How easy is it to fix a broken noise generator on a Moog Rogue? If its relatively cheap,easy to source parts and straightforward im thinking of buying one thats available. But need to know if the cheap price im getting for it will eventually become defunct through fixing it. Cheers
The Rogue uses a “digital-noise-on-a-chip” identified as MM5837. Easily found and easily replaceable (single 8 pin chip).
But a more important question is: why did your noise generator chip fail in your Rogue, in the first place ? These chips are very robust, and are used in many other synths of that same era, and are not known to fail often.
Are you sure it’s the chip that has failed ? And not the slider for the noise in the mixer section ?
The person im buying it off says that the sliders and buttons when he first got it were noisy when moved, so he cleaned them all and lubricated with deoxit. Now all the sliders etc are fine and everythings perfect but the noise generator stopped working. He says its either a problem with the noise generator itself, the slider,or it could be a dry joint. (not sure what a dry joint is). Anyway he’s selling it cheap because he doesnt want to pay the money to get it fixed to then sell it. Thanks for your reply hope this sheds a little more light onto the situation.
A “dry joint” or more often called a “cold joint” is a solder joint that has cracked, or is pitted, and isn’t making proper electrical contact anymore, due to overheat, time, or mechanical vibrations, or was simply badly done in the first place at the factory.
If the non-working noise is the only problem with the synth and the price is right, it shouldn’t be too hard to fix. Either by replacing the defective chip, of slider, or re-doing the faulty solder joint.
But if you’re not at ease with opening electronic devices and tinkering with them, better find a friend (or a tech) who is.
It arrives tomorrow so i will know then. The seller has also given me the option of a full refund if its not up to scratch. So im pretty confident the noise generator will be the only thing that requires attention. Thanks for your help. Ill look into someone else giving me a hand.
It’s a POS noise generator anyway. You can hear it repeat every second or so. I rarely if ever use it. You’d be better sending noise from an outside source into the Audio IN. FYI, I may have a spare slider laying around somewhere. If you so need one let me know and I’ll check if its the right value.
Yes indeed. It’s the dreaded digital noise generator MM5837 with its very short (too short) digital sequence of pseudo-random noise.
Later on the much improved MM5437 came out with a more than one minute cycle. More then enough to create the illusion of real randomness. But unfortunately it is not pin for pin compatible with the MM5837 (dumb design engineers at National Semiconductor), and therefore not a drop in replacement. It’s not impossible to make it fit (same 8 DIP casing) but the traces around the chip have to be cut and rerouted.
The white noise is so bad on the MM5837 that Korg stopped the production line of their Mono/Poly model very early on, to redesign one of the boards to remove this digital noise chip, and replace it with a more conventional transistor reverse bias design ! So only about 200 very early editions of the Korg Mono/Poly have this bad noise chip inside.
Just had The rogue delivered. Works perfectly apart from a few little things but it has an amazingly rich sound. Firstly Its 2 semitones out of tune so when i play a C it outputs a Bflat/Asharp. Any advice on how to tune it via the pot holes at the back? for example which hole corresponds to which osc etc. Another thing iv noticed is if i try to remedy this by using the tuning knob to get the White key to the left of the 2 grouped black keys (C) to actually output a C, then the F key and A key in the centre of the keyboard sound as if the bass has been removed from them (only in the lowest octave) This is with the tune knob tuned extremely flat obviously. This isnt a problem when the tuning knob is set to zero. Any thoughts on this? Also thanks a lot for the rapid, detailed replies. Its been a good experience getting started in this online community.
This might sound silly but, have you made sure the pitch bend wheel is at center position ?
As for calibrating the rogue, you will need a digital multimeter (or voltmeter). Don’t forget to let the synth warm-up for at least 15 minutes before attempting to calibrate it. You can find the procedure in the service manual here (under alignment procedure on page 3 and 4):
http://www.synthdiy.com/files/2013/MoogRogue-TechnicalServiceInformation.pdf
Note: the loss of bass in the higher notes might be caused by each oscillator not tracking equally, and they might somewhat cancel out each other when exactly at the same frequency… Should be resolved by calibrating each one properly.
Also make sure the “sync” switch is not in the “on” position, as the master will cancel the slave’s output when its frequency is above that of the slave’s. (since the sync re-starts the slave each time the master starts a new cycle, if the frequency of the master is higher than the slave’s the slave can’t even starts to oscillate before being restarted by the master and the slave will be silent.)
Oh, and is the noise working ?
The pitch wheel is definitely in the centre. But i can imagine its so simple a thing that it could be easily overlooked. Iv spent a lot of time with it in the past 24 hours so im pretty confident im not overlooking anything and making more work for myself.The noise does not work. I think im going to get a friend to help me with that. Maybe modify the better noise chip if possible. Other than that im going to head out soon and get a digital multimeter and give calibrating it a go. I realise that with the multimeters the more you pay the more accurate it is likely to be, but im on a pretty tight budget so is there anything i should look out for when buying? Cheers
Usually, quality DMM are rather expensive. If you can borrow one from a friend for a day maybe ?
You need one that can display voltages with at least 2 decimal digits accuracy (for example: 2.58 VDC).
You will also need an accurate tuner (or better yet a frequency meter). Or if you have another digital keyboard, you can play a note on it as audible reference and adjust for minimum beat between the Rogue and it when playing the same note on each (least expensive way).
And tuning an analog synth is like tuning a guitar, some adjustments will impact others somewhat. Follow the steps carefully and don’t rush anything. That’s why it’s called “stretch tuning” because you’re actually “stretching” the lower and higher parts of the keyboard’s pitch apart. Like stretching an elastic to an exact length while holding it with your hands in mid air and at the right place.
Thanks for your help ‘thealien666’ i appreciate your time. Youve straightened a lot of things out for me. Im going to see if i can wrangle some multimeters and tuners. Ill let you know in the near future how it went.
You’re welcome, and I hope everything turns out for the best…