I did some mic preamp research in an earlier post, and I ran across a deal on a Symetrix SX202 that I couldn't pass up, and since it was on my good list and in my price range (aka cheap) I bought it. The catch and main reason I went for it, there are tons of documented mods to this (main one by Monte McGuire), most of which involve changing the op amps out. So when I make the plunge for a high roller pre, I can mod this one up.
The main mod is changing out 4560 ICs and replacing the compensation caps on the new IC's. It should be a pretty straight forward process.
-The manual pdf
-The Gear Slutz Forum- This has good info and is the best starting place.
-A Tape Op Message Board Mod Post- it has some specific IC's to change out
and even has the digikey part numbers for the compensation cap change out.
-A Tape Op Message Board Mod Post- it has some specific IC's to change out
and even has the digikey part numbers for the compensation cap change out.
-A very in depth Audio Banter Board Post- with direct direction from Monte McGuire
-Audio Upgrades- They mod all kinds of stuff, and I saw on a board post that the did this pre for about $300 bucks. The main with the plan here is Jim Williams, and he has mad rep on the tape op and gearslutz boards.
-I am going to need this rack or something similar so I can be cool.
"The one mod you'll get the most bang-per-buck out of, after replacing
the output chips, is recompensating the SSM2015 chip. It's only three
small caps per 2015 chip, easy to do.
SSM 2015 Compensation:
----------------------------------------------------------------------
The next area for improvement is to change the way the SSM 2015 mike
amp stage is compensated. The SSM 2015 is the heart of the mike amp
and it provides all but 6dB of the gain of the completed circuit. The
SSM 2015 requires three small valued capacitors to set the internal
feedback structure at high frequencies. By changing these values, not
only is the stability of the circuit affected, but the high frequency
distortion and slewing behavior are also greatly affected.
The rev. C boards have less than optimal values, but the rev. G boards
have values that drastically increase HF distortion with no other
benefits. The capacitor betwen pin 1 and pin 13 of the 2015 is the
most critical capacitor, and the rev. G value of 47pF is simply too
large. Changing this to 7.5pF will move the frequency at which
distortion sharply rises up an entire decade from 3-4KHz to over
40KHz. The common mode amplifier capacitor should be increased to
56pF. I do not know why this improves HF distortion, but it does.
These caps are located at both ends of the 14 pin SSM 2015 chip and
look like little orange-ish tan discs with two leads. For rev. C
boards, change C9 and C18 from 47pF to 7.5pF, change C8 and C17 from
10pF to 7.5pF and change C7 and C16 from 47pF to 56pF. For rev. G
boards, change C12 and C29 to from 47pF to 7.5pF, change C13 and C30
from 47pF to 7.5pF and change C16 and C32 from 47pF to 56pF.
In case I got any component legends wrong, make sure these are the
capacitors connected to the SSM 2015 chip after you do the mod: 7.5 pF
between pins 1 and 13, 7.5 pF from pin 1 and ground and 56pF between
pin 6 and pin 7.
Select a quality monolithic ceramic capacitor with .2" radial lead
spacings that uses the NP0 / COG dielectric. You could use a
polystyrene capacitor instead, but it must be noninductively wound and
be connected with short leads to the PC board or it will not function
properly. Note that the NP0 dielectric is a very linear dielectric,
far different than conventional ceramics used in bypass caps. Since
the capacitance is so small, degradation is very unlikely even if the
dielectric weren't so clean, so, in my opinion, there is little
benefit from using anything but a high quality NP0 ceramic capacitor.
In my units, I made the 7.5pF capacitor up out of two series connected
15pF NP0 surface mount (0805 size) chip caps. It takes a little
dexterity and a tiny bit of hookup wire to arrange this, but it can
work out well. Alternatively, through hole parts can easily be used
here too.
To illustrate the benefit of this mod, a stock rev. G with 5532 output
amplifiers but the stock compensation caps will produce almost 1-2%
distortion at 100KHz, whereas the same amp with the recommended
compensation caps will produce less than .01% distortion at 100KHz.
This is measured with the circuit set for 40dB of midband gain, 150
ohm source, 600 ohm load and a -20dBV input. That's +20 into 600 ohms
at 100KHz... at .01% distortion!"
After having this unit for over a year, the power supply died. The specs= sx-202 power supply- Tamura- 420A0008- 16.5V AC 600mA. Symetrix doesn't make them anymore, and Tamura has changed the model number according to board posts. The problem was the strain relief bit the dust and the wires broke coming out of the wallwart. I did know it was the PSU as it started to show signs of a loose wire in my last session.
In my research I found the following recommendations.
-From All Electronics-
-New Model of Tamura (maybe?) on IC Supply-
-Per a Gearslutz recommendation- Go with Jameco-
-A TapeOP recommendation from this Boardpost- DigiKey version-
Update- 4-18-2011-
I went with the Jameco version. Part Number= 100108,16VAC/1A,and it was about $20 including shipping. It worked like a charm.
-----I am also copying and pasting part of a post by Monte McGuire off the google groups list (it is recited verbatium in above posts as well)-----
"The one mod you'll get the most bang-per-buck out of, after replacing
the output chips, is recompensating the SSM2015 chip. It's only three
small caps per 2015 chip, easy to do.
SSM 2015 Compensation:
----------------------------------------------------------------------
The next area for improvement is to change the way the SSM 2015 mike
amp stage is compensated. The SSM 2015 is the heart of the mike amp
and it provides all but 6dB of the gain of the completed circuit. The
SSM 2015 requires three small valued capacitors to set the internal
feedback structure at high frequencies. By changing these values, not
only is the stability of the circuit affected, but the high frequency
distortion and slewing behavior are also greatly affected.
The rev. C boards have less than optimal values, but the rev. G boards
have values that drastically increase HF distortion with no other
benefits. The capacitor betwen pin 1 and pin 13 of the 2015 is the
most critical capacitor, and the rev. G value of 47pF is simply too
large. Changing this to 7.5pF will move the frequency at which
distortion sharply rises up an entire decade from 3-4KHz to over
40KHz. The common mode amplifier capacitor should be increased to
56pF. I do not know why this improves HF distortion, but it does.
These caps are located at both ends of the 14 pin SSM 2015 chip and
look like little orange-ish tan discs with two leads. For rev. C
boards, change C9 and C18 from 47pF to 7.5pF, change C8 and C17 from
10pF to 7.5pF and change C7 and C16 from 47pF to 56pF. For rev. G
boards, change C12 and C29 to from 47pF to 7.5pF, change C13 and C30
from 47pF to 7.5pF and change C16 and C32 from 47pF to 56pF.
In case I got any component legends wrong, make sure these are the
capacitors connected to the SSM 2015 chip after you do the mod: 7.5 pF
between pins 1 and 13, 7.5 pF from pin 1 and ground and 56pF between
pin 6 and pin 7.
Select a quality monolithic ceramic capacitor with .2" radial lead
spacings that uses the NP0 / COG dielectric. You could use a
polystyrene capacitor instead, but it must be noninductively wound and
be connected with short leads to the PC board or it will not function
properly. Note that the NP0 dielectric is a very linear dielectric,
far different than conventional ceramics used in bypass caps. Since
the capacitance is so small, degradation is very unlikely even if the
dielectric weren't so clean, so, in my opinion, there is little
benefit from using anything but a high quality NP0 ceramic capacitor.
In my units, I made the 7.5pF capacitor up out of two series connected
15pF NP0 surface mount (0805 size) chip caps. It takes a little
dexterity and a tiny bit of hookup wire to arrange this, but it can
work out well. Alternatively, through hole parts can easily be used
here too.
To illustrate the benefit of this mod, a stock rev. G with 5532 output
amplifiers but the stock compensation caps will produce almost 1-2%
distortion at 100KHz, whereas the same amp with the recommended
compensation caps will produce less than .01% distortion at 100KHz.
This is measured with the circuit set for 40dB of midband gain, 150
ohm source, 600 ohm load and a -20dBV input. That's +20 into 600 ohms
at 100KHz... at .01% distortion!"
Power Supply Unit Issue
After having this unit for over a year, the power supply died. The specs= sx-202 power supply- Tamura- 420A0008- 16.5V AC 600mA. Symetrix doesn't make them anymore, and Tamura has changed the model number according to board posts. The problem was the strain relief bit the dust and the wires broke coming out of the wallwart. I did know it was the PSU as it started to show signs of a loose wire in my last session.
In my research I found the following recommendations.
-From All Electronics-
-New Model of Tamura (maybe?) on IC Supply-
-Per a Gearslutz recommendation- Go with Jameco-
-A TapeOP recommendation from this Boardpost- DigiKey version-
Update- 4-18-2011-
I went with the Jameco version. Part Number= 100108,16VAC/1A,and it was about $20 including shipping. It worked like a charm.
2 comments:
I just got one with the rev-c board in it. Just wondered what you've done with yours so far? I'm going to replace the three 8-pin opamps, the compensation caps, and if I can find a schematic, add the 511 ohm resistor in series to feed the output opamp. It's pretty clean as it is.
I have not even been cracked it open yet. I bought this because I had a project coming up that I needed a clean pre for, and I had read good things on the 202. As soon as I heard that there were mods, it sealed the deal for me. Right now, this is the best pre I have, and I don't trust my self 100% on changing it up.
But, once I get another pre, changing the op amps will be the first thing I do.
Also of note, I think my power supply is on the fritz. Sometimes the unit gets horrible fuzzy crackle (almost sounds like the sound when you have sample/bit rate issue in a computer, but in voltage and not 1's and 0's) when I have phantom. I am looking it to that more.
If you do mod it, take some pics and do some before and after recordings, I am stoked to see what comes out of it.
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