.

Maybe it depends on the combination of frequency and amplitude?

I just remembered something I read in the manual for my previous amp - an Ashdown RM 800 evo II. It always operates in bridge mode with an output of 800w into 4 ohm. My power amp in bridge mode puts 830w into 4 ohms in bridge mode so to me seems very similar.

9 hours ago, BassmanPaul said:

Are you turning the QSC's level controls to full on?

As per the manual I have the channel 2 gain at 0 and use the channel 1 gain to set the output as the output level pot on the pod is a bit scratchy (cleaner/lube on the way). I have read a few comments that the gain control on the amp should be set and left but don’t understand the relevance when there’s a single relatively low level input source that’s not having it’s signal mixed and monitored remotely.

There’s a switch on the back of the bass pod to select the output level “line” or “amp”. I have it set to line so pretty much getting all it’ll give although no doubt the power amp could take more. Can’t see what else I can do without adding more components, weight etc

Yeah I have the two reds connected to the cable. The output from the pod is unbalanced 1/4” into an unbalanced 1/4” in on the amp. It’s a shame there’s no balanced XLR out on the pod.

By the way power amps are a new thing to me so grateful of the comments 👍

1 minute ago, BassmanPaul said:

So you do bridge it. It's not that powerful an amp but it is still more than capable of damage. 

 

Do you know that some amps require a specially wired speaker cable for Bridge mode. In your case the Speakon connected to Amp! output gas to be wired +1 and +2 at the amp end and +1 and -1 at the cabinet end. This cable is not reversible and it's two ends should be clearly marked Amp and Speaker.

 

Cheers Paul, yes it’s currently connected with binding posts to jack as it’s only being used at very low power in the house. I have an NL4 plug on order to modify one end of one of my speakon cables. I ordered a red one to avoid mixing up the ends! That will be sorted before it gets used in anger 👍

Just now, BassmanPaul said:

Don't blow your speaker cabinet!!!

 

Don't get tempted to get 'every last watt' out of the power amp by bridging it. Run it in parallel mono with a cab on each channel.  if you only have one cabinet, run it on one channel and turn down the other.

Haha - funny you should say that. It’s bridged! The output from the bass pod is pretty low so having it run on one channel isn’t loud enough (I can have it on full in our detached house) and is no way near loud enough to keep up with a drummer. If I use my Hartke Ha3500 with this cab (250w into 8 ohm) is much louder. According to the specs it’ll put just under 600w into an 8 ohm cab in bridge mode. The power handling of the cab according to the VK website is 1200W which seems a bit optimistic but I feel I’m pretty safe unless anyone thinks otherwise? I did think about putting a channel strip between the pod and amp to bring the line level up but that would add weight and complexity I don’t want. I also don’t want to overload one amp channel and make it clip.