Category Archives: Gear

Anything related to electronic music equipment

Behringer Neutron calibration

Do you also have the problem that sometimes the an oscillator of your Behringer Neutron is out of tune when you bypass its tune pot?
I had that a couple of times now and didn´t know what to do about it until today.
I assumed being driven by 3340 ICs the Neutron would not need any warm up time but maybe I am wrong. However during boot the Neutron calibrates the OSCs internally. I found that when you lock a Tune pot and the corresponding oscillator is out of tune thereafter, you should switch power off and back on so to force re-calibration. Mine was perfectly in tune after having done so.

Midiverb II repair

I´ve had a broken Alesis Midiverb II lying around for quite some time now. Just recently I remembered that I´ve always liked Patch #28, even before I dove into ambient and drone. So I thought now was finally the time to open it up and give it a go, especially since not to long ago I aquired a Midiverb 4 from an old friend and thus had a working 9V AC/AC adaptor again which the Midiverb II also requires.

Symptoms

You´d plug in the power adaptor and nothing would happen, neither visually nor sonically. The unit was basically dead, or so it seemed …

Fault trackdown

It´s always a good start to make sure that all the supply voltages are there and within range. The Midiverbs rectify internally so I started at the power adaptor plug and made my way through the PSU unit. Power on all paths was present but at very low ratings. I unplugged it again and did some continuity measurements. I found a short circuit between the output and ground of the 7805 regulator. I took it out and found that it measured okay out of circuit so it itself couldn´t be the problem. I still had to replace it because the input leg simply broke with no real force applied,

The repair

So there was a short circuit on the 5V supply line. I measured continuity across all capacitors and marked al those that seemed short which I then soldered out. Basically I removed all ripple filter caps of the digital ICs. Subsequently I no longer measured a short circuit across the 7805. It turned out that two of the filter caps had shortened. I replaced those with 470pF that I had left over from the Opra 6 repair and put all the other working ones back in.
That was all it needed. Plugged in the adaptor and there it was up and running again.

Improvement

I noticed that the unit emitted a slight humn and a significant amount of noise when cranked up fully. I then remebered that the device has always been a little noisy. I then found that it might not be a bad idea to check whether the analog circuit could be improved upon. All opamps where LF347 and a little research revealed that the TL074 is compatibel and seemed to have better ratings. So I decided to replace all LF347 with TL074. I used sockets just in case that I where proven wrong and had to reverse it, which didn´t happen. I am quite stisfied with the improvement and really happy to have the unit back in working condition.

Midiverb 2 TL074
Midiverb II w. TL074

BCR2000 USB failure

If all of a sudden you are getting an error message on your Computer stating that your USB device failed then this is most likely due to worn out capacitors of the power supply.
I successfully got my device working again by replacing the two 1000uF electrolytics. The original ones where causing ripples on the supply voltage which lead to instable USB signals.

Poly-61 individual voice tuning

When I recalibrated my Poly-61 I had two voices significantly out of tune. Now since all oscillators are digitally controlled and therefore supposed to be in tune, KORG omitted attenuators for individual voices.

Here´s what I found as probable cause and fix: The parts most likely affected by the aging process in the area of voice CV appear to be the Cn02 (n=1..6) capacitors. I could not identify their exact type, but the marking sais they are 10nF with only 1% tolerance, so precision circuitry could be assumed. If I read the schematics correctly then together with the Rn02 resistors they form the input of the antilog. So there are two possible fixes. The first being to replace the capacitors with new high precision 10nF caps. The other fix is what I went for, firstly because I did not have the appropriate capacitors at hand and secondly because I felt that having control over the tuning would be handy. So I replaced R402 and R502 with precision trimpots.

Poly-61 trimpots for inividual voice tuning

Since Rn02 are 15k the best trimpot value would be 20k. I only had 100k at hand so it was a little fiddely to set the right value but it works for now. I still have to get a couple of replacement parts for proper fixes anyway so I will eventually replace all Cn02 with new ones and all Rn02 with 20k trimpots.