Hello everyone.
I have built a dual mono CLC F5 for my stereo project. I chose the F5 mainly because I have heard it in friends stereos, being totally quiet on 110db horn systems and not "burping"😉
This is my first DIY build ever, so the building process has been both fun, interesting and frustrating. Nevertheless, the amp is playing on some cheap fostex speakers before I plug it on to my main system consisting of ALE compression drivers. These are both fragile and expensive, so I want to make sure everything is in order before powering up on my main setup.
Now, one problem has surfaced. I found it a bit hard to get the DC level on the outputs very low when adjusting the bias. I got it below 10mV, and when the amp has warmed up and is playing it now shows 12mV and 14mV on left and right channel. The plan was to let the amp play for a while and then bias it a final time.
However, I measured the DC when switching the power on and I get around 50-60mV, that slowly falls towards 12\14mV after 30-40 seconds. This might no be a lot, but I am very scared of frying my precious ALEs.
I get a slight "thump" in the speakers when turning the amp on.
I have also measured DC when switching the power off, and it peaks at up to 200mV before going right down to 0mV.
My DIY friend that has built some F5 has not encountered these problems, so I was hoping that you would help me. I guess using a delay protection circuit would help alot, but I get the creepy feeling that something is a bit off.
Please let me know if I can test or measure anything to help you help me 😉
Sincerely
Magnus
I have built a dual mono CLC F5 for my stereo project. I chose the F5 mainly because I have heard it in friends stereos, being totally quiet on 110db horn systems and not "burping"😉
This is my first DIY build ever, so the building process has been both fun, interesting and frustrating. Nevertheless, the amp is playing on some cheap fostex speakers before I plug it on to my main system consisting of ALE compression drivers. These are both fragile and expensive, so I want to make sure everything is in order before powering up on my main setup.
Now, one problem has surfaced. I found it a bit hard to get the DC level on the outputs very low when adjusting the bias. I got it below 10mV, and when the amp has warmed up and is playing it now shows 12mV and 14mV on left and right channel. The plan was to let the amp play for a while and then bias it a final time.
However, I measured the DC when switching the power on and I get around 50-60mV, that slowly falls towards 12\14mV after 30-40 seconds. This might no be a lot, but I am very scared of frying my precious ALEs.
I get a slight "thump" in the speakers when turning the amp on.
I have also measured DC when switching the power off, and it peaks at up to 200mV before going right down to 0mV.
My DIY friend that has built some F5 has not encountered these problems, so I was hoping that you would help me. I guess using a delay protection circuit would help alot, but I get the creepy feeling that something is a bit off.
Please let me know if I can test or measure anything to help you help me 😉
Sincerely
Magnus
don't be afraid of frying your speakers with these temporarily appearing low dc voltages.
i test my speakers usually with a 9v block (9000 mV) and never broke not even a tweeter.
your turn on thump might vanish if you use a soft start unit and/or speaker protection.
this would also keep the 200mV at turn off from your precious speakers.
good luck!
i test my speakers usually with a 9v block (9000 mV) and never broke not even a tweeter.
your turn on thump might vanish if you use a soft start unit and/or speaker protection.
this would also keep the 200mV at turn off from your precious speakers.
good luck!
that's completely normal
all you need is to set it to 0 at temp equilibrium , lid closed ( OK , opened shortly for trimpot fiddling)
all you need is to set it to 0 at temp equilibrium , lid closed ( OK , opened shortly for trimpot fiddling)
My f5 also briefly shows 100mv of DC on startup and settles down to 5mv after warming up. No turn on thump though but my speakers aren't particularly sensitive.
I wouldn't worry about it. I bet your friends f5's shw a small DC spike when turned on too.
Most speaker protection circuits kick in (or off) at 1 or 2 VOLTS and a relay is probably not going to sound good. So, you really have nothing to worry about.
I wouldn't worry about it. I bet your friends f5's shw a small DC spike when turned on too.
Most speaker protection circuits kick in (or off) at 1 or 2 VOLTS and a relay is probably not going to sound good. So, you really have nothing to worry about.
i would use DC protection if you have hard to get and/or expensive drivers.
without it you risk saying bye bye to the drivers if one of the output transistors blows.
With a single pair of outputs you risk full railvoltage on the speakers if one of the output transistors blows.
without it you risk saying bye bye to the drivers if one of the output transistors blows.
With a single pair of outputs you risk full railvoltage on the speakers if one of the output transistors blows.
Thanks a lot. I actully manned up and fired the F5 up on my main setup last night, and it sounds very good indeed. Caps in series with both compression drivers.
I plan on installing protection, will these suffice:?
2X Audio Hi Fi Speaker Delay Protection C1237 UPC1237 Mono DIY Kit | eBay
I plan on installing protection, will these suffice:?
2X Audio Hi Fi Speaker Delay Protection C1237 UPC1237 Mono DIY Kit | eBay
I have two of those dc protection boards that i was using on a tripath amp. They work, thats about all i know. PMI if you are in the US I would send them to you if you want them.
Sorry, I'm in Norway, but thanks for the offer 🙂
I'm also building two F5 amps, so I needed four boards.
I'm also building two F5 amps, so I needed four boards.
Hello!
I got the protection circuit kits and installed them in the F5 I just finnished today. I immediately got problems when turning up the variac, the amp started drawing power from the mains allready at 1V from the PSU.
After some headscratching and troubleshooting I noticed something in the protection curcuit diagram. To feed the circuit I took 18VAC from the seconds of the tranformer as described. However, if you study the diagram and the PCB, the GND on P1 is connected to all GND points on the PCB, also the legs. This means that the 18VAC from the transformer is connected to the GND on the powerPCB, chassis the negative speaker out.
I can't understand how this is supposed to work?
Link to the diagram: http://analogmetric.com/download/C1237 schematic.pdf
I got the protection circuit kits and installed them in the F5 I just finnished today. I immediately got problems when turning up the variac, the amp started drawing power from the mains allready at 1V from the PSU.
After some headscratching and troubleshooting I noticed something in the protection curcuit diagram. To feed the circuit I took 18VAC from the seconds of the tranformer as described. However, if you study the diagram and the PCB, the GND on P1 is connected to all GND points on the PCB, also the legs. This means that the 18VAC from the transformer is connected to the GND on the powerPCB, chassis the negative speaker out.
I can't understand how this is supposed to work?
Link to the diagram: http://analogmetric.com/download/C1237 schematic.pdf
we need more info to help you
everything is simple and logical if you're using one diode bridge-center tap to gnd approach ;
if you're using separate secs with two diode bridges ( as in most FW amps) , you need separate small xformer for AC on protection board
everything is simple and logical if you're using one diode bridge-center tap to gnd approach ;
if you're using separate secs with two diode bridges ( as in most FW amps) , you need separate small xformer for AC on protection board
The second option, two diode bridges like most FW amps.
How would using another small transformer work better, as long as one of its lines are connected to the speaker outlet?
How would using another small transformer work better, as long as one of its lines are connected to the speaker outlet?
Sorry if I'm a bit slow. A seperate transformer for the two protection boards would not induce the problems I've encountered, or should I not encounter these problems at all?
The product specifications says that "supply voltage usually taken from the main power supply".
I don't have any room for another transformer 😉
The product specifications says that "supply voltage usually taken from the main power supply".
I don't have any room for another transformer 😉
just use separate small 18Vac/5VA xformer for supply rail marked AC
you can squeeze it in
wire its primary in parallel to main xformer primary
GND is part of main (positive) supply in amplifier
or you can wind additional 18Vac winding on main toroid ( if you're using it ) ;
say that enameled wire of 0,5mm dia is good enough , both for current and winding ease
you can squeeze it in
wire its primary in parallel to main xformer primary
GND is part of main (positive) supply in amplifier
or you can wind additional 18Vac winding on main toroid ( if you're using it ) ;
say that enameled wire of 0,5mm dia is good enough , both for current and winding ease
Last edited:
Since i built these dual mono, could I use the 18VAC from the transformer on the other side if the amp to feed the protection pcb?
no
even if dual mono , audio gnd of different channels will eventually meet somewhere
think about difference of gnd positioning between one vs. two diode bridges PSU and you'll know why you need floating AC , in your case
even if dual mono , audio gnd of different channels will eventually meet somewhere
think about difference of gnd positioning between one vs. two diode bridges PSU and you'll know why you need floating AC , in your case
Last edited:
They do not meet eachother, actually. The outlets in my house does not have ground, so I have not connected the gnd of the inlet to the chassi, nor the power PCBs or the amp PCBs. Not "safe", but since there is no gnd connection....well.
As far as I can tell, the 18vac output on transformer one is floating in reference to the other. Am I wrong?
As far as I can tell, the 18vac output on transformer one is floating in reference to the other. Am I wrong?
Or use a seperate wall wart type psu. Thats what i did when using these speaker protection units in the past. But you will not get the "delay" unless you use a 4pole power switch or power up the relays after you turn on the amp. If i remember right the speaker protection relays are open unless powered on. And there is a 2 second delay after power up.
- Status
- Not open for further replies.