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Re: Ross Phaser notes(for those who care!)

11/21/2002 10:57 PM
Mark Hammer Re: Ross Phaser notes(for those who care!)
Good question. You will note that the Small Stone and Univibe both use passive mixing to combine dry and wet (as do John Hollis' designs too). Assuming passive mixing is used (and with a Ross phaser the likelihood of input and output buffers a la BOSS is negligible) there is no requirement to use one of those op-amps to do the mixing. You can also make an oscillator from a single op-amp if you want (though perhaps not the world's greatest), so it is technically possible for the Ross to have 6 stages with only those 4 chips. If the input buffer is a transitor stage, that increases the likelihood of there being 6 allpass stages because now one of the op-amps doesn't have to be allocated to that.  
So, now I'm wondering what else is on the board.
11/21/2002 6:07 PM

My Orange USA Ross has the LM13600N ICs. Clearly the case color and even place-of-origin is not a trustworthy indicator of which circuit a given Ross unit has. What is the Model and Serial # on your Ross Phasers?  
Here's another twist - I have an Orange Taiwanese Ross Phaser; looks just like my USA Ross except there's a box around the Ross logo and the word Phaser is in heavier script. It sounds pretty much the same as my USA Ross (it's on the pedalboard in my Studio right now so I can't look inside.  
My USA Ross is P/N 405-0007-42, Serial# 70160; the Taiwanese is marked Model R99.  
Both my Ross Phasers sound great at a slow to medium sweep speed, but coarse and barely usable at high sweep speed. I'd love to find a way to correct this. Anyone else have this problem?  
Here's a good photo of the insides of an earlier model:
11/21/2002 6:27 PM
B Tremblay

The link Jim gave is for the photos of my Ross Phaser. There are (4) Malaysian RC4558P and a socketed 14-pin IC. The numbers on the 14-pin IC are:  
first line: double squiggle logo (NS?) 929  
second line: AM97C11CN  
I have no clue what this IC is.  
It's also curious that there is an empty 8-SIP socket on the board.  
11/21/2002 10:17 PM
Mike I.

AM97C11 is most likely a National Semiconductor CMOS analog switch or multiplexer chip - the old Nat Semi Audio Handbook showed a design using a AM9709 multiplexer chip (used for a FET variable resistance, not for it's intended purpose as a switch).  
Regards, Mike
11/21/2002 11:02 PM
Mark Hammer
A-ha! So if it is using the 9711, then there may well be 6 stages in there, or at least the components might well support 6 stages in the all op-amp version. If so, then the 3*13600 version may well be an attempt to get 6 stages more eassily and cheaply.  
(BTW I order 5 sets of 3207-3102 combos from L-Tronix. Should be able to pick them up on Saturday)
11/22/2002 12:08 PM
B Tremblay

I read somewhere (regarding a phaser's IC) that an equivalent chip of today's manufacture would have better bandwidth handling; is this true for the 9711 in my Ross Phaser? I only ask because it is socketed and would be an easy swap.  
I realize I could probably lessen noise by replacing the four 4558 with TL072, but they're not socketed...  
11/21/2002 6:28 PM

Is threre a second board under that one from the picture?  
I'm really interested in cloning one of these. I bet they sound killer. And not having to drill the MANY holes in my Small Stone CA3080 adaptation to have an OTA phaser would be great.  
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