Sonusthree said:Ooh Smiler... you are a tease!
Oops! The file was over the limit. I didn't get any kind of warning, it just posted without the attachment.
You can download it from here: http://users.ecs.soton.ac.uk/awm106/cyrus2sman.pdf.
Sorry for the kafuffle!
Hello Smiler !
Sorry, I have some lacks in vocabulary
The buzz you have , in any imput selector ?
I'm on the way to "refurbish " my Cyrus : I would change all electrolitic capacitors
I have bought high grade caps : BC/Vishay, Panasonic FC, Sanyo Oscon, Elna Silmic II
I think that electrolitics caps can be "dry" after > 10 years
The max voltage is for all caps , PSU smoothing and some 100µf , they have to be 50v ; to be sure, verify in the part List !
You can change a 100µf 25v, by a 100µf 50v , BUT NOT the opposite
Capacitors C33 and C34 (input offset ) are very critical : it's where to have high grade NP caps, there some place under the board to install
The NP 470µF from RS are correct
I changed C65/66 by BC/Vishay low ESR 10 000µf (were 6800µf Cyrus black on my Cyrus)
If you had a look to the manual, you can see different "logical"
component in the schematic :
The power supply
The secondary supply for MM/MC
The Preamp (used only with MC/MM)
The Main Amplifier
If I were in your shoes, I would change electrolitics caps from main PSU, and then C51/52, C53/C54.
The "buzz" may come from some ripple voltage ,when caps are "bad/old "
The Preamp with LM317/LM337 is only to feed the Pre /MC/MM..
I think aluminium foil is not useful ...
R.C.
Sorry, I have some lacks in vocabulary
The buzz you have , in any imput selector ?
I'm on the way to "refurbish " my Cyrus : I would change all electrolitic capacitors
I have bought high grade caps : BC/Vishay, Panasonic FC, Sanyo Oscon, Elna Silmic II
I think that electrolitics caps can be "dry" after > 10 years
The max voltage is for all caps , PSU smoothing and some 100µf , they have to be 50v ; to be sure, verify in the part List !
You can change a 100µf 25v, by a 100µf 50v , BUT NOT the opposite
Capacitors C33 and C34 (input offset ) are very critical : it's where to have high grade NP caps, there some place under the board to install
The NP 470µF from RS are correct
I changed C65/66 by BC/Vishay low ESR 10 000µf (were 6800µf Cyrus black on my Cyrus)
If you had a look to the manual, you can see different "logical"
component in the schematic :
The power supply
The secondary supply for MM/MC
The Preamp (used only with MC/MM)
The Main Amplifier
If I were in your shoes, I would change electrolitics caps from main PSU, and then C51/52, C53/C54.
The "buzz" may come from some ripple voltage ,when caps are "bad/old "
The Preamp with LM317/LM337 is only to feed the Pre /MC/MM..
I think aluminium foil is not useful ...
R.C.
Re: Sourcing parts and what's worthwhile
Cheers Smiler! Very enlightening!
My metal cased toggle Cyrus one and two pick up loads of mobile phone interference, just as much as my plastic Cyrus One, so I'm not sure that lining the case with foil will be a big help. I don't find it a problem but I do think about it from time to time.
A friendly Cyrus service agent once said (on this forum
) that he's seen some phono stages oscillating from dried out electrolytic caps. Maybe change all of those in the phono preamp.
Large power supply smoothing caps were slit foils in the later models. Maybe they're worth the extra money?
I would love to advise you on your cap choice but I feel like I messed up my own somehwere! I recapped my Cyrus Two (toggle) and I've gained bass control but lost the 'speed' for upper mid/treble. My Cyrus one sounds better much better for those frequencies. I used black gates, Elna and changed the input cap to a polypropylene Sonicap. I use a Cyrus PSX and recapped that with Mundorf Electrolytics too.
Cheers Smiler! Very enlightening!
My metal cased toggle Cyrus one and two pick up loads of mobile phone interference, just as much as my plastic Cyrus One, so I'm not sure that lining the case with foil will be a big help. I don't find it a problem but I do think about it from time to time.
A friendly Cyrus service agent once said (on this forum
) that he's seen some phono stages oscillating from dried out electrolytic caps. Maybe change all of those in the phono preamp. Large power supply smoothing caps were slit foils in the later models. Maybe they're worth the extra money?
I would love to advise you on your cap choice but I feel like I messed up my own somehwere! I recapped my Cyrus Two (toggle) and I've gained bass control but lost the 'speed' for upper mid/treble. My Cyrus one sounds better much better for those frequencies. I used black gates, Elna and changed the input cap to a polypropylene Sonicap. I use a Cyrus PSX and recapped that with Mundorf Electrolytics too.
Thanks both for your responses.
I'm wary of going crazy replacing perfectly good components, but unfortunately don't have any good way to test them. My multimeter does basic capacitance tests... up to 100µF! Oh well.
I think I'll try the PSU (C57/58 6800pF, C65-68 22µF), feedback (C41/42 470µF) and pre-amp (C19/20 1µF, C35-38 2.2µF) electrolytics and see what difference that makes. I discovered Hi-Fi Collective earlier today; would the Black Gate N make a good replacement for the feedback bi-polars? I'm very new to all this, so I'm intrigued by the other brands Hi-Fi Collective offer. This might sound naive, but do the plastic/ceramic caps 'dry out' too? Has anyone bothered to replace these?
Oh, and I think Sonusthree guessed this, by the 10mF caps are Elnas. They look pristine, but like I said, I have no way of measuring them (at the moment anyway).
I'm wary of going crazy replacing perfectly good components, but unfortunately don't have any good way to test them. My multimeter does basic capacitance tests... up to 100µF! Oh well.
I think I'll try the PSU (C57/58 6800pF, C65-68 22µF), feedback (C41/42 470µF) and pre-amp (C19/20 1µF, C35-38 2.2µF) electrolytics and see what difference that makes. I discovered Hi-Fi Collective earlier today; would the Black Gate N make a good replacement for the feedback bi-polars? I'm very new to all this, so I'm intrigued by the other brands Hi-Fi Collective offer. This might sound naive, but do the plastic/ceramic caps 'dry out' too? Has anyone bothered to replace these?
Oh, and I think Sonusthree guessed this, by the 10mF caps are Elnas. They look pristine, but like I said, I have no way of measuring them (at the moment anyway).
Any advice I offered about caps would be simply passing on what I've read elsewhere.... and there's too many people doing that in the world of HiFi methinks. I'll leave that to the experts.
As far as I understand it, plastic/ceramic caps don't degrade in the same way as electrolytics so they should be fine.
As far as I understand it, plastic/ceramic caps don't degrade in the same way as electrolytics so they should be fine.
I think only electrolitic caps may "dry out" (EL in part list)
Don't miss some 100 µF, from +Vcc, -Vcc, try Panasonic FC from RS, regarding the size on PCB! C53/54/55/56
Take care to polarity when positionning !!!
Sonusthree is right to change input caps to NP high grade, (SCR,Obbligato, Audyn, ....)
see http://www.humblehomemadehifi.com/Cap.html
R.C.
Don't miss some 100 µF, from +Vcc, -Vcc, try Panasonic FC from RS, regarding the size on PCB! C53/54/55/56
Take care to polarity when positionning !!!
Sonusthree is right to change input caps to NP high grade, (SCR,Obbligato, Audyn, ....)
see http://www.humblehomemadehifi.com/Cap.html
R.C.
Substitutions
Okay, I think this is it. The only thing I'm not sure on now is Mundorf or Elna for the pre-amp circuit. My system's pretty forward sounding, with an over-enthusiastic treble, so I avoided Black Gates (plus 2.2µF BGs aren't available). Can anyone suggest what to do here? Then I'll order all this so I can get cracking!
Okay, I think this is it. The only thing I'm not sure on now is Mundorf or Elna for the pre-amp circuit. My system's pretty forward sounding, with an over-enthusiastic treble, so I avoided Black Gates (plus 2.2µF BGs aren't available). Can anyone suggest what to do here? Then I'll order all this so I can get cracking!
Code:
Purpose Original Replacement
C19/20 MM output de-coupling 1µF/50V [url=http://is.gd/1bgN0]Mundorf gb50[/url] / [url=http://is.gd/1baML]Elna S II[/url]
C25-28 RIAA-stage de-coupling 2.2µF/50V [url=http://is.gd/1bgN0]Mundorf gb50[/url] / [url=http://is.gd/1baML]Elna S II[/url]
/--/
C41/42 Feedback dc blocking 470µF/6V [url=http://is.gd/1baML]470µF/16V Elna SILMIC II[/url]
C51-54 Supply de-coupling 100µF/50V [url=http://is.gd/1bhve]100µF/50V Panasonic FC[/url]
/--/
C63/64 Pre-amp PSU smoothing 470µF/50V [url=http://is.gd/1bbYa]470µF/50V Panasonic FC[/url]
C65-68 " 22µF/25V [url=http://is.gd/1bcje]22µF/25V Panasonic FC[/url]
VR1 Pre-amp -ve regulator LM337 [url=http://is.gd/1birb]LM337T NS[/url]
VR2 Pre-amp +ve regulator LM317 [url=http://is.gd/1biEa]LM317T NS[/url]
/--/
RV01 Volume control (pot) 10kΩ [url=http://is.gd/1a6Ez]10kΩ ALPS "Blue Beauty"[/url]
Ref PSX Connecting Direct to Caps on Cyrus Two
I Agree, cant see this is correct, as you say, beyond the fuses which isolates the caps, when removed ?? ??
Cant see it myself, As for the pre-amp this is powered permanently on using its own regs and smoothing caps, from the 18volt windings on secondary, so cant see that the psx has anything to do with this stage either, I think it just powers the power amp section using its own caps and unregulated 40v supply.
Regards to all
Mark.
I Agree, cant see this is correct, as you say, beyond the fuses which isolates the caps, when removed ??
??Cant see it myself, As for the pre-amp this is powered permanently on using its own regs and smoothing caps, from the 18volt windings on secondary, so cant see that the psx has anything to do with this stage either, I think it just powers the power amp section using its own caps and unregulated 40v supply.
Regards to all
Mark.
Hi Mark,
The power switch disconnects the supply from the amp section only. The power transformer and phono circuits are always running as long as the unit is plugged in. A power bar would fix that! The PSX does run the amp section independently of the original supply to the best of my knowledge. I'd have to look at one to tell you. This is not something I am concerned with. After all, how would you change the way it is?
I think the phono runs on 15 volt supplies, but it may very well be 18 volt. The NE5534A will tolerate those voltages. Heed my warning, many other op amps will not live long at 18 volts for each supply.
I have never seen bad capacitors in one of these unless the ventilation is restricted. The same goes for the PSX supply. I'm going to bet it's either left running, or it's sitting on top of the amp (BAD!). The rectifiers almost never require replacement, unless they die when the outputs go. The heat comes from the resistors lighting the power LED. Now, to check the condition of filter capacitors, just hang a 'scope on the power supply filter cap and look at the waveform. If you see a larger "pip" on the leading edge of the wave form, it's bad. If not, it's good. It is that simple, even in real life.
Speaking of outputs, TIP42C (or any flavor) are completely unsuitable for this amp. The On Semi MJE243/MJE253 are fine, who do you think made them in the first place! The fault may lie in the source of the parts.
People, if you want to repair a nice amp, why on earth would you use Ebay as your parts source? That makes no sense at all!. Buy real parts from a real authorized distributor. The BUV48C are the proper outputs to be used, although some of the newer parts from On Semi may work, I haven't tried them yet. I am not aware of any units being produced using On Semi or Motorola parts for outputs, but in a European market, anything can happen I guess.
The regulated preamp supplies will break into oscillation when the surrounding caps dry out. Just replace everything including regulators. They are probably noisy after so many years running hot. Use use thermal compound on the small heat sinks.
-Chris
The power switch disconnects the supply from the amp section only. The power transformer and phono circuits are always running as long as the unit is plugged in. A power bar would fix that! The PSX does run the amp section independently of the original supply to the best of my knowledge. I'd have to look at one to tell you. This is not something I am concerned with. After all, how would you change the way it is?
I think the phono runs on 15 volt supplies, but it may very well be 18 volt. The NE5534A will tolerate those voltages. Heed my warning, many other op amps will not live long at 18 volts for each supply.
I have never seen bad capacitors in one of these unless the ventilation is restricted. The same goes for the PSX supply. I'm going to bet it's either left running, or it's sitting on top of the amp (BAD!). The rectifiers almost never require replacement, unless they die when the outputs go. The heat comes from the resistors lighting the power LED. Now, to check the condition of filter capacitors, just hang a 'scope on the power supply filter cap and look at the waveform. If you see a larger "pip" on the leading edge of the wave form, it's bad. If not, it's good. It is that simple, even in real life.
Speaking of outputs, TIP42C (or any flavor) are completely unsuitable for this amp. The On Semi MJE243/MJE253 are fine, who do you think made them in the first place! The fault may lie in the source of the parts.
People, if you want to repair a nice amp, why on earth would you use Ebay as your parts source? That makes no sense at all!. Buy real parts from a real authorized distributor. The BUV48C are the proper outputs to be used, although some of the newer parts from On Semi may work, I haven't tried them yet. I am not aware of any units being produced using On Semi or Motorola parts for outputs, but in a European market, anything can happen I guess.
The regulated preamp supplies will break into oscillation when the surrounding caps dry out. Just replace everything including regulators. They are probably noisy after so many years running hot. Use use thermal compound on the small heat sinks.
-Chris
Ref Chris Last Post
Hi Chris, Ive just read your comments,
I think your comments may have been directed at the wrong person, as I have now fully serviced and restored both PSX and Cyrus Two, including a new paint job, Using the Cyrus Two service manual as a reference,
The Pre-amp power supply is totally seperate to the amp supply, and is 18 + - regulated
Not 15 Volt.
The NE5534A operates between 3v and 20v with a 10Mhz Band width 4ma quiescent supply current and Slew rate of 13, Most op amps (granted not all) will operate to 18v some up to 22v
The other op amp is the NE5532 again 3v to 20v same band width 10ma quiescent slew 9,
Even the good old General purpose 741 op amp is rated at 5 to 18v,
I have replaced all 4 output transistors with BUV48Cs as you correctly point out now are the replacements for the old PT77s as all four came to about £10 and wanted to keep the amp balanced.
The feedback caps are now supplied by CapXon, the cap is CapXon 470uf 16v 710 NK Series. Cyrus Electronics Sent me a couple free of charge. 6.3v no longer available apparently. but these sound very good.
I have the version 7 board, so had to adjust the quiescent value on one channel by changing resistor R81 to the next value 180R as the range was out a little should be between 8 and 20mv and was 14 on one channel and 29 on the other, now 14 and 11, dc offset at speaker terminals unloaded with vol at min should be between + - 50mvs mine is a respectable 11mv on both channels.
The regs were fine and still going strong on phono stage, but replaced 470uf caps, and 22uf filter caps.
Replaced all main Smoothing Caps as a matter of course, due to age, felt the amp deserved it. both in the PSX which were bulging and Cyrus two, although I dont think the ones in the Cyrus two got used that much as psx takes the strain.
MJE243 / MJE253 driver trans as you rightly state are correct replacements, and work fine.
On the note of the pre-amp being on all the time, That to my mind keeps the pre-amp at a steady temp, and probably does less harm then turning on and off. I play a lot of vinal, and prefer it powered up, ready to give its best, I think the phono stage is very good in this amp. a simple relay on the main power-amp switch I suppose could be used to disconnect the pre-amp power but hardly worth it really, Just something else to go wrong eventually.
I sourced some components from little diode, which is available via ebay, but is also an independent company. and have had nothing but good results from parts sourced there.
Other caps from Audio Cap, and CapXon
But there are many other good manufactures and suppliers out there, I guess there are bad ones to, But a bit of homework on the supplier before committing to purchase if your not sure usually pays off.
Thanks for replying to me, but I think smiler may be in need of a little help, seems to be doing a major upgrade program.
I quite like the sound of my amp, Has gained a little more refinement with the new feedback caps, and I would be concerned about totally changing the character of the amp by changing too many non original parts.
Kind regards
Hi Chris, Ive just read your comments,I think your comments may have been directed at the wrong person, as I have now fully serviced and restored both PSX and Cyrus Two, including a new paint job, Using the Cyrus Two service manual as a reference,
The Pre-amp power supply is totally seperate to the amp supply, and is 18 + - regulated
Not 15 Volt.
The NE5534A operates between 3v and 20v with a 10Mhz Band width 4ma quiescent supply current and Slew rate of 13, Most op amps (granted not all) will operate to 18v some up to 22v
The other op amp is the NE5532 again 3v to 20v same band width 10ma quiescent slew 9,
Even the good old General purpose 741 op amp is rated at 5 to 18v,
I have replaced all 4 output transistors with BUV48Cs as you correctly point out now are the replacements for the old PT77s as all four came to about £10 and wanted to keep the amp balanced.
The feedback caps are now supplied by CapXon, the cap is CapXon 470uf 16v 710 NK Series. Cyrus Electronics Sent me a couple free of charge. 6.3v no longer available apparently. but these sound very good.
I have the version 7 board, so had to adjust the quiescent value on one channel by changing resistor R81 to the next value 180R as the range was out a little should be between 8 and 20mv and was 14 on one channel and 29 on the other, now 14 and 11, dc offset at speaker terminals unloaded with vol at min should be between + - 50mvs mine is a respectable 11mv on both channels.
The regs were fine and still going strong on phono stage, but replaced 470uf caps, and 22uf filter caps.
Replaced all main Smoothing Caps as a matter of course, due to age, felt the amp deserved it. both in the PSX which were bulging and Cyrus two, although I dont think the ones in the Cyrus two got used that much as psx takes the strain.
MJE243 / MJE253 driver trans as you rightly state are correct replacements, and work fine.
On the note of the pre-amp being on all the time, That to my mind keeps the pre-amp at a steady temp, and probably does less harm then turning on and off. I play a lot of vinal, and prefer it powered up, ready to give its best, I think the phono stage is very good in this amp. a simple relay on the main power-amp switch I suppose could be used to disconnect the pre-amp power but hardly worth it really, Just something else to go wrong eventually.
I sourced some components from little diode, which is available via ebay, but is also an independent company. and have had nothing but good results from parts sourced there.
Other caps from Audio Cap, and CapXon
But there are many other good manufactures and suppliers out there, I guess there are bad ones to, But a bit of homework on the supplier before committing to purchase if your not sure usually pays off.
Thanks for replying to me, but I think smiler may be in need of a little help, seems to be doing a major upgrade program.
I quite like the sound of my amp, Has gained a little more refinement with the new feedback caps, and I would be concerned about totally changing the character of the amp by changing too many non original parts.
Kind regards
Re: Ref Chris Last Post
I think there's plenty of information on this thread about practically doing this, so I'm satisfied about that now. I'm very new to audio electronics though, and reading about the effects of different capacitors has bemused me somewhat. I guess I won't understand this until I try it out! I'm really looking forward to this now.
Mark, quick question: did you use any test equipment (sig gen, scope, etc.) to complete this? I wonder if I'll need them or not.
Thanks for your help guys!
I thought there were only the ±31Vac secondary windings, which are connected to the amp and pre-amp rectifiers. I wonder how the power amp supply develops ±40V from this actually; the rectified dc value is ~33V (I don't think this includes diode voltage drop either).Mark Cogley said:
A paint job? What did you paint? On my amp, I'd quite like to touch up the dials, where the paint has peeled (they're black-painted metal), but I'm not sure how to go about this. I really like the design of the original 06 version; I think it's less dated than the 07 revision.
I'm intrigued about these. CapXon N/NK are the only non-polar capacitors available from RS. I'm going to try these out, as well as SJE NP 16V from Farnell. I can't help thinking Black Gates would be overkill.
I personally worry about how much power this uses, being a poor eco-conscious student! I might try testing this as some point.
Not really. I'm holding off of the ALPS Blue for now; it's actually quite costly. I just want my amp back up and running, and I don't want to skimp on quality. I like the detail and quality of sound the Cyrus provides, but my system is generally top-heavy. I thought as I'm replacing the capacitors anyway, it could be an economical way to tweak the bass response. Ideally though, I know I need bigger speakers.
I think there's plenty of information on this thread about practically doing this, so I'm satisfied about that now. I'm very new to audio electronics though, and reading about the effects of different capacitors has bemused me somewhat. I guess I won't understand this until I try it out! I'm really looking forward to this now.
Mark, quick question: did you use any test equipment (sig gen, scope, etc.) to complete this? I wonder if I'll need them or not.
Thanks for your help guys!
Hi smiler,
If you look at my thumb nail picture, you will see a Gold Cyrus two and PSX with a modified top plate "I should have made a better job of that really but it will do" as I had to increase the height due to the Caps being taller then the originals. I could not make do with the rather grubby looking Battleship Grey that had started to flake so whilst I had the opportunity, pulled out all the stops and end results much nicer than original colour.
Ive been really lucky with my dials, they are still mint.
I used my Lazer Guided Bench Pillar drill with a wire sander to take the old paint off completely back to metal, then primed and resprayed and then added some chrome lettering and lacquered.
Yes I did wonder about the voltage, I read something about its got something to do with being unregulated, and beyond the spec the load actually required, so offsets the actual voltage slightly higher, hence having 50V caps in the circuit to cope with peaks and spikes. which ive upped to 63V replacements and my 470uf phono caps are rated at 100v.
Yes I use a Function Generator that I built myself from a kit, not that expensive either, and housed in an old Ortophon Cartidge Acrylic display case, does the job extremely well, has sine, square, triangle, and saw-tooth wave forms, and goes from 1hz to 40Khz. two outputs, one fixed at 5V for digital use, and one ajustable.
Default wave set at sine at 1Khz. was going to build a frequency counter into it but decided that the scope, and my DVM both have this facility.
Probably one of the most useful pieces of kit I have. so many uses. for instance, checking a motor speed on a cassette player, just record a 1K tone on a decent tape dec, quartz locked etc. and then play this on your machine you wish to test, use a scope to read the frequency, and adjust motor to 1k, job done. Loads more things you can do with it.
Put a test record on your turntable with a 300Hz tone, and again check the speed is set at exactly 33 and a third by ajusting speed until you get exactly 300Hz, yes I know you can use a strobe disk, but just demo on scope uses.
Which really answers your next question, yes I have a scope. but no you dont need one, to find a faulty stage in the amp. you can use any kind of pilot tone on the input, and use an audio amp "Small Speaker with a resister an probes connected to it" to fault find the fault, starting at volume control and moving either direction from there comparing each channel until the faulty stage shows up. Then do some tests with the DVM on the stage comparing it with the other channel.
Yes a scope is very useful, but not essential. I just like having and playing with toys.
For instance you can inject a 5mv sine wave into phono stage on mm setting, and using a scope trace its amplitude and wave form at each stage, showing up a faulty stage easily. so suppose I found each correct stage to be a factor of 10 increase at each stage.. you can spot a duff stage, in my case, the fault was a duff NP Cap on the feedback loop, which pulled down the gain and kept it at the previous stage level.
so would be 50mv as apose to other channel being 500 mv. etc
removing and testing component confirmed the scoped results, it was down from 470uf to just 16uf. and the casing was cracking up. replaced both channels anyway. retested. all is well.
Be very careful around the driver transistors, they are just to easy to blow. test these with no power applied to the amp with a diode test on your DVM.
Have fun
Mark.
If you look at my thumb nail picture, you will see a Gold Cyrus two and PSX with a modified top plate "I should have made a better job of that really but it will do" as I had to increase the height due to the Caps being taller then the originals. I could not make do with the rather grubby looking Battleship Grey that had started to flake so whilst I had the opportunity, pulled out all the stops and end results much nicer than original colour.
Ive been really lucky with my dials, they are still mint.
I used my Lazer Guided Bench Pillar drill with a wire sander to take the old paint off completely back to metal, then primed and resprayed and then added some chrome lettering and lacquered.
Yes I did wonder about the voltage, I read something about its got something to do with being unregulated, and beyond the spec the load actually required, so offsets the actual voltage slightly higher, hence having 50V caps in the circuit to cope with peaks and spikes. which ive upped to 63V replacements and my 470uf phono caps are rated at 100v.
Yes I use a Function Generator that I built myself from a kit, not that expensive either, and housed in an old Ortophon Cartidge Acrylic display case, does the job extremely well, has sine, square, triangle, and saw-tooth wave forms, and goes from 1hz to 40Khz. two outputs, one fixed at 5V for digital use, and one ajustable.
Default wave set at sine at 1Khz. was going to build a frequency counter into it but decided that the scope, and my DVM both have this facility.
Probably one of the most useful pieces of kit I have. so many uses. for instance, checking a motor speed on a cassette player, just record a 1K tone on a decent tape dec, quartz locked etc. and then play this on your machine you wish to test, use a scope to read the frequency, and adjust motor to 1k, job done. Loads more things you can do with it.
Put a test record on your turntable with a 300Hz tone, and again check the speed is set at exactly 33 and a third by ajusting speed until you get exactly 300Hz, yes I know you can use a strobe disk, but just demo on scope uses.
Which really answers your next question, yes I have a scope. but no you dont need one, to find a faulty stage in the amp. you can use any kind of pilot tone on the input, and use an audio amp "Small Speaker with a resister an probes connected to it" to fault find the fault, starting at volume control and moving either direction from there comparing each channel until the faulty stage shows up. Then do some tests with the DVM on the stage comparing it with the other channel.
Yes a scope is very useful, but not essential. I just like having and playing with toys.
For instance you can inject a 5mv sine wave into phono stage on mm setting, and using a scope trace its amplitude and wave form at each stage, showing up a faulty stage easily. so suppose I found each correct stage to be a factor of 10 increase at each stage.. you can spot a duff stage, in my case, the fault was a duff NP Cap on the feedback loop, which pulled down the gain and kept it at the previous stage level.
so would be 50mv as apose to other channel being 500 mv. etc
removing and testing component confirmed the scoped results, it was down from 470uf to just 16uf. and the casing was cracking up. replaced both channels anyway. retested. all is well.
Be very careful around the driver transistors, they are just to easy to blow. test these with no power applied to the amp with a diode test on your DVM.
Have fun
Mark.
Hi Mark,
The case would have been better anodized, as it is the heat sink. Paint isn't the best for heat conduction and radiation. Still, as long as you don't run it too loud, it shouldn't overheat.
The 741 is a terrible, noisy thing that I spent a lot of time with. I may still have some in the cans. At any rate, most op amps are rated for 15 volt supplies (bipolar of course). This has really only changed with more recent op amps. A 741 is still useful in non-critical applications I guess. Hmm, I may even have some709's lying about somewhere. I know I have some 711 comparators.
You've got it backwards. Device life time is simply runtime vs temperature. The failure rate increases exponentially with temperature. It takes less than 1/2 hour on the extreme outside for things to settle down properly from a cold start. A couple minutes is all the warm up you need unless the circuit is poorly designed. These aren't - mostly.
No need for relays, but it would be a nice touch. A relay would hardly be worrisome for reliability. That's only an excuse to not consider the option. I'm not saying you need one, just that the excuse doesn't cut it. You will have your volume reduced while lowering your tone arm anyway.
I think I may have responded to you in order to keep the record straight when it comes to servicing these. They are really nice amplifiers. Once rebuilt, their owners are more than happy to continue using them.
-Chris
That's possible. It had been a while since I had posted in this thread. I read quite a few problem posts.
The case would have been better anodized, as it is the heat sink. Paint isn't the best for heat conduction and radiation. Still, as long as you don't run it too loud, it shouldn't overheat.
To the best of my knowledge, there is only one secondary voltage. There are two bridge rectifier circuits and they should both yield the same DC voltages unless there is a problem with one set of filter capacitors. I have seen the 470 µF capacitors go open. Both DC power supplies are unregulated, the preamp supply before the regulators and the power amp supply both. Remember that both these supplies run off the same secondary winding. They are not really separate. I couldn't remember which voltage they were regulated at. Most circuits run from 15 VDC supplies and the difference would not really affect these anyway.
Yes, I know. I have seen other people change the op amps to a problematic end. It's the abs. max. voltage we are concerned about, so you can just state they have a 20 VDC limit. I'm pretty sure most of us know these numbers by now. From your comment I suspected that you looked up the data sheet and read right off the top part. I was correct.
The 741 is a terrible, noisy thing that I spent a lot of time with. I may still have some in the cans. At any rate, most op amps are rated for 15 volt supplies (bipolar of course). This has really only changed with more recent op amps. A 741 is still useful in non-critical applications I guess. Hmm, I may even have some709's lying about somewhere. I know I have some 711 comparators.
Did your amp come with two or four output transistors per channel? It is necessary to replace all the transistors in one channel when you are doing a repair. There is no reason at all to touch the other channel. There is really no "balancing" going on when you stay within the proper substitutes. You didn't hurt anything, just spent extra money.
Capacitors rated at less than 16 V tend to fail more often. I can't say that I'm sorry to see those NLA. I generally use the 16 VDC rating to keep to a similar size. That can be an important issue as caps that are too big tend to pick up noise. Don't forget that these connect to the inverting input and may inject noise. I haven't seen what the factory is using as we are expected to source those smaller bits ourselves.
Okay, now this is where you can reduce the distortion some. Match those input transistors. The DC offset will fall and the distortion will come down a little, the sound quality will improve more than what the numbers may suggest.
If they got hot (and they do run hot), replace them. Use thermal compound on the new ones. Your regulated voltages may be fine, but regulators can get noisy after running hot 24 / 7 for years.
I have rarely seen main filter caps that needed replacing. Use that 'scope of yours to check the ripple across filter caps before pulling out your soldering iron. The originals were very good, so as long as your new ones as as good, no harm done.
Nope.
You've got it backwards. Device life time is simply runtime vs temperature. The failure rate increases exponentially with temperature. It takes less than 1/2 hour on the extreme outside for things to settle down properly from a cold start. A couple minutes is all the warm up you need unless the circuit is poorly designed. These aren't - mostly.
It is.
No need for relays, but it would be a nice touch. A relay would hardly be worrisome for reliability. That's only an excuse to not consider the option. I'm not saying you need one, just that the excuse doesn't cut it. You will have your volume reduced while lowering your tone arm anyway.
The only way to ensure you are getting the real (not remarks or copies) would be to buy from the normal supply chain. Real distributors. Besides, littlediode is terribly expensive! Farnell or similar would be the intelligent choice for parts. You really do need to shop at an authorized distributor for real parts.
My pleasure.
I think I may have responded to you in order to keep the record straight when it comes to servicing these. They are really nice amplifiers. Once rebuilt, their owners are more than happy to continue using them.
-Chris
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