Phase 45 [used Search, found nothing of interest]

[Cortex]

Hey guys, let me start by saying a big THANK YOU all for your contribution here, I found so much interesting projects, and thoughts written here. You guys rock!

I built the Phase 45 circuit using this layout
http://solderman.fatabur.se/Mini_ph45/Mini%20_Phaser_45_Projectfile.pdf
which is the same layout like tonepad, but modified to be able to squeeze the phase into a 1590A enclosure. I've managed to do that, and the pedal is sweet as a candy!

Just because I was unable to get anything else, I ended up using BF245A as my phase FETs, matched perfectly at 1V. The zener I am using is 4.5V, trimpot of 250K. With this setup I am getting the phase somewhere around the middle of the trimpot as suggested by some people here on the forum. The effect is somewhat weaker than it should be I could say played clean...placed after a distortion pedal it kicks a$$!

QUESTION: I noticed by reading A LOT here and on other places on the web, that the recommendation is that FETs should be matched around half of the zener voltage. No one said this explicitly, but based on what I read on the subject, seems to me that everyone were saying pretty much this. RG Keen wrote that he likes to use a 3.1V zener and match FETs around 1.5-1.8V and that is the optimal setup for him. A friend, who is a much more experienced pedal builder than myself, also recommended 2.6V-2.8V with a 4.5-5.1V zener.
So the question is: If I get some other FETs [maybe 2n5484,2n5485], match them around half of the zener voltage would the phase effect be more pronounced than with matching around 1V like I did?

Thank you for your time.
Marko

[DavenPaget]

Hey guys, let me start by saying a big THANK YOU all for your contribution here, I found so much interesting projects, and thoughts written here. You guys rock!

I built the Phase 45 circuit using this layout
http://solderman.fatabur.se/Mini_ph45/Mini%20_Phaser_45_Projectfile.pdf
which is the same layout like tonepad, but modified to be able to squeeze the phase into a 1590A enclosure. I've managed to do that, and the pedal is sweet as a candy!

Just because I was unable to get anything else, I ended up using BF245A as my phase FETs, matched perfectly at 1V. The zener I am using is 4.5V, trimpot of 250K. With this setup I am getting the phase somewhere around the middle of the trimpot as suggested by some people here on the forum. The effect is somewhat weaker than it should be I could say played clean...placed after a distortion pedal it kicks a$$!

QUESTION: I noticed by reading A LOT here and on other places on the web, that the recommendation is that FETs should be matched around half of the zener voltage. No one said this explicitly, but based on what I read on the subject, seems to me that everyone were saying pretty much this. RG Keen wrote that he likes to use a 3.1V zener and match FETs around 1.5-1.8V and that is the optimal setup for him. A friend, who is a much more experienced pedal builder than myself, also recommended 2.6V-2.8V with a 4.5-5.1V zener.
So the question is: If I get some other FETs [maybe 2n5484,2n5485], match them around half of the zener voltage would the phase effect be more pronounced than with matching around 1V like I did?

Thank you for your time.
Marko

Why not try J201's , they're not hard to match and Element14/farnell/newark sells fairchild's J201's for 87cents SGD ( i don't know about farnell/newark ) if you buy more then 10 , so easy to buy 1 big batch and have like 5 matched pairs .

[Cortex]

Thank you Daven for your response, I might even try that, but it is irrelevant which FETs we use, if I understood correctly. As long as they are matched, Vgs under zener voltage, above or 1V, something like that.
I have a bunch of BF245C trannies, and I believe there are 8 of them with the same 2.62V vgs voltage. That's around half of the zener voltage allright. But I guess maybe I would have to put a bigger trimpot or somethin and the phase 45 is working very nice, I was just wondering if puttin' some other trannies with the vgs around half the zener voltage would have any impact sound-wise!

[DavenPaget]

Thank you Daven for your response, I might even try that, but it is irrelevant which FETs we use, if I understood correctly. As long as they are matched, Vgs under zener voltage, above or 1V, something like that.
I have a bunch of BF245C trannies, and I believe there are 8 of them with the same 2.62V vgs voltage. That's around half of the zener voltage allright. But I guess maybe I would have to put a bigger trimpot or somethin and the phase 45 is working very nice, I was just wondering if puttin' some other trannies with the vgs around half the zener voltage would have any impact sound-wise!

It would be best to use a trimpot to set and forget , helps all the time !
( Instead of a trimpot for my cmos dist pedal's LM317LZ , i used a standard pot , because adjusting headroom on the fly is WIN ! )

[Cortex]

Haha, yes, it is win, I concur!

You're a funny guy and please receive my kindest regards, but you are kinda not helping me

[DavenPaget]

Haha, yes, it is win, I concur!

You're a funny guy and please receive my kindest regards, but you are kinda not helping me

I've got nothing much to help when it comes to phasers
General transistor biasing i can answer but nothing else moar then that 

[Govmnt_Lacky]

I can't speak for the Phase 45 but....

I have built several Phase 90s and used 5952s every time. I always matched them to between 1.6-1.8 and I always used the recommended 5.1 or 4.7V zener.

Never had a problem and ALWAYS had a good phase come out of them 

My 2

[R.G.]

QUESTION: I noticed by reading A LOT here and on other places on the web, that the recommendation is that FETs should be matched around half of the zener voltage. No one said this explicitly, but based on what I read on the subject, seems to me that everyone were saying pretty much this. RG Keen wrote that he likes to use a 3.1V zener and match FETs around 1.5-1.8V and that is the optimal setup for him. A friend, who is a much more experienced pedal builder than myself, also recommended 2.6V-2.8V with a 4.5-5.1V zener.

I believe this is one of those correlations as opposed to cause and effect. In a 9V powered pedal, you're quite limited on voltage, so the things you can do on reference voltages are also limited.

So the question is: If I get some other FETs [maybe 2n5484,2n5485], match them around half of the zener voltage would the phase effect be more pronounced than with matching around 1V like I did?

Probably not. A JFET has a range of off to fully on that equals its cutoff voltage. When the gate is either open or shorted to the source, the JFET is as low a resistance from drain to source as it can be. Making the gate positive with respect to the channel doesn't help. When the gate is as negative (for N-channels, opposite for P-channels) as Vgsoff, the channel doesn't conduct at all, so making it more negative doesn't change anything. So the range of gate-source voltage is 0 to -Vgsoff. Each JFET has a little different Vgsoff, which is why we have to match them.

The channel resistance of the JFET is what causes phasing, and that can only vary between Rdson (usually fifty ohms or so to about 2K) and completely off. That range of resistance is independent of the actual value of Vgsoff or the zener/bias voltage.

The Vgsoff is a property of the JFET, not the bias voltage established by the zener. Some JFETs have Vgsoff of 10-12V, perhaps more. We don't use those kinds in pedals.    .

The opamps do need to be biased near the middle of the 9V supply so they don't give unwanted distortion. In a 9V pedal that means somewhere between 3 and 6V. And the bias voltage is where the JFET drains sit. The sources need to be at the same DC voltage or they'll amplify the control signal into the opamp, and that means that the gate has to be between the bias voltage and ground. So there's no real relationship of zener voltage to JFET matching, other than there are certain ranges they have to be in to work right. We pick JFETs to (loosely) match the voltages we have.

The depth of phasing depends on how well the dry and phase delayed signal cancel at the output mixer more than the zener voltage or JFETs. And the P45 is a very subtle phaser.

[Cortex]

Thanks a lot RG! This is a very thorough explanation of which I understood a big part but mostly intuitively. I am really grateful that you took the time.

Ok! So I'll try with some other FETs and see what I will get. I'll record a sound sample for you guys in an hour or two so that it will be easier to imagine how subtle my phase 45 works. A bit to subtle I would say, hence this topic. After distortion as I said, I am blown away by it's sound. It's spectacular just as it should be, not too over the top.

I tried for a moment BF245Cs perfectly matched around 2.62V, and I couldn't get any phase I'm afraid, I feel that I could, almost certainly if I would put a bigger trimpot in there. I presume I could swap a 500K or even 1M trimpot in there without any consequences to the rest of the circuit...

Thank you all, once again, I'll be back with the sounds.

[PRR]

Try putting more LFO at the FETs. Reduce the 3M9 to maybe 2m2 (or tack a second 3m9 across the existing 3M9). Re-trim.

But as R.G. says: two shift networks is not a strong effect.

[Thisisyoureading]

Just wanted to say how awesome these look.