Noisey Gear

[Your Add Here!]

I've got a Biamp M140 spring reverb that has been fun to use in the past in my recording setup. The problem is it has become very noisey. There is a broadband buzzing that I wish would go away. I've tried grounding the chasis and a I've tried ground lift adapter.

Do you suppose this is fixable? What is the likely problem?

[triez]

Have you checked the power supply filter caps? sometimes they break off at the solder joints.

[Marshall Simmons]

i have a benchmark pre and a ward beck pre that have noise problems....


The ward beck has an internal power supply that dave thomas made, and i have problems with noise at higher gain levels for my ribbon mics.... with the schoeps it isn't a problem cause i ususall have to pad it.


The benchmark has a unregulated power supply and i figured that was the problem. I'm going to go ahead and rebuild the power supply.


For the power supply, i'm going to use 3 regulators that drop the voltage incrementally, and a group of filtering capaciitors in parallel. I'll keep the transformer that is already there, since its rated for 15 amps

Marsh

[Tim Farrant]

Originally posted by Your Add Here!
I've got a Biamp M140 spring reverb that has been fun to use in the past in my recording setup. The problem is it has become very noisey. There is a broadband buzzing that I wish would go away. I've tried grounding the chasis and a I've tried ground lift adapter.

Do you suppose this is fixable? What is the likely problem?

mmmmmmmmmmm. I am not familiar with this unit. Is it still passing audio and/or making reverb ? If not, then the spring assembly is most likely the problem.

Sounds like it may have a bad earth connection somewhere in the preamp section or the power supply may be faulty as triez has suggested. But, if the power supply was loosing regulation, I would expect to hear a hum not a buzz. The output of the spring assembly is very low level so I would expect to find the problem somewhere in this area.

Sorry I cannot be of much more help. A Google search for a schematic turns up nothing for this unit.

Tim.

[Your Add Here!]

thanks. Yes, the reverb is working fine. It's too bad because it really sounds good too. The constant low-level buzzing makes too noisey to use. If I unplug the input source it still buzzes. When I jiggle the XLR out put the buzzing attenuates (wavers in volume) slightly.

[EveAnna Manley]

Marsh,
In order to help you with noise issues you need to describe what type of noise it is. Hiss? Buzz? Hum? What freqs? How much?

Was it always that way or it suddenly appeared?

Regulators do what the name implies: they keep the output volts steady no matter if the mains (input) votlage changes (within a range). Lack of regulators does not necessarily mean the power supply will be noisier.

If I were chasing down a "noise" in a unit, the first thing I would do is not "improve" the power supply. Must get noise out first.

I would:
a) Check the unit on the test bench. Sometimes buzz gets induced into gear from other gear in the rack. Hi-fluxy radiating tranny nearby, for instance. Sometimes a complicated grounding scheme in the studio is making certain gear hum or buzz. Get the unit on a simple setup on your tech bench to analyse the inherent noise of the unit.

b) Contact the manufacturer and see what issues they are aware of. Maybe the unit has always been inherently noisy and they discovered some fixes for it later in production.

c) Take them up on an offer of service or at least score schematics off them if you want to fix it yourself.

d) If you gotz hum, check for ripple on the rails. Maybe the unit is old or has been racked up in a hot rack and you have some power supply filter caps who have dried up not doing their filtering job anymore.

e) If you gotz hiss under higher gain, well, that's what you'll get with higher gain circuits. Try looking for quieter devices. Maybe get some kind of step-up transformer involved to score some gain for relatively small noise penalty then use your micpre in a lower gain setting.

I don't know that Benchmark in the slightest way, so I am speaking generally here...

[Tim Farrant]

Originally posted by Your Add Here!
. When I jiggle the XLR out put the buzzing attenuates (wavers in volume) slightly.

Aaaaahhh - sounds like a simple case of broken solder joints on the XLR if it is PCB mounted, or, the XLR is worn out and your loosing the pin 1 ground connection.

I'd open it up (unplug it from the mains first) and check for bad solder joints and loose connections.

Tim

[Your Add Here!]

I took it apart and broke out the soldering iron. I didn't find any obvious problem. I wiggled things around and tightened up the contacts to the tank. I was working on a table with a computer monitor on it and noticed that the RF from the monitor was dramatically increasing the noise. When I put it back together the noise didn't sound quite as bad. My real solution was to put a noise gate and EQ after it. I gated out the noise and notched out the most offending frequencies. It's very usable now. In fact it sounds terrific on a mix I'm doing - absolutely great on a guitar melody.

Thanks for your input!

[e-cue]

Sometimes blasting loud signal though spring reverbs, esspecially older units, can clean up the signal path. The ground is almost essential on the Biamp unit. Even then they are still a bit noisey.

[Geoff_T]

Originally posted by Marshall Simmon
i have a benchmark pre and a ward beck pre that have noise problems....


The benchmark has a unregulated power supply and i figured that was the problem. I'm going to go ahead and rebuild the power supply.


For the power supply, i'm going to use 3 regulators that drop the voltage incrementally, and a group of filtering capaciitors in parallel. I'll keep the transformer that is already there, since its rated for 15 amps

Marsh

Hi

I'm not sure what you are going to gain by wiring three regulators in series because you need good headroom for a regulator to work properly and, by dividing the voltage drop into three, you may be reducing the individual headrooms to a point where the regulator hasn't enough spare input volts to work properly.

A very good electrical design principle is "less is more". You should always look for the simplest, yet most effective, way of creating a circuit. Don't use three transistors where you could use two, don't use three regulators where you could use one.

From memory I recall that the fixed regulators are noisier than the variables... so cross off the 78 and 79 series from your shopping list and look at the LM317T and others of it's ilk. The 317 can handle a 40 volt input/output differential and has noise in the -80's.

I have a basic rule in life in that if there's more than 1mV ripple and noise on a power supply (around -60dBu) then it's crap. I always aim for noise in microvolts.

To achieve this you have to be very careful about the grounding around the regulator and keep all the capacitors and resistors close together. You want thick wires and thick PCB tracks... not just for current carrying reasons but to keep the impedances low. I know of one design of PSU that was cadded with thick tracks on both sides of the circuit board but a single, teeny, plated through hole joining the upper and lower tracks... it failed the 1mV test!

Actually, to be fair, my 1mV rule applies to 24v (or thereabouts) regulated power supplies. As the output voltage increases so this spec rises in proportion but I find it a good rule of thumb...

<1mV =