February 7, 2009 at 9:31 am #15166docduneParticipant
Are there any differences in the compression attack and release values between an SC2 version 1.05 and SC2 version 1.10. If so, what were they or any other design changes in the core compression circuitry.
ThanksFebruary 7, 2009 at 11:26 am #15457Ted FletcherKeymaster
There’s a lot more to this question than meets the eye (or ear).
The attack circuitry of all my optical compressors operate by making high surge currents available through the LED; initially, with the older Joemeek circuits, this worked to overcome the very slow response time of the light-dependent resistors (the light cells). Nowadays, this is less important as I use a much faster reacting cell.
The very early compressors used a little transistor array as the current drive, and in the earliest SC2 (the ones with a bevelled edge front panel) the power supply was only just capable of driving the required high currents, so the later compressors did sound just a little tighter because of an improved attack response.
The release circuitry was always a ‘compound’ circuit responding quickly to transients, and more slowly to steady sounds ( this system is usually called ‘auto’ by other manufacturers). This arrangement never changed on the SC2 through all the variants, except on very late SC2.2 models where I think I shortened the release times generally.
One of the ‘secrets’ of the SC2 sound was a little trick that I still use, to make the compressor release time actually shorten just before compression releases completely. This makes for a very odd looking release curve, but is great for compressing drums.
So, to answer the question directly, yes, the old V1.05 still had a slightly ‘soggy’ power supply and is probably the most collectable SC2 nowadays. The later ones had a slightly ‘tighter’ sound due to the attack curve being more controlled.
As a matter of interest, the new P38EX has settings that can duplicate the early SC2, but without the image shift that the early compressors were prone to suffer from.February 9, 2009 at 7:56 am #15455whitepapagoldParticipant
I noticed in another thread you repair your old units. Is the degradation of the photocells on the SC2 (I have the first revision 1.05) fixable as well? Without any changes to the circuit? Are the original parts still avaliable?
I ask because as expected, my left and right levels have fallen off especially during compression- so I assume its either the photocells or the unit is just out of spec and needs servicing. Even bypassed the left and right are slightly off .3 to .5 DB- which makes me wonder if its just the photocells.
Just curious- the problem isn’t horribly bad yet but it would be good to know its fixable if it gets out of hand!
JosephFebruary 9, 2009 at 9:14 am #15456Ted FletcherKeymaster
Joseph, it’s unlikely that there’s anything wrong with the old SC2 V1.05 other than wear in the input gain pot…. that’s the most common cause of unequal gain in the channels. This was particularly so with the ‘Omeg’ pots used at the time (easy to identify…. take the knob off and look at the shaft, if it’s black plastic, it’s an ‘Omeg’.) Later units used ‘Alpha’ pots which are superior.
It’s true that some LDR cells do deteriorate with time, but in the SC2 version 1.05 I remember we used a type of cell that is well sealed and I have not found one ‘aged’ yet.
Back to gain shifts…. this is a constant problem with all 2-channel systems; the accuracy of the pot tracks has to be VERY good to meet a criterion of even plus or minus 1dB. The old ‘Omeg’ pots had backlash between the tracks and were notoriously poor in this respect.
Yes, I do have stocks of the parts for the SC2, but not those input gain pots, we now use ‘Alpha’ pots and switches.February 10, 2009 at 1:45 am #15458whitepapagoldParticipant
Thanks so much Ted. It still amazes me I can ask you directly- extremely helpful and thorough! Especially considering I am so nuts for the SC2- its a fun compressor to work with. Ive got an la2a, 33609, 1176ln and NONE of them punches like the sc2!
I also noticed you added an external sidechain input to the p38-ex,very nice!
Again, thanks for being accessable!
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