Are you describing a problem with an SU-Z1 model amplifier or something else, as it would be better to start a new thread to raise a new topic about protection circuits perhaps?hi,who know why my amplifier will auto cut off the sound after 2 to 3 seconds when i on it
There is some protection, in the form of a discrete circuit connected to the STK2028, that shuts down drive to the chip when there is a fault voltage present. Check that there is no DC voltage at the output terminals (with no input or output connections!) It should not exceed ~40 mV. If there is a higher DC voltage, maybe even up to the rail voltage of near 40V, you have a failed STK2028 and probably one AN7060 too. This is very common on this amplifier, as this thread tells you earlier.
schematic: http://msc-media.co.uk/wp-content/uploads/2013/04/su-z1.pdf
schematic: http://msc-media.co.uk/wp-content/uploads/2013/04/su-z1.pdf
can i add heatsink and cooling fan to make it coller or how to make it more durable?,change the better stk chip or other chip?
I think you may not understand what the circuit requirements are. Simply changing the 2 chips and one transistor that make up the amplifier wont make any differences because there are almost no substitute parts. Also, I asked you to measure a voltage to find out if the hybrid amplifier has failed. If it has failed, it needs replacement but upgrades for old hybrid amplifiers are not easily done. You could increase the size and thickness of the heatsink and that would be a help in extending the life of a new STK2028. You could also substitute with ST2038 which is also in some versions but the same heatsink size increase is necessary. I dont know of any other substitute parts.
The problem lies in the expected use. If ambient temperature is high (Malaysia is quite hot) and you use low speaker impedance like 4R or 2 pairs of speakers, a small amplifier like this will be stressed because not enough cooling is available. It does need more cooling but fans are not necessary and also need their own power.
The problem lies in the expected use. If ambient temperature is high (Malaysia is quite hot) and you use low speaker impedance like 4R or 2 pairs of speakers, a small amplifier like this will be stressed because not enough cooling is available. It does need more cooling but fans are not necessary and also need their own power.
No! - STK2058 and 2038 are complete amplifiers, according to datasheets. I was misled by a previous post regarding STK2038. These are only available as used parts - no true guarantees they are good from Dalbani or other recycled parts sellers. Check what you are looking at first, similar numbers mean nothing.
STK2028 is the output stage transistors only - a hybrid pair of Darlington transistors for each channel. If you want to try substituting modules, you need to study the datasheets and application notes to be sure of what you have and build a whole new amplifier to suit them, unfortunately. STK2028 is designed to work with AN7060 as a high voltage input stage and VAS transitors are the only other semiconductors required in the SUZ1 amplifier design. Other parts are for a power supply and safety circuit.
STK2028 is the output stage transistors only - a hybrid pair of Darlington transistors for each channel. If you want to try substituting modules, you need to study the datasheets and application notes to be sure of what you have and build a whole new amplifier to suit them, unfortunately. STK2028 is designed to work with AN7060 as a high voltage input stage and VAS transitors are the only other semiconductors required in the SUZ1 amplifier design. Other parts are for a power supply and safety circuit.
Why not download the datsheet and see for yourself.
Here is the most recent generic model STK2038II that I think you refer to. Look at the schematic - note that it is a complete amplifier, not just output Darlington transistors. Now, see the number of pins?
Hi, I hope its ok to resurrect this old thread
I have a Technics SU-Z11 also with a STK2028 amp. I'm wondering if the symptoms my amp has leans towards a blown STK2028 also?
Symptoms are very similar, when I plug in headphones the amp works fine, even at very loud volume (but the headphones have 330 Ohm resisters in series). But when I plug in speakers to the right channel only the amp shuts down almost immediately, maybe 2 seconds later. Left is fine. I measured the speaker outputs for DC, both left and right have 30mV DC present.
One other thing, when listening through headphones the right channel seems louder at all volumes. My thoughts were the right channel is being overdriven but is that even possible with these STK chips? i'm not sure considering the biasing is internal.
Thanks for reading, cheers for now.
I have a Technics SU-Z11 also with a STK2028 amp. I'm wondering if the symptoms my amp has leans towards a blown STK2028 also?
Symptoms are very similar, when I plug in headphones the amp works fine, even at very loud volume (but the headphones have 330 Ohm resisters in series). But when I plug in speakers to the right channel only the amp shuts down almost immediately, maybe 2 seconds later. Left is fine. I measured the speaker outputs for DC, both left and right have 30mV DC present.
One other thing, when listening through headphones the right channel seems louder at all volumes. My thoughts were the right channel is being overdriven but is that even possible with these STK chips? i'm not sure considering the biasing is internal.
Thanks for reading, cheers for now.
I did similar thing to Z11 and also got tone controls working. For that I wired dual OP amplifier in a An7060s place(es). Reduced R317/R318 from 12K ohms to 1,5K ohms. Otherwise gain was too high. This worked but was too noisy, so I put loudness and volume potentiometer after former An7060s, now op amplifiers. Now it works normally.
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