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Need help with console modifications.
Old 30th January 2009
  #1
Gear Head
 
🎧 10 years
Need help with console modifications.

Thanks to all in advance for helping me. I recently purchased a Yamaha m1532. I got it for a very low price. I'd like to add a couple of features to the desk. I'll be doing this to one module, and if it all works out, I'll do the rest.

1. I'll be recapping the console. I've done a lot of research on this and feel confident that I can do this. It's not my first time soldering, modding and such on circuit’s way smaller than this thing has got. Just never on audio gear. I'd like to get info on if I should replace every single cap?

2. I'd like to add balanced direct outs to it. As you can see from the schem, this console has separate jacks for the send and return inserts. I'd like to combine those to a standard TRS insert and use the left over jack space to install the jack for the direct out. On this I really need a how to, I've been looking everywhere, and I know it can be done. I just don't know how. Any suggestions on where to get the signal from and how to wire it to be balanced?

3. This console has 2 sets of input xlrs. They can be switched via a switch on the module just like a mic line switch. However, it doesn't kick down the signal like a standard mic line switch. If I use the second xlr as the return from my DAW, is it going to be okay, or should I put something to kick the return signal down to keep from being blown out of my chair when I hit play?

I'd also read that replacing the op amps can change the sound of the console sometimes for the better, sometimes for the worse? Any recommendations from all m1532 and pm2000 owners out there?

I realize this isn't a top of the line desk, and I know some of you will most likely say why would you want to put all the time, money and so on in to it. I would answer, to learn more about it, that’s pretty much the reason I do anything like this. If this where a way more expensive console, I wouldn't have the guts to open her up.

Thanks

http://i293.photobucket.com/albums/m...mSchematic.jpg

The schematic uploaded funky, so its a bit tuff to read. If anyone can help, I'd be glad to email the original over.
Old 30th January 2009
  #2
Lives for gear
 
🎧 15 years
Hi
1. I'll be recapping the console. I've done a lot of research on this and feel confident that I can do this. It's not my first time soldering, modding and such on circuit’s way smaller than this thing has got. Just never on audio gear. I'd like to get info on if I should replace every single cap?

Only the electrolytics, especially for now but you could change the non electros later although I doubt that would improve the sound significantly.

2. I'd like to add balanced direct outs to it. As you can see from the schem, this console has separate jacks for the send and return inserts. I'd like to combine those to a standard TRS insert and use the left over jack space to install the jack for the direct out. On this I really need a how to, I've been looking everywhere, and I know it can be done. I just don't know how. Any suggestions on where to get the signal from and how to wire it to be balanced?

You will need an output amplifier to generate a balanced signal. You could happily use a DRV134 / THAT corp (i can't remember the number) or equivalent chip on a bit of prototype board or make up a load of small PCBs Wire it's signal either pre or post fade as you wish.

3. This console has 2 sets of input xlrs. They can be switched via a switch on the module just like a mic line switch. However, it doesn't kick down the signal like a standard mic line switch. If I use the second xlr as the return from my DAW, is it going to be okay, or should I put something to kick the return signal down to keep from being blown out of my chair when I hit play?

You could fit a 'pad' (3 resistors) in the wiring from the second XLR. This would involve track cutting if they are PCB mounted. Something like a pair of 6K8 resistors in series and another resistor say 680 Ohms across the transformer input (before the switch!) would give you about 20dB attenuation.

I'd also read that replacing the op amps can change the sound of the console sometimes for the better, sometimes for the worse? Any recommendations from all m1532 and pm2000 owners out there?
Socket and play with other chips after you have recapped.

I realize this isn't a top of the line desk, and I know some of you will most likely say why would you want to put all the time, money and so on in to it. I would answer, to learn more about it, that’s pretty much the reason I do anything like this. If this where a way more expensive console, I wouldn't have the guts to open her up.
It looks like a good one to 'play' and learn with, and short of a catastrophe you should be able to recover from whatever you do to it.
Components are pretty cheap but the PCB's are almost irreplaceable so be physically careful with them.
An original emailed copy would be handy if you want specific suggestions.
Matt S
Old 30th January 2009 | Show parent
  #3
Gear Maniac
 
🎧 15 years
1. I'll be recapping the console.

firstly, determine the baseline of where you are. measure noise floor, of the mix buss and then indiviual channels. note all bad channels, even slight differences.
1-measure the power supply noise. with a dvm look for <10mV Ac on DC rails.
2-inject squre wave signal on line inputs and notice the "squareness" of the channels outputs.
replace power supply resivour caps (big ones).
replace audio coupling caps. these are the ones on the schematic that bridge different sections of the circuits. ie from mic pre out to eq in there will be a cap. etc...

2. I'd like to add balanced direct outs to it.

Why? do you have a very EMF problem in your building? are you running the line outs a long distance to the recorder? otherwise its very expensive for no benefit. if so use a transformer to differentiate the signal.

3. This console has 2 sets of input xlrs.

does the daw have -10 outs as well as +4? protools does and that whats its for.

4. I'd also read that replacing the op amps can change the sound

slippery slope here. proper design requires a lot of homework. just replaceing the op amps will change the sound but you could be making it worse. there can be a better chip but you WILL need to do your homework, or find someone who has. and pay them.
Old 30th January 2009 | Show parent
  #4
Gear Head
 
🎧 10 years
Smile

Quote:
Originally Posted by Matt Syson ➑️
Hi
1. I'll be recapping the console. I've done a lot of research on this and feel confident that I can do this. It's not my first time soldering, modding and such on circuit’s way smaller than this thing has got. Just never on audio gear. I'd like to get info on if I should replace every single cap?

Only the electrolytics, especially for now but you could change the non electros later although I doubt that would improve the sound significantly.

2. I'd like to add balanced direct outs to it. As you can see from the schem, this console has separate jacks for the send and return inserts. I'd like to combine those to a standard TRS insert and use the left over jack space to install the jack for the direct out. On this I really need a how to, I've been looking everywhere, and I know it can be done. I just don't know how. Any suggestions on where to get the signal from and how to wire it to be balanced?

You will need an output amplifier to generate a balanced signal. You could happily use a DRV134 / THAT corp (i can't remember the number) or equivalent chip on a bit of prototype board or make up a load of small PCBs Wire it's signal either pre or post fade as you wish.

3. This console has 2 sets of input xlrs. They can be switched via a switch on the module just like a mic line switch. However, it doesn't kick down the signal like a standard mic line switch. If I use the second xlr as the return from my DAW, is it going to be okay, or should I put something to kick the return signal down to keep from being blown out of my chair when I hit play?

You could fit a 'pad' (3 resistors) in the wiring from the second XLR. This would involve track cutting if they are PCB mounted. Something like a pair of 6K8 resistors in series and another resistor say 680 Ohms across the transformer input (before the switch!) would give you about 20dB attenuation.

I'd also read that replacing the op amps can change the sound of the console sometimes for the better, sometimes for the worse? Any recommendations from all m1532 and pm2000 owners out there?
Socket and play with other chips after you have recapped.

I realize this isn't a top of the line desk, and I know some of you will most likely say why would you want to put all the time, money and so on in to it. I would answer, to learn more about it, that’s pretty much the reason I do anything like this. If this where a way more expensive console, I wouldn't have the guts to open her up.
It looks like a good one to 'play' and learn with, and short of a catastrophe you should be able to recover from whatever you do to it.
Components are pretty cheap but the PCB's are almost irreplaceable so be physically careful with them.
An original emailed copy would be handy if you want specific suggestions.
Matt S
I've emailed the schematic to you, thank you very much for you help. I'm not to worried about messing up the pcb, I've got a lot of soldering experience, mostly replacing bad components on motherboards with tweezers
Old 30th January 2009 | Show parent
  #5
Gear Head
 
🎧 10 years
Quote:
Originally Posted by amorris ➑️
1. I'll be recapping the console.

firstly, determine the baseline of where you are. measure noise floor, of the mix buss and then indiviual channels. note all bad channels, even slight differences.
1-measure the power supply noise. with a dvm look for <10mV Ac on DC rails.
2-inject squre wave signal on line inputs and notice the "squareness" of the channels outputs.
replace power supply resivour caps (big ones).
replace audio coupling caps. these are the ones on the schematic that bridge different sections of the circuits. ie from mic pre out to eq in there will be a cap. etc...

2. I'd like to add balanced direct outs to it.

Why? do you have a very EMF problem in your building? are you running the line outs a long distance to the recorder? otherwise its very expensive for no benefit. if so use a transformer to differentiate the signal.

3. This console has 2 sets of input xlrs.

does the daw have -10 outs as well as +4? protools does and that whats its for.

4. I'd also read that replacing the op amps can change the sound

slippery slope here. proper design requires a lot of homework. just replaceing the op amps will change the sound but you could be making it worse. there can be a better chip but you WILL need to do your homework, or find someone who has. and pay them.
Thanks for your help as well. The adding of direct outs I guess wouldn't have to be balanced. I want the direct outs to get to my daw.

I don't use Protools, I use cubase, and it might support -10 as well as +4, but I've never needed to know, so I don't know. But your thought will make me find out as to not do work I don't need to do.

As for the op amps, I'll probly do as Matt suggest and just try different kinds, they arn't that expensive.

Thanks
Old 30th January 2009 | Show parent
  #6
Gear Maniac
 
🎧 15 years
What op amps are where? some have jfet inputs, some bipolar. some drive currents some drive no current (to speak of). and if you ask too much from anything you get nothing!! keep your upgrades similar to what is there already and then you can compare apples to apples.
Old 1st February 2009 | Show parent
  #7
Gear Head
 
🎧 10 years
Quote:
Originally Posted by amorris ➑️
What op amps are where? some have jfet inputs, some bipolar. some drive currents some drive no current (to speak of). and if you ask too much from anything you get nothing!! keep your upgrades similar to what is there already and then you can compare apples to apples.
Right on Already making progress on this, with what time I have.

Anybody else got suggestions?
Old 1st February 2009 | Show parent
  #8
Lives for gear
 
🎧 15 years
Hi
As an observation, replacing some of the op amps in this desk could be tricky as there are several types used that are run from plus and minus 25 Volt rails, not many will do this as they usually stop at 18 Volts (+ and -), sometimes 22 Volts.
Matt S
Old 2nd February 2009 | Show parent
  #9
Gear Head
 
🎧 10 years
Quote:
Originally Posted by Matt Syson ➑️
Hi
As an observation, replacing some of the op amps in this desk could be tricky as there are several types used that are run from plus and minus 25 Volt rails, not many will do this as they usually stop at 18 Volts (+ and -), sometimes 22 Volts.
Matt S
Thanks for the observation Matt. I can see your point. IC1 is running +-23. IC2 and IC3 are running +- 25. However, at this point, I'm mainly trying to restore it and add features. Replacing the Op Amps is really at the bottom of the list as from what I can tell now, it doesn't sound bad the way it is. I'll be restoring one channel to factory spec and comparing it to the other channels, and if its not broke, why fix it? On the note of opamps, I've not alot of experience in audio electronics, could I simply replace the op amps with one of a lower voltage and use resistors to knock down the power rail? Or would this have a huge impact on other areas and the sound?

Thanks

edit: I havn't had time to compare the pm2000 schems to the m1532, but I had read they very much the same in many ways. I'd read somewhere on the google of someone using John Hardy 990's in the pm2000, wonder if they would work in this board. Hmmm.. just a thought..
Old 2nd February 2009 | Show parent
  #10
Lives for gear
 
🎧 15 years
Hi
You COULD lower the supply voltage to plus and minus 18 like most others but you will loose headroom.
Using 'discrete' op amps like the 990 is another way and if you really went for it then you could make up little sub boards to fit the 'holes' where the existing op amps are. Note that there are already discrete 'Line Amps' shown on the schematic for just this purpose and you could probably copy them. Single chip alternatives would have been cheaper for the original manufacture.
I am not so sure that this is really a worthwhile excercise sonically compared to getting it back to 'as new' by recapping and a few minor alterations.
Matt S
Old 3rd February 2009 | Show parent
  #11
Gear Head
 
🎧 10 years
Anybody know a place to find replacment fader knobs, I really don't like the ones on this desk. or even replacment faders to replace them all together>
Old 3rd February 2009 | Show parent
  #12
Gear Addict
 
BlueSprocket's Avatar
 
🎧 10 years
Quote:
Originally Posted by John Kent ➑️
Anybody know a place to find replacment fader knobs, I really don't like the ones on this desk. or even replacment faders to replace them all together>
Where are you located? If you are in the states then you can check out Mouser electronics. They sell Re'an stuff which is decent.

If you're looking for replacement faders, I believe the faders on the 1532 are 60mm (might want to check out the manual available on the Yamaha website). Penny & Giles and ALPS both make nice faders. Mouser carries ALPS and also Bourns faders in 60mm.
Old 4th February 2009 | Show parent
  #13
Gear Head
 
🎧 10 years
Quote:
Originally Posted by BlueSprocket ➑️
Where are you located? If you are in the states then you can check out Mouser electronics. They sell Re'an stuff which is decent.

If you're looking for replacement faders, I believe the faders on the 1532 are 60mm (might want to check out the manual available on the Yamaha website). Penny & Giles and ALPS both make nice faders. Mouser carries ALPS and also Bourns faders in 60mm.
I found a place, thanks for the info.

I need comfermation on that im correct in this mod for the Phantom Power. Check these images of the schem.
http://i293.photobucket.com/albums/m...owerRewire.jpg

http://i293.photobucket.com/albums/m...werRewire2.jpg

I believe that if I disconnect the 6.8k resistors at the red and green points and jumper them to the red and green points on the mic1-2 switch, I can bypass the phantom power to Mic 2 and by using this tutorial found here..

Uneeda Audio - Build your own attenuator pads

I can place a pad on the Mic 2 input and turn the mic 2 input into a line input and basically turn the mic switch into a mic line switch.. so i can use the mic 2 as a line return from my daw and I won't get blown out of my seat when I hit play and I won't chance feeding phantom power to my converter and I'll still have one button ease of use phantom power on mic input 1.

Am I correct, anyone, anyone?

Oh and I'm in Ohio...
Old 4th February 2009 | Show parent
  #14
Gear Addict
 
BlueSprocket's Avatar
 
🎧 10 years
As for bypassing the phantom, that should work. I would start by cutting the trace that feeds from the 6.8ks and then you can just jumper to the location on the switch.

As for the Pad idea, I would just remember to return the gain knob to the +4 setting. If you put a pad in place, then you will have that amount of attentuation all the time when the second input it engaged.
Old 4th February 2009 | Show parent
  #15
Gear Head
 
🎧 10 years
Quote:
Originally Posted by BlueSprocket ➑️
As for bypassing the phantom, that should work. I would start by cutting the trace that feeds from the 6.8ks and then you can just jumper to the location on the switch.

As for the Pad idea, I would just remember to return the gain knob to the +4 setting. If you put a pad in place, then you will have that amount of attentuation all the time when the second input it engaged.
Thanks for the confirmation. As for the pad, I'm not to worried about me forgetting to return to +4, its others. I've got this picture in my head of coming in to the studio to blown monitors for some reason. hmmm I might try it without the pad and if somethin happens, then I'll install the pads.

On another note, read the manual before you read the schematic to try and figue out how it works. I didn't and now I feel like an morron. According to the manual for this board, the eq outs in the insert section can be used as direct outs without desturbing signal flow to the rest of the board, as the signal isn't cut till something is pluged into the fader in of the insert section. There for it is the equivlent of take it to the first click, so, there is no need for direct outs on this board, it already has them. And depending on how I wire in a patch bay.. will you get the rest.. I'm an idiot... Forgive my stupidity. Good thing I figured that out before I did all the work...

So really the only thing I need to do is recap, clean and do the phantom power mod. I wouldn't even need to do the phantom power mod if I had enough external pres with phantom power as the board has a master swich to turn off the phantom power to the board. So its either break out the ol soldering iron and wire and work for a couple days, or spend 1000's of buck on pres or phantom power boxes... hmmm.. oh the choices...
Old 9th February 2009 | Show parent
  #16
Gear Head
 
🎧 10 years
Talkback Module

Well, as far as I can tell, the only problem the console has is the talkback isn't working as it should. When I push the talk back button, you can hear yourself, but its just not very loud even with everything cranked, you can hear the button kick in but not much else. I was wonding if anyone can tell me what the problem might be and how to test it. I would hate to buy a spare if all I need to do is replace a small component. I can just use a spare channel as the talkback.. but I want the button..

thanks
Old 9th February 2009 | Show parent
  #17
Lives for gear
 
🎧 15 years
Hi
Talkback is likely to be an area that has been modified in the past possibly to get it to interface with something a bit different. Rather than trying to get another module just fix yours either yourself or get someone in. Dimming of audio is probably correct to avoid feedback.
Matt S
Old 9th February 2009 | Show parent
  #18
Gear Head
 
🎧 10 years
Any suggestions on where to start?

Thanks
Old 9th February 2009 | Show parent
  #19
Gear Guru
Quote:
Originally Posted by John Kent ➑️
Right on Already making progress on this, with what time I have.

Anybody else got suggestions?
Got Scope???

You will need one to check your work. To do so without is beyond risky.

Jim Williams
Audio Upgrades
Old 9th February 2009 | Show parent
  #20
Lives for gear
 
🎧 15 years
Hi
With regard to getting the talkback running yes a 'scope would be handy but you can get a long way with a decent multimeter an a spot of 'lateral thinking'. A 'scope' lookalike using a soundcard may be sufficient but make sure you use a poly something capacitor of say 10uF in series with the input as soundcards are not known for liking high levels of DC shoved up them. Real 'scopes' are usually happy up to 200 Volts or more.
When you get into chip exchanging for 'faster' varieties you will need a decent, FAST 'scope. Something that will at least indicate signals up to 100MHz. OK you don't need to know exactly what the response is up there but you want to ensure that oscillation is NOT happening.
Matt S
Old 15th February 2009 | Show parent
  #21
Gear Head
 
🎧 10 years
Talkback???

Well, I've gone through everything I know how to check with the meter... all resistors are good, pots are good, continuity checks and down the curcuit.. I'm starting to think the transformer may be bad, but I'm not sure how I can test that with a meter, I've never done it before. I'm getting a scope next week.

Does anyone else know of anything I can check while waiting.

Thanks
Old 16th February 2009 | Show parent
  #22
Gear Head
 
🎧 10 years
Said to heck with it and bought the whole master section on ebay.. I figure it can't hurt to have the spares in case I screw somthin up in there which is probly going to happen anyway. I still want to repair the talk back so if I screw it up tryin I'll have a blanket and maybe I'll learn what not to do if nothin else..

Old 16th February 2009
  #23
Lives for gear
 
ulysses's Avatar
 
🎧 15 years
Quote:
Originally Posted by John Kent ➑️
2. I'd like to add balanced direct outs to it. As you can see from the schem, this console has separate jacks for the send and return inserts. I'd like to combine those to a standard TRS insert and use the left over jack space to install the jack for the direct out. On this I really need a how to, I've been looking everywhere, and I know it can be done. I just don't know how. Any suggestions on where to get the signal from and how to wire it to be balanced?
You don't need to add any additional amplifiers to provide the balanced direct output. My suggestion is to replace the insert send jack with an unswitched TS jack and make an impedance-balanced output by connecting the ring to ground through the same resistor and capacitor combination that provides the tip's buildout. I would even suggest replacing these components on the tip circuit so you can hand match them to the ring circuit for optimum common-mode rejection. I can't read the actual component values on your schematic, so I can't comment on whether I would suggest altering them at all.

Rather than turning the insert return into a send/return jack, I would leave it as just a switched return. This gives you a "half normalled" insert point, which is ideal. Using the insert send as a direct out doesn't break the connection to the insert return. Only inserting a plug into the insert return will break that connection.

If you want to balance the return, consider adding a transformer.
Old 18th February 2009 | Show parent
  #24
Gear Head
 
🎧 10 years
Caps!!!!!!!

Okay, I've got the caps list completed... lots oh' caps there are.

Most of the caps are 10uf 35v. I'd put the entire list of each cap type, however I wouldn't expect anyone to tell me what cap to get for each and every one. I'd just like some input.

I've been reading that the caps most prefered are Panasonic FM's, however as I've read and found out myself, those only go down to 22uf.

It seems the only ones available are made by Nichicon, Panasonic ECG and United Chemi-con, this is via mouser and digikey..

Any thoughts on the subject?

Theres also a couple of BP 220/25 's ... it seems my only choice is Panasonic ECG found here
Digi-Key - P1181-ND (Panasonic - ECG - ECE-A1EN221U)
or Nichicon's found here
UVP1E221MPD

What do you guys think of these.. I just wanna make sure I get the ones I should..

I appriciate everyones help so far...

Thanks
Old 18th February 2009 | Show parent
  #25
Lives for gear
 
🎧 15 years
hi
The 22uF would be fine in replacement of the 10uF. If you are interested in lowering LF phase shift you could increase them further. You can be selective or go for a blanket 47uF or 100uF.
Matt S
Old 19th February 2009 | Show parent
  #26
Gear Head
 
🎧 10 years
What about voltage. The 22uf's in a panasonic fm from didkey are 50 volt. Is it okay to increase the voltage value? If so, is there some sort of rule of thumb on this, like I should never use a cap that is so and so many times the original voltage?

Thanks
Old 19th February 2009 | Show parent
  #27
Gear Addict
 
BlueSprocket's Avatar
 
🎧 10 years
if thats the lowest voltage available then go with it. There isn't any problem with using a cap that has a higher voltage rating. There are some people who claim that caps will sound better if you match them closer to the voltage rails of the console.

I personally, have never taken the time to test that theory. If you get 50v caps you should be good to go.
Old 19th February 2009 | Show parent
  #28
Lives for gear
 
ulysses's Avatar
 
🎧 15 years
This is really a matter of preference, but I don't use bipolar electrolytics. It's really hard to find good ones. Aside from being bipolar, the two parts you mentioned are on par with some mediocre general-purpose Nichicon and Panasonic caps. I would rather use really good polarized caps instead of crummy bipolars.

As for the other parameters in capacitor selection: Use the parametric search functions on the Digikey and Mouser web sites to help you find the right caps. If you just search for "Capacitor" and then choose "aluminum electrolytic", you'll get to a parametric search engine on either site. I think Digikey's engine is much better, and their data contains fewer errors. But Mouser does have a wider selection of bipolar caps.

You can quickly narrow your search to caps of the right style (axial or radial lead - hopefully you're dealing with radial lead, because there aren't many choices left for axial). Choose a range of voltage ratings - 25V to 100V would be reasonable to get you started. Next choose your lead spacing and, if necessary, narrow down the choices for the length of the capacitor. These are the most important parameters, because your cap has to physically fit in the space available. From here, you just see what's available. You could just select the Panasonic FC and FM, and the Nichicon HE caps, but that might be too narrow for your needs. I suggest eliminating the 85 degree C caps, since those are not going to be the high-quality, long-life types - they don't bother making low-impedance caps with an 85-degree temperature rating.

Don't ever go down in voltage rating or capacitance. (Unless you know for sure that the original audio-coupling cap had an arbitrarily high voltage rating). Don't go up by more than a factor of 10 unless you're sure you know what you're doing. Mostly, just make sure your new caps are low-impedance, high-temp, long-life caps that fit in the space available and can sit firmly against the circuit board. Running long leads to accommodate oversized caps is usually counterproductive.
Old 19th February 2009 | Show parent
  #29
Gear Head
 
🎧 10 years
Quote:
Originally Posted by ulysses ➑️
This is really a matter of preference, but I don't use bipolar electrolytics. It's really hard to find good ones. Aside from being bipolar, the two parts you mentioned are on par with some mediocre general-purpose Nichicon and Panasonic caps. I would rather use really good polarized caps instead of crummy bipolars.
This may seem like a stupid question, but If I was going to replace the BP's with polarized caps, which way would I put them in, from a lead standpoint, or would you wire 2 polarized caps in series to make a BP?

Thanks
Old 20th February 2009 | Show parent
  #30
Lives for gear
 
ulysses's Avatar
 
🎧 15 years
That's not a stupid question at all. It's a really tough question. You could start by measuring the voltage on either side of the capacitor. If there's a polarizing voltage present, that'll tell you which way the capacitor should face. If there ISN'T any polarizing voltage present, then you don't need a capacitor. The problem is that the answer is likely to be someplace in-betweeen: There will probably be a very small polarizing voltage, smaller than the amplitude of the audio signals passed by the capacitor. This means that the capacitor gets reverse-biased for less than half of the typical waveform. There are several ways to deal with this annoying little problem. One way is to eliminate or reduce the offset until there isn't enough voltage to be a problem, and then just replace the cap with a jumper wire. Another solution is to increase the offset so that a polarized cap sees a nice polarizing voltage. The third option is to slap in a polarized cap and not worry about it, or maybe put a small film cap in parallel with it to do most of the audio-band work. And the fourth option of course is the bipolar cap. I think the 1st option is the best, but it can get complicated. There are several possible sources of DC offset. It takes some careful circuit analysis to determine all of the sources and eliminate them, or to determine where a little offset can be tolerated and a capacitor isn't needed.
DC offset in IC circuits can cause a problem in the following areas, perhaps among others:
1. When interfacing with the outside world. Your piece of gear doesn't know what offset is going to arrive on an incoming signal, and it doesn't know how any outbound offset will be tolerated by another piece of gear.
2. DC on (audio) pots and switches tends to generate pops and crackles when the controls are operated.
3. A small DC offset going into a high-gain amplifier stage will come out the other side as a large DC offset that eats up signal headroom - unless the amplifier is made to have unity DC gain (usually done with a capacitor).
4. unwanted DC current through transformer and inductor windings can saturate them and greatly reduce headroom, increasing distortion.
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