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PostPosted: Wed Feb 22, 2017 9:39 am 
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I have read some of the past posts (particularly by @Tark) regarding the 5.1 (1 Watt) zener diode supplying the reference voltage for the circuit. Measuring my build, I get a Vref of 4.1V with a 9.0 Volt DC source (from a Decibel 11 pedalboard power supply). Something @Tark proposed before was to try a lower wattage 5.1 zener. I have access to some 400mW. Was hoping for some confirmation as the zener is a bear to pull being under the IC socket on the other side of the PCB. What is Vref on some other builds? I am ultimately thinking that with an actual 5.1 Vref, a better phaser would result.

Would a 6V zener perhaps offer higher Vref? Thoughts also on upping the resisters in the phase shift networks from 22k to 100k? Would this create less draw on Vref and thus a higher Voltage?


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PostPosted: Wed Feb 22, 2017 10:28 am 
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Think I found my answer from the previous @Tark post on 4/23/13:

"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."


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PostPosted: Wed Feb 22, 2017 10:36 am 
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If you don't mind my asking, why are you trying to mod the Phase Royal? Is there something you're not happy with about it? You said 'a better phaser would result' - but better how? It's easier to target modifications if there's something specific you're after.

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PostPosted: Wed Feb 22, 2017 11:23 am 
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@Tonedeaf. Thank you for your excellent point for me defining what I am looking for. Always good to have a place to start from. The phaser is working well. I used a set of matched FETs from guitarpcb for the build so I am hoping that they are in the ballpark. Really didn't want to get into matching.

The first thing that I would like to better (not mentioned in this topic) is removing the clipping with higher output pickups. I can alleviate this by rolling back the guitar output about 25% but I lose some tone. I am really looking for a clean, bright phased tone. I am going first to try a previously mentioned post of @Tarks of installing a 68k resistor between the emitter and base of Q7. The other option i suppose is to connect the Q7 emitter directly to the 9V source rather than the Vref. Still looking for the bias resistor value (emitter to base) for the correct voltage on the base of 4.5V.

Secondly, I would like to get the phase cycles to have a bit more "oomph" on the bottom portion of their swing. More similar to a well tuned Script 90 or Univibe. The kit I have already had a 10uF for C12 and a 4.7uF for C11. I realize these are in the dry path, but that is what is shipping in the kit now.

My thinking is that with a Vref of 5.1 instead of the current 4.1, the phase-shift circuits would perform .... uh .... "tighter?" ;-). Ah well, its a stab at it. Wondering if 5% tolerance caps for the 47nF in the opamp circuits would have an effect?

Thanks again.


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PostPosted: Thu Feb 23, 2017 8:44 am 
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I had the time to try a few of the modifications to try to get higher headroom and a deeper phase. By far the most pronounced change came from swapping R31 from a 2M2 resistor to a 1 meg. This had the effect of really deepening the phase sweep. So much in fact that running the depth control at 12:00 was sufficient for a deep phase where before I was full out and still wanted more. The drawback was that the BIAS trimmer was full-on for the sweetspot. I am going to try a 1M5 for R37 and see if this allows the BIAS trimmer some room.

Placing a 68k across the emitter and base of Q7 was not a fix for me for increasing headroom. Still getting clipping with high output pickups. I am going to try connecting the emitter to the 9 volt source with a 33k across emitter and base and see if this helps.

I replaced the R37 10k with a 1k resistor. This did have the effect of increasing Vref from 4.1 to 4.85 Volts. This change did not have the pronounced effect of deepening the phase nearly as much as the R31 swap.


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