I found this at my local electronics outlet.
FK661 OCL 50W+50W stereo amplifier kit.
FUTUREKIT.COM :: HIGH QUALITY ELECTRONIC KITS - FK661: POWER AMPLIFIER OCL 50+50W STEREO R1%
Info here: http://www.funnykit.co.kr/bemarket/shin/menual/fk661.pdf
So with a little extra shopping I have pretty much all I need for a simple compact amp to use at my apartment in the big sand pit called Qatar! It should keep me occupied for a few evenings putting it together at least.
I'm not expecting much, well some noise at least though I'm guessing the "Fi" might be less than "Hi" 🙂
Here's what I have so far,
If I can source a suitable transformer I should be all set, already have a suitable bridge and some 22,000uF at 80v capacitors kicking about. My investment so far, a whopping £20, about US$34.
Any thoughts before I kick off?
Zed.
FK661 OCL 50W+50W stereo amplifier kit.
FUTUREKIT.COM :: HIGH QUALITY ELECTRONIC KITS - FK661: POWER AMPLIFIER OCL 50+50W STEREO R1%
Info here: http://www.funnykit.co.kr/bemarket/shin/menual/fk661.pdf
So with a little extra shopping I have pretty much all I need for a simple compact amp to use at my apartment in the big sand pit called Qatar! It should keep me occupied for a few evenings putting it together at least.
I'm not expecting much, well some noise at least though I'm guessing the "Fi" might be less than "Hi" 🙂
Here's what I have so far,
If I can source a suitable transformer I should be all set, already have a suitable bridge and some 22,000uF at 80v capacitors kicking about. My investment so far, a whopping £20, about US$34.
Any thoughts before I kick off?
Zed.
One source of a transformer cheap might be a dead stereo receiver. I sometimes scrap out old receivers that are not going to be repaired, and I save the transformers. As it turns out, today I am in the process of cleaning up my warehouse and will be offering a number of those transformers to local hobbyists.
Toroidal transformers seem almost unobtainable here so this is the arrangement I am planning.
Anything obvious I should think about or change from this basic layout?
An externally hosted image should be here but it was not working when we last tested it.
Anything obvious I should think about or change from this basic layout?
A quick thought... but visual symmetry in layout, while it looks good, doesn't always lend itself to the best electrical layout. There will be a lot of wiring carrying high AC charging currents that are close to both boards.
Transformer and caps close together at one corner might be a better option from that point of view.
Transformer and caps close together at one corner might be a better option from that point of view.
Also plan where you put your heatsink.. Output transistor jumper leads should be as close as possible. (I built one with long leads and it's doing fine, no hum but might as well be safe).
Thanks for the inputs. Heatsinks will be on the rear panel an I think I will mount the pcb's vertically on standoffs on the inside of the rear panel. This will give short leads to the output transistors and keep the boards as far as possible from the power supply.
I'll keep the psu toward the front of the case with the junction of the two smoothing capacitors as the star point ground.
I'll keep the psu toward the front of the case with the junction of the two smoothing capacitors as the star point ground.
So the amp is built up and basic testing indicates no smoke but I do have some of the dreaded DC offset, about 60mV on one channel and about 80mV on the other channel. Am I right in thinking all I can really do is to try better matching the input transistor pair? Or are there other tweaks I can try?
TIA
TIA
there is a couple of things that you have to do to improve stability ...In long term and if pushed your amplifier will fail from thermal run away ...
1) you need to find a way to mechanically place TR5 in a place on the heatsink that can sense temperature re adjust the amplifier bias after that again ..small tiny wires will do and even super glue will also do ...
2) from wiring aspects you need to separate the wiring of output transistors and of course keep them as short is possible .... First you need to separate PNP from NPN and then separate somehow the B lead since this is one is handling very litlle current compared to C and E leads so at some point C and E cables that handle "plenty" of current will somehow effect or interact with the B lead
3) it seems that there is no input filter for RF that is not really good you should do something there something like 1k resistor in series and a 330pf capacitor in parallel with R1
There is a small chance that your offset originates from oscillation or from parts mismatching...I would perform the wiring things first and then the bias thing ...see how far i could go with that and proceed from there
Kind regards
Sakis
1) you need to find a way to mechanically place TR5 in a place on the heatsink that can sense temperature re adjust the amplifier bias after that again ..small tiny wires will do and even super glue will also do ...
2) from wiring aspects you need to separate the wiring of output transistors and of course keep them as short is possible .... First you need to separate PNP from NPN and then separate somehow the B lead since this is one is handling very litlle current compared to C and E leads so at some point C and E cables that handle "plenty" of current will somehow effect or interact with the B lead
3) it seems that there is no input filter for RF that is not really good you should do something there something like 1k resistor in series and a 330pf capacitor in parallel with R1
There is a small chance that your offset originates from oscillation or from parts mismatching...I would perform the wiring things first and then the bias thing ...see how far i could go with that and proceed from there
Kind regards
Sakis
Many thanks for the feedback (sic). Okay on TR5, I can probably invert this on the board such that the head of the transistor makes contact with the rear panel. Heatsink is bolted to the other side of the rear panel so it's not a particularly good thermal connection but I suppose it will track, just need to measure carefully to avoid over stressing the solder joints I guess.
For the wiring it probably could be a bit shorter. I have all three leads in a fairly tight twist at the moment and about 70mm in length. Think I could easily separate out the B lead and reduce the length by nearly half.
For the input filter I get the point, not sure about the placement of components. 330pF in parallel with R1, the 15k then the added 1k goes where?
I swapped TR5 and TR1 on the worst board and now have the offset at pretty much 50mV on both modules.
I need to address the grounding, currently I have 4mm between the 2 smoothing capacitors, I'll add two more of these in parallel to bulk it up then bring all the ground points back to the centre of this strap, this is also the centre tap of the transformer.
The input ground is currently floating, isolated RCA connector, should I return this to the common supply and output ground as well?
Thanks again
For the wiring it probably could be a bit shorter. I have all three leads in a fairly tight twist at the moment and about 70mm in length. Think I could easily separate out the B lead and reduce the length by nearly half.
For the input filter I get the point, not sure about the placement of components. 330pF in parallel with R1, the 15k then the added 1k goes where?
I swapped TR5 and TR1 on the worst board and now have the offset at pretty much 50mV on both modules.
I need to address the grounding, currently I have 4mm between the 2 smoothing capacitors, I'll add two more of these in parallel to bulk it up then bring all the ground points back to the centre of this strap, this is also the centre tap of the transformer.
The input ground is currently floating, isolated RCA connector, should I return this to the common supply and output ground as well?
Thanks again
Oh, I have tried it as well 🙂 just some cheap old unpowered PC speakers but it makes music, well sound at least. So far so good 😎
fk661 kit
so , can u plz tell me if u are happy with the sound?im trying to build an discrete amplifier and this kit is actually cheap , the heatsink is included....
thanks
so , can u plz tell me if u are happy with the sound?im trying to build an discrete amplifier and this kit is actually cheap , the heatsink is included....
thanks
fk661 kit
so , can u plz tell me if u are happy with the sound?im trying to build an discrete amplifier and this kit is actually cheap , the heatsink is included....
thanks
so , can u plz tell me if u are happy with the sound?im trying to build an discrete amplifier and this kit is actually cheap , the heatsink is included....
thanks
Hello gabe75,
I'm sorry I never saw your question waaaaay back in January but I can tell you I finished putting the amp together and though I would say it's nothing outstanding it makes decent enough sound and is a great way of filling a room with some sound.
I found a pair of small Tannoy 603 speakers, made up some stands and it plays well enough, excellent vfm and I think eminently tweakable.
Weakness would be what seems to be a rather soft quality. This could be the speakers but I if it's the amp then maybe just not enough grunt from the power supply. Deep bass and drum sounds that I know well seem to lack slam and punch, they're also a bit one noting. Then again this could be the unknown sourced flac files that I've been using.
I'm sorry I never saw your question waaaaay back in January but I can tell you I finished putting the amp together and though I would say it's nothing outstanding it makes decent enough sound and is a great way of filling a room with some sound.
I found a pair of small Tannoy 603 speakers, made up some stands and it plays well enough, excellent vfm and I think eminently tweakable.
Weakness would be what seems to be a rather soft quality. This could be the speakers but I if it's the amp then maybe just not enough grunt from the power supply. Deep bass and drum sounds that I know well seem to lack slam and punch, they're also a bit one noting. Then again this could be the unknown sourced flac files that I've been using.
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