rtirion,
are you sure that 220 H stands for 220pF and not 22pF ?
For example:
http://www.avnetkent.com/static_fil...c/vign_managed/docs/pdf/Ceramic_Cap_Codes.pdf
Code = 2 significant digits of the cap value + number of zeros to follow:
10pF = 100
100pF = 101
1000pF = 102
22,000pF = 223
330,000pF = 334
thus 220 would be 22pF
are you sure that 220 H stands for 220pF and not 22pF ?
For example:
http://www.avnetkent.com/static_fil...c/vign_managed/docs/pdf/Ceramic_Cap_Codes.pdf
Code = 2 significant digits of the cap value + number of zeros to follow:
10pF = 100
100pF = 101
1000pF = 102
22,000pF = 223
330,000pF = 334
thus 220 would be 22pF
The coding one ceramic disc capcitors is according to your first link
2 digits for base value times a multiplier 10 power digit. Hope this makes sense.
i.e. 473 means 47 times 10 to the power of 3 so 47000pF = 47nF
This is not usually done on styroflex capacitors. At least I have never seen that. Most stryro's from Europe I know are from siemens. They did not use that type of coding on stryro's.
So I am pretty sure 220H means 220pF.
Also the location of the cap at the input make a 220pF look more in place.
Pity you do not have a schematic to verify.
Regards
2 digits for base value times a multiplier 10 power digit. Hope this makes sense.
i.e. 473 means 47 times 10 to the power of 3 so 47000pF = 47nF
This is not usually done on styroflex capacitors. At least I have never seen that. Most stryro's from Europe I know are from siemens. They did not use that type of coding on stryro's.
So I am pretty sure 220H means 220pF.
Also the location of the cap at the input make a 220pF look more in place.
Pity you do not have a schematic to verify.
Regards
thanks
I'm waiting for my silver micas, meanwhile I have changed the top styro to a ceramic, but not the two other styros... maybe they are damaged too, cause I hear some hum in my speakers, not very loud humming, but still too much.
would there be some connection here between styros and humming, or should I start to look for other damaged parts (resistors ?)...?
normally hum is caused by missing ground, or ?
I'm waiting for my silver micas, meanwhile I have changed the top styro to a ceramic, but not the two other styros... maybe they are damaged too, cause I hear some hum in my speakers, not very loud humming, but still too much.
would there be some connection here between styros and humming, or should I start to look for other damaged parts (resistors ?)...?
normally hum is caused by missing ground, or ?
I do not think the hum is due to the damaged styro's.
I would try to locate the hum as follow.
Use the RCA shorting plugs previously discussed as input for your
amp.
If the hum is still there, check all grounding connections.
btw I hope the hum is apperent with your original setup. And
not getting in with the new BOSOZ.
Did you check the entire PCB for bad solder connections?
Check the input resistors for correct value.
If the hum is gone (with RCA short) then I would take a good look
at the interconnects, and everything in front of the amp.
Even do a check with only one channel connected. This is to see
if there is no ground loop when you connect both channels
Hope this helps
Regards
I would try to locate the hum as follow.
Use the RCA shorting plugs previously discussed as input for your
amp.
If the hum is still there, check all grounding connections.
btw I hope the hum is apperent with your original setup. And
not getting in with the new BOSOZ.
Did you check the entire PCB for bad solder connections?
Check the input resistors for correct value.
If the hum is gone (with RCA short) then I would take a good look
at the interconnects, and everything in front of the amp.
Even do a check with only one channel connected. This is to see
if there is no ground loop when you connect both channels
Hope this helps
Regards
Thanks for instructions, rtirion
No, also hum using another source than BosoZ.
No, I didn't do the soldering check yet...
Hum is equal in both channels. Also hum with shortened RCA's.
I will check for resistors values, like you describe. And the solderings...
Finally I did the DC check with shortened RCAs:
@Left channel speaker 2,25 v
@Right channel speaker 814 mv
This doesn't look to good does it?
Should I start to look for a replacement for this amp.....
Zen 4 or Aleph 3?
No, also hum using another source than BosoZ.
No, I didn't do the soldering check yet...
Hum is equal in both channels. Also hum with shortened RCA's.
I will check for resistors values, like you describe. And the solderings...
Finally I did the DC check with shortened RCAs:
@Left channel speaker 2,25 v
@Right channel speaker 814 mv
This doesn't look to good does it?
Should I start to look for a replacement for this amp.....
Zen 4 or Aleph 3?
doesn't make me too happy to dump it. But I guess I would change my my mind if I listened to a Zen or Aleph amp.... :dizzy:I am afraid that does not look really good.
Finding the source of this will not be real easy without a
schematic.
If I would be you the first thing I would do is tedious reverse
engineering. i.e. using a multimeter, pencil and piece off paper
to draw up the total schema, incl. voltage readings on critical
points. This is not an easy task. But if my heart was with this
amp, I would probably enjoy it
From there on I would start the fault finding.
I know I am not making this any easier for you. So a ZEN V2 or V4
could be a very good option.
regards
Finding the source of this will not be real easy without a
schematic.
If I would be you the first thing I would do is tedious reverse
engineering. i.e. using a multimeter, pencil and piece off paper
to draw up the total schema, incl. voltage readings on critical
points. This is not an easy task. But if my heart was with this
amp, I would probably enjoy it
From there on I would start the fault finding.
I know I am not making this any easier for you. So a ZEN V2 or V4
could be a very good option.
regards
thanks, I will do my best 
A few final questions:
- what would normally cause DC offset?
This amplifier is from mid 80's and I can't be 100% certain that the hum and DC offset was caused by my BoSoz mistake....but I'm almost certain that the hum is new.
- why would I build a Zen 2 or Zen 4 instead of Aleph? It is easier to build isn't it? My BoSoZ is unbalanced only.
- could I use the toroid from the Audio 60 for a Zen? 500VA, 2*22 volts or something...
regards
A few final questions:
- what would normally cause DC offset?
This amplifier is from mid 80's and I can't be 100% certain that the hum and DC offset was caused by my BoSoz mistake....but I'm almost certain that the hum is new.
- why would I build a Zen 2 or Zen 4 instead of Aleph? It is easier to build isn't it? My BoSoZ is unbalanced only.
- could I use the toroid from the Audio 60 for a Zen? 500VA, 2*22 volts or something...
regards
>- what would normally cause DC offset?
DC offset on output can be caused by a few things.
1 - Aged emitter resistors i.e. values are no longer equal within
tolerance. (Yours got/get rather hot, so this would be on top of
my checklist)
2 - When the input of the circuit is constructed as a differential
amplfier and both transistors are not reasonably matched for
Hfe and/or Vbe, dc offset could result.
I think in your case the input is a dual diff construction.
But again, no schematic, so this is just guessing. Sorry
>- why would I build a Zen 2 or Zen 4 instead of Aleph? It is >easier to build isn't it?
Yes, I think ZEN are easier to built than ALEPH. Upcoming ZEN v4
will have PCB's and everything.
>My BoSoZ is unbalanced only.
Will work fine with either.
>- could I use the toroid from the Audio 60 for a Zen? 500VA, >2*22 volts or something...
I think this will not cause any problem. Watch to get proper
heatsinks though. You could look if there is a metal scrap yard
in your neighborhood. Maybe they have some serious sinks for a
reasonable price.
>there is a small blue pot/variable resistor (?) on the board >besides the transitors (see pic on page 1). Since I replaced all 8 >transistors wouldn't I need to adjust something with such a >variable?
I am pretty sure this pot is used to set the bias for your
output stage.
If you decide to turn this up, increased dissipation in the output
devices will be the result. If the heatsink can not handle the
increased dissipation (i.e. gets to hot) the output devices might
fail. This will ruin your speakers for sure, not to say the amp.
Hope this helps
Regards
DC offset on output can be caused by a few things.
1 - Aged emitter resistors i.e. values are no longer equal within
tolerance. (Yours got/get rather hot, so this would be on top of
my checklist)
2 - When the input of the circuit is constructed as a differential
amplfier and both transistors are not reasonably matched for
Hfe and/or Vbe, dc offset could result.
I think in your case the input is a dual diff construction.
But again, no schematic, so this is just guessing. Sorry
>- why would I build a Zen 2 or Zen 4 instead of Aleph? It is >easier to build isn't it?
Yes, I think ZEN are easier to built than ALEPH. Upcoming ZEN v4
will have PCB's and everything.
>My BoSoZ is unbalanced only.
Will work fine with either.
>- could I use the toroid from the Audio 60 for a Zen? 500VA, >2*22 volts or something...
I think this will not cause any problem. Watch to get proper
heatsinks though. You could look if there is a metal scrap yard
in your neighborhood. Maybe they have some serious sinks for a
reasonable price.
>there is a small blue pot/variable resistor (?) on the board >besides the transitors (see pic on page 1). Since I replaced all 8 >transistors wouldn't I need to adjust something with such a >variable?
I am pretty sure this pot is used to set the bias for your
output stage.
If you decide to turn this up, increased dissipation in the output
devices will be the result. If the heatsink can not handle the
increased dissipation (i.e. gets to hot) the output devices might
fail. This will ruin your speakers for sure, not to say the amp.
Hope this helps
Regards
DC offset
Well my friend..
The DC offset you measured is not normal. You should see something less than +-100mV. DC offset can damage your woofers!!!
It can be caused by missmatched input transistors , or aged components. I would really take into account the advice of the friend above to check the emmiter resistors.
The potensiometer may adjust the DC offset (i have seen that in an old, 70's Pioneer receiver) or it can adjust the quiescent current of the output stage. You can measure the dc offset and -at the same time- turn SLIGHTLY that pot to see what it does with a dummy load on the output. Remember to note the position of the pot before you do anything.
If it does not affect the dc offset, it changes the quiescent current.
By the way, the input stage is connected directy to the voltage gain stage, or the pre-drivers transistors. So check the devices connected directly to the destroyed ones.
Now, about the Nec output devices, check the databooks for replacements. Unfortunately i don't have mine with me now. Post the type.
About the input caps (22 or 220pF), measure those that are not destoyed. Most digital multimeters can measure capacistance.
Hope i helped...
Well my friend..
The DC offset you measured is not normal. You should see something less than +-100mV. DC offset can damage your woofers!!!
It can be caused by missmatched input transistors , or aged components. I would really take into account the advice of the friend above to check the emmiter resistors.
The potensiometer may adjust the DC offset (i have seen that in an old, 70's Pioneer receiver) or it can adjust the quiescent current of the output stage. You can measure the dc offset and -at the same time- turn SLIGHTLY that pot to see what it does with a dummy load on the output. Remember to note the position of the pot before you do anything.
If it does not affect the dc offset, it changes the quiescent current.
By the way, the input stage is connected directy to the voltage gain stage, or the pre-drivers transistors. So check the devices connected directly to the destroyed ones.
Now, about the Nec output devices, check the databooks for replacements. Unfortunately i don't have mine with me now. Post the type.
About the input caps (22 or 220pF), measure those that are not destoyed. Most digital multimeters can measure capacistance.
Hope i helped...
thanks.
Now after having replaced all six styros, dc-offset:
left: 472 mv
right: 720 mv
e.i. left down from 2500 mv to 472 mv.
Hum has also descreased. Have to put my ears close to speaker now to hear it. Hum in right side only, left no hum at all. Maybe it was always there...
Like when you buy a used car, after a couple of days you start to hear noises from the engine
I will go on with my work to find faults, however I wouldn't risk anything using the amp on a daily basis now, would I?
I'll go for the Penultimate Zen, but I need my amp in the meantime.
Now after having replaced all six styros, dc-offset:
left: 472 mv
right: 720 mv
e.i. left down from 2500 mv to 472 mv.
Hum has also descreased. Have to put my ears close to speaker now to hear it. Hum in right side only, left no hum at all. Maybe it was always there...
Like when you buy a used car, after a couple of days you start to hear noises from the engine
I will go on with my work to find faults, however I wouldn't risk anything using the amp on a daily basis now, would I?
I'll go for the Penultimate Zen, but I need my amp in the meantime.
Measure the voltage acrcoss the resistors connected to the emmiter of the output transistors. They are near the output transistors and rather big.
Their value varies between 0.22 to 0.47ohm. You will find one resistor for every output transistor.
You can't miss them.
Measure the voltage across one resistor on each channel. Divide the value you measure with the value of the resistor and you have the current.
15 to 100mA are normal values for a class B or AB amplifier.
Their value varies between 0.22 to 0.47ohm. You will find one resistor for every output transistor.
You can't miss them.
Measure the voltage across one resistor on each channel. Divide the value you measure with the value of the resistor and you have the current.
15 to 100mA are normal values for a class B or AB amplifier.
227mA is not a problem, as long as your amp does not get to
hot.
In the right channel however, their could be a problem with
the resistor on Q2 (272mA)
Try to measure the power resistors out of circuit for the right
channel. I suspect they are no longer equal in value within
tolerance. You could swap those for new ones. From one
of your pictures they look like 5 watt types to me.
Regards
hot.
In the right channel however, their could be a problem with
the resistor on Q2 (272mA)
Try to measure the power resistors out of circuit for the right
channel. I suspect they are no longer equal in value within
tolerance. You could swap those for new ones. From one
of your pictures they look like 5 watt types to me.
Regards
Ok, I will do that.
It doesn't get warmer than it used to.
Would you consider the latest DC offset voltages as within a safe margin to run this amp on a daily basis with my speakers?
The hum I can live with until my new amp is build.
I would consider my stupid damage fixed, after having replaced the 16 transistors and 6 styros... Like you mentioned before aged components might be one reason for the high DC offset...
thanks to all
It doesn't get warmer than it used to.
Would you consider the latest DC offset voltages as within a safe margin to run this amp on a daily basis with my speakers?
The hum I can live with until my new amp is build.
I would consider my stupid damage fixed, after having replaced the 16 transistors and 6 styros... Like you mentioned before aged components might be one reason for the high DC offset...
thanks to all
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