Tascam M-216 Question...

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Ignatius-

Ignatius-

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I've got to admit that I am a bit of a lurker on this forum - I just didn't know what to post - but I have a question concerning the Tascam M-216 I picked up a couple of months ago.

Almost everything works (and sounds) great, but the guy I bought it from bought it from a church that disconnected the power running to the VU lights. In doing this it seems that they also disabled the functions of the entire set of features on the very right side of the mixer (the MON options and the SOLO features), and the Phones output doesn't work.

I was just wondering how I might go about fixing this... I found a pdf of the manual and opened it up to take a look, but I didn't want to seriously mess around with it until I knew a little more about what to do.
 
Do the meters work?

You've likely got something else going on there. The meter lamps are powered off a 6VDC rail. The lamps are a parallel circuit. It looks like maybe the peak LED's work off the 6V rail too, but everything else on that mixer is off the +/-15VDC rails...hm...the SOLO and MON functions may depend on the 6V rail for logic switching though...and the headphone amp in that era is typically powered off the 6V rail too.

I'd start by (unplugging it from power...duh), and letting it sit for 30 minutes or so with the power switch ON to help dissipate the caps in the power supply, and then open it up and just look for loose plugs. Terminal 17 on the power supply PCB is what carries the 6V rail so just follow where that goes and make sure everything is plugged in...

But, again, do the meters work and specifically do the peak LED's work?

-EDIT-

My bad...looks like the phone amp is powered off of an unregulated supply besides the 6V and 15V rails...look where the wires from terminals 15, 18, 19, and 20 from the PSU board...should go to the phone amp PCB. Make sure that looks good too.
 
The VU meters work fine... but now that I think of it, the peak LED lights don't work. I will open it up and try what you suggested as soon as I get a little spare time.
 
So I just opened the mixer up again... I still don't really know what is wrong... and I am pretty confused. The cables running from terminals 15,18, 19, & 20 all look to be in order and I can't find something wrong with the terminal 17 cable - I only took the right side panel off, not the back panel. Also, I am not exactly sure what/where the 6 VDC rail is... I could not seem to find it in the mixer or the manual. What should I look for?

I did just remember, however, that when I first opened it up a couple of months ago both of the 1A-250V fuses (labled F003 & F004 on the Power Supply PCB) were popped out... I popped them back in last time but it still didn't work. Does the orientation of the fuses matter? Should they be going the same direction? Any help would be appreciated. Thanks.
 
F003 and F004 are the fuses that protect the 6V rail (that comes off the power supply PCB on terminal 17), and that unregulated rail that powers the headphone amp and monitor section (that comes off the power supply on terminals 18, 19, 20 and 15).

Do you have a multimeter? You should test those fuses using the continuity setting on a multimeter...even the cheapy ones will do the trick, but if the fuses don't pass the test then you should get new fuses. If those blow when you turn it on, you've got bigger problems.
 
Again, Thanks a lot. I don't have a multimeter, but I will work on getting my hands on one as soon as I can. If I do have to replace them, do you know the size of the fuse? It doesn't exactly say in the manual, and I don't really know where to look... Also, could I find it at Radioshack, or would I have to get it online?
 
Radio Shack should have them. In fact you can bring the fuses in and they will test them for you.
 
Good point, Beck. They'd be able to tell you.

You can also look on the fuse board. The values are usually printed on the board under each fuse...something like "1A 250V". The service manual says they are 1A 250V, but go by what the fuse board has printed on it if there is anything.
 
Yeah, so after closer observation it was clear that 3 of the 4 fuses were blown... so I went in to Radioshack and bought replacements. I switched out all of the fuses and when I turned it on the lights turned on, the peak lights were working, and the Monitor functions were working.

The phone jack was sending some signal but it was hardly audible in the headphones. I'll try it again soon, but maybe there is still an issue. Either way I appreciate all of the help.
 
Good to know.

By the way, I've owned an M-216 for years and I love it. I've done quite a few mods for it, but it's a good mixer right out of the box. I also have the M-208.

:)
 
Hey Beck, I've got an M-216 that needs help. Lotsa noise. Common with these I realise, but I would love to have a bit more information on the mods you have done. I've heard about extra filtering for the psu and some sort of grounding mod but I can't find any information on either. What have you done with your 216? Mine is in absolutly mint condition, post and faders are pristine...I just have additive noise whenever I bus a channel. every channel I add to the bus adds to the noise. After 3 or so channels have been sent to a bus, the noise is just too much. I'd hate to have to pitch this mixer.
 
Yeah, in addition to recapping the power supply (Always a good idea on older gear) I would replace the opamps on each channel and the mix buss with NE5532. What you have in there now are NJM4560D or DX. They aren’t the quietest or the best performing.

Switching opamps doesn’t always noticeably improve performance on audio gear, but in the M-200 series boards it can make quite a difference. You’ll get lower nose and IMO, subjectively speaking it sounds a bit better to me, especially how the EQ responds. I’ve tried a lot of different opamps, but I keep going back to the NE5532 for most vintage gear. Look for NE5532AP or NE5532AN. Anything with an “A” in the suffix because it’s a higher quality part guaranteed to meet the best noise spec. You might also like the RC4580 made by Texas Instruments. This is a newer amp specifically designed for Hi-Fi audio and is drop-in compatible with the 4558/4560 type. It’s the newest in the 45xx series.

Perhaps even more important for this mixer is to get the cheap carbon resistors out of the signal path and replace them with metal film resistors. I’ve got the ones to switch in some notes somewhere. (Anyone want to come over and help me straighten up my studio and help me find some of the cool crap I own, including notes on mods I’ve done? I’ve actually found stuff I forgot I owned… and it’s like Christmas all over again without having to spend a dime… great feeling!)

I still own an M-216 I bought new and an M-208 I bought later used. I wouldn’t describe them as unacceptably noisy… not like you’re describing with only a few channels causing so much cumulative noise. I haven’t done any of the grounding mods because I’ve had no issues that it would address.

:)
 
Thanks for the info Beck! Oh and by the way, I'm glad that my quest for clean sound has brought you joy through re-discovery. I'd come over and help you clean your studio, but I'm in Vancouver and the commute would probably be prohibitive. :) If you find the resistors to switch out, give me a holler! I'm going to go pick up some op amps today and get them in while the mixer is still all guts out.

OK, so the ps has been completly recapped and now the noise that I was describing is a thing of the past - but - I am left with a fairly loud grounding hum. I'm not sure if this unit came grounded, but there is a grounded cable on this one with the ground being connected to the metal chassis. I found this post on a forum from 2006. I sent off a mail for clarification but I don't think the original poster is around any more. Maybe you guys could clear things up for me. Here is a bit of his post about adding a grounded cable...

"be sure that you ground directly to the chassis. If you experience ground loop problems, you will then need to isolate the audio ground from the hard safety ground through a 10 ohm resistor with a .1uF cap across it."

My question, how do I isolate the audio ground from the hard safety ground? would I just solder the resistor and cap from the chasis to a grounded trace somewhere on the board? I'm unclear as to how to continue, or the best spot to choose...
 
Been doing a bit more research on grounding issues. First off, it seems that the m216 was shipped as an ungrounded device - 2 prong power only. Second, "ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor". So it seems to me that by disconnecting the ground that by all evidence someone added by themselves, I stand a good chance of removing the grounding hum that I'm getting. Make sense? I don't want to remove it if it's supposed to be there, but the service manual only shows an ungrounded connection...

whaddya think? am I risking a hair raising event by 86'ing the ground wire?
 
Let's get something clear here...just because a device only has a two-prong power cord does not mean it is not "grounded"...it just means that the ground reference of the device is not tied to the building ground. Does that make sense? The ground in the three-prong receptacle is there for safety in case the neutral leg fails...it gives the hot leg another path if the neutral fails other than through you.

Grounding issues that enable hum or other noise or interference are related to signal grounding issues. The two-prong device IS grounded, to ITSELF, usually the chassis. That's the 0 volt or gorund reference for the circuitry in the device, and if every device used the same convention as far as how signal circuitry grounds or shielding connected to that ground reference then the world would be a happy place as far as this topic goes. But they DON'T. Its been a long and ugly debate in the electronics world for DECADES.

The "pin 1 problem": different manufacturers have disagreed over the ages with how pin 1 is connected to the ground reference. Ground loops occur when there is more than one path for a ground pin to connect to the device ground reference. A common example is when pin 1 of an XLR jack is connected to the device chassis some length of cable away from the jack...that length of cable can become an open door for interference or other "noise". And then you layer in the whole issue (which is really the pin 1 problem) as to what happens when you connect the device to another device via a cable, and how pin 1 is handled at the other end. If the two devices aren't the same in this regard then it is possible for the shielding in the cable to become a noise inductor and then if one device's pin 1 isn't referenced to the chassis ground in the same way then that noise can enter the audio stream. It was fairly common for a lot of mixers in the lower and mid-price brackets in the 80's and 90's (and later) to have all the pin 1 connections star-grounded to a single point on the chassis rather than grounded to the chassis individually as close as possible to each entry point.

Best practices suggest you:

A. Confirm that the ground socket in your power receptacle ACTUALLY GOES TO THE PHYSICAL EARTH as close as possible to your electrical panel
B. Connect your audio gear to one receptacle that is on a dedicated circuit or at least is not shared by noisy devices (things with motors...appliances and the like)...avoid at all possible costs linking the chassis of multiple devices together that are ALSO connected to the single-point building ground reference at the receptacle.
C. If a device is two-prong then check to see if there is a chassis ground-lug on the device to which you can run a wire from the chassis to power distributor that is plugged into the wall
D. Start analyzing schematically or actually opening up the devices and looking at how the "-" or "shield" or "ground" paths in the cable interconnects connect to each device's ground reference or chassis and then resolving those issues via the most logical modification. Somethimes this will mean relocating those pin 1 or "-" connections on jacks from a star-ground lug to a point as close as possible to each jack, or dedicating special cables for a particular interconnect application and disconnecting the shield from pin 1 or the "-" terminal at one end of the cable (such as when the signal ground is not referenced to the chassis at one of the devices...)

Tell us more about the cable that was added...is there a 3-prong cable on the device now? How close is the cable ground connected to the chassis to where the cable enters the mixer? What does the condition of the of the grounding point look like?

If the schematic shows the device having a two-prong only power cable, you aren't going to hurt anything by disconnecting it, and frankly you wouldn't hurt anything even if the device originally shipped WITH a three-prong cable...you are just omitting the safety ground. I'd say try disconnecting the power cable ground from the chassis and see what you get.
 
thanks for the awesome info. used a ground lift to negate the safety ground - no difference.
 
I'm going to skip trying to find my notes on the mods I did. This weekend I'll open up my M-208 and list the resistors I replaced with metal film. Stay tuned.

:)
 
Beck said:
I'm going to skip trying to find my notes on the mods I did. This weekend I'll open up my M-208 and list the resistors I replaced with metal film. Stay tuned.

:)
Click to expand...

Hi Beck, Wanted to thank you for your excellent advice on modifying the M-216, you have been an invaluable source in the quagmire that is the land of the internet audio forum. I picked up my desk cheap (£50) and it is in practically mint condition, I took your advice and upgraded the op-amps for NE5532's and the difference is incredible! There is far less noise and the EQ (particularly the high shelf) is now USABLE and actually sounds pretty good, albeit after a brief listening the other night (it was about 4am after many hours of soldering and cursing). I am intrigued now to hear more about your resistor upgrade, as I have heard of someone else also recommending this. I am new to this sort of thing (electronics) and would really appreciate your guidance as to which ones to replace, and with what....? Any help you can offer will be much appreciated! You've already made my week with that op-amp advice so anything else is a bonus. Cheers, Ben
 
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