Hello ,
I need a circuit some like AX11 .. with short-circuit protection or VI limiter , because I want to use four chanell in my car with a switching power supply .
SMPS is ready it is +- 40V / 700W
APEX , now i see AX14P circuit . I like it very much . I have two AX14PCB and now will make only protect PCB .
How work this protect ?
Regards !
I need a circuit some like AX11 .. with short-circuit protection or VI limiter , because I want to use four chanell in my car with a switching power supply .
SMPS is ready it is +- 40V / 700W
APEX , now i see AX14P circuit . I like it very much . I have two AX14PCB and now will make only protect PCB .
How work this protect ?
Regards !
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What resistors should I change if I want to get a little more gain out of the FX8? Actually, I am running all 20k resistors in place of 22k's since I did not have any on hand. That may be affecting the feedback resistor and gain somewhat. My pre-amp was not able to drive it to clipping.
The feedback resistors are 22k from output to LTP base, and the 680R from the base in series with (100uF) cap to input ground. Gain is more or less 22k/680=32x. If you use 20k gain becomes lower: 20k/680=29x. You can use 20k/620=32x or if you want higher gain: 20k/560=36x.
Hmm... that's interesting how 29x voltage gain is about the same as 29dB. It sounds not as loud as my Dx amp so I wonder if something else is going on. Input impedance is 22k (or in my case 20k) should not be too low for the headphone outputs to drive.
The Dx amp with same power supply and CD headphones as input, can achieve about 17.6v output (into dummy 5ohm load) whereas I was only getting 12.7v with the FX8.
The 47uF 63v caps I have on there now are of questionable quality (bag of 50 from China for a song). Maybe try changing those out to quality Panasonic's to see if there is some improvement?
Just want to make sure that folks know I am not complaining but trying to figure out what I need to do to get it to play loud. It sounds very nice though at the loudness it does play. I may just try driving it with a pro-audio mixer preamp which has more oomph to see if it can go higher.
I do want to thank Apex Audio for the design and Sonal Kunal, Still4given, and Prasi, who I think all contributed to the PCB layout (sorry if I left anyone out...). It's a slick little package. Thanks!
The Dx amp with same power supply and CD headphones as input, can achieve about 17.6v output (into dummy 5ohm load) whereas I was only getting 12.7v with the FX8.
The 47uF 63v caps I have on there now are of questionable quality (bag of 50 from China for a song). Maybe try changing those out to quality Panasonic's to see if there is some improvement?
Just want to make sure that folks know I am not complaining but trying to figure out what I need to do to get it to play loud. It sounds very nice though at the loudness it does play. I may just try driving it with a pro-audio mixer preamp which has more oomph to see if it can go higher.
I do want to thank Apex Audio for the design and Sonal Kunal, Still4given, and Prasi, who I think all contributed to the PCB layout (sorry if I left anyone out...). It's a slick little package. Thanks!
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Replace 680R with 330R or add another 680R in parallel with exsisting.
Attachments
First of all, most of the DX amps have very high gain. Carlos hates preamps. All amps don't respond well to raising the gain. Sometime THD goes up as a result. Not saying that will happen here. It won't hurt to try, resistors are cheap.
I think you may be right about Carlos' amps probably having higher gain. I was using a Pass ACA and with 14dB gain, you need a sledgehammer of a preamp to get it to clip.
I just checked the DX Super A.. Feedback is 56k/1k2 = 56X. That is really high. My DX Super A is the highest gain amp I have. On my A/B setup the volume pot has to be reduced quite a bit to make it even with other amps. So this makes me wonder why you feel the need to clip the FX8? If you need that many dBs maybe you should build a more powerful amp.
Hi Erik,
Did you get my email with build details and attachments? There was no ack, so wondering if you got the mail.
reg
Prasi
I have the regular Dx - not sure if that is different from Dx Super A. I am actually good with volume wise for most music. I was planning on using this to drive a mid bass unit in a 3 way active system and need an honest 60watts out of it (into 5ohm load). Hence I was stress testing it and found I could not get the output of the PC's DAC to push it above 33watts.
Yes, the easiest way to influence sound of any amp is to change the gain. Higher gain is subjectively brighter (higher distortion perhaps?) and more dynamic. 50dBs is unnecessarily high gain for modern digital sources.
I am happy if I can get between 26dB and 30dB. Based in parts in my FX8, it should be about 29dB so maybe my PC DAC just needs a pre-amp.
56k:1k2 gives a DX gain of +33.6dB
increasing the lower leg resistor reduces the amplifier gain.
1k2 +33.56dB
1k3 +32.88dB
1k5 +31.67dB
1k6 +31.13dB
1k8 +30.13dB
2k +29.25dB
2k2 +28.45dB
2k4 +27.72dB
2k7 +26.75dB
increasing the lower leg resistor reduces the amplifier gain.
1k2 +33.56dB
1k3 +32.88dB
1k5 +31.67dB
1k6 +31.13dB
1k8 +30.13dB
2k +29.25dB
2k2 +28.45dB
2k4 +27.72dB
2k7 +26.75dB
I don't need to reduce the DX. I was just suggesting that he not assume his FX8 had too low of gain because it is not as loud as his DX.