Changing opamps in Symetrix 501 and 522

Changeng,
  Like you, I started off modding things by looking at opamps, and my experience and time here has taught me a lot. I've enjoyed Pauls' responses in this thread and have learned along with you about shoring up power supplies.
  My two cents...you won't notice as much improvement by playing with ICs as you will from replacing old electrolytic caps, especially in the signal path. I've found that putting signal path bipolars in gear like your Symetrix can help, since these things use electrolytics in place of transformers on the inputs and outputs. Bipolars give better response in the upper mids and high end, that can't be had in 'lytics, except perhaps with some bypass caps... but let's not get into that.
    Seems like you can tell which caps are in the signal path, so 'nuf said.
  There is improvement to be had in opamps, especially if you are upgrading from something like a 4560, but in mixers, stompboxes, compressors, interfaces, etc. I've found the caps have as much or more to do with the overall quality of sound.
    I put some bipolars in the ins/outs of a Delta 1010, based on info from another thread here, and was really pleased with the results.
    I'm modding a Symetrix EQ now. Will probably make similar moves with it's PSU.
    Thanks to Paul for clearing up something which makes total sense now that I understand what we're doing.

Thanks for your input, tchgtr

Paul has been great, as has been Kingston - I'm looking forward into this new adventure (and it's an adventure til I plug it in and NOT blow the place up...)

I expect the caps to be the more noticeable upgrade - if it works, i have lots of other stuff I'll be pimpin'.  I hadn't thought of a Delta upgrade - I have an old omnistudio that got blown out by a bad tube mic in december - what differences did you notice?  I might jump on that if you've noticed a huge difference.

Better/smoother freq response from @1k up was the most noticeable difference, which was important to me as I mix thru a board. The proverbial "blanket being lifted from the speakers thing", but not in a striking way, just a pleasing clarity to the upper mids and highs. Perhaps the low end is a bit tighter. It now sounds better to me than a MOTU 828mkII I also own, which did not used to be the case.
Of course, if the value of the cap is small enough, and a film cap will fit, that's preferable, but the values we are talking about here are bit too large.

tchgtr said:

I've found that putting signal path bipolars in gear like your Symetrix can help, since these things use electrolytics in place of transformers on the inputs and outputs. Bipolars give better response in the upper mids and high end, that can't be had in 'lytics, except perhaps with some bypass caps... but let's not get into that.

Click to expand...

As I understand it, bi-polar caps are two electrolytic caps back to back. They are primarily used when the DC voltage across a circuit is not defined. The DC voltage will drift (+) AND (-).

Generally, regular electrolytic caps will sound better if they have a constant DC voltage across them.

The high end response can also be improved by bypassing with a small value film cap.

Hopefully Paul can chime in with his nuggets of wisdom on this.

Mark

Hey tchgtr -

which eq are you modding?  I'm thinking of opening up an Aphex 109 and a dbx 242 to hotrod next.  Is yours a cap upgrade?

changeng said:

Hey tchgtr -

which eq are you modding?  I'm thinking of opening up an Aphex 109 and a dbx 242 to hotrod next.  Is yours a cap upgrade?

Click to expand...

  It's an SE-400 that I picked up off CL for peanuts. I'll put a photo below which shows the caps in one channel replaced with films and some polypros. Just stuff I got at the local surplus store. The old green and red caps can be seen on the right and the newer red and silver caps on the left. Can't find a schemo, but did find some suggestions from Jim Williams about upgrading, and it's pretty easy to follow the circuit once the box is opened. Didn't even have to dismantle it to replace the caps, there's so much room inside.
  Compared the two channels (obvious difference and improvement - much of the distortion gone), and then replaced the opamps in the same channel. I left the 5534 on the output of the i/o card, but replaced the input LF353 with TLE2072. Then on each EQ card I replaced the ICs with faster ones, my main purpose to get the 4560s out of there. Used 2072s for the highs and mids, and recycled their 353s to the lower channels. Might try some OP275s later, but for now it's much nicer. Lows are focused and have transients in the mod channel. Unmodded is flabby and vague. Highs are clear and transparent on modded, crunch and white noise on the unmodded.
  Did some power supply stuff today based on this thread, but I only had 100uf to replace the 4.7, so wondering if it was worth it. Easy enough to replace later. On the unreg. side I have 470uf, and found some iffy solder joints there and on the + side regulator, so it was good I checked. The power supply is different on mine from the 501 schemo, so that was a fun puzzle to figure out where the diodes went. I used 4004s as that was what I had on hand.
 I'm wondering if the 4.7uf 'lytics on the power rails of the connector strip that joins all the cards should also be upgraded to larger sizes...
 Its no GML but it's something I don't have in my studio so I'll be glad to rack it up.
  Might consider using bipolar (or Mark, maybe some bypass caps) on the ins and outs, and considered using the balancing info from the 501 schemo, since this unit only has 1/4 inch ins and outs, but (curiously) they left holes for XLR connectors, but plugged them up...
   Will do the other channel tonight. Having too much fun. Need to get a life.  
  Anyway, this thread helped me learn a little more about power supplies. So thanks.

cool!  looks like you've been popping in some little red WIMAs.  are you taking out all those tiny green guys?  I've been wondering what to do with those - they're all over the 522 like a cheap suit - seems like they're more for different functions than the actual signal chain - the 522 does comp, gating and expansion, so I imagine these little guys are handling all that administration.  You should start a thread withthe changes you're making - sooner or later everyone should band together and begin a site for specific modifications they did for specific old stuff.

btw - if you're looking for something kinda neato-keen, I picked up an old Shure M63 eq for $20 - hi and lo pass filters and bass and treble knobs (100 and 10K, I think).  Decent size output transformer and for the most part, decent bits inside - that may become a project soon for re-capping.  actually sounds kinda good as-is. I know some guys use this for bass.  wondering what it would take to make the "bass" and "treble" knobs variable frequencies.  You can cross the hi and lo pass filters with the bass and treble and get all up in it's hizzy.  a wee bit more control would be great, tho.  Odd - it has four or five different types of outs, but only two rca jacks as ins.  Makes an interesting insert tho.

So after five days of suddely dealing with my tax guy (big ups for tax breaks!) i'm finally going to order the parts for this recapping/dioding/opamping dance of danger.

A few last minute questions:

The Diode - Paul suggested 1N4002 diodes across the regulators - on Mouser, the choices are huge and confusing - which should I choose?  Here are teh options given:

1)Termination Style:  SMD/SMT or Through Hole

2) Reverse Voltage: 70 V or 100 V

3) Forward Voltage Drop: 1 V or 1.1 V

4) Forward Continuous Current: 1 A 1 A @ Ta = 55 or  C 1 A @ Ta = 75 C

5) Max Surge Current: 30 A or 45 A

6) Reverse Current IR: 5uA or 10 uA or 30uA

Since it's on the regulators, I'm kinda afraid to just experiment (plus, I love living indoors).

Please help?  If it's easier, here' s the link: http://www.mouser.com/Search/Refine.aspx?Keyword=1N4002

Many, many thanks!

Stuart

Get this one:

http://www.mouser.com/ProductDetail/ON-Semiconductor/1N4002G/?qs=sGAEpiMZZMtEwUVCuofpuN8xD8qvNRjUgL43CLGQgjc%3d

Get some extras; they're a useful general-purpose diode.

Peace,
Paul

Thanks again, Paul.  I feel like I owe you some muffins, or something!

So for all you kids following at home, my final order looks like this :

For the power supply:
6 units of :  URZ1V471MHD - Aluminum Electrolytic Capacitors - Leaded 35volts 470uF 12.5x12.5 20% 5LS

For the signal path: (actually need 20, but getting 6 extra - a gut thing)
26 units of:  UVP1V471MHD - Aluminum Electrolytic Capacitors - Leaded 35volts 470uF 12.5x25 20% 5LS

For the regulator diodes: (actually need 4, but the gut is honking again - maybe it's my diet)
12 units of :  863-1N4002G - Rectifiers 100V 1A Standard

And for the opamps (actually need 12, but I'm gonna throw three into my 501 cuz I'm feeling saucy)
15 units of:  TLE2072AIP - Op Amps Excalibur Lo-Noise Hi-Sp JFET-In Dual

If anything needs changing, PLEASE someone speak up!

And again, thanks one and all for helping me with this thing!!!!

Stuart

UPDATE:  i got the parts - the caps I ordered are physically far, far too large to fit in the 522.  DAMMIT.  I'm new at this and didn't take into account the literal SIZE of the caps.  So I put the 2072 opamps in place of the 4560's and as predicted by several here, the difference is minimal, if any change at all.  In fact, in the Symetrix 501, the 3 new opamps have a dulling effect!  In the Symetrix 522, it is slightly cleaner (since it took 12 new opamps I'd hope so!), but nothing dramatic.  I've only compared them using a mic tho, so i haven't tried any heavy compression yet - i don't imagine there will be much of a difference.

So now i'll re-order caps, hopefully the right size this time.  I hope I find a purpose for these big guys that are laughing at me from the Mouser box.

The "dulling effect" you're hearing in the 501 may be a decrease in high-frequency intermodulation distortion.

Peace,
Paul

Well, THAT makes me feel better!  Thanks Paul - I haven't really pushed the unit yet to see if there is a change to its crunch yet.  I imagine changing out the caps will give me a more obvious tone improvement.

I'm trying to wrap my head around the concept of caps and the tones they give.  Is it true to say that the higher the voltage, the greater the headroom?  And the greater the uF the cleaner the tone?  Or am I oversimplifying it?

  The big thing I notice with replacing such a slow op amp is less clipping of transients. Not so much a change of tone but a sharper attack on sounds. You might see if you notice that.
  Nice comment from Paul...these things can be deceiving.
  Looking at the schemo for the 501, I see it has an output trannie (nice!) and the first cap the signal sees (C7) is a 4.7uf NP (non-polar or bi-polar) after the first IC stage. If this is in good shape, I would rack it up and get to work!
Have fun...
 

Thanks - I'm probably not going to do anything else on the 501 - the schemo is from a later version, so i'm a little leery to pull stuff.  The 522 however is still in my sights, so tonight I go back to mouser and see where I went wrong.  DAM I feel stupid!

changeng said:

Well, THAT makes me feel better!  Thanks Paul - I haven't really pushed the unit yet to see if there is a change to its crunch yet.  I imagine changing out the caps will give me a more obvious tone improvement.

I'm trying to wrap my head around the concept of caps and the tones they give.  Is it true to say that the higher the voltage, the greater the headroom?  And the greater the uF the cleaner the tone?  Or am I oversimplifying it?

Click to expand...

Not oversimplifying, but talking about different things.

A higher voltage rating on the cap is just that -- it'll take a higher DC voltage on its plates before it goes BANG and sends bits of foil all around the room. That matters on caps that are connected to power supplies, usually not so much on caps connected as coupling capacitors for audio -- unless, of course, there is DC on the caps. Then it matters. When you're using an electrolytic for audio coupling, with no DC present, some folks have reported that the higher-voltage-rated capacitors sound a bit less grungy. Since I don't use electrolytics in that application, I don't have any firsthand knowledge about it.

A bigger uF rating means that, for a given load impedance, the bass rolloff frequency will be lower. It has nothing to do with the cleanness of the tone, or it shouldn't at any rate.

So, for example, a 1uF cap with a 10k load will have a bass rolloff frequency of 15.9Hz. A 10uF cap with the same load will have a bass rolloff frequency of 1.59Hz. That'll give you a little more audible deep-bass extension (because a circuit that's down 3dB at 15.9Hz will be about 1dB down at 32Hz, and at least some instruments make noise down there).

Peace,
Paul

Thanks again, Paul. 

I'm having trouble finding 470uF rated caps that will fit to replace the ones in there now - the old ones measure only 4mm diameter by 7mm length - since size is an issue, what is the smallest rated cap you would recommend that would actually make a sonic difference and still fit in this tiny space?  The caps in there now are pretty clean looking - I think they're original, but they don't look like they're worn out.

I really appreciate all your help on this!

Well, now, are they really 4mm x 7mm? Because that's a kind of rare size, if the Mouser catalog is any indication.

You've got two categories of cap here: the ones bypassing the supply rails, and the ones used as signal coupling capacitors. The signal coupling capacitors can probably remain 4.7uF, but it's a good idea to replace them with bipolars; Xicon makes some 4.7uF nonpolars that are 5mm in diameter, which will probably fit in the space.

As for the decoupling/bypass caps on the voltage regulator ins and outs, get the biggest cap that will fit into the space. Here's a hint: get a copy of the printed catalog. If you know what you want, the website's an easy way to find something, but if you want something as fuzzy as "the biggest value of uF at 25V that will fit into a ___ diameter space, it's much easier to look up and down the tables in the catalog.

Peace,
Paul

Hi;

Forgive the thread reincarnation, but for somebody that just bought a 522, this is a total cliff hanger.

What happened with this? I am quite curious about which caps to buy that are appropriately sized, that was where this left off.

I enjoyed the heck out of reading this (i have read it thru twice) andI look forward to trying this mod out at some point.

I start with the power supply improvements so that i can have the wattage needed to support the nicer opamps.

And yes, i do have a meter, a fluke even, and it's older than the 522.....

tnx for any conclusion to the story that anybody can provide.