I know you did this video years ago but I just rebuilt my driver board on my 9090db and used your video to make the adjustments. Thank you for the great detailed video.
Thanks for the explanation, i'm learning all of this stuff by myself. I'm working a bit on my luxman power amp probably not the best amp to learn on because it's quite valuable but the thing has a fault where the dc offset on one channel will just rise up to a whopping 1.2V and then it goes in protection. I think it's an IC that's broken, dc offset is controlled through it i think, a well known problem on them. Before i start on it i wanted to know how to do all this stuff because the manual makes it into a very complicated proces, they want you to use variable power supply and sine-wave generator. I'm just going to do it like you did it for now or at least check the current. The manual says it should be 140mA, much more than yours but its a very hot running amp with massive heatsinks. One thing i see a lot in these tutorials is to get better pots, it makes adjusting easier, you could try that too.
Excellent video! Just wanted to clarify @18:45 you advice to use a resistive dummy load, could you please explain why? Thanks so much for the help and great content.
Thank you very much for this instructional video, I have a Telefunken TR-400 DC Series and I have searched for any documents related to my receiver with no luck, I need to bias the unit and I have my scope and voltmeter, the outs are zeroed but no information about biasing, now we are stuck at home because the pandemics I have nothing else to do but to play with my gears, Thank you in advance and keep safe
May i suggest that you change all the little 1/4 and 1/2 watt flame proof/metal oxide resistors on that driver pcb. Those 8080 and 9090's were known for those resistors opening or change value causing the amp to go into and staying in protection. I noticed in the video you replaced the caps but not those known to fail resistors! Like I said.. well known for that unit!
For my 8080DB, I had no sound and I followed your method for the Dolby board. Now, the sound is going all the way to the BA312 ICs, and nothing after that. Do you know what might be my next step ? Thanks.
Due to the hunting of the voltage readings. I am thinking of replacing the vr's with bornes variable resistors. I think these will enable a more steady reading. what is your thoughts on this?
Olá, tenho uma amplificador Nakamichi Av10. O som de uma das colunas frontais é mais baixo que o da outra. O manual diz para ajustar o valor num potenciometro na placa de amplificação para obter um valor de 15 mv. Para isso diz 1ue tenho que curto circuitar a saida . Posso ligar o + (vermelho ) com o - ( preto)? Obrigado
Wouldn’t adjusting the bias to just under 30mA mean the transistors are not on? Also on my Yamaha it calls for a bias adjustment of 2.5-6.0mV not mA. Are some models adjusted in mA and others in mV?
The bias adjustment of 2.5-6.0 mV means that you measure the volt drop across the emitter resistors of the output transistors. So according to Ohms law V= I x R . So if you measure 6.0mV across a 0.22 Ohms emitter resistor then the current I should be I= V / R = 0.006V / 0.22 Ohms = 0.027A or 27mA
Thank you for this so much! I have a set of semi-rare active speaker amps I have to bias, although obtaining a service manual is not an option as the company is defunct as well. I do know the transistor set however (Toshiba 2sc3281 & 2sa1302). I discovered there is a model of Sansui made that used these same Toshi's. I just need to find out the exact model so I can search for a service manual.
So the dummy load is connected in parallel with the DMM, I didn't see how yours was connected, also do you center the balance control or adjust it to the channel you are working on? Does it matter? Would 10 turn pots be worth the time and effort, or affect the collectable value of the equipment? Do you recommend using a little de-oxit on the original vr's before adjusting them? Very informative video, thanks.
How do you go about generally cleaning dust and gunk out of these ? I used my compressor to clear it out and have the front and knobs all clean..and the glass looks good. I'd like to just have these nice shiny boards like you have hah.
I have a Kenwood KA-4000 and Id like to adjust the bias on the transistors...I was wondering if you could gave me some tips.. I watched this very inform video and think I can do it...
There is something I don't understand. If moving a magnet in this sense required a changing electric field then how could a DC Offset cause the speaker magnet to be "always up" or "always down"? Wouldn't the speaker initially move to that distorted point only when the amp was first turned on? Then once the change in voltage become no change "DC" and the magnet would fall back to it's rest state?
I have a sansui in my storage building. It has been there for years. The speaker jacks were acting up so I just quit using it. I gave 200 dollars for it back in the 80's. Been so long, I am not sure if it was a 7000 or a 9000, I think a 9000. There is no one around hear you could trust to work on it. I know it was a loud thing. I would love to get it working again but I don't have anymore speakers for it. I have some pa speakers now but I don't know if they are the right ohm. Back then I did not know anything about ohms and I ran any speakers I had and I may have damaged something. I may have to go get it out and see if I can see what is wrong, but man that thing is so heavy.
I have a 8060A multimeter like that, but it says IBM in the front; in the back, cast in the plastic, the usual John Fluke MFG Co Everett, Washington; i guess that IBM bought a lot of them back then,possibly?
Just watched this. Excellent video, especially for those of us who aren't that savvy in tech repair. I think I can actually do this! Wouldn't consider doing one on a Harmon Kardon 430 with a Simpson multimeter would you? ha
hi,l have B&k EX-4420 power amplifier , can you help me to found value of idling current (bias).l went on( hi fi engine) online and l can not found. Thanks.
I find it helps... slightly... to short all the other inputs. You'd think it wouldn't make any difference. I've made up a fair batch of shorted RCA plugs.
Very informative videos on your channel. However, using a tripod would greatly reduce headache and eye fatigue for the viewer. Continuous camera movement in videography is NOT a good thing. Thanks for your efforts.
I have an 8080db and had to set the DC offset and the bias after recapping the driver board. I had the exact same issues with the VR pots being too sensitive and not matching the manual. I was thinking of changing them out for 10 turn pots.
I dont agree whith a high curent level will result in clipping or such as ,only the pair transistor will have an curent that it will draw from the source trying to equilibrate one eatchother …
Too bad they didn't use a Bourns 5 turn VR in those bias circuits ! Those factory pots are way too touchy !! By the time you've cranked-up the volume, while playing one side of a Zepplin album..... The bias would be screwed-up again !!!
Obviously not the right video for you then If the technical information he is giving you sounds like "blah blah blah" then you must not be interested in the technical side of audio electronics engineering.
I know you did this video years ago but I just rebuilt my driver board on my 9090db and used your video to make the adjustments. Thank you for the great detailed video.
Absolutely exceptional explanation.
I definitely got the full understanding of it after seeing the video what great help.
Thank You 👍
You are making one heck of a contribution to the techs of tomorrow. Cheers for the great videos!
I have just biased my Sansui au 6600 thanks to your excellent video. Thank you
I have an 8080 and I want to repair and restore it. This video was helpful. Thank you.
Thank you very much for the clear instructions!!!
Thank-you very much for the info, much appreciated, I,LL PLAY AROUND WITH ADJUSTMENTS VERY CAREFULLY, IM LEARNING .
Thanks for the explanation, i'm learning all of this stuff by myself. I'm working a bit on my luxman power amp probably not the best amp to learn on because it's quite valuable but the thing has a fault where the dc offset on one channel will just rise up to a whopping 1.2V and then it goes in protection. I think it's an IC that's broken, dc offset is controlled through it i think, a well known problem on them. Before i start on it i wanted to know how to do all this stuff because the manual makes it into a very complicated proces, they want you to use variable power supply and sine-wave generator. I'm just going to do it like you did it for now or at least check the current. The manual says it should be 140mA, much more than yours but its a very hot running amp with massive heatsinks.
One thing i see a lot in these tutorials is to get better pots, it makes adjusting easier, you could try that too.
Excellent video! Just wanted to clarify @18:45 you advice to use a resistive dummy load, could you please explain why? Thanks so much for the help and great content.
Thank you very much for this instructional video, I have a Telefunken TR-400 DC Series and I have searched for any documents related to my receiver with no luck, I need to bias the unit and I have my scope and voltmeter, the outs are zeroed but no information about biasing, now we are stuck at home because the pandemics I have nothing else to do but to play with my gears, Thank you in advance and keep safe
May i suggest that you change all the little 1/4 and 1/2 watt flame proof/metal oxide resistors on that driver pcb. Those 8080 and 9090's were known for those resistors opening or change value causing the amp to go into and staying in protection. I noticed in the video you replaced the caps but not those known to fail resistors! Like I said.. well known for that unit!
Wow, really well done. I have a Marantz 4270 that I would like to check. I know nothing about electronics. This helps.
For my 8080DB, I had no sound and I followed your method for the Dolby board. Now, the sound is going all the way to the BA312 ICs, and nothing after that. Do you know what might be my next step ? Thanks.
Due to the hunting of the voltage readings. I am thinking of replacing the vr's with bornes variable resistors. I think these will enable a more steady reading. what is your thoughts on this?
Excellent video, thank you very much. Best regards!
Thanks! Very informative and lovely accent 😂
Applies to 9090 non dB too?
By the way, an exceptional job!
Olá, tenho uma amplificador Nakamichi Av10. O som de uma das colunas frontais é mais baixo que o da outra. O manual diz para ajustar o valor num potenciometro na placa de amplificação para obter um valor de 15 mv. Para isso diz 1ue tenho que curto circuitar a saida . Posso ligar o + (vermelho ) com o - ( preto)?
Obrigado
Wouldn’t adjusting the bias to just under 30mA mean the transistors are not on? Also on my Yamaha it calls for a bias adjustment of 2.5-6.0mV not mA. Are some models adjusted in mA and others in mV?
The bias adjustment of 2.5-6.0 mV means that you measure the volt drop across the emitter resistors of the output transistors. So according to Ohms law V= I x R . So if you measure 6.0mV across a 0.22 Ohms emitter resistor then the current I should be I= V / R = 0.006V / 0.22 Ohms = 0.027A or 27mA
Thank you for this so much! I have a set of semi-rare active speaker amps I have to bias, although obtaining a service manual is not an option as the company is defunct as well. I do know the transistor set however (Toshiba 2sc3281 & 2sa1302). I discovered there is a model of Sansui made that used these same Toshi's. I just need to find out the exact model so I can search for a service manual.
dose it change the sound?
I've got a Sansui au 9500. For the 0 mV offset adjustment is it better to isolate the preamplifier and then adjust the driver circuitry?
Have you ever biased a SAE Mark 31b? Just recapped mine with much better caps and now I have a transformer hum.
Do you have a parts list of all the caps that should be replaced for the 8080DB? Thanks in advance!
Is this information valid for any transistor based amp? Should I be setting my bias at this same 0 volts with my Class B amp?
Welcome Back yourself , its been awhile since your last video. We need out Blueglow fix ha ha ha
Thanks for sharing!!!
Did you have a video review about the Extech multimeter?
Dude, why would an electronic tech that restores classic music gear do a review on a random DMM?
So the dummy load is connected in parallel with the DMM, I didn't see how yours was connected, also do you center the balance control or adjust it to the channel you are working on? Does it matter?
Would 10 turn pots be worth the time and effort, or affect the collectable value of the equipment? Do you recommend using a little de-oxit on the original vr's before adjusting them?
Very informative video, thanks.
To take measures, and biasing, we need to connect the dummy load? Regards.
Many thanks for this video!
How do you go about generally cleaning dust and gunk out of these ? I used my compressor to clear it out and have the front and knobs all clean..and the glass looks good. I'd like to just have these nice shiny boards like you have hah.
I've never seen current jump so much...is it common to use a dummy load with solid state? My Marantz 2275 specifically did not call for dummy load.
I have a Kenwood KA-4000 and Id like to adjust the bias on the transistors...I was wondering if you could gave me some tips..
I watched this very inform video and think I can do it...
There is something I don't understand. If moving a magnet in this sense required a changing electric field then how could a DC Offset cause the speaker magnet to be "always up" or "always down"? Wouldn't the speaker initially move to that distorted point only when the amp was first turned on? Then once the change in voltage become no change "DC" and the magnet would fall back to it's rest state?
Are all Nichicon caps of the same quality, or are some better than others for audio grade use?
can someone explain why I need a dummy load rather than having a speaker hooked up? Great video!
i'd guess it's for a more stable load, speakers have capacitors and coils in them that probably mess with the results
I should also add another good reason to the use of dummy loads… If something mess up with the dc output you will avoid destroying a speaker I guess.
Do you have a schematic and bias instructions for a magnavox 1500 model 8896 chassis # R24503 DA
Thanks Mark for deleting the trolls comments much appreciated
Hey, who are you cutting a record with, 50cent or Jeezy? A little hard core rap?😁 Nice vid
I have a sansui in my storage building. It has been there for years. The speaker jacks were acting up so I just quit using it. I gave 200 dollars for it back in the 80's. Been so long, I am not sure if it was a 7000 or a 9000, I think a 9000. There is no one around hear you could trust to work on it. I know it was a loud thing. I would love to get it working again but I don't have anymore speakers for it. I have some pa speakers now but I don't know if they are the right ohm. Back then I did not know anything about ohms and I ran any speakers I had and I may have damaged something. I may have to go get it out and see if I can see what is wrong, but man that thing is so heavy.
I have a 8060A multimeter like that, but it says IBM in the front;
in the back, cast in the plastic, the usual John Fluke MFG Co Everett, Washington;
i guess that IBM bought a lot of them back then,possibly?
Just watched this. Excellent video, especially for those of us who aren't that savvy in tech repair. I think I can actually do this! Wouldn't consider doing one on a Harmon Kardon 430 with a Simpson multimeter would you? ha
hi,l have B&k EX-4420 power amplifier , can you help me to found value of idling current (bias).l went on( hi fi engine) online and l can not found. Thanks.
👍👍👍
Settings 1 and 2 as per the manual refer to DC Offset, not bias.
I find it helps... slightly... to short all the other inputs. You'd think it wouldn't make any difference. I've made up a fair batch of shorted RCA plugs.
You rule!
Very informative videos on your channel. However, using a tripod would greatly reduce headache and eye fatigue for the viewer. Continuous camera movement in videography is NOT a good thing. Thanks for your efforts.
I have an 8080db and had to set the DC offset and the bias after recapping the driver board. I had the exact same issues with the VR pots being too sensitive and not matching the manual. I was thinking of changing them out for 10 turn pots.
The video IS short when you consider the amount of information conveyed.
The reason that some your potentiometers don’t match up to the diagram is because your board is put in backwards
👍
I dont agree whith a high curent level will result in clipping or such as ,only the pair transistor will have an curent that it will draw from the source trying to equilibrate one eatchother …
Now I sure wish I hadn't sold my 9090
Too bad they didn't use a Bourns 5 turn VR in those bias circuits ! Those factory pots are way too touchy !! By the time you've cranked-up the volume, while playing one side of a Zepplin album.....
The bias would be screwed-up again !!!
I'm changing Channel
way to much bla bla bla!
You are way to impatient. He's giving an awful lot of good information.
Obviously not the right video for you then If the technical information he is giving you sounds like "blah blah blah" then you must not be interested in the technical side of audio electronics engineering.
Great video - thank you.