Hi Back;
When I did my measurement, I realized that 4ohm load was more difficult than 8 ohm load and there are some reasons : Mosfet needs more Vds and Vgs with current increase and the smps has an equivalent internal resistor, therefore you need larger voltage headrom.
Also I did increase progressively the source signal until the real-time fft shows some clipping. You see the clipping in term of harmonics spectra they all grow instantly like if the source was a square wave. see my post 3601 here http://www.diyaudio.com/forums/vend...-mosfet-amplifier-module-361.html#post4952735
as you can see on this larger picture : http://www.gopix.fr/image-2500_587BB19B.jpg
the thd is still good at 0.054% but increases very rapidely.
Doing the math:
with 45V smps you get 20Vrms (100W/4) clean so this means a headromm of 42-20*1.414= 13V
with 52V smps you get 25V (156W/4R) clean so this means a headromm of 49-25*1.414 = 13V
with 62V smps you will get the 250W/4R annouced in the SPEC with same sort of headroom.
I d just recomend every one using FO with other smps than hypex smps1200a400 to make a basic fft test into 4ohm to better understand the limits of your setup, and to identify the best/optimal vas bias in your configuration. Also to stress the smps and check the lowest value of vrail, use a 100hz or 120hz signal which is then synchronized with you mains 120/230V this seems to be the worst case scenario and where the quality of the 400V capacitor on the primary side of the smps makes the différence
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DC Sense
I'd like to use speakon connectors instead of the usual speaker terminals. The DC Sense will not fit the Speakons. Will the modules work OK if I simply wire them in series with the Speakon terminals?
I'd like to use speakon connectors instead of the usual speaker terminals. The DC Sense will not fit the Speakons. Will the modules work OK if I simply wire them in series with the Speakon terminals?
Hi All,
Finally managed to put these parts together and power on this beast. Just 30mins initial listening, super clean and transparent sound. Will compare with my FO-M once this beast settle down.
but according to my thermal camera, this Taobao sourced amp chassis's heatsink maybe too small, no technical specification on the china site for this heatsink. Only playing 30mins in my 25degree office the chassis went to almost 57 degree. I have not tune the biasing yet, just measure the speaker DC offset one side 20+ mV and the other 110+ mV and just connect a small speaker and turn it on. Maybe when I tune the biasing voltage temp maybe lower but still maybe I should find a bigger heatsink. Hope LC's FO-L mono chassis will be available soon. This beast is hot like my tube amp.
cheers
ck
Finally managed to put these parts together and power on this beast. Just 30mins initial listening, super clean and transparent sound. Will compare with my FO-M once this beast settle down.
but according to my thermal camera, this Taobao sourced amp chassis's heatsink maybe too small, no technical specification on the china site for this heatsink. Only playing 30mins in my 25degree office the chassis went to almost 57 degree. I have not tune the biasing yet, just measure the speaker DC offset one side 20+ mV and the other 110+ mV and just connect a small speaker and turn it on. Maybe when I tune the biasing voltage temp maybe lower but still maybe I should find a bigger heatsink. Hope LC's FO-L mono chassis will be available soon. This beast is hot like my tube amp.
cheers
ck
Attachments
Studley,
sure u can.. the DC Sense board holes does not fit to my china made chassis pre drilled speaker holes too, so I just solder 2 wire from the POS/NOS speaker wire to the DC board. See what I did in my picture above.
the DC board works as long as it is connected to the speaker wire(or speaker post).
cheers
ck
sure u can.. the DC Sense board holes does not fit to my china made chassis pre drilled speaker holes too, so I just solder 2 wire from the POS/NOS speaker wire to the DC board. See what I did in my picture above.
the DC board works as long as it is connected to the speaker wire(or speaker post).
cheers
ck
First FO L builder worldwide
Samcklee I have the honor to declare you the champion - first First One L builder wordwide, congratulations.
Very compact and packed amp chassis you have there, assembly looks nice and very professional.
Bias trimmer TR3 is set to min by default, so there's probably around 250 mA bias at 170 V, meaning 42 W of power dissipation per channel. This setup assures at least 100 mA per one output pair and that in your case looks at least 10 °C over recommended heatsink temperature. We can reduce the bias current to settle your heatsink to 45 °C by decreasing R42 (now 1,8 kOhm) simply by soldering 1 kOhm same size resistor on the top of R42 (new parallel value 643 Ohm). While this will make FO L amp underbias but at least the chassis will be saved and operational. 🙂
Samcklee I have the honor to declare you the champion - first First One L builder wordwide, congratulations.
Very compact and packed amp chassis you have there, assembly looks nice and very professional.
Bias trimmer TR3 is set to min by default, so there's probably around 250 mA bias at 170 V, meaning 42 W of power dissipation per channel. This setup assures at least 100 mA per one output pair and that in your case looks at least 10 °C over recommended heatsink temperature. We can reduce the bias current to settle your heatsink to 45 °C by decreasing R42 (now 1,8 kOhm) simply by soldering 1 kOhm same size resistor on the top of R42 (new parallel value 643 Ohm). While this will make FO L amp underbias but at least the chassis will be saved and operational. 🙂
Sure you can.. in post #3506 you can see in the pictures that the DC sense module does not fit on to the terminals and is soldered in place. You can do the same with your speakons.
R.
Oh I am honoured, but I would rather find a bigger chassis than to settle for less SQ with a lower bias current...
Thats the wonder of this DIY hobby.... we can choose the best all out design rather than settle for a compromise in commercial product due to costing.
and again... LC you are really guru in this. I was listening to my new active ATC SCM-50A for the past few days and when i turn on this FO-L with my IM-8300f I was shocked by the transparency and reality... makes me little regret buying the active version now. If this FO-L goes well, who knows maybe down the road I will get rid of the SCM-50 amp, get an electronics dac/crossover and powered the driver actively using FO-M and L 😱)
cheers
ck
Thats the wonder of this DIY hobby.... we can choose the best all out design rather than settle for a compromise in commercial product due to costing.
and again... LC you are really guru in this. I was listening to my new active ATC SCM-50A for the past few days and when i turn on this FO-L with my IM-8300f I was shocked by the transparency and reality... makes me little regret buying the active version now. If this FO-L goes well, who knows maybe down the road I will get rid of the SCM-50 amp, get an electronics dac/crossover and powered the driver actively using FO-M and L 😱)
cheers
ck
Rod Elliot has a heatsink calculator that is pretty accurate. Surface area is what makes a heatsink work, the problem with your one is that the fins don't go the full length and it doesn't have that many fins for the size of it. Have a look at some others as there are quite a few taobao ones that have a lot of fins and they will have a much lower c/w rating for the same length.
True, we found FO L here as neutral 'no limits amp' soundwisely, since we still didn't find the source or cables amp would not be able to reveal in most obvious manner accordingly to its resolution. 😎
i guess you can change only the heatsinks and keep the rest of the chassis which is very beautiful.
Thanks Fluid,
I remember Elliot has an article to make DIY heatsink too.. but maybe its the hot weather in Singapore... seems like we need a bigger heatsink than the one LC recommend. I will check around for more option.
cheers
I remember Elliot has an article to make DIY heatsink too.. but maybe its the hot weather in Singapore... seems like we need a bigger heatsink than the one LC recommend. I will check around for more option.
cheers
Well I ised medium-sized something closer to 4u and it works fine 120mm high
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You need to check the C/W rating is the same, not the size. LC is using Fischer ones which are high quality and are likely to have a better i.e. lower C/W rating for the same physical size as a Chinese one.
how big are your current heatsinks and what room temperature you have these temperatures?
Hi fluid, Agree with the china stuff. It's cheap but never high quality. But that's one of the larger chassis they have on their site. I go and hunt further.
Hi back, this clone Mark Levinson ML2 chassis measures internal 220Wx142Hx337D mm. U can find the taobao link here.
https://world.taobao.com/item/522786961327.htm?fromSite=main&spm=a312a.7700824.w4002-3863826164.22.
Hi aradan, this chassis is almost 4u height. I notice the hypex transformer is running at 60+ degree so maybe it contribute to more heating inside the chssis. Surrounding is around 27 degree in my office room. I think problem with this chassis heatsink is the fin height and density.
Ck
Hi back, this clone Mark Levinson ML2 chassis measures internal 220Wx142Hx337D mm. U can find the taobao link here.
https://world.taobao.com/item/522786961327.htm?fromSite=main&spm=a312a.7700824.w4002-3863826164.22.
Hi aradan, this chassis is almost 4u height. I notice the hypex transformer is running at 60+ degree so maybe it contribute to more heating inside the chssis. Surrounding is around 27 degree in my office room. I think problem with this chassis heatsink is the fin height and density.
Ck
I have bought from the same seller before, I actually think that the chassis are very good quality but to try and save money on materials sometimes they make some strange decisions on design.
Try this one from same seller, 400mm deep and can be taller too I think, heatsink fins extend the whole length rather than stopping.
https://world.taobao.com/item/4280757455.htm?fromSite=main&spm=a312a.7700824.w4002-3863826164.12.fd3Xvu
Well lots of chassis there are done by breeze audio.you can find the shop at taobao or aliexpress. Prices are good. They can even do customization if your total order amount is around 500usd. So if doing a group buy it is worth the catch
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