Yes, I used contact cleaner on both.. volume does not sound scratchy. There is no balance on this version..
There is a strange thing I am observing: everytime I connected the amplifier, I have done it with the lamp in series so I have some protection for over-current.
Not always, but sometimes when I raise or lower the volume, the lamp lights up a bit like it is drawing more current.
What could this thing be? I used contact cleaner from outside, and I do not hear any crackling sound when I am raising of lowering the volume.
Not always, but sometimes when I raise or lower the volume, the lamp lights up a bit like it is drawing more current.
What could this thing be? I used contact cleaner from outside, and I do not hear any crackling sound when I am raising of lowering the volume.
If the regulators in the RIAA section are too hot to touch there is likely to be a problem in that section.
This has an independent rectifier bridge and supply capacitors from the main amplifier which has enough closed loop gain that an additional line stage is not necessary and all other inputs can be switched via the volume control to the PA input.
Since the main capacitors in the RIAA supply - the light blue ones - are not original there has been some history in this section which may not have been properly resolved - possible instability infiltrating into the PA through the common earth reference.
This can be isolated by removing the rail fuses for the PA section and investigated.
This has an independent rectifier bridge and supply capacitors from the main amplifier which has enough closed loop gain that an additional line stage is not necessary and all other inputs can be switched via the volume control to the PA input.
Since the main capacitors in the RIAA supply - the light blue ones - are not original there has been some history in this section which may not have been properly resolved - possible instability infiltrating into the PA through the common earth reference.
This can be isolated by removing the rail fuses for the PA section and investigated.
For investigating the PA section it is possible to detect faulty parts by measuring voltages in circuit so leave them "in situ" for now.
I find it convenient to use Parrot clip test leads and to fit these with the power off - in that way the hands can be free to write down the voltages on the test part for each circuit designation on a paper copy of the circuit diagram. In particular I would be looking to see the voltage difference between base and emitter is about 0.6 - positive for NPN and negative PNP.
If you take this approach the light bulb can be dispensed with for fault diagnosis - the damage has already been done by a previous owner.
Since the parts at the greatest risk of failure are the output and driver transistors, the shortest route is test these first working from the output backwards to the input. There is some protection for the small signal transistors that shuts off their current supply if the output stage is over-driven. I would be surprised if the damage extends beyond the output and driver transistors.
If there is a need to replace any of these you will need some safeguard in place when you power up again - the light bulb. I have a pair of 100R 5watt resistors with alligator clips attached to either lead.
I fit these across rail fuse holder in lieu of the fuses with my meter connected to measure the voltage drop - and from Ohms law the current drawn. You can use this to get Iq in the correct range for final adjustment when the fuses are refitted.
As far as out of circuit tests go an NPN transistor is like a pair of diodes with the positive connection for each tied together forming the base and the cathodes being representative of collector and emitter.
It is sometimes possible to identify a faulty power transistor by comparing the diode junction behaviour between the same designated part on the neighbouring channel. It is easier to remove the leads of a faulty transistor from a board with the plastic body cut off.
Some years ago I built an in-circuit transistor tester from a magazine project - this has been very useful over many years.
I find it convenient to use Parrot clip test leads and to fit these with the power off - in that way the hands can be free to write down the voltages on the test part for each circuit designation on a paper copy of the circuit diagram. In particular I would be looking to see the voltage difference between base and emitter is about 0.6 - positive for NPN and negative PNP.
If you take this approach the light bulb can be dispensed with for fault diagnosis - the damage has already been done by a previous owner.
Since the parts at the greatest risk of failure are the output and driver transistors, the shortest route is test these first working from the output backwards to the input. There is some protection for the small signal transistors that shuts off their current supply if the output stage is over-driven. I would be surprised if the damage extends beyond the output and driver transistors.
If there is a need to replace any of these you will need some safeguard in place when you power up again - the light bulb. I have a pair of 100R 5watt resistors with alligator clips attached to either lead.
I fit these across rail fuse holder in lieu of the fuses with my meter connected to measure the voltage drop - and from Ohms law the current drawn. You can use this to get Iq in the correct range for final adjustment when the fuses are refitted.
As far as out of circuit tests go an NPN transistor is like a pair of diodes with the positive connection for each tied together forming the base and the cathodes being representative of collector and emitter.
It is sometimes possible to identify a faulty power transistor by comparing the diode junction behaviour between the same designated part on the neighbouring channel. It is easier to remove the leads of a faulty transistor from a board with the plastic body cut off.
Some years ago I built an in-circuit transistor tester from a magazine project - this has been very useful over many years.
Last edited:
Already at post 25, with many tips, more or less useful.
A diagnosis of Cyrus amp can be done in seconds if connected on the test bench and a successful repair in less than one hour.
So most work can be done quicker than writing this post. Ask an expert for repair and save time and money this way.
I managed to repair about 80 to 120 of these in the last 30 years or so.
On ALL incoming amps it was necessary to dismantle the input source switch and clean its silver contacts. Lubrication of the
switch alone is not sufficient, lubrication of vol and bal (bal not in this early version) is also useful.
Remember that both channels are working, but not properly, so many of the tips here would not apply in this case.
In my experience cap failures are very rare for the Cyrus and defective transistors also. Sometimes main filter caps of the regulators
have to be replaced. This would explain earlier work on this amplifier, but the blue caps look original. From what I can see on the
pictures in post 4 everything is still as manufactured. Do not replace random caps and semiconductors.
The regulators work for the phono section only. Operation of the power amp is not affected by these (a line amp is not existent).
They are of the 317/337 type, input is about 40 and output near 18 volts. Don't care about the supply voltage 38 or 41 volts as it
is dependent on your mains.
A useful service manual "for all models" is here: Cyrus 2 - Manual - Stereo Integrated Amplifier - HiFi Engine - registration required
(but I do not recommend HiFiengine any more).
A diagnosis of Cyrus amp can be done in seconds if connected on the test bench and a successful repair in less than one hour.
So most work can be done quicker than writing this post. Ask an expert for repair and save time and money this way.
I managed to repair about 80 to 120 of these in the last 30 years or so.
On ALL incoming amps it was necessary to dismantle the input source switch and clean its silver contacts. Lubrication of the
switch alone is not sufficient, lubrication of vol and bal (bal not in this early version) is also useful.
Remember that both channels are working, but not properly, so many of the tips here would not apply in this case.
In my experience cap failures are very rare for the Cyrus and defective transistors also. Sometimes main filter caps of the regulators
have to be replaced. This would explain earlier work on this amplifier, but the blue caps look original. From what I can see on the
pictures in post 4 everything is still as manufactured. Do not replace random caps and semiconductors.
The regulators work for the phono section only. Operation of the power amp is not affected by these (a line amp is not existent).
They are of the 317/337 type, input is about 40 and output near 18 volts. Don't care about the supply voltage 38 or 41 volts as it
is dependent on your mains.
A useful service manual "for all models" is here: Cyrus 2 - Manual - Stereo Integrated Amplifier - HiFi Engine - registration required
(but I do not recommend HiFiengine any more).
Did you check zero dc on the outputs? Sorry if this was already asked.
Last edited:
Very usefull information, although I think I already made some mistakes and observations:
a local electronics house had 4 BUV28, so I just changed the right channel transistors only to notice no difference 🙁
I also took note of the bias, and there is quite a difference, 8mv on right channel againt 18mv on the left channel.
The left channel sounds much stronger and doesnt have so much distortion.
I am not sure if it was a result of my "work" or if it was already like that, but C36 had one lifted leg... I will solder it again, but not sure if this is culprit of anything.
a local electronics house had 4 BUV28, so I just changed the right channel transistors only to notice no difference 🙁
I also took note of the bias, and there is quite a difference, 8mv on right channel againt 18mv on the left channel.
The left channel sounds much stronger and doesnt have so much distortion.
I am not sure if it was a result of my "work" or if it was already like that, but C36 had one lifted leg... I will solder it again, but not sure if this is culprit of anything.
I told you before, see post 14.
The bias difference is marginal.
"The meter reading should be in the range 8 - 20 mV".
Everything is in the manual, you are free to use it.
Did you dismantle and clean the switch?
I repeat myself ..
The bias difference is marginal.
"The meter reading should be in the range 8 - 20 mV".
Everything is in the manual, you are free to use it.
Did you dismantle and clean the switch?
I repeat myself ..
There is a protection fitted to the Cyrus2.
Look at the sch. It senses excess current through the emitter resistors and triggers the discrete Thyristor. That shuts down the input stage, so no audio gets through.
Remember to ALWAYS start up via the Mains Bulb Tester EVERY time you make any change.
Look at the sch. It senses excess current through the emitter resistors and triggers the discrete Thyristor. That shuts down the input stage, so no audio gets through.
Remember to ALWAYS start up via the Mains Bulb Tester EVERY time you make any change.
I will dismantle and clean the switch tonight... fingers cross it will be that the culprit.
From your experience, would a dirty switch make those noises and/or distortion?
If you have doubts this is the cause, try connecting an alligator test lead to R49 which would bypass the switch and take you directly to the PA input.
This has a high closed loop gain of roughly 100 times so tapping the other end of the lead with a finger should generate something of a signal that should be audible.
If it does then look at the switch. The odds could be this could be the problem since it has been a common servicing problem.
Also possibly relevant is some other experience - see post 10 - that C43 one of the brown capacitors might have gone open circuit.
In those circumstances the loop gain will have fallen to one (no signal amplification) as the feedback divider network no longer has a path to earth.
Oh boy, do I need to excuse myself and thank everyone who contributed to help me out!
All seems ok now, I cleaned the switch very well, I never thought this could be just the problem because I heard some almost "digital like" artifacts in sound that I thought could be a bad transistor.
Those who heard the sound file might know what I talk about.
Now you guys ask me, what was the sound sorce used for all the testing?
My cellphone 🙁
That was the reason I had those strange noises! What an awfull idea to use it to feed the amp while testing...
I guess I won some new transistors and capacitors, althought my poor art of soldering might have done more bad than good 😛
One thing still makes me wonder if it is alright: the voltage regulators are quite hot, can someone with a similar amp tell me if that's normal.
I know on Cyrus one they even do not have heat dissipators, but my Cyrus two v6 has dissipators and they are quite hot.
Maybe someone can tell me if that's normal. Apart from that, it sounds good so far and all seems ok with similar volume on both channels 🙂 Just need to test the MC position, one of the main reasons I really wanted this amp to work 🙂
Sergio
All seems ok now, I cleaned the switch very well, I never thought this could be just the problem because I heard some almost "digital like" artifacts in sound that I thought could be a bad transistor.
Those who heard the sound file might know what I talk about.
Now you guys ask me, what was the sound sorce used for all the testing?
My cellphone 🙁
That was the reason I had those strange noises! What an awfull idea to use it to feed the amp while testing...
I guess I won some new transistors and capacitors, althought my poor art of soldering might have done more bad than good 😛
One thing still makes me wonder if it is alright: the voltage regulators are quite hot, can someone with a similar amp tell me if that's normal.
I know on Cyrus one they even do not have heat dissipators, but my Cyrus two v6 has dissipators and they are quite hot.
Maybe someone can tell me if that's normal. Apart from that, it sounds good so far and all seems ok with similar volume on both channels 🙂 Just need to test the MC position, one of the main reasons I really wanted this amp to work 🙂
Sergio
Last edited:
Too hot is when you feel it is burning your finger. If it gets hot but is still comfortable to touch the regulators for several seconds these should be OK.
If things are too hot feel for heat on the IC's to see if one of these is hotter than the others.
A previous owner could have caused one of these to fail short circuit when probing around this area.
If things are too hot feel for heat on the IC's to see if one of these is hotter than the others.
A previous owner could have caused one of these to fail short circuit when probing around this area.
If we summarize it: many tips and nearly all of them going in the wrong direction.
Time and money wasted.
I apologitze that I did not reply early, only in post 17 and 20 as far as the switch
is concerned.
Many of the recommendations given here lead to damage of the amp if you
don't have repair practice. And if you have most of the endorsed precautions
would not apply.
The regulators drop 20 volts or more, so they will become warm. "Hot" is a relative
statement and we learned that we have to read your observations with caution also.
Time and money wasted.
I apologitze that I did not reply early, only in post 17 and 20 as far as the switch
is concerned.
Many of the recommendations given here lead to damage of the amp if you
don't have repair practice. And if you have most of the endorsed precautions
would not apply.
The regulators drop 20 volts or more, so they will become warm. "Hot" is a relative
statement and we learned that we have to read your observations with caution also.
From what I have been reading, it is normal. It is quite hot but I can hold my fingers there.
If I would get really burned, there would be a problem.
It is always on if amp is connected to mains, why did Mission do this? Won't this be a problem on longevity of components?
Regards,
Sergio
If I would get really burned, there would be a problem.
It is always on if amp is connected to mains, why did Mission do this? Won't this be a problem on longevity of components?
Regards,
Sergio
Cyrus "power" switches the secondaries to the power amp only, I don't know why.
Maybe this is due to the complication with additional supply PSX.
Check phono sens. switch also if you want to use a turntable.
Maybe this is due to the complication with additional supply PSX.
Check phono sens. switch also if you want to use a turntable.
This amplifier has a triple output stage - which may be more stable than an EF2 but due to the fact there is an extra stage involved, the Ic/Vbe transfer slopes are steeper and the critical crossover region on the plot is less.
The Cyrus 1 and 2 have the same switching arrangement and so when plugged into the mains the RIAA stage is operative and generating some heat inside the amplifier case.
I surmise the loading on the Regulators is not only to perform that function but to have some impact on the thermal environment in terms of the Iq sense transistor so this starts in the right zone when the power amplifier section is switched on.
If the current loading on the regulators is a little higher than one might expect this could well be by design - one of those things not apparent in service manuals or circuit diagrams.
The recommendation for Naim amplifiers is to leave them powered all the time. I once attended a demonstration of a new amplifier by the proprietor that he had brought with him to this country. He would not start the demonstration until it had warmed up thoroughly - somewhere between 30-60 minutes from memory.
The Cyrus 1 and 2 have the same switching arrangement and so when plugged into the mains the RIAA stage is operative and generating some heat inside the amplifier case.
I surmise the loading on the Regulators is not only to perform that function but to have some impact on the thermal environment in terms of the Iq sense transistor so this starts in the right zone when the power amplifier section is switched on.
If the current loading on the regulators is a little higher than one might expect this could well be by design - one of those things not apparent in service manuals or circuit diagrams.
The recommendation for Naim amplifiers is to leave them powered all the time. I once attended a demonstration of a new amplifier by the proprietor that he had brought with him to this country. He would not start the demonstration until it had warmed up thoroughly - somewhere between 30-60 minutes from memory.
On the last point it has to be remembered that heat will be absorbed into the metal and other material and the equipment may have been standing in a humid or damp environment. In the case of the Cyrus heat radiated from the active RIAA section would promote warm air movement/ventilation to expel moisture to the exterior air.
I notice in the pictures of the board in this example is fibreglass (good in my book) - I remember seeing some early Cyrus examples where the pcb were phenolic which was in common use in the 70's and 80's because it was cheaper - my memory on this is vague but I think phenolic material was better suited for r.f. applications on one hand but more absorbent of moisture and less robust mechanically than fibreglass on the other.
I notice in the pictures of the board in this example is fibreglass (good in my book) - I remember seeing some early Cyrus examples where the pcb were phenolic which was in common use in the 70's and 80's because it was cheaper - my memory on this is vague but I think phenolic material was better suited for r.f. applications on one hand but more absorbent of moisture and less robust mechanically than fibreglass on the other.
Heh... cellphones make lousy audio sources. You're probably hearing some oddness of the cellphone's internal class D amplifier which isnt there when it's driving headphones.
I disagree that the LM317/337 regulators running hot is the sign of a problem. They are dropping 35v down to 18v so that is quite a bit of dissipation even at the low currents that 3 opamps would draw. If you are concerned about the heat, and have no plan to use the phono input, you could simply remove the regulators.
I disagree that the LM317/337 regulators running hot is the sign of a problem. They are dropping 35v down to 18v so that is quite a bit of dissipation even at the low currents that 3 opamps would draw. If you are concerned about the heat, and have no plan to use the phono input, you could simply remove the regulators.
Input Selector (Rotary Switch Version" ALPS - 160595-3: is this the right part ?
ALPS - 160595-3 - Switch, rotary. Contacts: 4-Pole 5-Position.
(found under this overview with a wide range of rotary switches .
http://www.electronicsurplus.com/switches/rotary-switch/sort-by/price/sort-direction/asc/show/48 )
Maybe one of the members know, if this switch is the same than the genuine version.
Thank you very much for an advice.
I discover this offer:
ALPS - 160595-3 - Switch, rotary. Contacts: 4-Pole 5-Position.
(found under this overview with a wide range of rotary switches .
http://www.electronicsurplus.com/switches/rotary-switch/sort-by/price/sort-direction/asc/show/48 )
Maybe one of the members know, if this switch is the same than the genuine version.
Thank you very much for an advice.
This switch looks similar but as far as I remember the original switch has only 2 sets
of 7 contacts, not 4. Anyway if you buy a switch that has been in storage for a long
time the problem is the same. In each Mission amp this switch has to be desoldered,
dismantled and contacts cleaned, for instance with a glass brush. This together with
a suitable lubricant gives completely satisfactory results for years.
of 7 contacts, not 4. Anyway if you buy a switch that has been in storage for a long
time the problem is the same. In each Mission amp this switch has to be desoldered,
dismantled and contacts cleaned, for instance with a glass brush. This together with
a suitable lubricant gives completely satisfactory results for years.