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wardbeck m460-hiss with no mic connected?
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beatsnblunts
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#1
3rd May 2010
Old 3rd May 2010
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wardbeck m460-hiss with no mic connected?

Not being too familiar with this mic pre or electronics i ask this question.
I have a newly acquired pair of wardbeck m460's that i bought racked from a questionable person off of ebay. It took him a month to send them out because his tech was suppose to double check'em before they went out-never happened. SO when i got them i double checked the pin outs and psu voltages before turning them on and things looked OK. I plugged a Re20 in to test and it sounded ok. Now when i unplugged the mic i got a swell in hiss-re connected the mic-hiss was gone.

I do not notice this with other premps and am wondering what the cause might be or if this is normal for some preamps????. The wbs m460s are transformer discrete inputs with a couple gain stages and the outputs are electronically balanced. Does it have something to do with load on the preamp?

thanks,steve
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3rd May 2010
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You need a load on the input; 150 ohms is typical when checking noise..
And those pres are a little hiss'y anyway..
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3rd May 2010
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Quote:
Originally Posted by nosebleedaudio View Post
You need a load on the input; 150 ohms is typical when checking noise..
And those pres are a little hiss'y anyway..
yep.. a lot of the low noise specs are generated with the input shorted and not actual in use loading.. open will be the 'hissyest'
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beatsnblunts
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3rd May 2010
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thanks mike, would you say that this is 'normal'? i just don't recall noticing this with other preamps.
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3rd May 2010
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thanks for the replies guys! It's a pretty crazy difference from loaded and un-loaded. Like one snake to a basket full of snakes!
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3rd May 2010
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Quote:
Originally Posted by beatsnblunts View Post
thanks mike, would you say that this is 'normal'? i just don't recall noticing this with other preamps.
It depends..
Two things to comfirm this:
One: Have to be sure the gain is the same for two mic pres that you are comparing, if both are just cranked to max one might be 66dB of gain, the other 58dB for example..the 66dB will have more hiss..regardless..

2nd: terminate both with a 150 ohm resistor..
To make sure we are talking about the same pre, do you have a schematic?
Is Q1 and Q2 2N4401"s?

Plus a RE20 is a low level mic..
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3rd May 2010
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Any though other thoughts on these pre's?? I haven't had opportunity to really use em yet-seems like they have a crap load of gain. I bought em thinking they would be cool for rock n roll drums and guitar.
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3rd May 2010
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Quote:
Originally Posted by beatsnblunts View Post
Any though other thoughts on these pre's?? I haven't had opportunity to really use em yet-seems like they have a crap load of gain. I bought em thinking they would be cool for rock n roll drums and guitar.
There's your answer, the more gain a pre has the higher the noise will be...
For drums you will NEVER notice it..
Try'em and see..
I would guess you may need a pad, but I believe those had one on the PCB...
The schematic I have shows a pad..
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3rd May 2010
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mike,
they are the m460A-not sure of the rev. i guess i'll open it up and get back to ya. the schematic i have has Q1 & Q2 as 2n5209 on the pre amp card and pn3569 on the output card. Im getting in over my head here! Curiosity killed the cat-or shocked it.

and Yes it does have a pad switch.

thanks for the replies.
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4th May 2010
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Quote:
Originally Posted by beatsnblunts View Post
mike,
they are the m460A-not sure of the rev. i guess i'll open it up and get back to ya. the schematic i have has Q1 & Q2 as 2n5209 on the pre amp card and pn3569 on the output card. Im getting in over my head here! Curiosity killed the cat-or shocked it.

and Yes it does have a pad switch.

thanks for the replies.
OK, I may have the 460b schematic, may or may not be very different..
Either way just give it a good listen...
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4th May 2010
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Hello.

The M460 series is a very low-noise module superior in design to the later M470 series. You certainly do need to terminate as described by nose. The M460A and B are essentially the came module, just different routing options.

Please visit Tony's site the Ward Beck Preservation Society for all the help you need to get these wonderful units back to life properly.

Regards,
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5th May 2010
Old 5th May 2010
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thanks for adding Warren!
I've checked out wbsps-thats where i got the schematics. I will revist.

i've attached couple of pics

it looks like there's no resitor on the output and they are using the 'right out' for the output connection.

Excuse my lameness(im here to learn and hopefully pass along some knowledge in the future) but where would i connect the resitor-across hi and low or to ground??? ANd this would bring my output level down too?-which would prob help going into my AD.

thanks guys!
Attached Thumbnails
wardbeck m460-hiss with no mic connected?-wb460a-lower-pin.jpg   wardbeck m460-hiss with no mic connected?-wb460a.jpg  
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5th May 2010
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Bumpy bump for more termination info.
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25th June 2010
Old 25th June 2010
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more m460 pics

for your comments and to check termination. looks like my camera was upside down! doh!
cheers
Attached Thumbnails
wardbeck m460-hiss with no mic connected?-wbs460a-racked.jpg   wardbeck m460-hiss with no mic connected?-wbs460a-main-board-psu-caps.jpg   wardbeck m460-hiss with no mic connected?-wb460a-lower-pinout.jpg   wardbeck m460-hiss with no mic connected?-wb460a-upper-pinout.jpg   wardbeck m460-hiss with no mic connected?-wbs460a-psu-lower.jpg  

wardbeck m460-hiss with no mic connected?-wbs460a-phantom-switch.jpg  
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27th June 2010
Old 27th June 2010
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On some (most?) 460s the output wired "right out" makes the pan pot function as a trim. Engage the pan switch and that should give you a bit more flexibility dealing with the headroom/hiss issues. Worth a try anyway. That's how I always wire them up and, if I recall correctly, it was Dave T who turned me on to that quite some time ago.
Best,
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27th June 2010
Old 27th June 2010
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Quote:
Originally Posted by DrTom View Post
On some (most?) 460s the output wired "right out" makes the pan pot function as a trim. Engage the pan switch and that should give you a bit more flexibility dealing with the headroom/hiss issues. Worth a try anyway. That's how I always wire them up and, if I recall correctly, it was Dave T who turned me on to that quite some time ago.
Best,
DrTom
Thanks for that. Makes perfect sense now that you mention it. I will give it a turn.
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25th December 2012
Old 25th December 2012
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I'm racking up a pair of M460-LA, and ran into a similar/same issue.

I've got both of them racked up, running on the same power supply (JLM)
Voltages are good.
If I turn either one on and run signal, its clean and perfect.... When I turn the second one on and turn the gain up, I get a ton of noise (hissy snake noise) in the unit I've got my mic plugged into.

I've got the resistor network built in to compensate for the fader gain, and I'm using A out pot so I've got an output trim.
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25th December 2012
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Todd, use a scope to be sure the unit isn't breaking into oscillation at some ultrasonic frequency.

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30th December 2012
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I have a number of Ward Beck pres and eq's. If they haven't been re capped any of those could be bad. Or an Opamp could be bad. They are worth getting going however. Cool pres!
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