Hiss and TOO much Gain

Greg OH

I am using the DRPA in an Home audio set up . I built a three way set of speakers , Emmenence , 18 sound, Radian. The preamp is a Bryston BP 25 (Balanced) to the DRPA to two Anthem MCA 30 3 channel amps.( balanced) (vertical TRI amp) . I have the crossovers set and some low end PEQ . I have used the custom setting and it sounds great EXCEPT I have so much gain I can faintly hear music with the preamp turned all the way down. Also I cannot remove the hiss that I can easily hear out my Radian Compression Driver. I Tried an ATTY box and yes it worked , However I would need three and I don't believe I should have to go that route. ????

Dra

Try dropping the x-over gains way down. There will be a point where it will be cleanest... low x-over gain w/ mid preamp gain, very low x-over gain w/ high preamp gain, etc... Just play around with it.

Sorry I could not be more help.
Gadget?

DRA

PS - Some gear has original input attenuation settings.

Greg OH

DRA Thanks

I haved tried -50db on the High end with no effect.

I cannot elliminate the low level airy hiss / I have tried in the wizard section changing the low mid and high amp levels anywhere 0-100 no effect.

Anyone tried fixed ratio voltage dividers? I built one at 20k and 60k and tried it on the high end channel

---

NO luck

PS my amps have a fixed 29 db gain

Dra

Whichever driver has the worst hiss, set up the DRPA to have the same outputs, and connect to whichever amp channel seems to be the cleanest. Then swap hi to mid to low on the DRPA output and see if there is a change in the his level. If not, the preamp is way to hot to start, the DRPA has a problem or the amp.

DRA

Greg OH

DRA

I just read the specs on the BP 25 Looks like 30 volts on the balance outs. 15 v on the RCA . This could be the problem . I believe the DRPA likes 20 v max on the input ???????????

Dra

Do you have (or have the means to make) RCA to XLR adaptors? Sound like you've probably found the problem.

DRA

Greg OH

Yes No problem Thanks

Greg OH

The problem is between the Driverack PA and Amps I turned off the pre amp and still have hiss. ?

Dra

What happens if you remove the DRPA? Hiss or no.

DRA

jakobsladderz

Are you running your amps at maximum gain or do they not have gain controls? If the former then read up on gain structure, the latter and you'll need to make up some attenuators (probably start with potentiometers to let you adjust the levels, read up on gain structure anyway).
you basically want it such the when the amps are just clipping the driverack is just before the reds also. That gives you the best S/N ratio.

Dunc

Greg OH

Dunc and Dra
My amps are Anthem home audio amps with no gain adjustment and 29 db output. The DRPA has 20dbu output . I built one balanced fixed resistive attenuator using PRP metal film resistors calculated at a -15 db attentuation. The test input effectively reduced the hiss and air. However , I am considering using a product that can better handle the high input of the Bryston pre amp (30v balanced) and the high output of the amps 29db. Any suggestions ?????? Quality DSP with adjustable input and output level?

jakobsladderz

From an input point of view the 30v input is not too bad (+20dbu input is 7.75v rms, 10v peak so you're only losing ~4db of s/n ratio on the input, less if you attenuate it).
For the output, the same situation arises, you won't really lose anything in quality terms with attenuation so long as you use appropriate values (i.e. lowest impedance that the driverack will push to minimise noise).
Any DSP with adjustable output levels is either playing with the signal digitally (so no better for s/n ratio) or using digital pots on the outputs (again, questionably s/n and distortion). If you really want to get hi-fi, you can look at tapping into the output from the D/A convertors before the balanced output /gain stage to get a much lower level signal but I guess that is taking it the next step..
29db gain is fairly high for a power amp but sometimes it's necessary to have high gain to make a design stable...

Cheers,
Duncan

Greg OH

Thanks Duncan
Can you refer me to any thread or site to better educate me related to the options of modifying the output stage.

jakobsladderz

This is for a behringer crossover but I think it uses similar d/a converters. you can probably check this forum out for other DIY stuff too


http://www.diyaudio.com/forums/showthre ... ht=DCX2496

Greg OH

http://www.diyaudio.com/forums/showthre ... highlight=

The speakers I am using with the DRPA