School me on power amp/pre-amp setups

[bucephylus]

OK Bob's post is even more to the point; but, mainly same thing.

Anyhow, probably worth the review; but, now that the matter is settled, should move on.

 

[Downunderwonder]

OP sure is getting schooled.

 

[bucephylus]

 

[Passinwind]

Gain staging is essentially having each unit in the chain operating in its sweetspot to achieve maximum clean headroom, ramping up and attenuating as necessary. The Rane note is great.

The ProSoundWeb article linked in the Rane one is pretty useful as well, since saying essentially the same things in different ways often works better for some people than others.

 

[gurensan]

Also, I've never seen an amp that can handle 2 ohms when bridged (doesn't mean they don't exist, but I haven't seen one). Generally, if they will handle 2 ohms, it is only when the two 1/2's are being used independently (not bridged).

Crest CA series can do 2, bridged. I once read a review where the writer used one on a DJ gig and cranked it (CA 4 I'm assuming) bridged into a 2-ohm load. He said his Crowns had issues with it, which is why he tried it. He said the Crest's fans turned on, eventually.

Personally, I see 5U as an absolute minimum because I use a rack tuner.

1U power conditioner
1U Tuner
1U Pre
2U Amp

Along with "power conditioning," the power conditioner serves as your power strip so that you can plug the rack into a single outlet. It can also give you a light on the rack

Since 5U racks are very hard to come by, and since that leaves no room for any unforeseen expansion, it's 6 for me if I use a pre. 4's are a lot handier size, but, what are you gonna do?

Currently I'm running a 4U rack, but that's cause I'm using a conventional 2U bass amp. So: Conditioner, Tuner, Amp = 4U.

Check garage and estate sales for racks.. no joke! I picked up a 6, an 8, and a 10 for a grand total of $20 this summer. I had to give the 10 back because it wouldn't fit into a Ford Focus no matter how I tilted it, but the 6 I got at an estate sale for $10 with a huge milk-crate-filling ball of cabling, the resonator from a Dobro, and no fewer than 3 wireless units, one of which was a rackmount Nady. I still haven't gone through the entire pile.

On another note, I've heard that some power amps do put out crazy magnetic fields. I haven't experienced it myself but it's been ingrained into my skull that I need to leave at least one space between pre and power and not just for heat reasons. I can't vouch for it myself.

 

[BurningSkies]

If Crest is saying that they can bridge into 2ohm loads, my understanding is the implication is that the amp is safe down to one ohm loads per side. I find that 'suspicious' at best.

 

[::::BASSIST::::]

No, not necessarily to crank the preamp's master volume.

• Get maximum signal from your bass.
  
• Set the input gain of the preamp high enough to put a decently strong signal level through without clipping any of the preamp processing stages (EQ, filtering, FX, etc.).
  
• Set the preamp master high enough to drive the amp input strongly without clipping the preamp output or the amp input.
  
• Dial in your volume with the power amp gain control.

Perfect, thanks!

 

[Downunderwonder]

Same goes for bass amps all in one, unless clipping the pre is what you want.

 

[Major Softie]

Check garage and estate sales for racks.. no joke! I picked up a 6, an 8, and a 10 for a grand total of $20 this summer.

Damn, you scored!

 

[Bob Lee (QSC)]

If Crest is saying that they can bridge into 2ohm loads, my understanding is the implication is that the amp is safe down to one ohm loads per side. I find that 'suspicious' at best.

I'm skeptical of that myself. I remember the Crest 10001 could, but that was a unique case. IIRC, the design group got the idea to use PTC thermistors as emitter resistors, which act as a backstop current limiting scheme.

 

[Jim Carr]

The Crest CA series Manual, page 11 states:

Use extreme caution when operating the amplifier in Bridged Mono Mode. Never ground either side of the
speaker cable when the amplifier is in Bridged Mono Mode; both sides are “hot.” If an output patch panel
is used, all connections must be isolated from each other and from the panel. The recommended minimum
nominal load impedance in the Bridged Mono Mode is 4 ohms, which is the equivalent to driving both
channels separately at 2 ohms. Driving bridged loads of less than the recommended minimums will activate
the IGM circuitry, resulting in a loss of power, and may also lead to a thermal protect condition.

 

[will33]

The Crest CA series Manual, page 11 states:

Use extreme caution when operating the amplifier in Bridged Mono Mode. Never ground either side of the
speaker cable when the amplifier is in Bridged Mono Mode; both sides are “hot.” If an output patch panel
is used, all connections must be isolated from each other and from the panel. The recommended minimum
nominal load impedance in the Bridged Mono Mode is 4 ohms, which is the equivalent to driving both
channels separately at 2 ohms. Driving bridged loads of less than the recommended minimums will activate
the IGM circuitry, resulting in a loss of power, and may also lead to a thermal protect condition.

I interperet that to say, "beware, this $#!+ is dangerous.....and fun! "

 

[Jim Carr]

The 4 ohm would be fEARful or Markbass. I do not really intend to run it as a stage rig, I know the Markbass and Epifani pair poorly from a tonal standpoint, I was just curious how to do it, since I have to try it at least once.

The amp can make 850 watts into 2 ohms and 700 into 4 ohms per side.

You could hook any two of the 104HF-4, 1212/6, or UL310 to any one channel, and the third one to the other channel.

Should you?

No.

 

[SemiDriven]

I interperet that to say, "beware, this $#!+ is dangerous.....and fun! "

Yeah that sentence "Driving bridged loads of less than the recommended minimums will activate the IGM circuitry, resulting in a loss of power, and may also lead to a thermal protect condition" caught my attention!

For a second there I thought I was reading about the dangers of IGM's (Integrated Guided Missiles) of the nuclear variety.

 

[Major Softie]

Yeah that sentence "Driving bridged loads of less than the recommended minimums will activate the IGM circuitry, resulting in a loss of power, and may also lead to a thermal protect condition" caught my attention!

For a second there I thought I was reading about the dangers of IGM's (Integrated Guided Missiles) of the nuclear variety.

So, are you saying the thermal protect condition will protect one from nuclear explosions? Wow, they are really building some fine safety features into that amp.

 

[Jim Carr]

Yeah that sentence "Driving bridged loads of less than the recommended minimums will activate the IGM circuitry, resulting in a loss of power, and may also lead to a thermal protect condition" caught my attention!

For a second there I thought I was reading about the dangers of IGM's (Integrated Guided Missiles) of the nuclear variety.

You mean Intercontinental Ballistic Missiles? IIRC, weren't ICBMs what Gov. Palin said the russian inuit people were threatening to hurl at Alaska?