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  #1  
Old 02-16-2006, 05:53 PM
SCHORN SCHORN is offline
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The Urei's trademark hiss.

Dear All,

I recently went Class A in the amplifier field and have noticed a very noticeable hiss coming through my speakers when using my Urei or Bozak.

The speakers that I use are extremely efficient, so this hiss is much more audible than it might be with other, not so efficient speakers.

Anyhow, I was wondering if maybe Mario or someone might have an idea on how to eliminate this problem?

I was thinking that it maybe the power transformer and maybe removing the power transformer from inside the Urei and making some kind of custom system where as the power supply is totally separate from the mixer.

The hiss in question can be heard by plugging in a set headphones to a Urei and just listening, this is what I'm hearing through my speakers.

Anyone else encountered this problem or is it just me?

For all the Urei users out there, do you get a nice hiss through your headphones and speakers too?

ANYONE?

Thanks
Schorn.

Last edited by SCHORN : 02-17-2006 at 04:29 PM.
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  #2  
Old 02-16-2006, 06:17 PM
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DSA.audio DSA.audio is offline
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i use a hi efficiency, horn loaded system and UREi

I get the hiss... not really dramatic or offensive, but there for sure....

I think it is the ICs.... to get rid of it, I play music.


edit.....
there is a slight mention of the 'hiss' in this thread....

http://64.233.179.104/search?q=cache...ln k&cd=1</a>

edit....
oops looks like the link doesn't talk about the tl0 hiss, but him changing caps and gettign hiss and wanting to swap out opamps to mellow the sound....

sorry
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Last edited by DSA.audio : 02-16-2006 at 06:29 PM.
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  #3  
Old 02-16-2006, 07:56 PM
Richi Richi is offline
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Does this come through on the line level too?
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Last edited by Richi : 02-02-2011 at 07:03 PM.
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  #4  
Old 02-16-2006, 09:27 PM
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Rotarymadness Rotarymadness is offline
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Re: The Urei's trademark hiss.

Quote:
Originally posted by SCHORN
Dear All,

I recently went Class A in the amplifier field and have noticed a very noticeable hiss coming through my speakers when using my Urei or Bozak.

The speakers that I use are extremely efficient, so this hiss is much more audible than it might be with other, not so efficient speakers.

Anyhow, I was wondering if maybe Mario or someone might have an idea on how to eliminate this problem?

I was thinking that it maybe the power transformer and maybe removing the power transformer from inside the Urei and making some kind of custom system where as the power supply is totally separate from the mixer.

The hiss in question can be heard by plugging in a set headphones to a Urei and just listening, this is what I'm hearing through my speakers.

Anyone else encountered this problem or is it just me?

For all the Urei users out there, do you get a nice hiss through your headphones and speakers too?

ANYONE?

Thanks
Schorn.


UREI or Bozak? which one?

1.if you are talikng about bozak. it has some problem with trangister or something
basicaly this unit never say anything if you don't desire.

2.but if you are talking about UREI
"BE FRIENDLY WITH IT"
and don't enjoy the "silence" enjoy the "music" from urei mixer

3.if you are talking about both
check the cables. use balance conection or "grounded" unbalance cable.

peace

taisei
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  #5  
Old 02-16-2006, 10:49 PM
djmariog djmariog is offline
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Re: Re: The Urei's trademark hiss.

hello,

Please explain more.

rca or xlr , booth or house

any eq or amp

location of eather

Mario G.
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  #6  
Old 02-17-2006, 08:55 AM
thermionic thermionic is offline
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If you're talking about a high-pitched "hiss" it can't be the power transformer. The AC field generated by a transformer will correspond to overtones / harmonics related to your mains frequency, i.e. 60hz in the US, and you'll be talking about a sinusoidal-type interference, not "hiss".

Moving a PSU outboard not only keeps hum at bay (as mentioned above) but it also keeps RFI away from your audio circuitry.

RFI can be generated by rectifier diodes (a classic problem; many high-end designs implement "soft recovery" fast-switching Schottky diodes for this reason - in a nutshell, they emit less RFI.

Regulators can emit RFI.

One way of controlling RFI is to fit "snubbing" caps around your rectifiers and regulators (this is basic and cheap)

Another way to control RFI is to put the PSU in a separate box (states the obvious).

"Hiss" can be a product arising from many issues, and without hearing the hiss for oneself, looking at it on a ‘scope and having a peek under the bonnet, it's the kind of thing that's difficult to diagnose via this medium...

You could have contaminated grounding btw - dirty ground connections are probably the first place to look; remove all ground connectors and clean them up with spray / fine glass paper etc. If extra impedance is introduced to ground, you could have noise issues arising.

In short, there is probably no simple answer; experiment empirically by all means, but if that doesn't solve it you'll be in for a sizeable bill from a qualified Tech I'm afraid.

Justin

edit: For clarity's sake, "RFI" stands for "Radio Frequency Interference" and encompasses "hiss".

Last edited by thermionic : 02-17-2006 at 08:59 AM.
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  #7  
Old 02-17-2006, 10:55 AM
SCHORN SCHORN is offline
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Thanks for your reponse guys.

Mario, this is that Urei I brought to you a few weeks ago, remember you replaced the rca's and found out that they had been put in the wrong way around when the mixer was made?
The hiss is there when using rca, xlr, booth or house.
I don't use an eq (don't want one either to be honest) and my amp is about 4 feet below the mixer on the bottom shelf.
Like I said before, when I listen to my headphones through the Urei I can hear this hiss, even when there is no music playing and all the pots turned down - this hiss I hear in the headphones is exactly what I hear in my speakers.

Thermionic, it's not a high pitched hiss but I really think that it could be the RFI as you mentioned.
I would really like to have the PSU removed and kept seperate, I'm sure it has something to with this problem.

I know it's not that major, and yeah when I play music it's not as bad but it drives me nuts because I can still hear it when I get to a quiet passage / ending of a song.
If something can be done to reduce it I wanna do it and see if it helps.

Thanks again guys for your input.

Regards
Schorn.
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  #8  
Old 02-17-2006, 12:39 PM
Criscodisco Criscodisco is offline
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It could your particular Urei. If it's not that, also consider the new Urei or Allen & Heath V6-the newer good equipment's generally going to be cleaner with a lower noise floor.
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  #9  
Old 02-17-2006, 01:01 PM
clubman5 clubman5 is offline
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The IC,s used to drive the outputs in the urei are set up to produce gain. The hiss ( ssssss )you hear is residual noise from the IC,s!

I have 16 bullets, and when no music is playing, you can hear them hissing if your standing under them. But, you dont hear it over the music. So, I dont bother with it.

Anything that produces gain, will raise the noise floor, and send some residual noise into the system.

Better IC,s might help to some degree, BB IC,s are known to be less noisy, TLO84,s are known to be more noisy. But, the Urei wasnt designed with all this in mind.

I dont think youll get it to be much quieter than it is without significantly altering its sound character.
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  #10  
Old 02-17-2006, 01:35 PM
SCHORN SCHORN is offline
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You're most likley right Scott, would still like to pull the PSU out though - thanks for your response man.
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  #11  
Old 02-17-2006, 02:05 PM
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RETRODISKO RETRODISKO is offline
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that hisss is normal i think, all old ureis have it is normal as far as i know
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  #12  
Old 02-17-2006, 02:54 PM
thermionic thermionic is offline
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I see the point about music masking the hiss, and if you can live with the hiss that's cool (I'm sure we can all think of units that have an ultra-low noise-floor but don't have an agreeable tone, and vice-versa: units that are a tad noisy, but sound "euphonic").

But having said that, this is an interesting experiment to see how noise masks low-level information: say you have a mix set up on a studio console with a useable range, but some residual hiss from old outboard.

When you hit "Play" you can't notice the hiss. However, if you go around the channels muting sources that aren't in use, it will amaze you at the difference...

In all honesty, the studio console experiment is a real eye-opener... Even though the noise isn't heard directly when the mix is in play, when you mute those old delays the difference in clarity is shocking...

IMHO, a low noise-floor is worth fighting for. If you know a Tech that genuinely knows what they're doing, you will be able to make improvements without destroying the original character.

TL-084 aren't as quiet as modern AD or BB devices, but their inherent noise is far lower than you might think - it's all about implementation. If a TL084 is noisy, it could be down to other issues; even in the early '80s they had ICs that were capable of 120dB+ dynamic range, fact!

The UREi's output-stage is its nicest part IMHO; IIRC, it's descended from their legendary outboard such as the 1176 compressor etc. The complementary 2N6716 / 6728 configuration transistors can dissipate 2W+, and I believe this is the main reason kick drums have so much "thump" through a 1620.

It's the hungry time of the day for me - excuse any typos!

Justin
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  #13  
Old 02-17-2006, 03:13 PM
SCHORN SCHORN is offline
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Hi Justin,

Thanks for your expert reply, you really know what you're talking about.

Yeah I really think I want to try and tackle this problem as I don't think I can live with it forever.

I'm in total agreement as far as the effect this hiss is having on the low level infromation of the source recording which is why I'm so interested in trying to reduce the noise floor.

It's like listening to a record you own that's got a little background noise and then cleaning it on a VPI record cleaning machine and hearing how that bit of background noise really masked that low level information - you just notice details in the record you couldn't hear before.

Cheers

Schorn.
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  #14  
Old 02-17-2006, 04:41 PM
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DSA.audio DSA.audio is offline
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if your UREI has the IC sockets, you could (***edit*** easily) just swap them out and try the BB or whatever other flavour of OP Amp that you wished....

but that practice raises the theoretical question of why have XYZ equipment (that ppl like for it's specific sound reproduction characteristics) if it doesn't sound like XYZ equipment anymore...

to each their own though.... it's your equipment afterall.....
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Last edited by DSA.audio : 02-17-2006 at 05:01 PM.
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  #15  
Old 02-17-2006, 07:06 PM
clubman5 clubman5 is offline
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Justin is correct, as always, but, I found that with other IC,s in the urei, the hiss levels change. BB was the quietest. It is definitely more accurate, more clean sounding. Also quite dynamic.

There are many things a good tech that understands what they are doing, can implement to really improve the urei, but for the cost of a few chips, you might find you solve your problem, and get something sonically to boot.

You may really like the BB IC,s, the audiophile community does.

Or you can also look into the Excalibur series from Texas Instruments available from Digi-Key. TLE2074ACN
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Last edited by clubman5 : 02-17-2006 at 07:23 PM.
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  #16  
Old 02-17-2006, 07:23 PM
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LuvLatins LuvLatins is offline
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Now I feel good. My Urie LE has no hiss at all. Orignally if I turned my power amp way way up I heard a low hum. I reseated my pono cart in the TT and it is gone.

How high is he turning up is master volume ? I am sure if you set both to MAX you will hear something. As resonable levels he souuld not hear a hiss

JB
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