Alto D1 power amp can't be driven to maximum gain

Damokles · #1 10-20-2010, 09:14 AM

Hi there,

currently my rack consists of these three main components (BBE BMax, Engl e530 (both are used as separate preamps) and an Alto D1 Class-D power amp).

My problem with the power amp is, that even with the gain and master knobs on both the BBE or the Engl turned fully clockwise it is not possible to light up the signal LED on the Alto. I already made sure that the power amp works properly.

The Alto has an input impedance of 10 k ohms unbalanced and an input sensitivity of 1 Vrms.

The BBE has an output impedance of 1 k ohms unbalanced, the output sensitivity is (if I get it right) 0.775 mVrms.

So my main question is, how to transform the signal to the corresponding values ofthe Alto? Could a DI-box do the job?

Regards,
Damokles

bongomania · #2 10-20-2010, 10:26 AM

A DI box absolutely cannot do the job, unless it is one like the "Sansamp" product line that's more of a preamp that the manufacturer just calls a DI.

Generally speaking, a DI box is for balancing and signal isolation. What you need is a gain stage. A clean boost, even from something as simple as an EQ or compressor, or anything that has a gain stage.

T-Bird · #3 10-20-2010, 10:45 AM

Hi.

What bongomania said.

What you do need is some sort of a third amp stage between the pre's and the power amp, but that will increase hiss. A small mixer would most probably do the job, as long as it's output is at least 1Vrms.

Most modern amps can be switched (internally) for different sensitivities AFAIK, so contacting Alto may be the wisest course of action.

Regards
Sam

Damokles · #4 10-20-2010, 10:46 AM

@ bongomania:Thanks! Since I'm not experienced at all with electronics and stuff it was what made most sense to me. So a pedal like the MXR MC 401 would be ok?

Bob Lee (QSC) · #5 10-20-2010, 10:57 AM

A BBE BMax can put out several volts. Make sure you use a line-level output.

Damokles · #6 10-20-2010, 11:03 AM

@ Bob Lee: According to the manual I connected the BBE and the Alto via the main out of the BBE. So it should be at line level

rpsands · #7 10-20-2010, 11:07 AM

Check with the power amp vendor; there could be a switch or something or a jumper that's adding extra attenuation to the input signal. Crest amps very often have a high and low sensitivity setting, for example.

A Bmax should be able to overdrive the hell out of a 1vRms input.

M0ses · #8 10-20-2010, 11:10 AM

Quote:

Originally Posted by T-Bird

Hi.

What bongomania said.

What you do need is some sort of a third amp stage between the pre's and the power amp, but that will increase hiss. A small mixer would most probably do the job, as long as it's output is at least 1Vrms.

Most modern amps can be switched (internally) for different sensitivities AFAIK, so contacting Alto may be the wisest course of action.

Regards
Sam

A mixer is the last thing I'd use to get a dB boost. They're designed for a completely different job and would be super clumsy. How about, I dunno, a boost pedal?

Bob Lee (QSC) · #9 10-20-2010, 11:10 AM

A line-level output (including on a BMax) can put out several volts. You have the manual, so check it and make sure you're using the right one.

How do they define "output sensitivity"?

Damokles · #10 10-20-2010, 11:34 AM

@ Bob Lee: As mentioned before I#m using the "Main Out", just as suggested in the manual! Output sensitivity is not defined in the manual.

Bob Lee (QSC) · #11 10-20-2010, 11:39 AM

Yes, and make sure you're using a line-level output. The "Main Out" might or might not be. That's what you need to check out. A BMax is capable of several volts out, and IIRC it has more than one output. So you have to make sure you're using the right one.

Damokles · #12 10-20-2010, 11:42 AM

Well, the other option would be the DI-out or the send of the effects-loop. More outputs don't exist!

bongomania · #13 10-20-2010, 11:43 AM

Quote:

Originally Posted by Bob Lee (QSC)

A line-level output (including on a BMax) can put out several volts.

I don't know about the BMax specifically, but I can absolutely say that a large percentage of rackmount bass preamps are not capable of putting out "several volts" at normal EQ and input gain settings. Maybe if you dime the EQ knobs and drive the input into clipping, then you can get "several volts", but by and large you are lucky to get 1V RMS.

The hangup is that you are thinking "line level" means +4dBu, which it does in recording studios and pro PA systems. But in a surprising majority of bass preamps, the "line level" output is at either -10dBu or 0dBv.

What's weird is that mic preamps and channel strips are all made with the +4dBu in mind; it's only the bass-specific preamps that run the bogus lower output levels.

Bob Lee (QSC) · #14 10-20-2010, 11:55 AM

Quote:

Originally Posted by bongomania

I don't know about the BMax specifically, but I can absolutely say that a large percentage of rackmount bass preamps are not capable of putting out "several volts" at normal EQ and input gain settings. Maybe if you dime the EQ knobs and drive the input into clipping, then you can get "several volts", but by and large you are lucky to get 1V RMS.

The hangup is that you are thinking "line level" means +4dBu, which it does in recording studios and pro PA systems. But in a surprising majority of bass preamps, the "line level" output is at either -10dBu or 0dBv.

What's weird is that mic preamps and channel strips are all made with the +4dBu in mind; it's only the bass-specific preamps that run the bogus lower output levels.

That's all true (except for the part about what I'm thinking about), but unless they recently redesigned the BMax, it's capable of several volts out.

The "+4 dBu" (1.23 V rms) level you refer to usually used as a nominal or average level, and equipment designed to run at that level can typically put out at least 10 V rms before clipping. I'm not claiming that the BMax does this, but the last I saw of one, its line out could put out several volts before clipping, just as its predecessor (the 383) could. That's way more than enough to drive a power amp that has an input sensitivity of 1 V. Keep in mind that an amp's "input sensitivity" is the input voltage that at maximum gain will drive it to the threshold of clipping, not the average or nominal level of the input signal.

Damokles · #15 10-20-2010, 12:08 PM

Thanks to bongomania again. I checked the manual again and the maximum output is +22dBu, so I guess Bob Lee is right when he speaks of several volts. So I guess the power amp is the troublemaker.

What confuses me the most: When I turn on the power amp and hit the strings just immediately I manage tolight up the signal LED and the clip LED.