PL700B's...White Oak or Pine Box

[grapplesaw]

Glen , have you successfully bridged a 700 and tested it?

I built the bridged amps to see if I could. I

Glen , have you successfully bridged a 700 and tested it?

i think that bridging the 400’s are nice option as you can use regular house breaker. must use 16 or 8 ohm speakers. The 400’s rail voltage is best fit for the mj21195/96 combo.

 

[laatsch55]

Have you tested one?

 

[grapplesaw]

Have you tested one?

I have not Blown it up if that‘s understandable Lee. I have taken the 700 up passed 1400 watts then tripped the circuit breaker. I need to get back to a proper go at it with a 20 amp circuit.

 

[laatsch55]

That's all I was askin Glen..just wondered if ya had. How did distortion look?

 

[grapplesaw]

That's all I was askin Gl.1en..just wondered if ya had. How did distortion look?

if memory serves me it was about .012%. Not bad considering. When I get back home I’ll upgrade the power supply and see what it does. Lee there is not enough power supply head room for continuous output in my opinion. But for that big base note is seams to be enough.

 

[laatsch55]

I hear ya there Glen..

 

[Peter S]

1400 Watts sounds good already! I already have 4 breakers dedicated to the amp rack. I am prepared to run #12 and change 2 breakers to 20 Amp. I can't imagine this would be necessary, as I have seen a clip light flash on the Crest, and it is driving the two LF channels from a single 15 Amp breaker.
My concern at this point is; how stable is a PL700 driving a 4 ohm load, which I assume would be the effective current/voltage ratio for the amp in bridge mode driving an 8 ohm load. Would the higher precision emitter resistors in the WO backplanes be vital to this application?
Has anyone power output tested a WOPL'ed 700 into a 4 ohm load? (in regular stereo mode)

 

[laatsch55]

Yes, into a 4 ohm load, 770 watts before taking out 5 amp rail fuses.
The PT 2400 has 2 dedicated #12 power cords, one for each channel.
Perusing the 2400 specs Glen posted, they showed 818 at clip, I showed 838.

 

[mlucitt]

taking out 5 amp rail fuses.

Amazing that the 5 Amp fuses lasted that long. So, with 8 Amp fuses... more than 775 Watts with both channels driven?

 

[laatsch55]

That's my guess Mark but never went that far. That was one channel driven. I think the power supply would run out of gas there or a little lower.

 

[Peter S]

So here is the manual I bought in 1979 for my first PL, a 700. It suggests installing 8 amp fuses for "Industrial or PA use" I now see a spec for power into 4 ohms.
About Bridging, I am driving the amplifiers with a miniDSP 4 x10 HD. The DSP functions as pre amp, EQ, and Crossover. It has unbalanced RCA as well as balanced outputs with up to 8 V RMS. Could I connect two series resistors (maybe 1 k ohms each?) across the +and - balanced output, then ground the centre point to the PL input ground. The + side of the resitor string would drive one channel, the - side would drive the other.
Voila! Amplifier is bridged! Am I missing something?

 

[Gepetto]

Balanced source outputs provide you with a lot of flexibility. Direct use into a single ended connection may subject you to a certain amount of common mode noise since signal purity is defined from hot to cold not from hot to ground or cold to ground. This will vary depending on the design of your source.
Try it and see what results you achieve.

 

[Peter S]

I will have to test and report back, this was my wishfull thinking

 

[Gepetto]

I will have to test and report back, this was my wishfull thinking

Low cost balanced to single ended converters exist to do this task. You can flip one channel balanced input to such a converter, swap hot and cold.

Samson S-Convert RCA To XLR Converter With Power Supply | eBay


Nobsound makes a few low cost offerings too but haven't dug into their lineup.

 

[Peter S]

My first 700B has a non functioning left VU meter. It is the coiled spring with jewel bearing type rather than the torsional ribbon. One of the coils broke, years ago. I was actually able to reattach it, the outer end of the coil was the issue. It held for 20 years but now the inner end of the coil has broken from the armature connection. This time it's down for the count, I'm afraid.
Anyone have a spare meter kicking around?? Bet this is not the first time someone has asked!

 

[Peter S]

(Thanks, Joe)
I think I've had my dose of Phase Linear blues for the weekend. I swapped meters from one of my newly acquired wrecks, only to find that the Torsional band type meters are ever-so-slightly taller! Good grief! A couple of those fancy new Chassis are starting to sound nice...

 

[Gepetto]

 

[Gepetto]

Balanced to single-ended converter (XLR to RCA / BAL to SE) | Super Best Audio Friends

 

[Peter S]

Thanks again, Joe. I'm going to experiment with the resistors first. I was really hoping to avoid transformers (probably for no good reason with a good transformer but I have this compulsive aversion because of hum susceptibility, low frequency roll-off, phase shift, bla bla bla)
So more meter muddling; I installed the taut band meters in the old amp and one of THOSE was getting stuck in mid travel. This time, the patient seems to have survived the operation. Black ferrous dust was stuck in the armature gap. It was removed with masking tape and the meter seems to move freely now.

 

[Peter S]

Has anyone considered fitting an 'off shore' movement into the case of a damaged meter?