skal1

help help fabio neve driver board
« on: August 01, 2008, 04:50:47 PM »
I have built this circuit and it works ok but for one thing .When i try and set the bias i am getting  a loud hissy noise from the out put ,i have manged to trim most of it out , but i can still hear a slight static noise can any one help me with this.

heres the schem link{ http://www.thediypill.phx.com.br/forumfiles/neveout solder.pdf}

edit {iam a newbie this is my first circuit}
regards

skal 1


dissonantstring

help help fabio neve driver board
« Reply #1 on: August 02, 2008, 12:47:07 PM »
hi skal,
i noticed you posted another post on the same thing.  rather than making an new post might i suggest that you bump your original thread, then for prosperity, people can reference one thread rather than having multiples. (sorry, rant over). :grin:

now for your problem with your neve output driver circuit.  can you give a description of the test circuit (or a picture of it).   what are you driving the output with (preamp/tone generator/etc.)?  what is your input level going in?  is the level actually being amplified by the circuit?  is the output transformer hooked up properly?
i'm not the most experienced here, but I'll try to help if I can.
regards,
grant

skal1

help help fabio neve driver board
« Reply #2 on: August 02, 2008, 02:57:13 PM »
Hi dissonantstring

ok then basically i have carnhill o/p and i am driving i/p with  hhb cd recorder .Everything is fine accept for the hiss ,i think its coming  from the biasing section of the driver, you can almost get rid of the noise to little static crackle , are trans bad bc184 or the 2n3055. I don't know.


skal1

Bless up

dissonantstring

help help fabio neve driver board
« Reply #3 on: August 02, 2008, 03:32:34 PM »
hi skal1,
so you've biased the circuit with the trim pot to get symmetrical clipping on the wave form and you're still getting the hiss, thus wondering what else could be the problem.  is that correct?
have you tried any other input signals or measured the signal level going into the circuit?  how many V is the input signal?  no time to really research this now, but hiss seems to be a s/n ratio problem.  too low input signal possibly?
also, the neve output is can put out a lot of volts so be very careful how you trim.  parts are likely to burn if not careful.  
regards,
grant

skal1

help help fabio neve driver board
« Reply #4 on: August 02, 2008, 03:43:41 PM »
my modem is a bit so bear with me. ok this hiss is there with no  input connected to the driver board.
skal1

dissonantstring

help help fabio neve driver board
« Reply #5 on: August 02, 2008, 04:13:10 PM »
hmmm,
if not your monitor output putting out the hiss, then maybe it's the active components (as you've probably already guessed).  try Q4 first, though i suspect Q6.

skal1

help help fabio neve driver board
« Reply #6 on: August 02, 2008, 04:18:04 PM »
ok forgot to mention it does this on both channels , my monitors are genelec 8030as .i will try what ypu mentioned.



thanks again


skal1

dissonantstring

help help fabio neve driver board
« Reply #7 on: August 02, 2008, 04:37:15 PM »
hi skal1,
if you have an oscope or audio probe easy DIY version you can trace from the input signal and see where the hiss starts at least and tell at which component the problem starts.
this probe is pretty easy to make and has helpful in a few builds.
good luck.

skal1

help help fabio neve driver board
« Reply #8 on: August 02, 2008, 04:49:33 PM »
ok thanks for help


regards


skal1

skal1

help help fabio neve driver board
« Reply #9 on: August 02, 2008, 05:44:46 PM »
done a test followed the circuit through a 10uF 35v tantal and then a resistor  2,2k into the first bc184c  at the junction of the first bc the signal is decouplled by c13 to the emitter..ALL the trouble starts at the first bc 184c..


this can not be the problem can it ,that means the batch of bc184 are shizit..
I changed these about 3 times already, they must be bad ?


skal1


skal1

help help fabio neve driver board
« Reply #10 on: August 02, 2008, 06:29:51 PM »
i just pull out the second bc184c and everthing seems fine no hiss.Then i put another bc184c in it place and the hiss comes back, what kind of madness is this ?

skal1

SALSA

help help fabio neve driver board
« Reply #11 on: August 03, 2008, 06:39:48 AM »
FWIW

Did you compare Hfe and selected > 600 ?

Cheers,

Mike

skal1

help help fabio neve driver board
« Reply #12 on: August 03, 2008, 07:56:22 AM »
Quote from: "SALSA"
FWIW

Did you compare Hfe and selected > 600 ?

Cheers,

Mike


what do you mean by this SALSA ?


I think i know whats wrong.It goes like this ,the signal enters the base of Q4 and then comes out of the collector which feeds the base of Q5 every thing is ok to here it seems when q5 and q6 inter act this is were the problem starts correct me if i am wrong.

Samuel Groner

    Z├╝rich, Switzerland
  • Posts: 2935
help help fabio neve driver board
« Reply #13 on: August 03, 2008, 09:34:51 AM »
Quote
This hiss is there with no input connected to the driver board.

Any preamp will have much more noise with nothing connected at the input!!! Short the input or connect a mic--if there's still so much hiss to make the output unusuable then there's a problem, otherwise not.

Samuel

skal1

help help fabio neve driver board
« Reply #14 on: August 03, 2008, 10:37:22 AM »
well i think your right samuel the sound is killer with a signal going into it with no  notice able hiss  ,may its me because i am used to digi world  :thumb:

skal

first time hurts second it wonderful

SALSA

help help fabio neve driver board
« Reply #15 on: August 03, 2008, 11:50:15 AM »
Quote from: "skal1"
Quote from: "SALSA"
FWIW

Did you compare Hfe and selected > 600 ?

Cheers,

Mike


what do you mean by this SALSA ?


I had the impression you were swapping transistors and some worked fine and others not ... afaik it is recommended to use in this Neve circuits BC184C's with Hfe > 600 for low noise. But apparently the noise came from an open input.

Cheers,
Mike

skal1

help help fabio neve driver board
« Reply #16 on: August 03, 2008, 12:56:44 PM »
Quote from: "SALSA"
Quote from: "skal1"
Quote from: "SALSA"
FWIW

Did you compare Hfe and selected > 600 ?

Cheers,

Mike


what do you mean by this SALSA ?


I had the impression you were swapping transistors and some worked fine and others not ... afaik it is recommended to use in this Neve circuits BC184C's with Hfe > 600 for low noise. But apparently the noise came from an open input.

Cheers,
Mike



i am interested about this hfe term ,can you explain what this Hfe means .


skal1

Sleeper

help help fabio neve driver board
« Reply #17 on: August 03, 2008, 01:38:43 PM »
HFE IS SOMETHING YOU FIND IN TRANSISTOR DATASHEETS (sorry my cat turned on the capslock) you can measure it on some digital multiumeters and in some circuits you want to select your transistors to be within a certain hfe range.
you can buy some transistors already selected for hfe ... bc190a and a bc190c have a different range of hfe.
Functionally its the amount of gain the transistor is going to push out (within a specific test circuit). some circuits are only happy with specific hfe transistors in specific locations.   In stereo units I often try and match hfe of the transistors in each channel, this would/should give me similar performance on each channel.
Technically, well,  you'll have to look it up cause i can't explain it and PRR, BCorso, Groner et al shouldn't have to.
it must be in wikipedia for starters.(.3333=/*0.33333333333333111111111111111111114444444444444444444
4444444444444444444444444===========================111
1111011111111111111111=/0144444444000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000)
more cat typing sorry.
Kelly


 

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