Fuzz/Phase shifting effect (muskito flying by) in the mids

[Froumy]

Good Luck Ricky Lee. I can't even hear it, but I'm going to slap them in there just in case....

Billy Batz - Better late than never? By all accounts, sounds like this could be the cure. Makes sense, anyway.

No, that is normal - you will get a larger output swing from one phase to the other when you hit clipping - that is a characteristic of a long-tail pair phase inverter. The "input" side, which is functioning as a common-cathode stage, will have a larger clipped output than the "other" side, which is effectively functioning as a common-grid stage - remember, it is amplifying and inverting the "clipped" wave from the other section.

Having said that, the relative matching of the two sections, while unimportant when the PI is not clipped (due to the local and global feedback that tends to stabilize the gains), will affect the drive when clipping, so you may see a difference with different tubes.

Randall Aiken

Always read that the Long tail pair was unbalanced. Just really surprised that I had such a huge difference when dimed! 30% less! Didn't expect THAT much. It was nearly identical at lower volumes. Go figure. Thanks for the explanation. Scope has turned out to be a really useful learning tool.

18w implementation schematic here, if you missed it. http://www.paulamps.com/18watterbuzz.html#ResistiveLoad

[5150loveeddie]

18w implementation schematic here, if you missed it. http://www.paulamps.com/18watterbuzz.html#ResistiveLoad

This is a fuc***g great page man, thx!!

I found some Zeners near my place but they didn't have most wanted values, found some 43v ones........ WOuld that be in the ball park if the bias is around 35ma??

Will give it a try anyhow...

[Froumy]

Good that there is so much info out there. You guys aren't the only ones who have wrestled with this. Your Zener voltage seems a little high from Randall's start point recommendation(pretty damn close, though), but I'd definitely try it to see what happens. I'll grab a variety, as I may change my finals, and I occassionally use the 100v tap of the Ho attenuater. Could definitely change the Zener requirements.

5150, you ought to slap that scope on there. Worst case scenario is that you'll at least see it(and learn something). If you want to start taking voltages with it, it's important to remember that your DMM is reading RMS voltage. Scope will read V peak(0 crossing to peak), V p-p. Here's a calcultor(about half way down) if you don't feel like using the formulas.

http://www.sengpielaudio.com/calculator-db-volt.htm

Osilloscope tutorial:
http://oscilloscope-tutorials.com/

[Ricky Lee]

With dual voltage switching in my 12xxx my bias on the low voltage side (400v) is set to 40ma, the high side (500v) is set to 33ma hopefully the 43v Zener will suffice both voltages. Most of my other amps have a 35ma bias setting so the 39v Zener is what I ordered for those and is probably the most popular since the -35 is probably the most used setting with the plexi's.

[5150loveeddie]

Good that there is so much info out there. You guys aren't the only ones who have wrestled with this. Your Zener voltage seems a little high from Randall's start point recommendation(pretty damn close, though), but I'd definitely try it to see what happens. I'll grab a variety, as I may change my finals, and I occassionally use the 100v tap of the Ho attenuater. Could definitely change the Zener requirements.

5150, you ought to slap that scope on there. Worst case scenario is that you'll at least see it(and learn something). If you want to start taking voltages with it, it's important to remember that your DMM is reading RMS voltage. Scope will read V peak(0 crossing to peak), V p-p. Here's a calcultor(about half way down) if you don't feel like using the formulas.

http://www.sengpielaudio.com/calculator-db-volt.htm

Osilloscope tutorial:
http://oscilloscope-tutorials.com/

Cool sites thx dude, exactly what I needed

Qts? Has 18w did, if we put two Zeners in series the voltages add up correct? ex.a 10v with 27v= 37v, I know how to add pretty good lol That way we can try mostly any values...

thx again boys

[novosibir]

I found some Zeners near my place but they didn't have most wanted values, found some 43v ones........ Would that be in the ball park if the bias is around 35ma??

With dual voltage switching in my 12xxx my bias on the low voltage side (400v) is set to 40ma, the high side (500v) is set to 33ma hopefully the 43v Zener will suffice both voltages.

Keep in mind, that it's not the bias current, what matters!
You have to check your negative bias voltage and then you have to add somewhat about 3...10V to this, to get to the zener's voltage you shouldt try.

These about 3...10V is the ballpark, wherein after Randall's suggestions you should experiment, to get to the ~right~ zener's voltage.

Larry

[Froumy]

You can put zeners in series, and they add up. Will also be able to take more heat/current for reliability.

By the way, did anyone try upping the tail resistor yet?

[raiken]

You can put zeners in series, and they add up. Will also be able to take more heat/current for reliability.

This is indeed true, but there is very little power dissipation in a signal clipper circuit (on the order of a few mW), so you don't need to worry about that. This means you can use the low-power 500mW DO-35 package zeners like the 1N52xx series or smaller.

RA

[5150loveeddie]

You can put zeners in series, and they add up. Will also be able to take more heat/current for reliability.

This is indeed true, but there is very little power dissipation in a signal clipper circuit (on the order of a few mW), so you don't need to worry about that. This means you can use the low-power 500mW DO-35 package zeners like the 1N52xx series or smaller.

RA

OK fine enough thx all, it is tweaking time now......weeeeeee

Not yet for the tail resistor tweaks Froumy!!

[5150loveeddie]

[Keep in mind, that it's not the bias current, what matters!
You have to check your negative bias voltage and then you have to add somewhat about 3...10V to this, to get to the zener's voltage you shouldt try.

These about 3...10V is the ballpark, wherein after Randall's suggestions you should experiment, to get to the ~right~ zener's voltage.

Larry

So our reference would be from pin5's correct? ANd not from our actual bias draw?????

YEs or no here???????? MErci beaucoup!!

[Froumy]

Randall, Is there anything you don't know? I've seen a few places where guys were using in them in series for "reliability" for heat/current. Same misconception as me. Nice having you around Randall.

[raiken]

Randall, Is there anything you don't know? I've seen a few places where guys were using in them in series for "reliability" for heat/current. Same misconception as me.

There's a LOT I don't know!! Don't ever take anything I say as the gospel truth, unless you can verify it yourself!

Zeners in series for reliability works when you are using them to drop large voltages at relatively high currents, like putting them in the CT of the power transformer to lower plate voltage.

RA

[Billy Batz]

What if your next set of tubes is far off or you use a different type of tubes? That would be a pain.

[raiken]

What if your next set of tubes is far off or you use a different type of tubes? That would be a pain.

It shouldn't be that critical - that's why you want to clip a few volts over the bias level, but close enough to prevent pushing the signal down too far.

RA

[5150loveeddie]

[Keep in mind, that it's not the bias current, what matters!
You have to check your negative bias voltage and then you have to add somewhat about 3...10V to this, to get to the zener's voltage you shouldt try.

These about 3...10V is the ballpark, wherein after Randall's suggestions you should experiment, to get to the ~right~ zener's voltage.

Larry

So our reference would be from pin5's correct? ANd not from our actual bias draw?????

Yes or No here , merci beaucoup!!