Thanks for the tutorial. I had to replace a STK0050II hybrid amplifier module in my SR 4000 receiver, but I can´t find any adjustable resistors to adjust the DC bias. The link to download the service manuals is down for new users.
Hi there is no DC bias ajustment on the Marantz SR4000 just a led meter calibration adjustment. If you require the manual just email at arcadeimages@gmail.com
@@MichaelYates Hello Michael. Thanks for the clarification, because without having the service manual and seeing that everyone has to adjust the DC bias in his amplifiers, I was worried. On the website of the link you mentioned it is no longer possible to download the Marantz manual, so I would appreciate it if you could give me an alternative. Many thanks from a Valladolid at 40ºC.
Thank you so much for putting this video together. What is bias and why is it even done. It sounds like some sort of calibration to mirror the two channels so that they operate identically from an electrical perspective is this correct? Great video!!
Its done to get the optimal out of the transistor while not over powering the transistor, keep the distortion to the lowest, stop clipping as much as possible, to keep both channels running smoothly and at the same level, ie both channels set to the same bias.
Just what I need Thanks. I repaired mine by changin only one transistor. All the rest is original. I don't fell like changing capacitors considering that it sound pretty good. I'd like to conserve it as original as possible considering the great internal conditions. Some suggestions ?
I to like to keep my amps as orignal as possible, why replace something that sound fine is what I think. But sometimes if they sound that bad then the caps might need replacing. I have read on a lot of forums replacing the caps in this au101 can make the tone a bit to bright. At some stage I will get another 101 and replace all the caps and compair the 2 as a matter of curosity. But stock is my preference to
Hi Michael, wondering if you have the time to help or offer some advice! I have a Teac ax 5030, was working but after a short while of playing the treble Freq seemed to drop, so I thought I'd adjust those pots and take the readings from the emitter resistors, well like a plonka I shorted the pin from the emitter to heat sink, the amp blew a fuse, emitter (ceramic o.22x2 dual emitter) I have a burned resistor, think output transistor might have gone and blew main power fuse and puffed a 47uf 100v cap, also burnt a track on the board! I am sourcing parts for repair, the manual says set the bias to 6Mv, how do i see this reading on a digi MM? Would you like to repair it for me lol?
Hi Mark, Sorry I can not help to much at the moment as right in the middle of house moving. But I have done this many a time in the past and the reasons I dont do repairs as its so easy to do, even easier now my hands shake a little lol. I try and use a very small crocadile clip if possible. By the sounds of it there will be quite a few componets that need replacing here. I could not find a service manual for this amp, but I would have thought the manuel would show you were to take the reading for the DC bias from normally across one of the 0.47 ohm resistor on the output transistors for each channel by setting the multi meter to the lowest DC volt setting and adjusting a trimmer pot. Wish you good luck with mending the amp
This was the following dc offset from my 7.2ch av reciever Is it good ? Dc offset Front right -0.5 mv Front left -0.2 Center -5mv Surround Right -35.7 Surround left 5.1mv Height right -29mv Height left -12mv Or should the surround and height right be corrected ?
I have spoken to a few people about the acceptable DC offset level and we think that under 25mv as good and under 50mv is ok though nearer that 0mv would be pefect, with vintage units getting near 0mv can be hard. So I would say your readings are ok, but if you can adjust the -35.7 and -29 to under -25 that would be good
@@MichaelYates do you think this was caused by dc being present in the power line ? I have a doubt on that And possibly high thd in the line as well Because i also hear hums and my equipements heat too quick I can try to call the power company if this could be signs I hear the reciever transformer buzzing too Not too loud but it's there
@@kuronekosan2830 The receiver power supply will smooth any DC spikes if there is any, as for the hum if its coming from the speakers it could be the power caps, bad earth loop amoung others. The transformer humming or buzzing could be from it drying out over time, but nothing to worry about some do, if it get really loud I do have a few repair videos on channel for that. Some amps and receivers do run hot, old Marantz for one. If its only just happened then could be caused by DC bois needs a little adjustment. But with the readings you gave I would not worry to much until they got a lot worse. Also you could get a external power supply conditioner that smooths out spikes.
Hi, probably a stupid question but... How would you adjust the amp if the amp boards don't have trimmer pots. Restoring a HMV Stereomaster 2018 and after capacitor replacement sounds like its clipping/distortion at about half volume on both outputs. thanks. Any help appreciated thanks.
After a recap this can happen and not an easy one as the unit has no trimmers. If it did it did they could be anyware connected towards the Base of the output driver transistors I would have thought but were I dont know to be honest. With a circuit diagram it might be worth joining a forum where a lot of users are more experiance than me on this. Wish you luck getting it sorted
Would it be odd for a seller who's capable of servicing amps, not to bother with doing it before selling? I'm curious as I'm interested in an amp but have asked if the bias and offset have been set but told its just been cleaned up. It's an old amp from the early eighties. I didn't think it was an unusual request for someone who fixes amps? Cheers
Would have thought it would be in the sellers interest to set the bias up as manual and offset checked, would have been a great selling point and give any buyer piece of mind. So yes seems odd to me. Some sellers serviced / refurbished is just a clean inside with a hoover or brush to remove dust, not what I would call a refurbished / service unit.
@@MichaelYates this is what I've noticed. But this chap has changed the terminal outputs and the input potentiometer bar for this amp, and is selling another that's been recapped by himself. I think i need to take a step back. He said doing this would be part of a service, but I just see it as good practice. It's a nad 3150
@@CM-dw3gh If he has done a re-cap and changed the potentiometer then it would just take a few minutes to adjust bias and offset. As this video shows ua-cam.com/video/JbMhWKOgx_I/v-deo.html , wish you good luck in which ever way you decide to go.
Hi George, I am measuring across the fuses and using DCA for current drawn and not across the 0.5 resistor at the transistors emitter that would be DCV
Best tutorial on youtube. Excellent
Thanks and hope it was helpful
This is great! I just bought an AU-101 and this is exactly what I needed
You bought a nice and well regarded amplifier
Thanks for the tutorial. I had to replace a STK0050II hybrid amplifier module in my SR 4000 receiver, but I can´t find any adjustable resistors to adjust the DC bias. The link to download the service manuals is down for new users.
Hi there is no DC bias ajustment on the Marantz SR4000 just a led meter calibration adjustment. If you require the manual just email at arcadeimages@gmail.com
@@MichaelYates Hello Michael.
Thanks for the clarification, because without having the service manual and seeing that everyone has to adjust the DC bias in his amplifiers, I was worried. On the website of the link you mentioned it is no longer possible to download the Marantz manual, so I would appreciate it if you could give me an alternative. Many thanks from a Valladolid at 40ºC.
Good one.
Thank you so much for putting this video together. What is bias and why is it even done. It sounds like some sort of calibration to mirror the two channels so that they operate identically from an electrical perspective is this correct? Great video!!
Its done to get the optimal out of the transistor while not over powering the transistor, keep the distortion to the lowest, stop clipping as much as possible, to keep both channels running smoothly and at the same level, ie both channels set to the same bias.
Just what I need Thanks. I repaired mine by changin only one transistor. All the rest is original. I don't fell like changing capacitors considering that it sound pretty good. I'd like to conserve it as original as possible considering the great internal conditions. Some suggestions ?
I to like to keep my amps as orignal as possible, why replace something that sound fine is what I think. But sometimes if they sound that bad then the caps might need replacing. I have read on a lot of forums replacing the caps in this au101 can make the tone a bit to bright. At some stage I will get another 101 and replace all the caps and compair the 2 as a matter of curosity. But stock is my preference to
Hi Michael, wondering if you have the time to help or offer some advice! I have a Teac ax 5030, was working but after a short while of playing the treble Freq seemed to drop, so I thought I'd adjust those pots and take the readings from the emitter resistors, well like a plonka I shorted the pin from the emitter to heat sink, the amp blew a fuse, emitter (ceramic o.22x2 dual emitter) I have a burned resistor, think output transistor might have gone and blew main power fuse and puffed a 47uf 100v cap, also burnt a track on the board! I am sourcing parts for repair, the manual says set the bias to 6Mv, how do i see this reading on a digi MM?
Would you like to repair it for me lol?
Hi Mark, Sorry I can not help to much at the moment as right in the middle of house moving. But I have done this many a time in the past and the reasons I dont do repairs as its so easy to do, even easier now my hands shake a little lol. I try and use a very small crocadile clip if possible. By the sounds of it there will be quite a few componets that need replacing here. I could not find a service manual for this amp, but I would have thought the manuel would show you were to take the reading for the DC bias from normally across one of the 0.47 ohm resistor on the output transistors for each channel by setting the multi meter to the lowest DC volt setting and adjusting a trimmer pot. Wish you good luck with mending the amp
This was the following dc offset from my 7.2ch av reciever
Is it good ?
Dc offset
Front right
-0.5 mv
Front left
-0.2
Center
-5mv
Surround
Right
-35.7
Surround left
5.1mv
Height right
-29mv
Height left
-12mv
Or should the surround and height right be corrected ?
I have spoken to a few people about the acceptable DC offset level and we think that under 25mv as good and under 50mv is ok though nearer that 0mv would be pefect, with vintage units getting near 0mv can be hard. So I would say your readings are ok, but if you can adjust the -35.7 and -29 to under -25 that would be good
@@MichaelYates do you think this was caused by dc being present in the power line ? I have a doubt on that
And possibly high thd in the line as well
Because i also hear hums and my equipements heat too quick
I can try to call the power company if this could be signs
I hear the reciever transformer buzzing too
Not too loud but it's there
@@kuronekosan2830 The receiver power supply will smooth any DC spikes if there is any, as for the hum if its coming from the speakers it could be the power caps, bad earth loop amoung others. The transformer humming or buzzing could be from it drying out over time, but nothing to worry about some do, if it get really loud I do have a few repair videos on channel for that. Some amps and receivers do run hot, old Marantz for one. If its only just happened then could be caused by DC bois needs a little adjustment. But with the readings you gave I would not worry to much until they got a lot worse. Also you could get a external power supply conditioner that smooths out spikes.
Hi, probably a stupid question but... How would you adjust the amp if the amp boards don't have trimmer pots. Restoring a HMV Stereomaster 2018 and after capacitor replacement sounds like its clipping/distortion at about half volume on both outputs. thanks. Any help appreciated thanks.
After a recap this can happen and not an easy one as the unit has no trimmers. If it did it did they could be anyware connected towards the Base of the output driver transistors I would have thought but were I dont know to be honest.
With a circuit diagram it might be worth joining a forum where a lot of users are more experiance than me on this. Wish you luck getting it sorted
@@MichaelYates Thanks man, was hoping for something simple haha. Appreciate your time in getting back to me, tc.
Would it be odd for a seller who's capable of servicing amps, not to bother with doing it before selling? I'm curious as I'm interested in an amp but have asked if the bias and offset have been set but told its just been cleaned up. It's an old amp from the early eighties. I didn't think it was an unusual request for someone who fixes amps? Cheers
Would have thought it would be in the sellers interest to set the bias up as manual and offset checked, would have been a great selling point and give any buyer piece of mind. So yes seems odd to me.
Some sellers serviced / refurbished is just a clean inside with a hoover or brush to remove dust, not what I would call a refurbished / service unit.
@@MichaelYates this is what I've noticed. But this chap has changed the terminal outputs and the input potentiometer bar for this amp, and is selling another that's been recapped by himself. I think i need to take a step back. He said doing this would be part of a service, but I just see it as good practice. It's a nad 3150
@@CM-dw3gh If he has done a re-cap and changed the potentiometer then it would just take a few minutes to adjust bias and offset. As this video shows ua-cam.com/video/JbMhWKOgx_I/v-deo.html , wish you good luck in which ever way you decide to go.
@@MichaelYates cheers mate.
Your multimeter should be set to DcV not DcA
Hi George, I am measuring across the fuses and using DCA for current drawn and not across the 0.5 resistor at the transistors emitter that would be DCV