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PL 700 Pro Build
- Thread starter George S.
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The Cylons calibrated perfectly. Going to screw down the top plate and hook her up to the JBL Millenniums and listen to some music. Next weekend she'll be doing sub duty.
Looking at it I'm not struck or impressed by what I've done building this from a kit. What impresses me is one man had the drive and desire to engineer and produce such a complicated, sophisticated machine, and offer it to us.
Thank you Joe.
Looking at it I'm not struck or impressed by what I've done building this from a kit. What impresses me is one man had the drive and desire to engineer and produce such a complicated, sophisticated machine, and offer it to us.
Thank you Joe.
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- Those who enter the man cave will get WOPLed
Yup, different. Not as elegant as the other 700s. I think the Clair's are better looking.
So last night I played a Robin Trower digital file through her, then listened to some FM between the dog walk and locking up the house for the night. It works well, and somehow is slightly different from the 400 WOPLs, hence the following question related to the 50k attenuators in the 700 versus the 100k in the 400.
I think Joe has answered this, but I don't quite understand, so here's the question. If I measure resistance at a RCA jack between the center conductor and shield, I see close to 50k ohms on the 700 and 100k ohms on the 400s because of the pot value. Does the preamp "see" this resistance and what are it's effects?
So last night I played a Robin Trower digital file through her, then listened to some FM between the dog walk and locking up the house for the night. It works well, and somehow is slightly different from the 400 WOPLs, hence the following question related to the 50k attenuators in the 700 versus the 100k in the 400.
I think Joe has answered this, but I don't quite understand, so here's the question. If I measure resistance at a RCA jack between the center conductor and shield, I see close to 50k ohms on the 700 and 100k ohms on the 400s because of the pot value. Does the preamp "see" this resistance and what are it's effects?
Yes your preamp does see this input impedance, for sure. The consequence depends on your preamp output stage. Recall that the series 1 PL400 with no pots in the signal path present 49K ohms to the preamp. So your 700 measurement is very close to that.
If your Pro 700 pot is all the way up, you should see somewhere around 25K ohms (50K pot in parallel with 49K control board input resistance).
As I mentioned earlier, the Acurus pre that I use has an output impedance of 47 ohms so it doesn't really care if it is driving 25K ohms or 100K ohms and will have negligible effect. If your preamp has 50K output impedance then you will see some effects related to the preamp that is driving the amp, such as you will have to turn the preamp output up more to account for the attenuation of the combined preamp/amp resistor network.
If your Pro 700 pot is all the way up, you should see somewhere around 25K ohms (50K pot in parallel with 49K control board input resistance).
As I mentioned earlier, the Acurus pre that I use has an output impedance of 47 ohms so it doesn't really care if it is driving 25K ohms or 100K ohms and will have negligible effect. If your preamp has 50K output impedance then you will see some effects related to the preamp that is driving the amp, such as you will have to turn the preamp output up more to account for the attenuation of the combined preamp/amp resistor network.
I was seeing much higher gain out of the 700 versus the 400s for a given volume setting. Seemed like the difference in the higher # of outputs didn't totally account for this, and the pot values did.
For those of you reading and wondering about this, note this is with the pots at minimum value close to zero ohms. If I measure resistance of the center conductor from the RCA to the control board, the value is close to zero ohms.
This question has to do with the resistance measured at the RCA between the center conductor and the shield.
Joe's given us something to think about and ponder.
For those of you reading and wondering about this, note this is with the pots at minimum value close to zero ohms. If I measure resistance of the center conductor from the RCA to the control board, the value is close to zero ohms.
This question has to do with the resistance measured at the RCA between the center conductor and the shield.
Joe's given us something to think about and ponder.
The other effect that is noticed when more outputs are added is that the Cob increases with each additional output device that is added. This is the total base capacitance seen by the driver transistor (the first MJ21195 or 96 in the output chain) which drives these paralleled bases. Thus it becomes harder to drive the output stage (you could use the analogy that it becomes more sluggish). As a result of that, the op amp will have to drive harder to correct for this and thus will require more error signal to produce that drive. In simple terms, this means the amp distortion increases slightly as you add each output device.
This is a real world effect, if the transistors were ideal devices, they would not have this base capacitance and you could add an infinite number of output devices without degradation.
This is a real world effect, if the transistors were ideal devices, they would not have this base capacitance and you could add an infinite number of output devices without degradation.
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Thanks! Will eventually revisit the preamps and tuner once I gain more skill and equipment. There's still more to be done, especially with those plastic output jacks. Was thinking about it this afternoon, still not resolved on the best solution. Luckily I still have the test preamp to play with to figure it out.