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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  PH-1r problem, need help. 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: PH-1r problem, need help.  (Read 3278 times)
wui223
Posts: 282


PH-1r problem, need help.
« on: April 29, 2007, 09:37:02 PM »

My friend sent me a Boss PH-1r for repair. It got effect sound all time, problem is i couldn't switch it to bypass mode and the LED is light up all time. As i couldn't find a schematic or service manual for it, i am looking for advice on how to fix it.
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tonda
Posts: 10


Re: PH-1r problem, need help.
« Reply #1 on: September 25, 2007, 11:50:38 AM »

My friend sent me a Boss PH-1r for repair. It got effect sound all time, problem is i couldn't switch it to bypass mode and the LED is light up all time. As i couldn't find a schematic or service manual for it, i am looking for advice on how to fix it.



I need the schematic for PH-r too... Can anybody help me?
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Mark Hammer
Posts: 22226


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Re: PH-1r problem, need help.
« Reply #2 on: September 25, 2007, 12:29:42 PM »

I have the PH-1 schematic.  How close are they?

BTW, nice to see you back Tonda.  icon_biggrin   It's been too long.

EDIT:  Is this it?
« Last Edit: September 25, 2007, 12:33:50 PM by Mark Hammer » Logged
Mark Hammer
Posts: 22226


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Re: PH-1r problem, need help.
« Reply #3 on: September 25, 2007, 12:47:58 PM »

Here's the PH-1 schem:

As far as I can tell, the chief difference between the 1 and 1r is the presence of a Resonance/feedback control (there is NO feedback in the PH-1).  I imagine the rest of the circuit is the same.  If the issue is somewhere outside the feedback loop then the PH-1 schematic should do you just fine.
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tonda
Posts: 10


Re: PH-1r problem, need help.
« Reply #4 on: September 28, 2007, 05:36:30 AM »





Thanks, but PH-1 R uses different PCB and ICs:(
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tonda
Posts: 10


Re: PH-1r problem, need help.
« Reply #5 on: September 28, 2007, 05:38:18 AM »

http://picasaweb.google.cz/tondasalvation/Ph1r
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tonda
Posts: 10


Re: PH-1r problem, need help.
« Reply #6 on: September 28, 2007, 08:02:39 AM »

And my problem is: pedal in ON mode is A LOT LOUDER than in bypass mod. I need to mod it for lower volume when pedal is on:(
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Mark Hammer
Posts: 22226


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Re: PH-1r problem, need help.
« Reply #7 on: September 28, 2007, 08:34:40 AM »

Again, I am not certain if the schematic I showed above for the PH-1 is identical to the PH-1r, but it likely has one characteristic that might be the problem. 

Normally, in many commercial modulation pedals, the "bypass" consists of a single FET that completes or lifts the connection between the modulated signal and the mixer stage.  In the case of the PH-1, at least, you can see that the control line from the flip-flop circuit turns Q5 and Q6 on and off simultaneously.  What it looks like is that in bypass mode, Q5 and Q6 are off, such that the phase-shift signal does not reach pin 3 of IC2, and R18 (5k6) is placed essentially out of circuit.  With the mixer-stage's gain set by R21 (10k) and R19 (1M), it is effectively a unity-gain stage.  When Q5 turns on, however, R18 is placed in parallel with R19, raising the gain to roughly x2.79. 

I gather the gain change is to compensate for the loss in volume produced by the notches, and maybe even to provide just a tiny bit of increase in overall level for solos.  It is easy to imagine that a 5% tolerance on R18/19/20/21 could lead to the gain-compensation in "ON" mode being adequate in theory but too much in practice.  For example, if R21 was on the high side (a bit higher than 10k), and R18 was a bit on the low side (lower than 5k6), the gain would be slightly higher than the theoretical x2.79 in effect mode.

Does that make sense?  Does it fit what you hear?

NOTE:  Although the board has a different layout, much of that can be attributed to use of 4 dual op-amps instead of two quad op-amps.  My guess is that there is really not very much changed in the basic design except for the addition of regeneration/feedback.
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Sindran
Posts: 31


Re: PH-1r problem, need help.
« Reply #8 on: October 22, 2007, 09:16:44 AM »

I just got my "new" PH-1r.  Cheesy

Its great sounding phaser. Finally the sound I've been looking for...BUT

The pedal definitely has a huge volume boost.

SO: Is there a simple way to lower the output of the pedal, maybe by adding a trimmer on the output stage???

PS.
I have Small Stone also. Another great sounding phaser, but I cant use it because of the volume drop!!!  Sad
I've been trying to found a good and usable phaser for years, can it really be this difficult to match the output of  phaser with clean signal???
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tonda
Posts: 10


Re: PH-1r problem, need help.
« Reply #9 on: January 01, 2008, 03:31:45 PM »

Hi,

so, schemo is here: http://www.geofex.com/FX_images/Boss%20PH-1r.pdf

Please,
hat is the best way to LOWER WET signal?

Thank you all in advance

Tonda
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R.G.
more
Posts: 16296


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Re: PH-1r problem, need help.
« Reply #10 on: January 01, 2008, 05:41:33 PM »

It turns out that there are inherent design issues with phasers which merely cancel the phase delayed signal. These problems lead to a simplest solution of having a careful balance of dry and wet signal as well as output level.

In the PH-1r, the dry signal goes through the input buffer transistor (gain appx 1), then to the regen mixer (IC1B), again with a gain of about 1. Out of the regen mixer stage, the dry signal goes to the output mixer stage at a gain of 1, and to the phase line with a gain of 1/2. The phase delayed (wet) signal comes out of the phase delay line and is mixed into the output mixer with a gain of 2 to make up for the loss of 1/2 at the input to the phase stage. The wet signal is interrupted before the output mixer to do a "bypass".

And the design issues center on the fact that to get good phase notches, the dry signal and wet signal must be of the same size at the output mixer. However, with regen, the mixed output signal is apparently louder than the dry signal. So you can't really up the dry signal size or cut the wet signal size; you have to keep them balanced. And that balanced mix is a different volume than the dry signal when you just switch out the phase delayed wet signal.

The simplest good way to do it is to take another switching JFET and change the gain of the dry signal path when in "bypass" mode, then to rebalance both dry and wet signals into the output mixer so that they have the same apparent loudness when mixed and the effect is enabled.
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R.G.

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