Anyone have a Sharp MS200 / Kenwood DMC-G7R?

[Ral-Clan]

Hi, I was given (for free!) a Kenwood DMC-G7R, which is actually a re-branded Sharp MD-MS200 minidisc portable. It's an older SP recorder. I am really impressed by the build quality and features (all metal casing, heavy duty, big display, etc.).

http://www.minidisc.org/part_Sharp_MD-MS200.html

I was hoping to use this as a portable field recorder. The odd rechargeable battery it uses will only hold a charge for about 15 minutes. Probably too expensive to replace. No problem, I thought, anywhere I was going to record I could use the AC/DC adapter.

However, whenever I record using the AC adaptor, there's a TERRIBLE 60-cycle hum on the mic input (which is recorded to the MD too). Unplug the adaptor and the hum goes away entirely. Plug it back in and there's the hum again.

Here's what I've tried to remedy the situation (none of these helped):

- replace the adaptor with a different one

- try a different outlet / different outlet in a different house.

- open the unit up and re-touch all the solder points of the mic-jack with a soldering iron

- try a different mic (have tried at least four microphones).

- move the unit away from sources of EM/RF interference.

I know the person I got the unit from treated it well and hardly ever used the mic recording feature (if at all).

So, it just seems to be a problem with the mic-preamp when using power supply power. Have any other Sharp/Kenwood users noticed this problem? Is there a fix? I have other recorders, but this one seems like such a nice rough and tumble unit, I'm a little disappointed. Well I guess it still makes a good playback and line-in recorder.

I realise I could use an external mic-preamp, but that means having another battery to worry about, more cables, extra hassle. Kind of takes away from the elegance of an all-in-one unit.

Edited April 16, 2008 by Ral-Clan

[THIS SUCKS]

maybe you could build your own battery pack and plug it into where the power cord goes?

[Ral-Clan]

maybe you could build your own battery pack and plug it into where the power cord goes?

I did think about that. The rechargeable in it already is 3.6V I believe. Soo....how many AA's would I need (three?).

The thing that sucks about that, is that it makes the unit cumbersome to use, also, since this is an older unit the battery life is not that great (especially when recording). An adaptor would have been the perfect solution, if not for the hum.

I just wish I understood what was causing the hum in the first place. It's really loud (and gets louder when you turn the REC level up).

[bland10000]

7.00 usd to replace the cell...site selling the AD-MS10BT.

Edited April 16, 2008 by bland10000

[Strungup]

I have 1 of those , cool machine , I have the 5FR as well ,

Odd about the mic noise , I dont get it on mine , what kind of mic are you using ? might be a cable shielding problem .

[Ral-Clan]

I have 1 of those , cool machine , I have the 5FR as well ,

Odd about the mic noise , I dont get it on mine , what kind of mic are you using ? might be a cable shielding problem .

Well, I'm using some simple home-made microphones which have not given me any problem on a Sony MZ-R700 (been using them for years). They are simple piezo elements on the end of a two foot cable taken from a pair of headphones. I also have a home-made mono mic (single piezo element soldered onto a male mini-phono connector). The mono mic gives me a little less hum, but it's still there.

I've tried plugging in a Shure SM-58 and another self powered condensor microphone. Again, less hum than the stereo home-made one, but it's still there.

The most interesting thing is that if I touch the chassis of the minidisc recorder, or lay my hand on it completely, or even turn it around in different ways, the hum lessens or is almost gone. It's obviously some short of grounding or shielding problem.

Maybe a ferrite core on the mic-cable would help? But I can't get a straight answer on whether ferrite cores are meant to prevent external interference, or prevent EM emissions.

Edited April 17, 2008 by Ral-Clan

[Ral-Clan]

Just tried using Ferrite Cores on both the power supply cord & mic cord. No improvement at all. This has got to be an internal grounding issue.

[THIS SUCKS]

try the unit outside or at another location. maybe there is a source of noise in the area you are trying to use the unit at.

[Ral-Clan]

I did already try it in another location (brough it to work). No improvement. Remember, this hum only occurs when the unit is using the power adapter plugged into the wall mains. Not when battery powered. So trying it outside wouldn't really help.

Last night I opened the unit up. I noticed that if I touch any part of the metal interior (i.e. the drive cage, or grounding points on the circuit board) during recording, the hum on the mic-preamp in GREATLY diminished. Not entirely, but a lot. I'm pretty sure it's a grounding problem. I think at this point only someone who services MDs would be able to advise me. It's not worth getting this old unit repaired, but if anyone knows what is causing it I would appreciate being steered in the right direction. Thanks.

Edited April 18, 2008 by Ral-Clan

[THIS SUCKS]

you could try attaching a wire from the metal case to the negative battery terminal. if just touching the wire fixes the hum they you could get someone to solder it permanently for you.