Tascam 3700 (and 3500) grounding issue

[GregGreg]

Hi there

I've acquired a Tascam M 3700 and I've noticed that (although every other single channel is dead quiet, including the group bus outputs), the main Stereo Out channel has some grounding hum on it. This is obviously internal (nothing else connected!). Does anybody know of a pictorial grounding scheme that'd take me step by step through the process to deal with the hum? If not pictorial, obviously just a step by step process would be fine!

Secondly, even with all faders down and listening through the headphone socket, there's a hum on the headphone output. This is obviously of secondary importance to the main outs but could probably be cured at the same time. Any ideas?

Many thanks

 

[witzendoz]

When you say all the faders down, do you also mean the main stereo fader and does the hum increase and decrease with the fader. That is what I get. If it's there all the time it's a different problem.

I do get some hum on my M3700, however it is very low compared to the signal going through, i.e. if you had the console turned up so you could hear the hum the level of the music would be extremely loud.

Things I have found that reduce the hum. Muting all the effects sends (mute button) and all the monitor faders (mute button) reduces the hum even if the faders / sends were already turned fully down, mute anything you are not using.

I have an earth cable connected between the console chassis and the monitor power amp chassis, reduced the hum by about 80%, however this may or may not work and may make it worse, just try it. I used screws that tapped into the chassis to connect the wires.

I also have the earth lifted on the audio cables going to the monitor amp reduced hum by another 10%, I know it sounds strange lifting the audio earth then adding a chassis earth, but it reduced the hum the most this way. By the way I don't have a problem with the amp on my second pair of monitors, this amp has no mains earth and has a double insulated design.

I should also point out that almost all the hum seems to be between the console and the monitors, the recording chain has almost none.

The other thing that reduced hum and other noise, was that between the console and my stereo sound card that I send the stereo mixes to (my PC) I have isolation transformers on both the outgoing and incoming signals, this is now super quiet.

I know the M3700 gets a bad rap from some, but it's a very usable console. I also think that the M3700 had improved earthing over the M3500, but I don't know for sure as they may have changed earthing through production.

Cheers
Alan.

 

[GregGreg]

Hi Alan

Thank you for your prompt response. Very much appreciated!

"When you say all the faders down, do you also mean the main stereo fader and does the hum increase and decrease with the fader. That is what I get. "

Absolutely - when I increase fader levels on the stereo fader, the hum increases and vice versa. The actual channel faders and bus faders have no hum using the faders. Only normal channel noise is increased - as is expected - when faders are ridden, and is very low.

When listening via the headphones directedly plugged into the mixer (without even an amp plugged in), there is some headphone hum (even with all faders down) and headphone level at zero! This is obviously the headphone amp itself, rather than any recording or monitoring audio channel - thankfully! However, listening through the headphones, if I increase the stereo fader level, I also detect the SAME hum I had going through to the monitor amp (even with the amp plugged out) so I suppose the hum must be coming from within the mixer itself.

However, you're right, the hum is quite low so would probably be masked by music, but if mixing down at +4 via the desk on quieter pieces via the main outs, could prove a problem. I suppose I could mixdown via one of the group buses instead, but that would be at -10.

Anyway, currently, I'll be mixing within Cubase, so will be using the desk for recording and monitoring, but not mixdown so probably won't be a problem just now.

As regards my thoughts about the M3700, it's a lovely mixer, feels incredibly professional and solid and robust. I'm very impressed with it! I believe it was the mainstay of many a studio and I'm aware many professional and notable musicians still use the desk today.

I genuinely think I have a little gem here and I'm pretty certain in years to come it will prove to be appreciated by aficionados! I wouldn't be suprised if a well-kept desk commands a higher premium than the rock-bottom prices it's currently fetching on eBay, considering that in the 1990s they cost £16K (when £16K was even more than it is today!) These things were obviously built to last!

Anyway, thank you so much for your advice. I'll keep your notes handy. Any other advice you think of would be very welcome regarding the mixer!

Greg