Monday, February 1, 2010

Integrated Circuit IC Upgrades

I remember and respect the great, late Tim Smith for his among other things paper and work regarding upgrading synth signal paths and digital synth D/A sections/reconstruction sections. Thank you Tim for the great information and friendship, and God bless and keep you always.

Tim was into the Analog Devices OP275 dual opamp and IIRC the Burr-Brown 0604 as well. He made the ARP 2600 into a new beast through this and other modifications.

I am sorry to have to eventually slightly differ on this, but taste is for each person and there are many choices. Tim and I start with the early discrete machines as a reference, such as the Moog 901 series oscillators, which he called "as close to listening to current as is possible" (again, IIRC, close paraphrase). The Moog and Buchla second-generation and later version oscillators went to early ICs on the outputs (CBS Buchla 158 has LM301A). Going discrete in these cases would be wonderful, but for those with these items, upgrading the ICs is of interest.

I note that the TL071 was created (indicated in the specs) to directly replace the 741, as a direct drop-in, hopefully at least in audio-related circuits (check the paperwork). This should be easy to try on the Moog 921 series oscillators, for example.

I recommend the 071 to at least try as it is much faster than the 741 (and you may only wish for 741-style phase and bandwidth characteristics in vintage phasers, delays, and not in oscillators). In some cases the bandwidth limiting etc. may be required for desirable spectral balance, the Oberheim FVS Four Voice etc. being a possibility, would have to hear the new next to the old to decide. The later opamps have slew rates of 25V per microsecond and over, and depending upon the circuit in which it is used, can result in tight, closed-sounding, controlled, slightly hard or glossy treble and overall character. You might like this. I am tending to the middle ground 07X type, as the discrete oscillators do not sound closed, controlled, tight, etc.

Again, I'd have to listen to two versions side-by-side in order to decide. I'm willing to do so :)

It's a very interesting question, especially regarding oscillators and filter signal paths.

I am of course aware of those who will mock the use of earlier opamps. They should be aware of the effect such opamps have in the signal path of early effects devices compared with their modern counterparts. Some phasers etc. can become too clean, and lose that gut-level musical "Yeah!" result. The same with synthesizers.

Overall spectral balance, especially on a multitimbral device, is very important. You may have seen the EQs in mastering labs; they may have 0.5dB adjustment increments. A musician will be able to hear these adjustments as they are made. A mastering engineer knows where to make these adjustments resulting in an overall musical improvement. I venture that the same occurs in synthesizers.

When I was at Alesis, a musician brought back a prototype of a new version of the QS line, saying that there were (specific problems) in the audio, compared to the older version. We craned our necks and cupped our ears listening for it, and it was there, subtle but definitely measurable on the test equipment. Yes, it was slightly brighter, and yes, this made a difference in overall character and musicality (spare me the "QS sucks!" remarks; I'm well aware, and was working to improve them while I was there, which was part of my personal goal at the company.).

Subtle changes in spectral balance can produce large musical results. Or the inverse.

Pasted from a thread:

Of course I don't recommend swapping the high speed devices into circuits made for the early low-speed devices, without planning ahead regarding optimisation, although it's worth doing blindly in circuits featuring the mid-level ICs such as the 072, just to see what happens. Even in "correctly designed" circuits, I find that the new ICs aren't quite for me, re-read the comments regarding even subtle spectral shifts. Big spectral shifts from "upgrading" or using "new" parts may provide lots of treble, but this immediately reminds me of hi-fi stores back in the day, selling speakers with graphic equalizers set to a "smile" configuration so that it was all boom and zizz. Perhaps impressive to some on a showroom floor, yet useless when considered over time. Some speakers were perhaps even made to this curve...shameful.

"More treble" is not automatically "better". I've long since stated this regarding the spectral balance of certain discrete vintage modules, and stand by it from a long-proven musical perspective. ADAMs, anyone? And again, listen for that closed, tight treble in circuits using the fast ICs. Some call it "audiophile"; I call it "closed and tight". Depends upon what experience you define as "music"...and to reiterate from the above: ..the discrete oscillators do not sound closed, controlled, tight, etc.

The 4558? It's in the TR808, good enough for me. Nice that you and Jurgen have listened to me regarding the need for such "slow" ICs as used in vintage FX, to provide that vintage FX sound. Thanks for listening. I see 741s in Jurgen's Schulte phaser clone, so that it will sound that close to the original. Very, very good. The 4558 is only just better than the 741, I -will- look into substituting it out in my CD changer, but will replace it if nothing sounds better -to my ears-.

Also, don't overlook the J-FET chips such as the LF353. Very useful for good-sounding upgrades of early chips, but not "too far" into the changes described earlier. Same sort of slew rate as the 072.

I am however perplexed at the need to use a $4.00 opamp to achieve the frequency reponse, dynamic range, and musicality of the old discrete transistor output sections, which are far less expensive and already a standard of sorts...

Isn't the 748 in the output sections of the Moog 921 and 921b? Don't have time to refer to the schemo. Yep, that should be replaced (by whatever is to you, musical). I'd prefer some sort of cheap, discrete transistor output as it's established and less expensive than some opamp choices.

luka wrote:

i agree re: 4558s in 808 jeff found that in mb808 using tl072 made the sounds to clean and lost the 808 vibe. 741s in the schulte phaser sounded great

I replied: Interesting about it "losing vibe". Yes, I agree (and many high-end stereo designers also agree) about vibe or musicality being first, being the goal. Yesterday I was reading a review about a particular Pass amplifier, about it being supremely musical (paraphrasing?) and that this negated its weaknesses. I'm in that school of things.

the bad producer:

071s are a good idea, as listed in its paperwork. Drop them right in without worry of any sort. You'll likely get a much cleaner sound, which you might or might not enjoy. I find that I prefer phasers to have that "vintage" midrange blur and whoosh. It gets me to say "yes!" and is to me musically inspiring. The Moog is the only recent phaser which causes in me a grinning musical response. I wonder what they're using, and how much is the result of the excellent overdrive circuit.

Muff wrote:

Well put, I think that's the heart of it. If one person likes a sort of character to sound, and another likes it differently, neither is wrong. Preferred musical style is the same. We do this for fun and enjoyment! I don't understand people who deride the preferences of others when it comes to subjective things. No matter what the test equipment may or may not say, if you like it one way, you like it that way. Simple as soup.

This is an interesting thread. Many may not realize that parts of their gear can easily be swapped in and out to change the sound character. This is fantastic for those who like to tweak, explore, tailor things to their liking. There's no wrong move if it is an improvement to the ears of the owner. Thanks for posting this Mike.

I replied:

IIRC in the DIY world there is a preamplifier which allows the user to select the opamp they most prefer, and a number of ICs are suggested for review. I really love this idea, and would love to see it take hold in the synthesis field. Including discrete opamps such as the inexpensive kits on Doesn't the Cirroco synth use discrete opamps? I wonder what that would do, on oscillator outputs, summed together, of if that doesn't do much, on the oscillator mixer and VCA outputs.