Altec 811B Horn + Big Woofer DIY System

Could be the not-super-intuitive minidsp interface. For troubleshooting, unhook the tweeter amp (so you don’t blow anything), try to get the woofer amp outputting full range music through the woofers. Once that works, try to configure a low pass xover on woofers. Once that’s working you’ll prolly get the tweeter part going just fine.

 

Ps: my minidsp pops when loading a config from file. In case that explains your popping...

 

Well im stupid, I just found that my dac had switched inputs. I just tested the tweeter amp, as its also a headphone amp, and it worked fine. Ill try everything now.

 

No, popping still happens every time I turn on the woofer amp. I tried disconnecting the minidsp, then turning on the woofer amp, no pop. Something with the minidsp is causing the popping. Im not sure if sound would still play after the pop, but im afraid it will damage something, so I turn the amp off.

 

Are you hooking the amp up directly to the horn tweeter? You really need a capacitor to block DC.

 

yeah, but the popping is in the woofer. Im not sure if it happens in the tweeter.

 

Ok, really weird, it happens even with the outputs of the minidsp muted...

 

Ok, so im stupid, again. I wired the one speaker wrong, I connected amp 1 to woofer + and tweeter -, amp 2 to woofer - and tweeter +.

However, a new issue has arrived. Everything works properly now, crosses over frequencies right. But there is a very loud hum in both the woofers and tweeters, a higher pitched hum in the tweeters. If I lower the volume on the tweeter amp, and increase pre amp volume to get to same level, no hum. However, woofer amp doesn't have volume control, so I cant do this. Any thoughts on what this is?

 

Reading this article here, it seems like I might have a problem with gain structure, and my amplifiers have too much gain? I tried changing the input sensitivity jumpers in the minidsp too, and that didn't help.

 

Aha! lowered the gain in minidsp software, fixed it!

 

If you are wondering right now how I could make so many stupid mistakes, I invite you to look at my setup. Instead of using 4 conductor wire, I used 2 2 conductor speaker wires, so a cabling mess:

Excess speaker wire going to speakers:

 

I'm getting you some Techflex for your birthday

Also, this stuff is pretty decent for the price: https://www.monoprice.com/product?c_id=102&cp_id=10239&cs_id=1023902&p_id=4042&seq=1&format=2

 

Yeah, 4 conductor speaker wire would have been better, but the 2 conductor wire I used was free because I already had a roll...
PLus its a temp setup until September when I move it into college.

 

How does it sound?

 

Im working on fine tuning it still, plus been pretty busy, so haven't really listened yet. Ill update once I do.

 

Ok, so my right woofer sounds terrible. There is heavy distortion, sounds like distorted guitar. Not sure why...

 

Switched it back to not bi amped, woofer was like that the whole time, just not as noticeable as the tweeter was a bit over overpowered. I think I know why... I noticed significant voice coil sag, I could feel it rubbing on magnet when pressing it in. I flipped the woofer to try and undo this, but it seems it's too far gone. I'll have to recone or get new one.

 

This happened to me once. After a looot of troubleshooting I figured that the minidsp started processing biquads as if they were for 48 Khz sampling rates instead of its native 96, effectively ruining all the filters. Firmware update fixed it. Not sure if that's applicable to your problem, but still chipped in. No idea how it's possible it happened on one channel, or how it happened at all.

 

Thanks, but I tried removing the mini dsp and I still hear it.

 

Swap L/R channels, see if it persists. Might tell you if it's in the woofer/box or amp/pre.