Home Brew Al K Universal crossovers.

[Gepetto]

Among other things...

There are only 3 of the small(est) boards inside the PL4000 that matter, the RIAA Phono Amp, Logic Board and the Tone Amplifier. The rest of them are junk that gets bypassed when you put the Peak Unlimit, Active Equalizer and Correlate in the OUT position.

These 3 boards are all straight Class A amplifiers, simple gain circuits that rely on discrete transistors, TIS93 and 97.

The coupling of the volume pot to the Tone Amplifier is critical. If a poor connection exists between the 2, you get a nice wall-wall 48KHz square wave output that will blow all the fuses in your amp in a heartbeat.

 

[laatsch55]

I still have a gob of 93's and 97's if ya need some. 48khz square wave eh??/ Coolness...

 

[Gepetto]

I still have a gob of 93's and 97's if ya need some. 48khz square wave eh??/ Coolness...

Yeah I have a boatload of them too Lee, from you

Yes, the circuit becomes a very stable oscillator when the connection is bad right where they decided to partition the circuit. It bleeds into everything inside the preamp when it goes off.

This thing is not a paragon of low crosstalk.

 

[laatsch55]

I guess that means a great amp guy does not a great pre-amp guy make...

 

[Gepetto]

I guess that means a great amp guy does not a great pre-amp guy make...

Not even close Lee. Single 35.5V rail powers it rather than a split +/-18V setup which is far more common. I had 150mV of DC offset on one output and 275mV on the other (and this is a preamp). Leaky, cheap electrolytic caps. You can imagine what that does to the front end and DC offset at the amp output.

 

[laatsch55]

Blows it clean out of the water!!

 

[laatsch55]

So when is Joe gonna design a pre-amp his amps are worthy of?

 

[laatsch55]

A couple years ago I had dialed back the mid horns because they were over powering the woofs, gonna have to change back to the original tap settings now. For all my yappin about hearing this and hearing that, I couldn't even tell my speaks were out of phase..............

 

[BubbaH]

Could one of the speaker guru's enlighten us to what out of phase actually is, and why its important. Ive heard a few peeps tell me that my setup would be out of phase for running 2 amps with 2 different sets of speakers. Its always sounded great to me, so I just pushed that aside. Never really put much thought into it, and would like to know more. Always had the "if it aint broke" attitude towards my setup.

 

[laatsch55]

When running the + lead of the left channel out to the left speaker and hooking it to the - side of the speaker posts and the right channel hooked + to + and - to -, you are thusly out of phase. As one woofer is going out the other is going in, in effect cancelling a lot of the acoustical output.


Now why running 2 amps and 2 sets of speakers would in and of itself make them out of phase, that doesn't make sense....

 

[Gepetto]

When running the + lead of the left channel out to the left speaker and hooking it to the - side of the speaker posts and the right channel hooked + to + and - to -, you are thusly out of phase. As one woofer is going out the other is going in, in effect cancelling a lot of the acoustical output.


Now why running 2 amps and 2 sets of speakers would in and of itself make them out of phase, that doesn't make sense....

in of itself, running that configuration should not matter from a phasing perspective. Even if the amp was inverting (doubtful) that can be fixed by flipping the speaker leads to compensate.

 

[laatsch55]

With the 700 on these running at Mach 8 they are F%^%&*^ DANGEROus!!!!!!!!! Nothing in the mancave stands a chance...

 

[laatsch55]

Jazz couldn't take it..

 

[BubbaH]

Thanks for the response's Lee and Joe. Typically I keep the + and - the same on the 901's. But as for my Elites they have an XLR at the speaker end, will that matter if +/- are reversed on the amp? If so then ill need to figure out which side is which and follow the cable from the XLR to the amp. There is no indicators on the wire itself and they are 40 feet long.

 

[Gepetto]

Thanks for the response's Lee and Joe. Typically I keep the + and - the same on the 901's. But as for my Elites they have an XLR at the speaker end, will that matter if +/- are reversed on the amp? If so then ill need to figure out which side is which and follow the cable from the XLR to the amp. There is no indicators on the wire itself and they are 40 feet long.

You bet it will matter. XLR is differential and converts internally to single ended inside the amp usually. They have a +/- convention on XLR wiring but who knows if that was observed or not.

 

[laatsch55]

10 seconds with a DMM will tell you.Standard XLR is Pin 2 is signal positive, pin 3 is signal negative, pin 1 is shield..

 

[BubbaH]

They are bare wire at the amp end. How would I test them? Simply for continuity?

 

[laatsch55]

Yes, and mark them to coincide with what you have at the speaker end. Are the pin designations marked on the speaker connection legend?

 

[BubbaH]

Yes, pin 1 is ground 2 is hot.

Ill have to pull each wire out and test for continuity on 2, then ill know which is + and which is -.... cool thanks guys.

 

[laatsch55]

Makes a hell of a difference if they're phased right, I know that...