Build Your Own Clone Message Board

It is currently Thu Mar 28, 2024 11:15 pm

All times are UTC - 6 hours




Post new topic Reply to topic  [ 60 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
PostPosted: Sat Dec 15, 2012 9:38 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
I hacked in a temporary parallel 100K for an equivalent 50K and I can use just about the entire range of the pot now. It craps out in the last 1/8th of the turn. I'll probably end up with something a little less to ensure that the entire sweep works. You really wouldn't need any more feedback though since the effect is so intense at max.

BYOC should consider updating the PR to these specs. It now starts from a phase 90 but goes way beyond. In stock form my BYOC couldn't reach phase 90 territory (in my opinion).


Top
 Profile  
 
PostPosted: Sun Dec 16, 2012 12:18 am 
Offline
User avatar

Joined: Fri Sep 11, 2009 9:42 pm
Posts: 5689
Location: Brewtown, USA
somebody needs to STICKY this thread. mods??? :)

_________________
Muad'zin wrote:
I want Pterodactyl sounds dammit, not a nice little analog sustain.


Top
 Profile  
 
PostPosted: Sun Dec 16, 2012 8:23 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
I ended up with a 39K for the feedback op-amp. Now the full range of the resonance pot is usable.
Here is a quick example of what the resonance does now with Tark's mods. The clip is done with depth full, mix noon, resonance starts on min and is swept through to max and back to min again. After that there is an example of the RP used on a classic phase 90 tune.

https://soundcloud.com/jreinhard60/phaseroyaltest


Top
 Profile  
 
PostPosted: Tue Dec 18, 2012 2:38 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
I've been playing more with the bias setting to get the resonant frequency of the effect closer to the sound of my original phase 90. What I found is that the setting I want for the bias to get the best tone results in insufficient depth. So I made a couple of additional tweaks. I am using a 1M multi-turn trimmer for the bias to get better control over the adjustment. I'll replace it with a 250K multi-turn when I get one. To get more effect I replaced R32 with a strap. I'm not sure what the 56K resistor is used since the direct voltage follower output would be equivalent of the original circuit.

Also, I reduced R27 to 130K to get closer to unity gain overall. The 150K had too much gain for me.

Results are here if anyone is interested: https://soundcloud.com/jreinhard60/phaseroyaltest2


Top
 Profile  
 
PostPosted: Tue Dec 18, 2012 9:55 pm 
It may be a bit tricky to get either the original Phase Royal or the modified version to sound exactly like an MXR Phase 90 because, for one thing the MXR appears to have used a 3V Zener to supply the bias (which does not look like a good design decision, I'd say the 5.1V in the BYOC design is a better choice even though as previously noted it is run current starved) and it looks like it used 0.05uF caps in the phase shift sections, rather than the rationalised 47nF values in the Phase Royal. It also seems to have used a simple resistive feedback for the resonance so I'm not sure how effective that is / would have been.

As I'm sure you realise the modulation FETs have a fairly narrow gate voltage range over which they can be controlled as variable resistors. The idea of the bias is to set the gate voltage so that without any LFO signal applied the FETs are biased to the middle of their drain to source resistance range. Then when the LFO sweep signal is applied it swings either side of that bias point and when the Depth pot is at maximum the FET resistance should swing between the maximum and then minimum that the FETs are capable of (or at least somewhere close). The 56K feeding the depth pot simply limits the maximum sweep that can be applied and was presumably chosen because the Depth pot at maximum was found to push the FETs beyond their maximums (or possibly because it was felt the effect was just too extreme).

Since the bias trimmer sets the centre of the modulation sweep it also sets the centre notch frequencies about which the sweep swings. If the centre of the modulation sweep does not correspond with the notch frequencies you would like to hear, unless you change all the phase shift capacitor values, you are unlikely to get both the full sweep range and the desired frequencies by setting the trimmer. And as already mentioned the original MXR does seem to have used slightly larger capacitors.

That output stage (Q7) is a bit of an abortion and the problem with messing with the 150K to change gain is that it is also a bias resistor and will therefore affect the stage clipping point. Apparently MXR Phase 90 freaks like the sound of this output stage and that is why it was retained in the BYOC design. Although of course the original output stage is both direct coupled to the rest of the circuit and biased by the 3V Zener. The BYOC stage is AC coupled and biased by the 5.1V Zener so they aren't really equivalent, but still uses the same resistor values, which is why distortion in this stage is improved by re-biasing it with the extra resistor. Although the exact bias point for this output stage is quite dependant on the current gain of the particular transistor used.


Top
  
 
PostPosted: Thu Dec 20, 2012 10:58 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
So I think I see where all the extra gain is coming from in the modified circuit Tark. The mod to IC1a results in a gain of almost double with the resonance pot off. So rather than adjust the gain of the output stage (Q7), how would one reduce the gain at IC1a so it is closer to the unity gain of the original circuit?

On another note, after replacing R32 with a strap I have also increased R33 to 220K to get the same LFO swing that my phase 90 has. Using a scope to set the bias, both pedals are very close in that regard now. All the phase shift capacitors on my phase 90 (reissue) are 47nF like the RP so the sound is getting pretty close.

I also replaced the 4558s with TL072s to match the phase 90.

Thanks in advance.


Top
 Profile  
 
PostPosted: Fri Dec 21, 2012 6:51 am 
You are absolutely right, so sorry, my stupid mistake, I had forgotten the gain calculation for op-amps is G = 1 + Rf/Rg
On top of which I only ran the simulation for AC Analysis / frequency response and not for Signal / Transient response.

In the Soaring Skillet (which I referred to for the feedback circuit mod) the negative feedback (270K, 470K) around the input amp sets an input gain of 1.57 (note - not unity). The feedback opamp is set for a gain of 2.8 (18K, 10K).

So to replicate that gain structure in the Phase Royal the feedback resistor around the input amp can be 270K and the feedback resistor around the Resonance op-amp can be 82K to 91K. You will probably also need a 330pF across that 91K to keep things stable.

Thanks for trying out all these mods and for being patient with my mistakes. I have run the sims with these values in and I get vicious resonance with the Resonance control at max but the transient sim shows the circuit is still stable. I hope these values work for you.

Good move on the TL072 opamps since they are a more recent design than the 4558s and should offer better performance.


Top
  
 
PostPosted: Fri Dec 21, 2012 9:34 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
I tried a 100K for the feedback of the input opamp because I didn't want too much gain and used the 47K/100K combo at the resonance opamp. It works well when using the 4th stage tap but I have an issue when using the 6th stage tap. With no input signal, at a certain point in the sweep there is a burst of what sounds like white noise (not overly loud but annoying). Scoping the output stage 6, I see a perfect sine wave at 200Khz that corresponds with the burst of noise. This occurs with the resonance completely off. It doesn't show up on simulation however. It also doesn't occur in the original circuit which is what I am using currently. It must have something to do with the use of the 100K feedback at the input opamp. I didn't notice it when I had a 470K at that location. There must be signal getting through the mixer back to the input opamp creating a loop.

When doing this mod, care must be taken with the location of the resistors to minimize noise in this circuit. Keeping the input and feedback resistors as close to the opamp as possible is best. At one point I had a DPDT to toggle between the new circuit and the original circuit (minus the feedback) but found it was a little noisy due to resistor location.

At this point I'm not sure if I am going to debug the oscillation problem with the 6th stage tap. I find that I prefer no feedback most of the time and the feedback circuit does at some noise (albeit minimal if the resistors are placed carefully). The new circuit also adds some gain which could be plus or a minus depending on taste.

Thanks for the help Tark. I still have most of the resonance mod in place if you would like me to try something.


Top
 Profile  
 
PostPosted: Sun Dec 23, 2012 6:59 am 
Did you add the 330pF across the feedback resistor for the resonance opamp?

You may need a similar small cap across the input opamp feedback. There are a few feedback paths and lots of phase shifts going on in that pedal, not too surprising I suppose that it can take off at 200 KHz


Top
  
 
PostPosted: Sun Dec 23, 2012 2:59 pm 
Offline

Joined: Sat Dec 15, 2012 12:33 pm
Posts: 8
330pf across the input opamp did the trick. The 330pf on the resonance opamp didn't seem to be necessary but I left it there for safety.

Using the reference numbers in the modified simulation I ended up with:
C13 - 47nF
R43 - 100K plus 330pf
R33 - 47K
R47 - 22K
R46 - 470K
R44 - 180K plus 330pf
R45 - 68K
Plus using the reference numbers on the original schematic:
R33 - 220K
R32 - 0
C14 - 15uF
C1 - 100nF
C11 - 220nF
C12 - 100nF
C13 - 100nF
R37 - 2.2K
R16 - depopulated
C8 - depopulated
R1 - depopulated
VR5 - 1M multi-turn trimmer
TL072 for all opamps

I wanted to keep R44 as low as I could but still have the resonance pot have plenty of effect. Actually much more than 180K and the feedback starts to cause oscillation issues anyway. The extra gain of the overall circuit is visible on a scope but not really perceptible to the ear when the resonance pot is off.

The overall sound with the 4th stage setting and resonance pot off is so close to my phase 90 that I don't think anyone could tell which was which in an A/B test. I used a scope to match the LFO swing between the two pedals. The PR has more options beyond that point now with the resonance and the 6th stage. I am happy with pedal at this point so I think I am done. Thanks for all the help Tark.


Top
 Profile  
 
PostPosted: Mon Dec 24, 2012 5:19 am 
Yay! we seem to have nailed it !

Let's hope BYOC issue a revised version. I might actually buy one then.


Top
  
 
PostPosted: Sat Mar 02, 2013 4:10 pm 
Offline

Joined: Sat Jan 23, 2010 4:18 pm
Posts: 44
Looks like I'm about 2 months late for the party on this thread but I had to say that I just finished the first 3 mods suggested by Tark and my phase royal has been transformed. I've built six byoc kits and the pr was the only one that never worked right, after a lengthy attempt at troubleshooting it finally got relegated to the closet for over a year as I found it unusable. The sweep was really lopsided and the phasing was weak. I think solving the reference voltage was probably the biggest factor unfortunately I did all the mods at once. Now I really like the effect, especially having the functionality of the mix knob. Great work Tark!


Top
 Profile  
 
PostPosted: Fri Mar 22, 2013 6:50 am 
Offline

Joined: Wed May 27, 2009 4:27 pm
Posts: 25
just a quick question, kinda new to all this.

I'm going to try the 5th mod that you recommended,

5. (Recent edit) Low end is a bit lacking. Solution - take C11, C12 47nF up to taste. 220nF should be more than sufficient.

So I'm swapping out my C11 and C12 for 220nf's, how do I know on the board where these are located? there are 12 of them.

also, will these work

http://www.ebay.co.uk/itm/20-Polyester- ... 53e8dda344

Cheers


Top
 Profile  
 
PostPosted: Fri Mar 22, 2013 7:07 am 
Yes those caps you link to are suitable.

The PCB layouts for all BYOC product are available in a sticky thread at the start of each section, like this -

http://www.buildyourownclone.com/board/viewtopic.php?f=29&t=39393

The Phase Royal is the second layout down.
C12 is on the left of the PCB, just above the diode and C11 is to the immediate diagonal right of C12.


Top
  
 
PostPosted: Tue Mar 26, 2013 6:10 am 
Offline

Joined: Wed May 27, 2009 4:27 pm
Posts: 25
just a quick reply after i've modded my circuit.

Sounding so much better. Yet to play it through a big amp but it's really noticeable difference,

Thanks

B


Top
 Profile  
 
PostPosted: Tue Apr 23, 2013 8:08 am 
Offline
User avatar

Joined: Thu May 15, 2008 11:39 pm
Posts: 1898
Location: Melbourne, Australia
I did the Q7 base/emitter resistor mod...no difference at all. My byoc phaser is a major disappointment in comparison to the many other builds I've done. I'll work through the other mods but right now it's sounding very ordinary. I have a vintage Block logo phase 90 and Boss PH1-r also for comparison.

_________________
tonedeaf wrote:
If you like it, boom - there's your last glory hole filled.


Top
 Profile  
 
PostPosted: Tue Apr 23, 2013 8:42 am 
I'm afraid the BYOC Phase Royal is not one of their better efforts, as should be obvious from the level of mods I suggest, there is a lot of room for improvement.

The output transistor circuit (Q7) is I believe inherited from the MXR phasers and in those it generates a certain amount of distortion. Because of that it is regarded as part of the MXR sound and MXR nuts insist on having it, even though it isn't a very good way of output buffering. In the MXR circuits it is DC coupled to the op-amp and the Vref biasing arrangement is a different from the circuit as adopted by BYOC. The original reason I suggested the mod was that that transistor ended up very poorly biased and tended to generate a lot of distortion. The mod attempts to re-bias that stage to provide an increase in signal swing before clipping.

Note that in the BYOC implementation Vref is connected to the emitter of that transistor. I would suggest you do the Vref mod as well since that will affect the biasing of that transistor. It might be enlightening for you to measure your Vref (which is supposed to be 5.1V).


Top
  
 
PostPosted: Tue Apr 23, 2013 3:04 pm 
Offline
User avatar

Joined: Thu May 15, 2008 11:39 pm
Posts: 1898
Location: Melbourne, Australia
Thanks Tark.
I measured voltage between base and emitter of Q7 and it was something like 1.8v.
Very low. Is this where I measure vref?
Maybe I could swap r37 for a trim so I can dial in the correct voltage.
I really hope to get this in the ballpark of my vintage Block logo, cos I wanna put the phaser and flanger in one box.

_________________
tonedeaf wrote:
If you like it, boom - there's your last glory hole filled.


Top
 Profile  
 
PostPosted: Tue Apr 23, 2013 7:26 pm 
The base to emitter voltage on any forward biased silicon transistor can never be much greater than 0.6V so either there is something wrong, or you are measuring the wrong points, or your meter is not set correctly / is faulty.

The emitter of that transistor is connected to Vref so you should measure between circuit ground and that emitter. You would likely see something like 3V.

Using a trimmer for R37 is not the right thing to do.

Vref is supposed to be a stable reference and its voltage should be set by the zener diode D2 which is specified as a 5.1V zener so ideally Vref should be 5.1V. However there is a manufacturing tolerance on zener diodes of perhaps 20%.

The zener diode provides a stable Vref because it has a fairly constant reverse breakdown voltage drop (in this case 5.1V) over a range of currents. The current flowing through the zener is set by R37 as follows 9V (the supply) minus the zener voltage of 5.1 = 3.9V. R37 is originally specified as 10K so the current flowing through it and the zener is I = V/R = 3.9/10 = 0.39mA.
What is required is that R37 provides enough current for the zener diode to operate at its rated voltage drop and to supply any extra current required by the other pats of the circuit connected to Vref. Now the problem is that at 0.39mA there is not really enough current flowing for the zener to stabilise at its rated forward voltage. I have only just managed to find a data sheet for the 1N4733 and that particular zener is rated at 1W and specified at its rated voltage at a forward test current of 49mA !!! (at 49mA the 1N4733 is still only operating at about 1/4 of its rated power).

One might suspect that in fact the 1N4733 is the wrong part to use in the Phase Royal circuit, a zener rated to stabilise at currents of only a few milliamp might be a better choice. I did not realise until now that BYOC were shipping such a heavy duty zener in that kit.

Anyway as I say in my original mod notes, even with a lower wattage zener, the zener is current starved and does not reach its stabilising voltage. A 2.2K or even a 1K resistor for R37 would be a better choice. It does not need to be a variable, once a fixed resistor is chosen and fitted that allows the zener to do its job that is al that is needed.


Last edited by Tark on Tue Apr 23, 2013 8:07 pm, edited 1 time in total.

Top
  
 
PostPosted: Tue Apr 23, 2013 8:05 pm 
Well that's weird - I have just looked at both Small Bear and at Mammoth and they only seem to stock these relatively high power 1W zeners.

If you go to even a 0.5W rated part like the Vishay BZX55C5V1, that zener is rated to give its specified forward voltage of 5.1V at only 5mA (with a manufacturing tolerance of between 4.8V and 5.4V).
You could get away with running that zener via a 1K resistor in the Phase Royal or if you really wanted to save on the effect supply power drain you might be able to increase it to 1.8K.

Even better would be a 300mW or even 200mW zener, but one of the problems today with sourcing low power zeners seems to be that they are mostly only available in surface mount packaging, which may explain why BYOC are using such an inappropriate and in this instance, poorly performing, part in their kit. A few years ago in the heyday of analogue guitar pedals, axial lead low power zeners were the standard and in plentiful supply.


Top
  
 
PostPosted: Tue Apr 23, 2013 9:18 pm 
Offline
User avatar

Joined: Thu May 15, 2008 11:39 pm
Posts: 1898
Location: Melbourne, Australia
Great info mate thanks.
In my haste to try a trim this morning before work I obviously exceeded that zener's specs and I fried the bugger
Damn. I'll revisit it tonight.

_________________
tonedeaf wrote:
If you like it, boom - there's your last glory hole filled.


Top
 Profile  
 
PostPosted: Wed Apr 24, 2013 12:11 am 
Offline
User avatar

Joined: Thu May 15, 2008 11:39 pm
Posts: 1898
Location: Melbourne, Australia
Excellent work on that Zener!

So if it replaced with a 500mw or 300mw Zener, does R37 still need to be swapped out for a lower value of 2.2k? Or will the 10k resistor in R37 work well with a lower mw Zener?

_________________
tonedeaf wrote:
If you like it, boom - there's your last glory hole filled.


Top
 Profile  
 
PostPosted: Wed Apr 24, 2013 2:21 am 
The short answer - R37 should be somewhere between 820 ohms and 1.5K. 820 ohms is more likely to give you a stable 5.1V but places a higher load on the battery if you use one.

Any change to Vref will require re-biasing the FETs with the VR5 LFO Bias trimmer (this is partly why Vref needs to be a stable voltage - you don't want that bias drifting around with changes is temperature or battery voltage).

The original 10K will give you only 0.39mA flowing through the zener which is still way too low to produce a stable 5.1V in that circuit.

The choice of resistor is on the one side governed by how much you need through the zener to achieve a stable zener voltage, and on the other by how much you are prepared to load your battery by (if you use one).

If you choose to increase your battery load by about 5mA then 5mA would be a healthy current for the zener and should ensure stable operation. Don't forget, that resistor has to supply current to everything that is connected to Vref and current that is diverted to all of that stuff is not flowing through the zener. So if you calculate the value of the resistor just for a certain current through the zener the actual current flowing through it will be lower. For 5mA ... R in K = (9 - Zener voltage)/5 = 3.9/5 = 0.78K. 820 ohm is the nearest.

If you want to keep your battery drain down you can perhaps sail a bit closer to the wind on the zener and double that to roughly a 1.5K (2.6mA). How low you can go on the current and still get a stable 5.1V depends on the zener characteristics. My previous suggestion of 2.2K was really optimistic.


Top
  
 
PostPosted: Sun Jul 21, 2013 7:13 pm 
Offline

Joined: Tue Jan 17, 2012 12:43 pm
Posts: 643
Location: Between sjaustin and duvoodooman
About to start by build. Can I assume that BYOC has not changed anything yet and these mods are all still potential "mods"?

_________________
Twisting and tinning is for chumps.


Top
 Profile  
 
PostPosted: Sun Jul 21, 2013 8:03 pm 
Offline
Moderator
User avatar

Joined: Wed Apr 26, 2006 5:14 pm
Posts: 8659
Location: Truckee, CA
oldlefty wrote:
About to start by build. Can I assume that BYOC has not changed anything yet and these mods are all still potential "mods"?

Yes, your assumption is correct. The circuit has not changed.

_________________
MasterDelayer/Reverbrador/Ampaholic/TopJacker


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 60 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 6 hours


Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group