Hi
I own amplifier Technics SU-7100K.
Inside is chip STK 0039.
I wanted to gain more power from the amplifier is it possible to change the stk 0039 stk 0100, few of resistors and transformer with a higher voltage and power rating.
Here is service manuale :Technics SU-7100 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
I own amplifier Technics SU-7100K.
Inside is chip STK 0039.
I wanted to gain more power from the amplifier is it possible to change the stk 0039 stk 0100, few of resistors and transformer with a higher voltage and power rating.
Here is service manuale :Technics SU-7100 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
Forget it!
You are much better off buying a better amplifier or gutting this old technics unit and building a more powerful amp in the chassi.
To even notice a increase in volume, you pretty much have to double, triple or even quadruple the output power.
Doubling the power is only around 3dB increase in sound pressure if i remember right.
You are much better off buying a better amplifier or gutting this old technics unit and building a more powerful amp in the chassi.
To even notice a increase in volume, you pretty much have to double, triple or even quadruple the output power.
Doubling the power is only around 3dB increase in sound pressure if i remember right.
Problem is, you can't replace just the power amp in this unit. It's a pre+power integrated affair that does all the voltage gain in the power amp and has the tone comtrols in the power amp's feedback loop. The volume pot is is rather on the high-impedance (read: noisy) side as well. So you'd need a new preamp section, too, which would be an opportunity to get its performance closer to state of the art. Rod Elliott has one that would work.
And then there still is the issue with the fuses in the speaker line, so you'll want some protection circuitry as well. I don't think you'll want to route the output across those contacts in the headphone socket either. If you're doing a new preamp anyway, this would be the ideal opportunity to implement a decent headphone output by modern standards, so you may want to tap off the signal between pre and power amp for a unity gain buffer using a NJM4556 with <10 ohms of output series resistance (it normally doesn't need any if you've got a decent PCB layout).
(Don't forget you'll also need a bigger heatsink.)
It is certainly doable, but expect a major project and having to learn A LOT (maybe more than you'd like).
And then there still is the issue with the fuses in the speaker line, so you'll want some protection circuitry as well. I don't think you'll want to route the output across those contacts in the headphone socket either. If you're doing a new preamp anyway, this would be the ideal opportunity to implement a decent headphone output by modern standards, so you may want to tap off the signal between pre and power amp for a unity gain buffer using a NJM4556 with <10 ohms of output series resistance (it normally doesn't need any if you've got a decent PCB layout).
(Don't forget you'll also need a bigger heatsink.)
It is certainly doable, but expect a major project and having to learn A LOT (maybe more than you'd like).
Thank you sgrossklass!
You're right it's a bit too much for me.
Maybe you have some suggestion to get a bit more quality/power from the amplifier!?
You're right it's a bit too much for me.
Maybe you have some suggestion to get a bit more quality/power from the amplifier!?
The STK0039K are a darlington power pack , comprising
the two drivers and power transistors as well as a VBE
multiplier.
The front end is a discrete differential as well as a VAS
with a beta enhancer.
The only valuable mod would be to add a current mirror,
although the 15pF compensation cap should be
increased in such case or even replaced by a TMC
compensation network
In this respect this amp is better than a DX or other
usual LIN even without the mods i quoted above.
the two drivers and power transistors as well as a VBE
multiplier.
The front end is a discrete differential as well as a VAS
with a beta enhancer.
The only valuable mod would be to add a current mirror,
although the 15pF compensation cap should be
increased in such case or even replaced by a TMC
compensation network
In this respect this amp is better than a DX or other
usual LIN even without the mods i quoted above.
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I thought all these stk module amps were considered mediocre at best as well as less reliable and more prone to failure than full discrete amplifiers.
Right that there were prone to failure but it was because
they not always had internal power transistors emitter resistor and that
a few manufacturers didnt bother to add external ones , mind you..😉
Since they had a built in inherently fast VBE tracker they somewhat managed
to survive in a good proportion.
This Kenwood has external power transistors emitter resistors,
wich explain that it went through time with no damage.
Be aware that the STK discussed here were just final stages
as the differential and VAS are external , built with good quality
transistors.
Other STKs can have the whole amp integrated and are often
of average quality although later parts were quite good.
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Hi,
I just bought 5pcs of STK0039 from UTsource.
They all have 360ohms between pins 0 and 9.
This leads to almost full positive voltage on pin 0.
Above +30V
Do you think I got fakes?
This amp has only like 4 transistors per channel in addition to the STKs so I am pretty sure I have checked everything well enough.
I am thinking if there are different versions of STK0039?
Service manual from hifiengine says SVISTK0039K???
Also if you check the internal equivalent diagram of the STK in this service manual.
Technics SU-7100 Manual - Stereo Integrated Amplifier - HiFi Engine
and compare it to the one mentioned earlier in this thread...it is different.
Anyway a rather low resistance between some pins does not seem right.
Anyone have lot's of information and ideas?
And yes in my SU-7100 it seems like both STKs have blown in different ways.
Both shorted somewhere and one output fuse was blown.
Both gave full DC, one positive the other channel negative 🙂
If somebody wants to struggle with this amp I can give it away for free.
Stupid of me to pay 34 euros for it broken.
Probably worth less than a hundred when it is working 🙂
I could put a pair of LM3886 in it, but then it's not a Technics anymore 🙂
I just bought 5pcs of STK0039 from UTsource.
They all have 360ohms between pins 0 and 9.
This leads to almost full positive voltage on pin 0.
Above +30V
Do you think I got fakes?
This amp has only like 4 transistors per channel in addition to the STKs so I am pretty sure I have checked everything well enough.
I am thinking if there are different versions of STK0039?
Service manual from hifiengine says SVISTK0039K???
Also if you check the internal equivalent diagram of the STK in this service manual.
Technics SU-7100 Manual - Stereo Integrated Amplifier - HiFi Engine
and compare it to the one mentioned earlier in this thread...it is different.
Anyway a rather low resistance between some pins does not seem right.
Anyone have lot's of information and ideas?
And yes in my SU-7100 it seems like both STKs have blown in different ways.
Both shorted somewhere and one output fuse was blown.
Both gave full DC, one positive the other channel negative 🙂
If somebody wants to struggle with this amp I can give it away for free.
Stupid of me to pay 34 euros for it broken.
Probably worth less than a hundred when it is working 🙂
I could put a pair of LM3886 in it, but then it's not a Technics anymore 🙂
https://www.dropbox.com/sc/4fmuc501l6dn2qp/AADdUV439LbThbKjJsFOgKC4a?n=62274186
Sawed it open.
To me it looks like:
2 power transistors
2 drivers
3 small transistors
6 black single resistors
up in the middle it looks like some double resistor, 3 wire?
Diodes yesno?
And yes there definitely is a resistor between pins 9 and 0, around 360ohms...hmm
Also the collector (bottom plate part I think???) of the right side power transistor is connected to pin 7 and not 9 (as in all internal diagrams of the chip I have seen so far).
I just have the feeling that if someone wanted to make fakes as cheaply as possible it would just be a lump of epoxy or something.
This could be the wrong IC relabeled or a failure to make a compatible one or what do you think?
Sawed it open.
To me it looks like:
2 power transistors
2 drivers
3 small transistors
6 black single resistors
up in the middle it looks like some double resistor, 3 wire?
Diodes yesno?
And yes there definitely is a resistor between pins 9 and 0, around 360ohms...hmm
Also the collector (bottom plate part I think???) of the right side power transistor is connected to pin 7 and not 9 (as in all internal diagrams of the chip I have seen so far).
I just have the feeling that if someone wanted to make fakes as cheaply as possible it would just be a lump of epoxy or something.
This could be the wrong IC relabeled or a failure to make a compatible one or what do you think?
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