I've deleted my message because I thought we were talking about the FE...
Some answers still apply, some not, like the one on C102/C202 or on DC offset, as already pointed out by Andrew.
OK, I finally wired up the MyRef C (original version from UDaily), and went through all of the checks with the light bulb tester, however some problems, the chief of which is no sound.
The strange thing, apart from no sound, is the power LED's. Only one channel had the LED shine when I switched on, the other channel's LED didn't shine. However, when I switched off the amp, after a few seconds the channel who's LED didn't shine, lit up briefly.
Now both channels LED's do not shine, although that is my fault as my probe slipped on the LM318 when measure for voltage. There was no smoke, but the one working LED went out. However, when I power the amp off, after a few seconds both LED's shine briefly and then go out.
From reading the threads it looks like the LM318's are the culprits, although I don't understand the LED behaviour.
All my LM3886's are insulated from the heatsink, including the shoulder spacer for the screw.
I've checked the polarity of all the capacitors and they are fine, however I don't hear the relays kicking in anymore. One certainly did (the channel who's LED originally worked), but after I'd had a slip with the probe, that relay stopped clicking in.
Comments on my issues, and symptons?
- Rails measure fine at 35 V dc
- OpAmps measure at a little over 12V dc
- LM3886 has 35V dc at the pins
- DC Offset is around 3mVdc
The strange thing, apart from no sound, is the power LED's. Only one channel had the LED shine when I switched on, the other channel's LED didn't shine. However, when I switched off the amp, after a few seconds the channel who's LED didn't shine, lit up briefly.
Now both channels LED's do not shine, although that is my fault as my probe slipped on the LM318 when measure for voltage. There was no smoke, but the one working LED went out. However, when I power the amp off, after a few seconds both LED's shine briefly and then go out.
From reading the threads it looks like the LM318's are the culprits, although I don't understand the LED behaviour.
All my LM3886's are insulated from the heatsink, including the shoulder spacer for the screw.
I've checked the polarity of all the capacitors and they are fine, however I don't hear the relays kicking in anymore. One certainly did (the channel who's LED originally worked), but after I'd had a slip with the probe, that relay stopped clicking in.
Comments on my issues, and symptons?
The rails look ok, and the output DC offset is fine (this should be measured between the output and PGND). You probably need to re-check the protection relay circuit - values, shorts, opens.
Another quick sanity check is to swap the LM318 with a TL071. If it works with the slower TL071, then it's probably a stability issue with the LM318.
Another quick sanity check is to swap the LM318 with a TL071. If it works with the slower TL071, then it's probably a stability issue with the LM318.
Thanks Linuxguru.
Values I can easily check, however how would I go about checking for shorts and opens, apart from visually checking it?
I'm confident my soldering is good, so I doubt it's a dry joint, however you never know, so that leaves shorts.
Oh, and what particuar TL071 would you recommend?
Thanks
Values I can easily check, however how would I go about checking for shorts and opens, apart from visually checking it?
I'm confident my soldering is good, so I doubt it's a dry joint, however you never know, so that leaves shorts.
Oh, and what particuar TL071 would you recommend?
Thanks
Hi all
Some partial success; I now have one channel working, however the original channel that would not work, still will not work.
I've replaced the LM318's with new ones, and I've also tried a TL071, but it refuses to work.
I'm thinking that it's now more likely to be an issue with the relay/related fuse values, however some expert advice would be appreciated.
Thanks
Edit: I just turned the amp on without any Op amp in the channel that refuses to work, and and I now get the power LED lighting up, whereas before (with the op amp in place), the power LED would not come on.
Some partial success; I now have one channel working, however the original channel that would not work, still will not work.
I've replaced the LM318's with new ones, and I've also tried a TL071, but it refuses to work.
I'm thinking that it's now more likely to be an issue with the relay/related fuse values, however some expert advice would be appreciated.
Thanks
Edit: I just turned the amp on without any Op amp in the channel that refuses to work, and and I now get the power LED lighting up, whereas before (with the op amp in place), the power LED would not come on.
Check your input-side grounding and shielding setup. PGND is best left floating (isolated) from chassis ground (earth) for minimizing hum. Also, a toroidal or R-core trafo will radiate less mains hum than an EI core. The secondary-side wiring from the trafo should be braided to minimize the AC loop area.
Other things being equal, my MyRefs are quieter at no input signal than my SMSL T-amp, which is also very quiet, but has a very faint background fuzz from its switching power supply.
Obviously the heatsink must be insulated from the LM3886T.
No problem with the LM3886TF
Heatsink was not grounded. Tried grounding and did help a little. chip is LM3886TF.
Input wiring is shielded, secondary winding is braided.
Doesn't have noticeable noise on my 'normal' Rogers 2-way speakers. But on my 110db goto horns, it is no good. Can hear buzzing non stop.
Also, still pops on startup and big sounding pop on shutdown. Sounds pretty good powering the Rogers... but unfortunately I don't think this type of amp is what I'm after to run my Goto horns.
Input wiring is shielded, secondary winding is braided.
Doesn't have noticeable noise on my 'normal' Rogers 2-way speakers. But on my 110db goto horns, it is no good. Can hear buzzing non stop.
Also, still pops on startup and big sounding pop on shutdown. Sounds pretty good powering the Rogers... but unfortunately I don't think this type of amp is what I'm after to run my Goto horns.
"fast off" of the protection relay will achieve the necessary speaker isolation @ power OFF.
"slow on" (or speaker delay) should already achieve the necessary speaker isolation @ power ON.
An input mute or source output mute will isolate Source start up noises, IF the mute knows that the Source is started out of sequence. A common power ON/OFF switch solves this fairly easily.
>100dB speakers will require a very low noise value at the amplifier output.
Chipamps do not have that required very low noise value. Peter Daniel developed his implementation that he uses (or used) with 95/96dB/W@1m speaker, I cannot recall if he had reservations on noise.
"slow on" (or speaker delay) should already achieve the necessary speaker isolation @ power ON.
An input mute or source output mute will isolate Source start up noises, IF the mute knows that the Source is started out of sequence. A common power ON/OFF switch solves this fairly easily.
>100dB speakers will require a very low noise value at the amplifier output.
Chipamps do not have that required very low noise value. Peter Daniel developed his implementation that he uses (or used) with 95/96dB/W@1m speaker, I cannot recall if he had reservations on noise.
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