Help improve pp-18 tone
Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon
- Bronsboi
- Newbie
- Posts: 96
- Joined: Sat 03/06/10 2:00 am
- Location: Bradford, England
- Contact:
-
- Frequent poster
- Posts: 914
- Joined: Mon 12/10/07 2:00 am
- Location: Melb, Aust
- Contact:
-
- Frequent poster
- Posts: 914
- Joined: Mon 12/10/07 2:00 am
- Location: Melb, Aust
- Contact:
Someone on The Amp Garage was having this problem where the Ruby mod fixed the fizz problem at high VVR settings but became ineffective as the VVR was turned down. After trying out a number of different suggestions I was going to post the variable zener circuit which I'd put up in this thread, saying it was very much unproven. Before getting that far he tried zeners with much smaller threshold voltages and seems to have found a very simple answer.
He used 3V 5W zeners in the standard Ruby mod and says that it now doesn't fizz across the whole VVR range. Using zeners of too low a value risks clipping the negative side of the power grid signal before the power valve is cut off. This would introduce unwanted distortion. Paul Ruby's document suggests picking zeners a couple of volts higher than the cathode bias voltage. He aimed to make the clipping around symmetrical with the grid clipping on the positive side. But in theory there's no reason the zeners can't be lower than that as long as they don't clip before the power valve reaches cutoff.
I've never tested the cutoff voltage of EL84s in 18W amp conditions. From the data sheet curves it might be something like -20V. Bias is typically 10.5 - 12.5V, but that cools off under signal even before output clipping. So the 3V isn't that unreasonable. Anyway, something for people to try if the Ruby mod is the only fix to their fizz problems and they want VVR as well.
Here's the thread for those with a login at TAG:
http://ampgarage.com/forum/viewtopic.php?t=18157
He used 3V 5W zeners in the standard Ruby mod and says that it now doesn't fizz across the whole VVR range. Using zeners of too low a value risks clipping the negative side of the power grid signal before the power valve is cut off. This would introduce unwanted distortion. Paul Ruby's document suggests picking zeners a couple of volts higher than the cathode bias voltage. He aimed to make the clipping around symmetrical with the grid clipping on the positive side. But in theory there's no reason the zeners can't be lower than that as long as they don't clip before the power valve reaches cutoff.
I've never tested the cutoff voltage of EL84s in 18W amp conditions. From the data sheet curves it might be something like -20V. Bias is typically 10.5 - 12.5V, but that cools off under signal even before output clipping. So the 3V isn't that unreasonable. Anyway, something for people to try if the Ruby mod is the only fix to their fizz problems and they want VVR as well.
Here's the thread for those with a login at TAG:
http://ampgarage.com/forum/viewtopic.php?t=18157
0 x
- Bronsboi
- Newbie
- Posts: 96
- Joined: Sat 03/06/10 2:00 am
- Location: Bradford, England
- Contact:
-
- Frequent poster
- Posts: 914
- Joined: Mon 12/10/07 2:00 am
- Location: Melb, Aust
- Contact:
- zaphod_phil
- Builder, Admin
- Posts: 15208
- Joined: Wed 03/19/03 2:00 am
- Location: YYZ
Now that's really cool information!He used 3V 5W zeners in the standard Ruby mod and says that it now doesn't fizz across the whole VVR range. Using zeners of too low a value risks clipping the negative side of the power grid signal before the power valve is cut off. This would introduce unwanted distortion. Paul Ruby's document suggests picking zeners a couple of volts higher than the cathode bias voltage. He aimed to make the clipping around symmetrical with the grid clipping on the positive side. But in theory there's no reason the zeners can't be lower than that as long as they don't clip before the power valve reaches cutoff.
I've never tested the cutoff voltage of EL84s in 18W amp conditions. From the data sheet curves it might be something like -20V. Bias is typically 10.5 - 12.5V, but that cools off under signal even before output clipping. So the 3V isn't that unreasonable. Anyway, something for people to try if the Ruby mod is the only fix to their fizz problems and they want VVR as well.
Here's the thread for those with a login at TAG:
http://ampgarage.com/forum/viewtopic.php?t=18157
0 x
Nature abhors a clean tube amp
-
- Occasional poster
- Posts: 159
- Joined: Thu 09/18/08 2:00 am
- Location: Jo´burg, South Africa
I actually tried this out using my rotary zmulti value zener fix. The lower zener value does work over the whole usable range of the VVR pot. (From about 10 o clock)
However, when the VVR is maxed, you do lose a little of the swirl at the end of the note decay. But, not anything you would notice in the mix with a band behind you. I'll try dig up the lowest zener value I used, but from my experience so far, it works.
(Of course, since I've already drilled a hole for the rotary, it stays!)
Thomas
However, when the VVR is maxed, you do lose a little of the swirl at the end of the note decay. But, not anything you would notice in the mix with a band behind you. I'll try dig up the lowest zener value I used, but from my experience so far, it works.
(Of course, since I've already drilled a hole for the rotary, it stays!)
Thomas
0 x
-
- Frequent poster
- Posts: 914
- Joined: Mon 12/10/07 2:00 am
- Location: Melb, Aust
- Contact:
- Bronsboi
- Newbie
- Posts: 96
- Joined: Sat 03/06/10 2:00 am
- Location: Bradford, England
- Contact:
- Gary
- Newbie
- Posts: 93
- Joined: Fri 08/18/06 2:00 am
- Location: Leeds - as in "Live At ..."
-
- Occasional poster
- Posts: 159
- Joined: Thu 09/18/08 2:00 am
- Location: Jo´burg, South Africa
Hi Gary
The swiil is present at max VVR with the usual +/-10v zener, and reducing VVR corresponding with my rotary zener selector. However, some of the swirl disappears at max VVR when keeping the rotary at lowest value (around 4v if memory serves me right)
My lowest usable VVR volume is a bit higher than TV volume, but not more than a loud stereo. Certainly not going to annoy the neighbours too much.
Regards,
Thomas
The swiil is present at max VVR with the usual +/-10v zener, and reducing VVR corresponding with my rotary zener selector. However, some of the swirl disappears at max VVR when keeping the rotary at lowest value (around 4v if memory serves me right)
My lowest usable VVR volume is a bit higher than TV volume, but not more than a loud stereo. Certainly not going to annoy the neighbours too much.
Regards,
Thomas
0 x
- Bronsboi
- Newbie
- Posts: 96
- Joined: Sat 03/06/10 2:00 am
- Location: Bradford, England
- Contact:
I definitely agree with the above.My lowest usable VVR volume is a bit higher than TV volume, but not more than a loud stereo. Certainly not going to annoy the neighbours too much.
I tested this in normal and cascade mod (ZP intergalactic mod) You still get a bit of fizz with VVR at full tilt but nothing compared to when the ruby fix is switched off. With the VVR at about 8-9 oclock it sound great and not much louder than a stereo.
I have installed the 3v zeners and the 13V zeners on a switch...They both are an improvement on the "no ruby fix" tone.
The 3v zeners improve the punch and fullness of sound across the whole range of the VVR... Yes the fizzy swirl is gone, but to my taste, that's no loss!!
I think the 13V zeners are redundant now, cos the 3V zeners improve the sound even when not using the VVR (don't know how!!). I am gonna hard wire the 3v zeners in and get rid of the switch.
I have dialed up the treble a bit to compensate, but that is the only drawback, to my ears at least.
Just one question I could only get 0.5 watt zeners. Is this enough?
Really pleased with how this has worked out. Thanks to Katoplan, Tom Olsen and ZP for all the help and advice. I'm really grateful
0 x
-
- Frequent poster
- Posts: 914
- Joined: Mon 12/10/07 2:00 am
- Location: Melb, Aust
- Contact:
-
- OEM Amp builder
- Posts: 44
- Joined: Thu 12/27/12 2:49 pm
Re: Help improve pp-18 tone
Since this thread is SO long I haven't read it all, but fizz can be helped in easier ways I'd think. One that instantly comes to mind, is the 820 ohm resistor in the PI vs the vox value 1k2, (that was mentioned already) and I don't know about this one, but one way I like to tame fizz is just to put a 47pf cap across the plates of the PI tube, it has worked for me many times on several amps. I hope if you hadn't fixed it already, that this will help.
Rock city, regarding your amp being loud, try installing a PPIMV (post phase inverter master volume). Search that on this 18watt forum and you should get lots of older threads regarding it. Hope that helps you, it has helped others, also you could look into getting a good attenuator.
Rock city, regarding your amp being loud, try installing a PPIMV (post phase inverter master volume). Search that on this 18watt forum and you should get lots of older threads regarding it. Hope that helps you, it has helped others, also you could look into getting a good attenuator.
0 x
-IsaacGDS/Guytron Amplificationhttp://www.GDSamps.com" onclick="window.open(this.href);return false; http://www.Guytron.com" onclick="window.open(this.href);return false;
-
- Unrated
- Posts: 2
- Joined: Thu 10/31/13 3:51 pm
-
- Unrated
- Posts: 3
- Joined: Sun 10/20/13 5:39 am
Re: Help improve pp-18 tone
Cheers!Isaac Stuckey wrote:one way I like to tame fizz is just to put a 47pf cap across the plates of the PI tube, it has worked for me many times on several amps.
This way?
0 x
-
- OEM Amp builder
- Posts: 44
- Joined: Thu 12/27/12 2:49 pm
Re: Help improve pp-18 tone
Yea I've done it on several different amps. Actually never on an 18w based... but I never needed it there. The 1974x's always work for me, they are special.
0 x
-IsaacGDS/Guytron Amplificationhttp://www.GDSamps.com" onclick="window.open(this.href);return false; http://www.Guytron.com" onclick="window.open(this.href);return false;
-
- Unrated
- Posts: 3
- Joined: Sun 10/20/13 5:39 am
Re: Help improve pp-18 tone
Cheers, I'll give it a try. What kind of cap should it be please? (Aye, I'm green as a leaf.. just assembled the PP18 few days ago)Isaac Stuckey wrote:Yea I've done it on several different amps. Actually never on an 18w based... but I never needed it there. The 1974x's always work for me, they are special.
0 x
-
- OEM Amp builder
- Posts: 44
- Joined: Thu 12/27/12 2:49 pm
Re: Help improve pp-18 tone
A regular 47PF will work fine. I have used a 100PF too before I think, but I'm not sure. Either way, assuming I've only ever used 47PF, it has always gotten rid of some fizz/buzz and made it a little smoother. 100Pf will be more extreme, but not bad. Don't go too high otherwise you will get rid of all the highs, anyway, just experiment with it, and try it with more than one guitar, since you could use a tele and it has less treble and it sounds awesome, but it might not be as good with a les paul. Just experiment.
0 x
-IsaacGDS/Guytron Amplificationhttp://www.GDSamps.com" onclick="window.open(this.href);return false; http://www.Guytron.com" onclick="window.open(this.href);return false;
-
- Occasional poster
- Posts: 216
- Joined: Sat 07/01/06 2:00 am
- Location: Rancho Cucamonga, CA
Re: Help improve pp-18 tone
Just make sure the cap is of the appropriate voltage for the section.
0 x