Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

[laatsch55]

Offset lrft channel---.002, offset right channel---.012 Bias left channel .375 in the middle of adjustment range, Bias right channel--.375 at 1/3rd of adjustment range.

 

[laatsch55]

THD & N coming up.....

 

[laatsch55]

Misc first... 2 watts into 8 ohms...

 

[laatsch55]

God I love this analyzer...

 

[laatsch55]

Left channel, THD & N 1` watt into 8 ohms...

 

[laatsch55]

Still got some work to do here.................

 

[Gibsonian]

Cathy is misbehaving badly! Just glad she is with you and not me during these trying times Lee.

 

[laatsch55]

As you know Scott most of those were self-inflicted, although we are learning a ton from it. Thank you for your patience. How's the Spec 1 project going??

 

[laatsch55]

BTW-- the waveform for the severly distorted section featured a very sharp top, not very round.

 

[Gibsonian]

Spec 1 project has not moved. Parts received but still in box. I've been rebuilding some crossover and drivers for friends lately.

 

[Gepetto]

BTW-- the waveform for the severly distorted section featured a very sharp top, not very round.

That is to be expected Lee with no bottom side pulling against the top side that has that bootstrap working for it...

 

[laatsch55]

This is after the left channel fix. This is the right channel acting up now, and R41 is good on it.

 

[Gepetto]

Is the left channel offset now solid with the range of bias settings?

 

[laatsch55]

Yes it is Joe, and THD & N was good, gain was good.

 

[laatsch55]

Offset was amazing----.001

 

[Gepetto]

So is the right channel offset stable with the range of bias settings? You indicated earlier that it may not be.

Here is the output stats on the last 700B that I had through here.

 

[Gepetto]

Lee

Output offsets are typically -0.009 to -0.011V based on the front end bias current through the 39K resistor with the inputs totally open and nothing connected.

Was that with inputs grounded or open (that is, not attached to anything)?

 

[laatsch55]

DAYAM!! Those are some good numbers!! Talked to AP the other day, they recommendede 75 ohm Rg because the 75 was much better shielded than the 50 ohm. Got some made up test cables on order.


Why are MF resistors so much more expensive than MO??

I'll get it warmed up and check that Joe.

 

[laatsch55]

Lee

Output offsets are typically -0.009 to -0.011V based on the front end bias current through the 39K resistor with the inputs totally open and nothing connected.

Was that with inputs grounded or open (that is, not attached to anything)?

Inputs hooked to the AP with the AP off.

 

[Gepetto]

Yeah I worked that amp over to get those numbers Lee. It started with several percent TH+N. I was pleased with the L/R consistency and it was all stuff attached to the chassis that I did to improve that.

Not sure on the resistor question Lee. MO are not precision on value, typically 5% but they are low noise, non inductive and rugged whereas metal film are precision on value and have lower tempco than MO. I think it boils down to MO being easy to make and MF not easy to make.