Hi,
I purchased an F6 built according to this guide by another member here. Tonight I turned on the amp and got a high pitch through the left channel. Shut it down, turned it back on, no high pitch but a low hum. I looked at the board and R4 is blown out. I had been using the amp with no problems for Everything else looks fine. I had been using the amp for a couple of weeks with no problems. I don't know much about circuit design, but I can follow directions well.
Is there any thing else I should look at or test after replacing R4?
Does blowing this particular resistor point to particular possible problems elsewhere?
Thanks for any suggestions.
I purchased an F6 built according to this guide by another member here. Tonight I turned on the amp and got a high pitch through the left channel. Shut it down, turned it back on, no high pitch but a low hum. I looked at the board and R4 is blown out. I had been using the amp with no problems for Everything else looks fine. I had been using the amp for a couple of weeks with no problems. I don't know much about circuit design, but I can follow directions well.
Is there any thing else I should look at or test after replacing R4?
Does blowing this particular resistor point to particular possible problems elsewhere?
Thanks for any suggestions.
desolder and lift one end of both source resistors (R1 and R2)
in cold state check everything for shorts (mosfets , resistors)
write here what you found , do not power it on yet
ref. to attached schm
Thanks to both of you for your help.
R4 was the only thing showing a short (except for the source and drain on Q3 and Q4, but I think that is normal?). After replacing R4, I checked the resistance between the zeners, mosfets, and jfets on both boards. Everything matched except the resistance between the source and gate or the drain and gate of Q3 and Q4. On the good channel the resistance was showing about 47k, while on the bad channel the resistance was showing about 250 ohms.
Does this point to blown input jfets? If so, do all jfets need to match between both channels, or just the two jfets in a single channel?
Thanks again!
Is it important to match all four (both channels) or just those for the single channel I had problems with?
Sure. I am a bit embarrassed to say what took out the buffer in the first place. I was changing the configuration of a Pass active crossover because I wanted a full range signal going through the low pass leg for woofer measurement purposes, but I mis-configured one of the jumpers in the left channel. When I turned on the amp, the crossover sent some awful stuff into the left channel. I shut down the amp quickly and corrected the mistake on the crossover, but then the amp was producing a ugly hum through the left channel. That's when I found the smoked R4, and received the advice about the JFETS. I replaced R4 and the JFETS after running a check for shorts and making sure resistance figures agreed between both channels. Powered up and nothing ugly happened. I biased the channel up to 0.55 V after an hour, and nulled the offset.
I wonder if one of the original FETs was not in great shape prior to me destroying it, as I would get a fair amount of wandering values when I had previously worked on nulling the offset. I don't know enough to make an educated guess about anything though. The amp sounds quite a bit more dynamic and punchy now though, so maybe there was something amiss.
Is F6 (and all class a amplifiers) proper with 90db spl speakers?
Someone told me that speakers with SPL under 100db are hard to be moved by the class a amplifiers. It is true?
I certainly want to build a DIY amplifier and I'm especially interested in F6, so, is or isn't F6 proper or even compatible with the spl 90db (and 8 ohms) speakers which I have?
And if it is not, can you recommend me please, an other Diy amplifier (or more) that can be proper?
Please, excuse my questions, I'm a newbie and generally speaking I need advices, also from the theory but much more from your experience.
Thank you very very much.
Someone told me that speakers with SPL under 100db are hard to be moved by the class a amplifiers. It is true?
I certainly want to build a DIY amplifier and I'm especially interested in F6, so, is or isn't F6 proper or even compatible with the spl 90db (and 8 ohms) speakers which I have?
And if it is not, can you recommend me please, an other Diy amplifier (or more) that can be proper?
Please, excuse my questions, I'm a newbie and generally speaking I need advices, also from the theory but much more from your experience.
Thank you very very much.
I think it'll work fine. It may come down to room size and your volume expectation.
In my case, my room isn't large. None of my speakers are over 90dB and even
5 or so watts can be plenty loud.
You might want to try the test outlined here to get an idea how much peak voltage/power your speakers are using:
A Test. How much Voltage (power) do your speakers need?
Cheers,
Dennis
In my case, my room isn't large. None of my speakers are over 90dB and even
5 or so watts can be plenty loud.
You might want to try the test outlined here to get an idea how much peak voltage/power your speakers are using:
A Test. How much Voltage (power) do your speakers need?
Cheers,
Dennis