Discussion in 'Amps [BG]' started by TravTrav, Feb 18, 2014.
What specs should I look at to know what preamp will drive my power amp?
output voltage some amps take .775V some 1.2 and other 1.4 need to make sure you can drive the amp. My current situation I have a WTDI and don't know whether to get Crest Audio Prolite 2, Peavey IPR2 or Crown Drivecore. Also want to bridge @ 4 ohms
Output level(s) of your bass(es), played by you
Gain of the preamp at settings that sound good to you
Max output of the preamp at suitable power amp impedance load
Input sensitivity and input impedance of the power amp
That says it.
I also have a WTDI. I don't know the nominal output. I can say that it is not 1.4 volts unless you have the gain and master knobs up pretty high. At levels that I use the output does not properly drive an amp that wants 1.4 volts.
I have pretty much decided on a Crest Prolite 2 DSP .775Vrms. That is pretty much what i said output voltage from preamp.
How would I know the preamps output is suitable for my power amps impedance load? Like, could you throw me some numbers/an example.
Aguilar Tone Hammer - They don't say. Eden WTDI - They won't tell ya. It is... ah... uncommon for the equipment manufacturers to openly publish such specifications. Even if they tried, the numbers would be difficult to make standard.
Matching a preamp to an existing power amp is about as backwards as I can imagine doing it. The preamp is the voice. Power amp be darned. Find the preamp you like then figure out how to make it work. Trade the power amp, buy an inexpensive line mixer, etc...
Read the specs of the preamp and find "output voltage".
Read the specs of the power amp and find "input sensitivity".
Those are the main two parameters to look at.
I have an Alembic F-1X tube preamp. The output voltage is 1 volt.
I have a Fender MB1200 power amp. The input sensitivity is 1 volt.
That means my preamp has the capability (the "horsepower" if you will) to drive the power amp to its fully rated output power.
If my Fender power amp had an input sensitivity of .775V, then I could easily drive my power amp using my 1 volt output preamp and have horsepower to spare in my preamp. If my power amp had an input sensitivity of 1.4V, then my 1 volt output preamp would not have enough horsepower to drive my power amp to its fully rated output power.
Hopefully that info helps!
Perfect! Thanks so much, sacto.
You are very welcome, good sir!
Oddly enough, a lot of manufacturers don't seem to list output voltage in their manuals for preamps. Seeing output level instead, and that's in decibels.
.775 volts = 0dB - a few power amps' input sensitivity
1.0 volts = +2.2dB
1.2 volts = +3.8 db - many power amps' input sensitivity
1.4 volts = +5.14db - some power amps' input sensitivity
Ahh, good stuff. So, according to this www.bbesound.com/products/instrument-preamps/bmax.aspx the bmax should more than adequately drive the RMX850 I have. The RMX850 has an input sensitivity of 1.15v.
The Alembic F2B is the classic worst case that I know of. It has a high output impedance and although Alembic says 10K or higher works OK for a load, in my experience a bit higher tends to work better, or at least did with the one I owned. As long as the load is 10X or more the output impedance of the preamp, no worries; below that it's one of those "just depends" deals.
Knowing just the max output voltage of the preamp is not always a perfect indicator of how it sounds at that level, or how much EQ boost, drive, how hot a pickup, etc., it takes to get there. For example, the early BMax version was plenty hot for driving any amp I tried it with, but keeping it dead clean and doing that was a bit tricky in some cases. I've heard that they later toned it down some on front end gain though, which worked a lot better for me when I did that mod myself. And of course, in many cases you may never need to fully drive a big power amp anyway.
Oh, man. I see why so many people just use amps that are designated bass heads. Good info, though. Thank you.
It's not always that dire by any means, but I would highly recommend trying stuff first or buying used at prices that allow painless flipping.
As I know so very little technical information/ application..I have employed blind luck with great success.
In my quest for 'tone-supreme', I purchased a Furman PQ-3 [ 3-band fully parametic EQ and pre-amp....either use the preamp or the EQ individually].
I used my Furman front-end..into my trusty 1971 Kustom 200-B head. which vastly improved tone and volume..made an otherwise anemic amp sound awesome. Once at a jam, I was actually asked to turn down by an humbled guitarist.
Of course I would love to run my pre amp into raw power amp, with the Furman as tone/ volume control. My only regard for the amp specs would be watts RMS and distortion %.
Ignorance is bliss..proving that sometimes we over think things too much.
I M O ..Probably whatever amp you can afford will be well suited to whatever pre amp you use.
When it doesn't work it's very unsatisfactory. You've got this rack with a serious looking pre and pwr amp into some cabs and the 1x15 combo from the opening act blows it away.
There is a point when if the pre isn't putting out the right voltage that there just is no more volume from the amp. This may be right when the drummer starts playing.
Crank that amp and you're amplifying nothing. The tone is weak, you can hear it but all the punch is missing. Or it is full in some frequencies and appears to disappear in others.
My comments come from gigging pre amps and pwr amps live in duos, trios, and large band settings. The same rig that sounded like it would work from my home practice would be woefully inadequate live. I'd shake my head and wonder why my 1000w was so weak. Drummer is frowning, honeys aren't dancing.
This isn't rocket surgery. One just has to obey the laws of physics or electrical engineering in this case.
"It should work" or "it's called a bass pre" or "it's +4" or on TB "it works for me" won't save the gig if you've ignored the facts.
Bringing the big boom is our job. The band will rock with other players and frequencies missing. If we sound flaccid the whole presentation suffers.
Separate names with a comma.