Yao what Mooly says then once it's runnin you can change the feedback resistors. 4.7k and 1k will be fine.
the pre amp works perfect and sound grate 🙂
i put it in marantz 2226
this amp has a problem that I did not succeed yet to over come .
right chanel is stornger than left chanel about a 20%
( i tested voltage with 1khz MP3 )
the pre amp is perfect both chanel identical
so the problem is with the main amp
I checked allmost all resistors in the main amp and they ok
i replaced the the two difrential transistors with new ( q701-4 )
do you guys have any idea what the problem should be ?
thank allot
i put it in marantz 2226
this amp has a problem that I did not succeed yet to over come .
right chanel is stornger than left chanel about a 20%
( i tested voltage with 1khz MP3 )
the pre amp is perfect both chanel identical
so the problem is with the main amp
I checked allmost all resistors in the main amp and they ok
i replaced the the two difrential transistors with new ( q701-4 )
do you guys have any idea what the problem should be ?
thank allot
Attachments
That's good, pleased you got it working.
The gain of the power amps is determined by the feedback network. The transistors and virtually all other components won't change the gain one jot. C705, R717 and R713 are the components in the top channel but I doubt there will be anything wrong there. Usually problems like this are caused by such things as poor tracking on the volume/balance controls.
The gain of the power amps is determined by the feedback network. The transistors and virtually all other components won't change the gain one jot. C705, R717 and R713 are the components in the top channel but I doubt there will be anything wrong there. Usually problems like this are caused by such things as poor tracking on the volume/balance controls.
In practice yes. Increasing it will extend the amplifiers response a little lower although other factors still limit that. 100uf may alter any switch on/off thumps as the time constant is different although if there is a relay delay in the speaker feed then that won't be apparent.
It is not the volume or balance because the preamp left and right chanel is identical
(I checked voltage with 1khz MP3 )
so the problem must be in the main amp
I checked the R713 R717 and R15 and they OK ,
the R705 47uf is new cap so I think they ok
(I checked voltage with 1khz MP3 )
so the problem must be in the main amp
I checked the R713 R717 and R15 and they OK ,
the R705 47uf is new cap so I think they ok
I don't know what test gear you have available so what I would do is lift the left hand end of R701 and link it with a wire to the left hand end of R702. That will feed each power amp with an identical signal. See if the problem is still apparent.
If you have a scope and generator then it's just a matter of checking levels. If not we have to prove where the problem is.
If you have a scope and generator then it's just a matter of checking levels. If not we have to prove where the problem is.
i did it and you right both chanel was allmost identical
so i remove the balance , and now the result are like this , in mili AC VOLT
left right
45 60
70 80
1.3 1.4
2.02 2.02
as you can see until 2 v right chanel is litle bit stornger and after 2 VOLT the chanel identical .
I belive its the volume fault .
so i remove the balance , and now the result are like this , in mili AC VOLT
left right
45 60
70 80
1.3 1.4
2.02 2.02
as you can see until 2 v right chanel is litle bit stornger and after 2 VOLT the chanel identical .
I belive its the volume fault .
Replace input coupling caps C701/C702. Famously troublesome in these old guys.
All good fortune,
Chris
Ok i replaced the 701\702C in new one
and test again both chanel allmost identical with slightly change i think it is normaly and verery thing ok ,
I waiting to relay board kit , after that I will uplaod video to youtube
thanks every one may god bless you 🙂
and test again both chanel allmost identical with slightly change i think it is normaly and verery thing ok ,
I waiting to relay board kit , after that I will uplaod video to youtube
thanks every one may god bless you 🙂
It's common for volume controls to mistrack at very low levels. If you work the difference out as a figure in db's then it looks much better. Even the 45/60 low level result is better than 2.5db matching. The 70/80 result just over 1db mismatch.
Good channel matching in pots is a problem even today and one reason why pots such as ALPS are often used... but it comes at a price.
Good channel matching in pots is a problem even today and one reason why pots such as ALPS are often used... but it comes at a price.
You can't easily modify this to give a boost to just the lower frequencies, it needs a major reworking. Something like this kind of thing maybe,
Stereo Preamplifier with Bass-boost - circuit diagrams, schematics, electronic projects
Stereo Preamplifier with Bass-boost - circuit diagrams, schematics, electronic projects
Not really... that's about as simple as you can do it I'm afraid. I can't just think of anything else.
ok thanks molly ,but i didn't understand how to modify my preamp .
can you please draw it ? thanks .
can you please draw it ? thanks .
You can't just "modify" it to do what you want. It's a either a total redesign or an add on circuit to go before or after the preamp. To boost just the bass and leave the mid and treble alone needs an active circuit using opamp. You can't do it by just adding a couple of parts to the existing design.
Here's another one,
Bass Booster
they are all based on the same principles.
Here's another one,
Bass Booster
they are all based on the same principles.
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