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Double check all you transistors first. Make sure you didn't mix your output devices. Check to see if your output devices are shorting to the heat sink. If that's okay, unhook the first channel and power it up again.
you can't use bulb tester with fully loaded PSU (first channel soaking juice)
de-attach first channel , then proceed with bulb tester for second channel........ if everything is ok , remove it and proceed with biasing procedure
when done , connect again first channel , check Iq an offset
de-attach first channel , then proceed with bulb tester for second channel........ if everything is ok , remove it and proceed with biasing procedure
when done , connect again first channel , check Iq an offset
it may indicate a short. check resistance between center leg of output transistors and sink. and make sure the pots is at minimum resistance. 0 ohm (or Close to 0) across R5/R6.
EDIT: never mind. missed that the first ch was still attached.
EDIT: never mind. missed that the first ch was still attached.
Last edited:
Of course 😀 did not know that
disconnected the first channel and tested, the bulb went dim very quickly 🙂 ... I will now proceed with the bias setting
Double checked and all seems fine. Bulb test is ok with 2nd channel alone. thanks
Yes I did check that. No shorts. The pots are at 0. Double checked by moving the pot and measuring R5/R6 to see in which direction the pot works.
Anyway, now with the 1st channel disconnected, the bulb test works fine. Thank you
KJ
Hello again 🙂
Followed Zen Mod instructions and all went great. Connected both channels and checked bias. Both channels are around 0.59v/06v and under 2mV offset... I just listened to some music in stereo this time and it was grrreat
Thank you all so much for helping out and making this adventure enjoyable for beginners.
I have a question, what do you think about adding speaker protection to the F5? is it too risky running it like this? Mr. Pass minimized the number of parts in the audio path so it seems a bit counter productive to add more ..on the other hand I would be really pissed off if this amp blew up my main speakers, so 😕..would appreciate to have your opinion on this.
Again many thanks guys/girls...this forum rocks🙂
Cheers
KJ
Followed Zen Mod instructions and all went great. Connected both channels and checked bias. Both channels are around 0.59v/06v and under 2mV offset... I just listened to some music in stereo this time and it was grrreat
Thank you all so much for helping out and making this adventure enjoyable for beginners.
I have a question, what do you think about adding speaker protection to the F5? is it too risky running it like this? Mr. Pass minimized the number of parts in the audio path so it seems a bit counter productive to add more ..on the other hand I would be really pissed off if this amp blew up my main speakers, so 😕..would appreciate to have your opinion on this.
Again many thanks guys/girls...this forum rocks🙂
Cheers
KJ
I've built gazillion power amp and I believe that adding a speaker protection is always a smart move. Thay don't cost much and you protect your expensive speakers. Many are available (DIY store, e-bay, etc), this module will normally require a separate 12-15Vac tiny power supply which will be powered at the same time as your power amp. These spkr protector monitor the Output of each channel and are therefore not in the signal path, the only addition between the amp and your speaker is a relay which will be ON when all goes well and will go OFF is the module detects a certain DC signal (lets say above 1.5Vdc), look for upc1237 on e-bay, it's a dedicated IC.
Congrats on your amp.
BR,
Eric
Thanks Kevin. Without the support from this forum, I would have never been able to do it 🙂
Zen Mod & Eric, Ok, I will go for it. I ordered this (2x Speaker Protection C1237 (UPC1237) Mono DIY Kit_Delay Protection_Accessories Kit_Analog Metric - DIY Audio Kit), hopefully there will be no severe impact on the sound quality.
Have a great day everyone
KJ
Zen Mod & Eric, Ok, I will go for it. I ordered this (2x Speaker Protection C1237 (UPC1237) Mono DIY Kit_Delay Protection_Accessories Kit_Analog Metric - DIY Audio Kit), hopefully there will be no severe impact on the sound quality.
Have a great day everyone
KJ
bulb test the transformer alone.
Then the transformer + rectifier
Then + PSU
Then + one channel
Then ......
Then the transformer + rectifier
Then + PSU
Then + one channel
Then ......
You might want to find a stereo version for your protection. In a perfect world two of these would work well but there may be a slight difference in timing of two of these having one channel start or stop at a different time from the other. Might be kind of annoying.
hmm... did not think of that. I assumed 1 dedicated circuit per channel would be best. Oh well, it's already ordered, so will try and see. If any problem, I would try a stereo version as per your suggestion.
Thank you
KJ
Hello again 🙂
I was never able to make that circuit work 🙁 the seller was very friendly, we tried troubleshooting, no success, so he refunded me... I ended up buying the Velleman k4700U kit and it worked fine.
I have a problem though. My Grant Fidelity Tube-DAC 11 trips it when I use the tube out. No problem with line out. Anyone has any experience with the GF DAC 11? DC is a bit high on the tube output (50-80 mV), is this normal? can it be removed before it gets to the amplifier.
P.S. I now swapped the F5 boards with Aleph J boards ... not sure which one I like more 🙂, they are both great though.
do you have a schematic for the Source?
What is the difference between "tube out" and "line out"?
Normally we expect to have a DC blocking capacitor at the input of all our audio gear and another DC blocking capacitor at the output of all our audio gear.
Using DC blocking capacitors prevents unknown Sources or faulty sources damaging subsequent audio gear.
The F5 is DC coupled. It has no DC blocking capacitors. Not to protect itself, nor to protect what follows.
What is the difference between "tube out" and "line out"?
Normally we expect to have a DC blocking capacitor at the input of all our audio gear and another DC blocking capacitor at the output of all our audio gear.
Using DC blocking capacitors prevents unknown Sources or faulty sources damaging subsequent audio gear.
The F5 is DC coupled. It has no DC blocking capacitors. Not to protect itself, nor to protect what follows.
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