Mixer Advice

[Linnovice]

Hi, I use a Tascam M30 8 channel mixer to feed my studio (home) tape decks. I've had some problems with it since I bought it with regard to various switches and sliders being crackly or not working. I decided recently to give it a thorough clean and dust up internally to try and eliminate these problems. Which to a large degree. I've been successful. I have a couple of queries though. The standard settings overall are -10dB in and -10dB out +/- 0.5dB, put simply. On most of the inputs the readings are well within spec but on three of them they are not. I have -8dB, -9dB and -8.5dB respectively. Not massively out I know but the odd thing is there is no way of adjusting them. There are no trimmers on the pdb's other than for VU meters and overload leds. As far as using them for recording I can adjust it out with there relavent sliders but it just seems odd that there is this difference. Can anyone suggest where I should be looking to bring them into line with the rest of the unit? Cheers, Mike.

[percivjr]

First of all, let me say that I know absolutely nothing about your Tascam mixer.

In the absence of any sounder (no pun intended) advice, and since the out-of-spec channels are louder than the rest, perhaps you can add your own pre-set potentiometers between the sliders and wherever they connect to. I'd chose a value of, say, 5-10 times the resistance of the sliders, to avoid shunting them too much. Not sure how linear the result would be.

Just a suggestion.....

[Linnovice]

Hi percivjr, thanks for the suggestion. In truth though, I think your suggestion is a bit beyond my skill set or knowledge. It has been suggested that the problem is caused by caps degrading and starting to fail. Problem is the channels are not individually removable for checking and servicing. When I take the bottom panel off the boards are packed very tightly together with a spiders web of cabling. All very neat and tidy but a bit daunting and difficult to get into with test probes. I needs completely disassembling to actually access the pcb's. The other strange thing is that all channels work ok on the mic inserts, both xlr and jack.

Another thing I don't understand. As I said originally. The setup is for -10dB in to -10dB out which is fine but the onboard VU meters are set at 0dB. Why? Does anyone know?

[jamesperrett]

Originally Posted by Linnovice

Another thing I don't understand. As I said originally. The setup is for -10dB in to -10dB out which is fine but the onboard VU meters are set at 0dB. Why? Does anyone know?

Using dB on its own is meaningless as it is simply a ratio between two values. You need to supply a reference level to relate to your dB reading to the real world. Your mixer's operating level is probably -10dBV which means 10dB below a reference level 1 volt. Confusingly, for historical reasons, professional audio levels use a different reference level of 0.775V which is 0dBu and the standard operating level is +4dBu. Some equipment can be set to use either level by changing internal jumpers.

Your meters show you how loud the signal is compared to the operating level - so in this case they're actually displaying a ratio of signal level to operating level. When they're showing 0dB it means that the signal level is the same as the operating level.

There are plenty of articles explaining dB and how they're used in more detail if you do a search.

[Linnovice]

Thanks for the explanation. I do roughly understand that now and as an aside I've found out that my Studer can be adjusted with jumpers to match up more closely to the output from the mixer. Having now done that the recordings I am making sound terrific. (Even though I say so myself :-( ).

Going back to the mixer. I'm just checking and adjusting where possible according to the manual. I find it strange that on two of the eight pcb's the levels of dB are marginally higher than the norm and there are no obvious (to me) ways of adjusting them. Does it indicate that some components are likely to fail?

[Malcolm G6ANZ]

There is a service and user manual here http://www.tascamvintage.com/tascamManual.htm
This gives a quite detailed description of dB as well as block diagrams and setting up.
Malcolm

[John_BS]

It's difficult to be precise without the entire collection of schematics etc, but from what I could find on the web, Tascam used 5% carbon resistors in the feedback (gain-defining) loops along the signal path. It's possible either that there has always been some level variation (up to 1dB max) or that some of the R's have drifted with time. Anyway, that's one place to look / modify if you want the channels matched to pro standards.

John

[Linnovice]

Thanks everyone, I much obliged for the explanations and suggestions. I think for the time being I will leave well alone. I have six channels working more or less perfectly. The slight variation on the remaining two I can live with. The main thing is that the sound quality I get overall from the unit is superb. I've very happy with the recordings I'm making.

Mike

[dseymo1]

While I understand your desire to 'normalise' your mixer, it's unlikely that your sources will be very closely matched in output anyway. Expensive studio models aside, even different examples of the same microphone often vary a bit.

[Linnovice]

Yes, I'm sure you're right. I'm probably getting a bit too busy about it. I'll just enjoy what I've got and listen to the music. Spent too much time listening to the kit in the past.

A quote from Flanders and Swan "Oh, we never listen to music much, it's the Hi Fidelity" A few dB here and there won't matter much, keep on making music.