Tech in Newcastle/Sydney to calibrate 1176s to 50HZ

[asagaai]

Hi

I have a couple of mohog mofet 76 compressors (1176 compressors) that need to be calibrated for 50Hz mains. Could someone guide me as to whether there is a decent tech in Newcastle or Sydney who could do this.

I would prefer local (Newcastle/Sydney) as I do not want to post the units given some very recent bad experiences with post of very nice high end eq.

Any suggestions would be much appreciated.

Cheers

[headman]

Just take it to Mick Sampson in Waratah with the schematic. He probably has never worked on an 1176 but he is the analogue king in Newcastle. And he is quick !!

[Dr Benway]

Yep +1 for Mick. He is the man in Newcastle for gtr amps I know that!!
He looked over a couple of Neve amps (not mine) and as far as I know they came up a treat.

[Linear]

I have no idea why you would need to do this...

Chris

[asagaai]

I have no idea why you would need to do this...

Chris

Cause the units were built in a country with 60 hz mains and when used in 50 hz land like in Australia can have excessive hums and need re-calibration.

Thanks for the replies so far- please keep them coming.

Thanks

[Gian]

I agree with Chris, I am not sure why you would want to do this.

Perhaps I am missing something, but the mains voltage (AC) gets changed to DC voltage (through a transformer) so it should not make any difference.

I am happy to learn if I am mistaken.

[asagaai]

Well-I am a knob twister- not a tech- so the whys/why nots are beyond me.

But the manufacturer is going to pay for the calibration, and has said that the units when used in 50 hz land (instead of 60hz land) can have increased hum which is reduced with calibration. The units came with the manufacturers handbook which raised hum in 50 hz land and provided a step by step guide to calibrate for 50 hz land but requires voltage meters and tech kowledge that is beyond me.

Anyway- take it that I just need a good tech who is used to working on outboard like 1176's to help me with the process and any further suggestions with tech names in Newcastle/Sydney would be appreciated.

Cheers

[Linear]

sometimes the frequency of the AC does matter, such as AC motors that are frequency dependent. A Hammond organ has an AC motor and if the frequency is wrong it doesn't play in tune.

But for normal power supplies, the AC gets rectified into DC anyway so the frequency shouldn't matter too much. I especially don't see why it would lead to more hum - if you're 1176 is humming then it sounds like the power supply needs recapping.

Chris

[Chinagraf]

I have 2 from US that have never been altered and they sound awesome just as they are.

[asagaai]

I have 2 from US that have never been altered and they sound awesome just as they are.

Hey- thats good to hear.

I have two with excessive hum- that need calibration. My various other comps including an MC77 have no hum....not a big deal- obviously just a minor calibration issue that I need a good tech to follow the manufacturers calibration booklet... not giving the Mohogs a spray- the tone/action is awesome-the hum is a little loud tis all

Anybody else with details of good techs in Sydney/Newcastle- would be appreciated.

Cheers and thanks

[Ausrock]

Well others beat me to it but definitely contact Mick Sampson.

[rob]

Baffling!


I'd love to know what the calibration is for a different mains frequency. I do know that some gear designed for US 115volts hums when the mains transformer is reconnected to suit 230 volts, but that is due to poor dressing and proximity of the mains circuits to to audio circuits.

[Gian]

Thanks Rob, I find it baffling too.

If there are not enough filter caps in an unregulated power supply it might make a bit of difference going from 60 to 50 Hz, but if it is regulated, then DC is DC? no?

Only other explanation is caps have gone and need replacing. But that is different to 60 to 50 Hz calibration.

[headman]

Well what ever the problem, and I've never had to worry about anything I've purchased from overseas, Mick Sampson can fix it.


headman

[Alastair Reynolds]

The only thing I've found with US produced gear humming is the transformers tend to be a bit smaller for 60Hz , i.e. less iron, Eventides used to vibrate a lot for that reason. A 50Hz designed transformer fixes this, something like a nice toroid. If a modern unit is well built and uses a half decent transformer in a linear supply it should not need any additional work, unless the 1176 clone uses some obscure AC drive from an un-rectified part of the supply. really well built gear used to be rated from 50 to 400Hz, so you could use it on aircraft, but that's a whole other story

[rick]

400htz aircraft ...? sounds like a story i would like to know
you mean all those dodgy videos players and insane ovens run at 400htz ..?
i am all ears .. i feel like i no nuthing

[rob]

Yep, AC power in aircraft is 400Hz. At Least "vintage" aircraft.

[rick]

really .. well you learn something every day
whats the standard voltage ?

[asagaai]

Hey guys...

Does this blurb mean anything.... "Your unit might need calibrating over time. If you find the unit to be excessively noisy if your mains power is 50Hz, it might need to be recalibrated....You will need a precision screw driver, oscillator with 1K sine wave and good volt meter.

Q Bias- adjust the trimmer in the GR control amp on the pcb and in Meter driver amp full CCW. The trimmers are the little blue components with a small adjusting screw. Bypass the unit. Set to 1:20 and release to full CW. Turn the output full CW and input full CCW. Insert a 1 KHz .775vAC signal, or -4 on the VU meter in input mode. Turn input CW until the VU meter reads +1 in +4 mode. Adjust the trimmer in the GR control amp CW until a level drop of 1DB is achieved.

GR meter Tracking: set ratio 20:1, bypass unit. Input a 1khz, 50 mV signal. Set release full CW. Set input level to 12 o'clock. Set ouput level so you get a 50mV at the output also. Now set the meter to GR mode and switch attack to full CW. Slowly turn up the level of your input signal (at the signal source, not with the input level control) while you monitor both input and output levels with a voltmeter. When you reach a point where output level is half the input level, you have 6db gain reduction in the unit. Adjust the trimmer in the meter driver amp CW until the meter reads -6.5. Turn attack back to bypass abd re-adjust the GR zero meter. Switch attack back to full CW. And adjust the Meter trimmer. The point is to adjust and go back and forth until the meter reads 0 in bypass and -6 when attack is turned full CW."

This is all a bit gobblygook to me-all I know is I got 2 new units (1 has a noisy hum- other one is a bit noisy) and it seems that the above servioce should reduce teh noise based on the manufacturers handbook.

Mick Sampson is away until mid April. Any other recos for people who have worked on outboard in Sydney.

Cheers and thanks for the replies so far.

GJ
Newcastle/OZ

[Alistair]

Seems pretty similar (though not exactly the same) as the calibration of an Mnats DIY 1176, which is obviously pretty similar to a Urei 1176- just variations of the standard calibration. All you're really doing is setting the behavior of the compressor section and making sure the meter follows gain reduction correctly. I'm not 100% sure, but I guess the first step could potentially reduce gain introduced somewhere, which would lead to less overall hum/noise in the circuit, but I'd be surprised if this has anything to do with 50hZ at all. I know the Mnats calibration has another trimpot for distortion adjust, but this doesn't seem to mention that.
It's a pretty easy job if you can find someone with the tools (which any decent tech will have).

[The Tasmanian]

Have you checked to see if they still hum when isolated from a rack - and no equipment above or below the unit you test?

[rob]

That's just typical 1176 calibration. It has jack shit to do with hum. If it hums, either the wiring to the unit is bad ( ground loop) or the unit is faulty

[The Tasmanian]

Who's Jack Shit?

[asagaai]

Who's Jack Shit?

seriously though- its not other gear effecting the units-I have trialled the units with all other gear off save for converters.

I am using neutrik connecters and mogami cable to connect patchbay to Mohogs- but just to make sure I will as a last step use the hosa cables connecting the MC77 to patchbay (which is quiet) and will again trial with Mohogs to take out the mogami/neutrik cabling/patchbay being bad.

Just having a bad run with overseas gear lately- a manley mini massive is back at manley at present for repairs, a tube mike psu had its vu meter and lights punched in (despite being in cutout protective case foam and a metal case) from a trip to AUS from USA......couriers must be pretty bad temepred these days...

GJ
Newcastle/OZ

[Chris H]

Who's Jack Shit?

These Guys.......$19.80 at Amazon

http://www.amazon.com/Jackshit/dp/B000069DQY

[asagaai]

Who's Jack Shit?

These Guys.......$19.80 at Amazon

http://www.amazon.com/Jackshit/dp/B000069DQY

Bastards- how did they access my studio......

[Alastair Reynolds]

Well Rick, it goes sort of like this, in a nutshell, when generating power by spinning a magnet in a coil, the faster you spin it , the more volts it generates, so to generate 400Hz. The windings, field coils etc can be smaller and hence lighter by virtue of needing less copper than one that generates 50 or 60Hz. Standard Voltages for aircraft were and for many still are 115V at 400Hz and 28V. Some aircraft have a 3 phase 28V generator. A problem that does arise using 400Hz though is losses due to impedance and transmission of the higher frequency current... Swings and roundabouts.... So at 400Hz , generators and transformers can be smaller, use less copper windings and need less iron in the cores. The small Ramjet (Ram Auxilliary Turbine or RAT) that you see usually in the tail of a passenger plane drives an auxilliary power generator to run the aircraft while the main engines are stopped.

My old Fuzz -Linear power amps from the mid 70s are rated at 50-400Hz, I think Crowns and SAEs were as well, but someone else may be able to comment on that.
Modern switch mode power supplies operate at high frequencies (e.g. 100KHz) for similar reasons, transformers can be far smaller and as such more efficient but you then need much higher speed diodes to be able to cope with the switching speeds needed without vaporizing, and good filtering to remove harmonics and prevent noise being injected back down the mains and turning up on something else that has inadequate filtering . Cheap switchmodes are one of the greatest sources of noise in the modern audio plant.If you're ever getting strange noise in audio paths, turn off the PCs and anything computer related first and see if it goes away.Of course this problem "never" occurs with a well made linear power supply using quality components, but they're far from cheap.

[rob]

Nicely explained Alastair.

[rick]

as always thanks

[Chinagraf]

[quote="asagaai"]
a tube mike psu had its vu meter and lights punched in (despite being in cutout protective case foam and a metal case) from a trip to AUS from USA......couriers must be pretty bad temepred these days...

GJ
Newcastle/OZ[/quote]

I had some gear come by Fedex from the US about a couple of months back , when the Superbowl was on. I only mention it because it looked like this had been thrown, kicked, tackled then spiked at the end zone. Facia
cracked, several parts broken, but... no damage to the box. I trust the people it came from and best we can guess is it was dropped from a great height. Like off the tail of a 747.
Insurance covered it, but *&^% me.