Jer's PLWO to be... (Jer vs the 700, Round 2... it's "Personal" this time)

[jbeckva]

Shit.. look at this guys!

This is basically the same thing I saw on the other channel. Whoever replaced this cut the dang lead way too short. On this channel it was the base lead.. aint that some crap??

Well I'm going to try the same thing.. all depends tho on how much clearance I need for the heat sink that goes on top.

This is one of those MM4003's. For all I know I might have the modern replacement for it? What should it be replaced with?

 

[mlucitt]

The bias (operating, not output) voltages for Q6 come from voltages dropped by R33 and R34. I would check both of those for value drifting, R33 gets hot in operation. The voltage for the base of Q6 is further reduced by the diode string of D5, D6, and D7. Other components that could affect Q6 are D8 and the overload transistor Q7. You can remove Q7 and Q8 for testing because they can influence your readings if there are problems in the outputs. Just remember to put them back in after you locate the problem. Some people leave them out and claim the amp sounds better, I think not.

The PNP MM4003 can be replaced with 2N5415 or 2N5416.

Good Luck

 

[jbeckva]

Had just enough lead left. That's more like it!

 

[jbeckva]

Thanks Mark.. I'll see if I have some around. It is almost like the leads rotted off.. maybe someone using acid flux??

in the meantime.. 20mV right, 10mV left offset.. (dem' pots ARE touchy!!). Time to bring out the scope and dummy loads...

 

[laatsch55]

In a 700 don't use the '15, go with the '16

 

[laatsch55]

Dem pots are touchy, amen.

 

[jbeckva]

Well heck!

Put it as far as I dare to go (Lee ya got bigger kahones .. and dummy loads too.. heheh). I still need to get a voltage divider made up so I can see where it clips, but as far as I could tell with the traces all the way down, I couldn't see the clip at all.. Pushed it at 60, 440, and 15K... no problemos at all...

I guess I could listen.. hmmmmm... I just don't want that turn on n off thump that would probably happen without having the DCP installed.. but I know curiosity is going to get the better of me...

 

[jbeckva]

ps.. Power's been off of it for 10 mins and them lil dummy loads are still nice and toasty!

 

[laatsch55]

It may not thump at all Jer, offset's pretty close. I'd say a kerfluffle is all.

 

[laatsch55]

measure the voltage, where it goes buggers is clip.

 

[jbeckva]

Too late.. curiosity's got me so I'm puttin' the plates back on now.. hehe

btw.. I did get them caps... almost time to "hot rod" it...

 

[jbeckva]

Hah.. damn that's a THUMP... enough to probably wake up shebear downstairs...

But... hell... it's ALIVE and SINGING.. Sounds pretty good for a non Joe-boarded PL. But as ya know Lee n Joe and others.. it can sound better!

Yup.. I can deal with this heheh

 

[jbeckva]

But hmm.. yeah.. still has some rough edges... I notice it in the bass region where I can hear some distortion going on there.

Time for some parts ordering to take 'er up to the PLWO standard... Lee you're going to still want that 071 board, right?

 

[jbeckva]

ps... shebear did get me...

 

[laatsch55]

Yep, I do want it.

 

[mlucitt]

Shebear is probably the one that told you about the bass region distortion.

 

[Gepetto]

No turn on or off thump with the Rev C board Jer

 

[jbeckva]

No turn on or off thump with the Rev C board Jer

Looking forward to getting one for it. I suspect the pots on the old board really can't stand still very well (for example). Bet the DC offset drifted a little bit plus the bias?

Hey as Lee said I'm going to need those outboard bias transistors too, right? Where can I get the metal case straps, or do I need to find some old ones that have been shot to rob off of?

 

[laatsch55]

I have some converted and ready to go with the new 5088';s in em.

 

[jbeckva]

Ok, seems we got's the parts a comin, one way or another (dem caps? hmmm... those might be delayed as they're coming in from NJ)... thanks Joe and Lee!

Now in the meantime... just wondering here... The basic issue is it seems that the amp just doesn't "have it", but only in the low end... It is like the amp's out of juice! I can hear some very audible "bad juju" in the low end, if playing music through it with a bit more demanding bass than a typical "beat", per se. But aside from that, I sure heard some GOOD sound from it too, the other night!

Think it could be them caps? Not enough spare capacity left for transient storage, perhaps?