Hello everybody. Where can I find the work files for FX-8? I downloaded a lot of things here, which confused the workers and which are not 🙂
There are 3 or 4 variants of the FX8. You will have to read the last 2 months worth of posts to determine which you like. The ones I have made are the 50mm square one and the Bimo mod one. All the Gerber or pdf files are posted by Sonal Kunal or Prasi. Do a search for FX8 and Prasi and you will find them. The latest one is a hexFET mod to the FX8 called the FH9 it is posted by Prasi a few pages back. I have built a modified version of the FX8 to get the FH9 but not that particular board yet.
FH9
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-735.html#post4704683
FH9
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-735.html#post4704683
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nicely done...
The small 1 uF caps that you are using appear to have very small footprint. what kind of film caps are those and their voltage rating? generally i use something similar to these BFC237011105. - VISHAY - Film Capacitor, MKT370 Series, 1 µF, ± 10%, PET (Polyester), 63 V | element14 India .
Also the one in the middle appears to be too big, it may create problem for heat sink fitment.
The small 1 uF caps that you are using appear to have very small footprint. what kind of film caps are those and their voltage rating? generally i use something similar to these BFC237011105. - VISHAY - Film Capacitor, MKT370 Series, 1 µF, ± 10%, PET (Polyester), 63 V | element14 India .
Also the one in the middle appears to be too big, it may create problem for heat sink fitment.
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Hi,
If you want DIY iron transfer files, the one given in http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-624.html#post4612680 post #6235 is good to go as it built by three different members including me🙂.
reg
Prasi
Thanks for noticing and I actually wasn't quite sure what type of cap to use. The ones on the side appear to be power supply bypass caps so I am using 50v ceramics (hence small). The one in the middle appears to be connected to the bias trimpot so may have more of an effect on audio signal path so I used a nice MKP 250v film cap (big). I will have to order some more smaller 1uF 63v film caps if that is what you think is best for the ones near the sides.
Finally, is it Ok to use a larger value than 220uF for the one on the bottom? As I recall, this one is the bigger the better.
It will be a few days before those 2SC1845's show up so I still have time to make changes. Although I don't think the 1uF ceramic bypass caps will matter much vs film caps from SQ standpoint?
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Ok. I dont think it (1uf rail bypass) will matter much, I thought they were of some different value/lower voltage.
The most important components and Bimo's recommendations are in http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-711.html#post4682946 (post 7109).
regarding 220uF cap, I feel it is better to stick to schematic as intended by designer and only change if testing reveals some other value is better.
reg
Prasi
edit: read 3.3 and 3.4 http://sound.westhost.com/articles/coupling-caps.htm#p33
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Prasi,
Thanks for reminding me of that post. I managed to guess that C8 was indeed inportant to have MKP. I am using NP0 on C2/5/10/11. Will match Q1 and Q3 from a bag of 50 when they arrive. I will try to find a 220uF for C4. Currently I think 1000uF is there.
Thanks for reminding me of that post. I managed to guess that C8 was indeed inportant to have MKP. I am using NP0 on C2/5/10/11. Will match Q1 and Q3 from a bag of 50 when they arrive. I will try to find a 220uF for C4. Currently I think 1000uF is there.
2SC1845's are difficult to find and expensive when you do find ones that aren't Chinese counterfeits.
Did you order them from a U.S. seller?
Most IC's and semiconductors come from China, Singapore, or Malyasia. When I buy from Digikey, often the certificate of compliance states parts are genuine and sourced from China. Anyhow, I buy all my components from China (Aliexpress) except the IRFP240/9240 and the Renesas 2SJ/2SK's. I also bought a set of the lateral FETs from China so we will see how they work. All my small signal transistors have come from Ali and only ones I have had a problem with were the OPS Toshiba 2SC5200/2SA1943's. But they refunded me when I said they were no good. The shops on Ali have stiff competition and none want a black eye bad review so they aim to get you stuff that works. Anyhow, I am hoping the 2SC1845's will not be an issue. I may end up having to cross the pins on my Chinese BC546's to serve as the inputs if these 1845's don't work out.
If you can't get 2SC1845 and are going to twist the pins you may be better off using BC550. They a closer match to the 1845's.
Thanks for the tips guys - before I saw Still4given's recommendation for BC550's I decided to test the amp out with BC546's with twisted legs. No matching or anything like that just stuck it in and set bias current to 175mA using external 10ohm safety resistors on the power supply leads. It plays music and sounds OK but the gain is very low compared to my other FX8 or FH9. I think at least it confirms that the PCB is good and no errors as it plays music. The VAS transistors get hot so I did not want to play too long. I am still waiting for the heatsinks to get in. In meantime I will check out Mouser or Digikey for KSC1845.
Is the lower gain simply a function of the feedback resistors or is it the much lower Hfe of the BC546 vs the 600 Hfe of the 2SC1845's? It sounds like maybe 20dB vs 31 dB which is where my other FH9 is at.
Here it is playing music with a pair of BC546's.
$7 for 5 KSC1845 on Amazon:
http://www.amazon.com/utsource-5pcs-KSC1845/dp/B00UOAESUY
$4 for 5 2SC1845:
http://www.amazon.com/utsource-5pcs...e=UTF8&qid=1462948331&sr=1-2&keywords=2sc1845
But these obviously come from China as shipping is like a month...
Is the lower gain simply a function of the feedback resistors or is it the much lower Hfe of the BC546 vs the 600 Hfe of the 2SC1845's? It sounds like maybe 20dB vs 31 dB which is where my other FH9 is at.
Here it is playing music with a pair of BC546's.
$7 for 5 KSC1845 on Amazon:
http://www.amazon.com/utsource-5pcs-KSC1845/dp/B00UOAESUY
$4 for 5 2SC1845:
http://www.amazon.com/utsource-5pcs...e=UTF8&qid=1462948331&sr=1-2&keywords=2sc1845
But these obviously come from China as shipping is like a month...
Attachments
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FX8 Bimo mod schematic
So looking at the schematic shows that the gain is set by R12 over R11 or 22k/1k=22 or about 27dB. Maybe that is the difference I am hearing - 4 dB difference?
Edit: Ok, bonehead mistake on my part. I had a mislabeled bag of 2.2k 1w resistors labeled as 22k. So gain was only 2.2 😛
Just replaced with a pair of 47k 1/4w in parallel for 23.5k 1/2w. Sounds great now 🙂
Nice sounding amp!
So looking at the schematic shows that the gain is set by R12 over R11 or 22k/1k=22 or about 27dB. Maybe that is the difference I am hearing - 4 dB difference?
Edit: Ok, bonehead mistake on my part. I had a mislabeled bag of 2.2k 1w resistors labeled as 22k. So gain was only 2.2 😛
Just replaced with a pair of 47k 1/4w in parallel for 23.5k 1/2w. Sounds great now 🙂
Nice sounding amp!
Attachments
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So looking at the schematic shows that the gain is set by R12 over R11 or 22k/1k=22 or about 27dB. Maybe that is the difference I am hearing - 4 dB difference?
Edit: Ok, bonehead mistake on my part. I had a mislabeled bag of 2.2k 1w resistors labeled as 22k. So gain was only 2.2 😛
Just replaced with a pair of 47k 1/4w in parallel for 23.5k 1/2w. Sounds great now 🙂
Nice sounding amp!
Listening impression? How compare with other amplifiers?
Hi Bimo,
It was pretty late here when I finished so could only listen to like 2 tracks and not very loudly at that. However, what I did hear was excellent. Nothing anomalous and highs were very clear, mids were smooth, bass was authoritative and deep. I want to set the gain resistors to match my other amp. I think I am using 20k and 550R. Or change the other amp to match this one so I can do AB test. Although don't I need to wait for the 2SC1845's to arrive to truly realize the potential of this mod as it seems to be a critical part change for the IPS?
It was pretty late here when I finished so could only listen to like 2 tracks and not very loudly at that. However, what I did hear was excellent. Nothing anomalous and highs were very clear, mids were smooth, bass was authoritative and deep. I want to set the gain resistors to match my other amp. I think I am using 20k and 550R. Or change the other amp to match this one so I can do AB test. Although don't I need to wait for the 2SC1845's to arrive to truly realize the potential of this mod as it seems to be a critical part change for the IPS?
I think 2SC1845 will make S/N ratio slightly better. But the noise is not the most important in the power amplifier. I suggest you to choose highest hFE and matching them. It will make the distortion and DC Offset lower.
That's what I plan to do with the bag of qnty 50 2SC1845's when I get them. The spec sheet says Hfe of 600 is typical. That is surprisingly high - partly why you chose it of course.
I will then put them in thermal contact and put shrink tube around them to make one unit.
I will then put them in thermal contact and put shrink tube around them to make one unit.