Removing caps from a NE5532 based mixing console

[GrievousAngel]

Hello to all as I am a new member of this forum. I have a mid-level knowledge (EET) of audio cicuits and applications with ~30 yrs. hands-on in both studio and live sound applications.

I picked up a used Tascam M5000 (with VCA) a few years back and am just now getting into playing (mod'ing) with it. It is 100% NE5532 opamp based with coupling caps EVERYWHERE! I have been told Tascam really over-cooked the use of caps to make the cicuitry stable at the cost of sound and as cheap as possible to be in the mid-level pro audio market. some of the balanced amp circuits appear to be somewhat complicated for the '95 era. anyways . . .

i am replacing the NE5532 with OPA2604 and OP275 with the OPA2604 in the most critical functions (mic / line) including the summing in the master section of the console. I am using OP275 in the EQ circuits and other misc. functions. as a rule the input coupling caps are being by-passed and replacing the output coupling caps with Panasonic FC type Elect. caps of 2-4x the OEM cap values.

specific questions:

1. are the feedback caps (~10pF to ~54pF etc) considered in the audio path, i.e. should these caps be replaced with the same value of poly caps? if so, which type of poly caps are best for audio?

2. Are the Panasonic FC type OK to used in critical audio paths or is there a better type or brand? I was told Panasonic FC are really good.

3. also i was told that the OPA2604 may be alittle unstable, but i have found only one circuit to oscillate (so far). I am using a oscope @ pin1 & pin7 to sniff oscillations. is this where oscialltions would ONLY occur? would loading the opamp output with a 0.05 cap (capactive load) be a real-worl test for stability?

4. in terms of currect requirements, a mixture of ~ 50-50% OP275/OPA2604 be equal to 100% NE5532? per specs it appeears to be k.

5. i am removing the VCA circuits as I will not use the Tascams old Pilot Mix Automation (Mac based) system.

Please consider these steps and offer opinions on my methods.

THX.

peace,
billy

[mediatechnology]

Thanks for joining us GrievousAngel!

I'm not sure that I'm qualified to answer some of your questions as they relate to sonics.

The 5532 is a pretty good performer. You might want to visit Doug Self's site where he compares many of the common op amps:
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm

1. are the feedback caps (~10pF to ~54pF etc) considered in the audio path, i.e. should these caps be replaced with the same value of poly caps? if so, which type of poly caps are best for audio?

I wouldn't bother to change them. Yes they are sort of in the audio path but provide rolloff and compensation. I don't think you'd be able to hear much difference, not as much as you would changing coupling caps.

2. Are the Panasonic FC type OK to used in critical audio paths or is there a better type or brand? I was told Panasonic FC are really good.

I can't comment on the FCs but I've always had good luck with Panasonic caps. As someone who did service for many years I replaced lots of failed caps in MCI consoles with Panasonics. I can count on one hand the number of Panasonic caps I've had to replace. I've got some NOS that are getting close to 25 years old and they still measure well. Of course heat is the enemy of all electrolytics.

3. also i was told that the OPA2604 may be alittle unstable, but i have found only one circuit to oscillate (so far). I am using a oscope @ pin1 & pin7 to sniff oscillations. is this where oscialltions would ONLY occur? would loading the opamp output with a 0.05 cap (capactive load) be a real-worl test for stability?

That is where you would want to look. If you don't see oscillation in circuit I wouldn't worry.

4. in terms of currect requirements, a mixture of ~ 50-50% OP275/OPA2604 be equal to 100% NE5532? per specs it appeears to be k.

Take a look at Self's site. The OPA2604 does have a rising HF THD but IIRC it's second harmonic and some people like the sound. You might want to build up one or a pair of modules and compare them to the unmodified. Be aware of differing supply current requirements and make sure that you don't run out of PSU current headroom. I don't have a 2604 datasheet in front of me right now to compare it to the 5532. The 5532 is not exactly low current so you may not get into trouble.

Thanks again for joining us! I'm pretty sure others will come along and chime in.

Wayne

[JR.]

The 5532 is a fair performer so I wouldn't expect night and day differences from massive swap outs there/
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Regarding the small caps, yes they are in the audio path but typically LPF tuned for 10's of kHz. Logically any non linearity would cause distortion well above the passband but in practice you could also have in band IMD products. This is generally pretty insignificant but you can get small value caps in NPO characteristic which should be adequately linear for that node in the circuit. Do you have access to test equipment? If something is distorting you can measure it.
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I'll second the good experience with panasonic, while in production I have had good experience with most manufacturers, and the few bad experiences were more a consequence of large scale mass production and "stuff" happens. I once experienced thousands of 2200uF electrolytic caps that went open circuit shortly after production when a swaging tool at the capacitor factory that was fastening the lead to the foil failed. I actually had to recall a container full of product when we caught that one, but better to pull back the container than deal with replacing all those caps on the other side of the ocean.
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Power supply demand shouldn't be glossed over in a console. Several extra milliamps in every opamp, times a whole console adds up.. Look at the spec sheets and do the math.
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Stability likewise can be parsed from the spec sheets. The 5532 is unity gain stable, so if replacing with an opamp that isn't unity gain stable you need to look at each circuit and determine if the feedback commanded ranges below stability for the opamp being considered for replacement.

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You have something against VCAs ? Or just old Tascam VCAs


JR

[mediatechnology]

What I would do first is recap the electrolytics in a single channel using Nichicon or Panasonic bipolar electrolytics instead of monopolars like FCs.

Roger makes a good point WRT bipolar coupling caps.

While you're at it you would want to replace the electrolytic supply rail bypass caps, for those you would want to stay with polarized caps.

[snatchman]

Hello. I would definately like to follow this thread. I have the Tascam M-2600 mkII console and have been told that it sorta shares design traits with the M-5000..Especially since mine has been acting up lately and probable just 'itching" to be modded!.... ..Carry on and thanks!........

[snatchman]

Snatchman

I don't know how that console is built, but I would open it and measure the diameter of any signal coupling caps to see if something better would go there. Also check what type of op amps are in there. If it has switch/pot problems things get more difficult. With old electrolytic caps, you will usually notice a low frequency roll off.

rf

Hey Roger. Thanks for the reply. I was told by the Tascam techs that it has 5532s and all the components that's in the signal path, is thru-hole. Don't know what kinda caps, etc are in there. As I thought when I first started researching this, the reason people steer clear of modding the M-2600mKII is they think it's SMT technology! Never heard of anyone modding one.I'm hoping the OP will continue and share his finding on his M-5000 and maybe it'll relate in some way to mine.... ..Continue on please....