MJE340/350 on VAS can be replace by 1381/3503 and it will have more slew rate, lower THD at high frequency, and better stability. Even you can reduce the compensation a bit.
I found some time to hook it up to a +-59V PSU, 20,000uF per rail. The sound is very good as expected. Square waves look beautiful It clips at 32vac into an 8 ohm load for about 128W.
Things of note.
The MJE350 runs very hot. The little heatsink is uncomfortably hot to grasp.
The offset is very high at turn on but settles fairly quickly. There is a noticeable sound through the speakers until this happens. I would say a speaker protection with delay would be in order.
Things of note.
The MJE350 runs very hot. The little heatsink is uncomfortably hot to grasp.
The offset is very high at turn on but settles fairly quickly. There is a noticeable sound through the speakers until this happens. I would say a speaker protection with delay would be in order.
Attachments
Thanks for doing the high power test. For an amp with this much power, speaker protection is probably mandatory. Do you have a favorite Apex design you can recommend for the protection?
I wonder if the turn on thump is the 1000uF feedback cap charging up?
Maybe a circuit design with the MJE350 mounted on main heatsink would help - or a larger heatsink?
Did you happen to snap a photo of the square wave? What frequency did you take the square wave at?
Thanks.
I suggest this stereo protect with over current, DC and anti klik (delay on)
Attachments
Mr. Mile, is there a schematic of the protect PCB for mono version (for subwoofer-high power)?. Also if pro is not connected, will still function with DC detect and start delay? or should i use NE555 mono protect without pro. (willJJ PCB) available somewhere in the middle posts of this thread.
reg
Prasi
Hi Sonal,
as usual very nice pcb. if i understand correctly, there is a small daughter board that goes along with it, which will enable pro- pin on any BJT amp . that consists of a couple of transistors and 4-5 passives. not sure if it can be adapted to FH-11 2-pair here.
reg
prasi
Only as my preference. I like to have indicator for fault and standby for the speaker protect. Built it and works great.
Attachments
apex stereo protect
hi
Mr apex,my first attempt ,please check for any mistakes ,i have attached the schematic,eagle brd file,screen shot of the brd file. only changes i have made is added parallel irf 540, as done by rensil in the post 7692,thank you
hiMr apex,my first attempt ,please check for any mistakes ,i have attached the schematic,eagle brd file,screen shot of the brd file. only changes i have made is added parallel irf 540, as done by rensil in the post 7692,thank you
Attachments
Last edited:
I'm sure you are right about the large feedback cap.
Probably a larger heatsink would suffice.
Here are some scope shots.
Attachments
Thank you! Wow - that does look pretty clean, no ringing at all, and not too shabby up to 20kHz given the whole lack of a low impedance driver for the gates.
I can see why it sounds good.
Having never used a protect circuit - what do the connections mean? Speaker "+" vs "-" and "out?
Out goes to amp?
Yes, out goes to amp and to speaker '+', this protect with mosfets SS relay disconect speaker '-' from GND. AC AC connect to bridge rectifier in amp PSU.
Hallo andrewlebon.
If it is so i also shoud build the FX9. In my listening experience i have find out that i like
more H2 signature and bit lower damping to speaker in sound.
The nice sounding simple FX8 plays after 2 weeks in use with better sorted image and
opens a bit more- very pleasant.
I have a little question to sonal: wich pcb layout Programm u use?
On weekend i have tested KICAD and Express PCB, but i am to dump to import files to
work on it or it is not possible.
I have seen in Juan clip- he works with Sprint Layout you can import files and rearrange
it.
For me it needs to much time to create a schema and work step by step- i am search a
short way to work on Bimos FX8 mod board for example.
If any other can give me advise- all is welcome- thanks.
Nice work here again the new FH11 !
Cheers Bangla.