Zach's 700B Thread

[laatsch55]

Don, I have the 700 on the bench now, I see an oscillation on it too,, but can't attribute it to your board yet as thi s amp has taken a lot of hits.

 

[Zach C.]

Doesyour 700 havew the bypass caps on the 3 terminal strip on the back wall?? If not it could get funky without a zoebel. When you lifted the zoebel in stock mode did you have the amp loaded? What was your input and ouput voltages?

bypass caps- nope
loaded- 8r dummy load (might be inductive come to think of it, but surely not nearly as much as a speaker )
voltages- not sure. Inputs were open, outputs, IDK.

I'm going to have time to look at this again this weekend, so I'll try to get answers to your questions soon.

thanks,

Zach

 

[Zach C.]

As I recall Zach bought the board from me a year ago and he has been fighting this since then. I'd forgotten all about it. Early on in this thread I thought I saw where he was using a scope and saw an oscillation. Maybe that was somebody else. The 700B fix I previously mentioned returns the amp to the stock, as built, configuration which ties the input ground to the output binding post. Zach, If you want me to look at your amp send me a P.M. I'd like to put this to bed as much as you would.

I have not scoped the output when things are flaky, but I could if helpful.

For the moment, I'd rather keep dinking around with this myself (even if it is with the help of those who know more) since this should (might?) improve my understanding of the problem in the end. This is subject to change, of course.

Also, to say "fighting this since then" overstates the situation. Mostly it just sits there waiting for me to get the time and the motivation to work on it at the same time, which hasn't happened much. It's just a toy. I have a lot of toys.

thanks

Zach

 

[laatsch55]

Loaded with inputs open?? I bet it was pretty noisy in that configuration....

 

[wattsabundant]

Loaded with inputs open?? I bet it was pretty noisy in that configuration....

Once I have an amp completely reassembled, the last test I do before shipping is to pull the input cables and connect my test speakers. Level controls are set at max. If there is any hum/buzz above the noise of the flourescent lights something is wrong.

 

[Zach C.]

Slow Progress

So, I finally got the parts to do the rewiring and cap additions for this dude, and I have a question about the caps on the bridge rectifier. In mlucitt’s drawing, there are four .22uF caps on the BR terminals and C25 across the A/C lines is removed (not sure what this cap is called on the 400- I only have a schematic for the 700B.) I understand that these are there to shunt high frequency switching noise from the diodes in the BR. I also understand that the original .22uF C25 across the A/C terminals is there to shunt HF noise on the power line. (Is that right?)

It seems to me that leaving C25 in while adding the other .22uF caps across the four BR terminals will give “multiple resonances†and could lead to a reduction of noise at two different frequencies, since they are effectively in parallel. At the same time, it seems like it could give just a single new effective cap value which is that of the two added caps in series with each other and in parallel with C25 across the A/C lines.

My main question is this: Is there a reason to remove C25 other than redundancy?

Good?
Bad?
Indifferent?

I’m not sure how this works out, and would appreciate any advice and/ or links to reference materials to help me really understand what is going on here. As I have said, I am always open to constructive criticism and corrections to my understanding of things. This is how we learn.

Thanks,

Zach

p.s. A/C wiring improvements are done- thanks Joe!

 

[laatsch55]

Put .01uf self healing polyester film caps accross all 4 tabs of the BR. These are to take care of the rectifier switching noises as the diodes turn on and off. Don't knopw why PL said .22's. .01's are kinda standard and what Joe spec's out.

400 volters, Mouser # 5989-400V.01-F

 

[Zach C.]

...400 volters, Mouser # 5989-400V.01-F

OK, thanks.

I on a related note, I have on hand 667-ECQ-E2334KB, .33uF 250V to use for the DC to common at the output devices. This should work fine, right?

Zach

 

[wattsabundant]

OK, thanks.

I on a related note, I have on hand 667-ECQ-E2334KB, .33uF 250V to use for the DC to common at the output devices. This should work fine, right?

Zach

Ok if it fits. I typically use .10's for decoupling caps. As far back as I can remember (the early Dynaco days), the standard cap for ac noise and contact bounce was .01uf/1kv ceramic. They're pretty common, cheap, and Radio Shack used to stock them. The self healing that Lee recommends are fine too. Might cost a little more. You want at least 250VAC. Attached is a page out of the 400 manual on this subject.

 

[laatsch55]

And to all who may read this, the problem I was having with the 700 on the bench WAS NOT related to Don's board, not seeing the forest for the trees maybe , but not Don's board.

 

[wattsabundant]

And to all who may read this, the problem I was having with the 700 on the bench WAS NOT related to Don's board, not seeing the forest for the trees maybe , but not Don's board.

Thanks Lee. What's the final analysis on the 700b power oscillator?

Back in post #74 you put out a "Don's fair game". Should it be retracted? I'm not too worried as I haven't seen anyone lurking in the woods.

 

[laatsch55]

That was effectively retracted by my previous post. The oscillation was self induced by reversing C10R and C18R. On Joe's board that's a no-no. Nothing to do with Don's bopard. The 400 will be investigated after I get the 700 sent off this week.

 

[laatsch55]

I guess I should have prefaced that with a wee bit of humor as that was the gist of that post Don. So now be it said that , that statement was not accurate. I had no problem with the 700 board, the 400 though was confirmed by you. No biggie. If you'll read some more, I've exonerated your board in a few other threads Don.

 

[Zach C.]

Ok if it fits. I typically use .10's for decoupling caps. As far back as I can remember (the early Dynaco days), the standard cap for ac noise and contact bounce was .01uf/1kv ceramic. They're pretty common, cheap, and Radio Shack used to stock them. The self healing that Lee recommends are fine too. Might cost a little more. You want at least 250VAC. Attached is a page out of the 400 manual on this subject.

OK, thanks.

I was looking at using the ones I mentioned on the recommendation of another member. He mentioned (and I knew) that even though you see ceramics in this application all the time, they may not be ideal. I might have the ceramics for the bridge decoupling.

In my most recent post though, I actually meant the caps which are added to the supply rail to common near the output devices in mlucitt's diagram posted in this thread. I'm pretty sure the ones I have will work, just wanted a 2nd opinion.

Zach

 

[Zach C.]

Thanks Lee. What's the final analysis on the 700b power oscillator?

Back in post #74 you put out a "Don's fair game". Should it be retracted? I'm not too worried as I haven't seen anyone lurking in the woods.

I'd like to point out that I did not and do not blame your board for whatever is going on with my amp. Since you have experienced the same with another amp, but many boards have been installed without trouble, it stands to reason that something is funny with these two amps rather than your board. I hope to find out what that is.

I'm just glad (in a way) that you have experienced the problem yourself and have found a workaround for it. I figured you would think I was just nuts.

Zach

 

[Zach C.]

Ok if it fits. I typically use .10's for decoupling caps. As far back as I can remember (the early Dynaco days), the standard cap for ac noise and contact bounce was .01uf/1kv ceramic. They're pretty common, cheap, and Radio Shack used to stock them. The self healing that Lee recommends are fine too. Might cost a little more. You want at least 250VAC. Attached is a page out of the 400 manual on this subject.

I misread this the first time around. You are talking about both uses that I mentioned.

My mistake.

Zach

 

[mlucitt]

I updated the PL 400 Improved Wiring Diagram to reflect Joe's recommendation to re-route the AC wiring to the thermoswitch and Lee's recommendation for .01uF caps across the bridge rectifier. I was using .22uF because I thought more cappage is always a good thing; after Lee's excursion into oscillator-land, maybe not!

Mark

 

[Zach C.]

Threadjack!

At the risk of jacking my own thread...

I didn't get as much done on this project this weekend as I might have liked, but did manage to do something pretty cool. Went to a friends and helped him finish setting up the active system in the crappy pic below. He did the VAST majority of the work on this- I was mostly a technical consultant. The front mains are actually curved front and back like the Sonus Faber Stradivarius, though you can't tell it in the pics. We started this project last summer when my buddy asked if there was a far out design I had wanted to try, so we started out to make two sets of these cabs. (Mine still need a lot of work, but they exist.)

It's an active set up using the minidsp 2X8 and several refurbished vintage Carver and an Emotiva surround sound amp and prepro. There's also a 15" ported sub at the back of the room. He likes bass.



Loud, and super clean. My ears will never be the same, but we just couldn't help ourselves. Damn, that was fun.

On topic, I did get a few caps soldered in, and noticed that my "meter slam" is gone. Not exactly sure when that happened, but they no longer peg out on start up. All I've really done so far is the A/C rewire and bridge rectifier caps. I'll get more done soon, but didn't want to drive into town to get the sleeving I want to use on the legs of the caps at the output supply rails.

Zach

 

[laatsch55]

Dr Lucitt and I like it loud too. He coined the phrase---"sublimely insane" sound pressure levels. I like getting pushed around by my music too.

 

[Zach C.]

Dr Lucitt and I like it loud too. He coined the phrase---"sublimely insane" sound pressure levels. I like getting pushed around by my music too.

Dr. Lucitt?

Are congratulations in order?