Jer's 400 PLWO Thread

[jbeckva]

Throw some 909's on there...

Not the one's I pulled out... even if I test 'em, I wouldn't trust 'em.

Why is the 15024 an issue with the 400, but not the 700? That's what I have in my 700... 15024 drivers and 21196 outputs (close nuff to the 21194's, right??)

 

[laatsch55]

They're an issue with the 700 too.

 

[laatsch55]

The reason I use the 21194's is that I think they sound a wee bit different than the 96's, ........uhm....sweeter... perhaps...

 

[jbeckva]

They're an issue with the 700 too.

Whaaaa? I've had the 700 running fine for five months!

 

[laatsch55]

And I've sent out a few 700's with em as drivers also.It's not an everytime thing, but the chances of oscillation are greater with the 24's as opposed to the 410's.

 

[Gepetto]

Thanks. Well I didn't see so much ringing as I did overshoot, and it was definitely better on the 700 so it's not the input signal. But the overshoot is on both halves.. nothing different on the negative half, Joe.

I'll get the 410's back in and see what difference there is. What else besides the 410's can I use that won't cause this?

Predriver transistors with a low Ft. You need one to be the dominant and early pole in the configuration.

It does not matter on the upper half, no local feedback involved with that side.

 

[jbeckva]

Predriver transistors with a low Ft. You need one to be the dominant and early pole in the configuration.

It does not matter on the upper half, no local feedback involved with that side.

When you say predrivers I am thinking you are talking about the ones on the driver board?? Do you mean Q9 and 13, specifically.. and related to what - the outputs Q10-12, 14-16? Can you elaborate more?

 

[jbeckva]

Predriver transistors with a low Ft. You need one to be the dominant and early pole in the configuration.

It does not matter on the upper half, no local feedback involved with that side.

And like I said.. I did not see any asymmetry between upper and lower halves of the waveform, but I did see significant overshoot on both leading/trailing edges. Is that also a symptom of this, or is that something else entirely?

 

[Gepetto]

When you say predrivers I am thinking you are talking about the ones on the driver board?? Do you mean Q9 and 13, specifically.. and related to what - the outputs Q10-12, 14-16? Can you elaborate more?

Output predrivers are Q11 and Q12, normally the RCA410 or SJ2741 devices.

Output drivers are Q13-Q18 in the PL400.

Q11 predriver works in Darlington mode with drivers Q13,15,17
Q12 predriver works in Darlington mode wiht drivers Q14,16,18

These are all on the back wall of the amp.

 

[Gepetto]

And like I said.. I did not see any asymmetry between upper and lower halves of the waveform, but I did see significant overshoot on both leading/trailing edges. Is that also a symptom of this, or is that something else entirely?

That is good that the symmetry looks good Jer. The overshoot is fine as long as it is slight and does not ring after the overshoot. Some of the overshoot may be instrumentation (scope) related depending on the speed of your Oscilloscope and where your probe ground was attached to.

 

[jbeckva]

That is good that the symmetry looks good Jer. The overshoot is fine as long as it is slight and does not ring after the overshoot. Some of the overshoot may be instrumentation (scope) related depending on the speed of your Oscilloscope and where your probe ground was attached to.

Thanks Joe. To clear the air as to why I'm asking, I did start to notice something "off" which was only on the left channel. Basically at low levels, I started to hear an intermittent "cutout" where it sounds like a scratchy pot. I am wondering if what I am hearing is really this oscillation issue or perhaps I knocked something loose in replacing the predrivers. Going to open it up again this evening and check things out...

 

[Gepetto]

Thanks Joe. To clear the air as to why I'm asking, I did start to notice something "off" which was only on the left channel. Basically at low levels, I started to hear an intermittent "cutout" where it sounds like a scratchy pot. I am wondering if what I am hearing is really this oscillation issue or perhaps I knocked something loose in replacing the predrivers. Going to open it up again this evening and check things out...

Let me know what you find Jer.

 

[Gepetto]

Relay dirty? My Yamaha does that at low levels sometimes, got to replace the speaker relays one of these days.

 

[jbeckva]

Relay dirty? My Yamaha does that at low levels sometimes, got to replace the speaker relays one of these days.

The relay's part of the DCP - brand new.

Well since the channel where I heard the anomaly was the same one with the blown up socket (actually the one for Q13!), I figured it may be a good idea to replace the socket for Q9 too. Q10's socket looked kind of weak so both of those.

Listening now.. so far, so good.. no probs. Joe can you explain more about how gain between the drivers and predrivers can cause this condition? I'm really curious to know how it all works.. really!!

 

[laatsch55]

To put it in parts changer terms------ Cause if the trannys are to close in parameters and things are hot and heavy, pretty soon the driver wants to output and the output wants to drive.

 

[jbeckva]

To put it in parts changer terms------ Cause if the trannys are to close in parameters and things are hot and heavy, pretty soon the driver wants to output and the output wants to drive.

Ok, so I think Joe said it was the GBP that mattered? Yeah in that case the predriver and outputs are both 4MHZ, whereas the RCA410 would be 2MHZ. If it was the gain tho.. hmm.. the 15024 is rated between 15 and 60 @ 8A.. the 21194 between 25 and 75.. RCA 410 I think.. 10 minimum? (only thing I could find).

Still listenin... no smokin'..

 

[jbeckva]

How about a 2N6547?

http://www.st.com/web/en/resource/technical/document/datasheet/CD00002665.pdf

12 to 30 gain, 3MHZ, 850V/15A... hmmmm...

 

[laatsch55]

Hmmmmmmmmmmmmmmmmmmmm......................

 

[Gepetto]

I said it was the Ft Jer, the transition frequency. Effectively where the dominant pole of the transistor occurs, its 3dB point.

 

[jbeckva]

Hmmmmmmmmmmmmmmmmmmmm......................

BUV22G?? Just thinking man.. they don't make the 410's anymore, do they... just too "dark" a sound for me...