The BOM I've linked is the correct one for v1.6 boards like yours, it just omits parts for the FE original compensation:
- R3=684-MP930-0.5
- R39=754-RG2012P-474-BT5
- C10=598-CD10ED330JO3F
C14 and C15 are not critical parts of the speaker protection circuit, you can use the ones in the most recent BOM without problems...BTW C14 never changed and C15 in ealier versions was 647-UFG1E220MDM
C39??? Maybe you meant R39?
I'm not getting what you want to do...
It should be this one (it will be available for a day or two): https://docs.google.com/spreadsheets/d/1PL78q0UOt5OcLbuPbROI2yDioUvclqgJKVHxqtVHjGc/edit?usp=sharing
That's it ! Thanks!!! Damn... I'm gonna shelve an amp with Amtrans and Caddock... :|
Hello Clave,
I have a couple of questions about FE, if its not a problem..
I am looking at July 2020 schematic, i assume that one is latest.
It is frankly impressive how much evaluation you did on the board for each component, and how much incremental improvements, so it is not obvious to me what can be "safely" altered..
Q1: Red LED1 can be replaced by 2.5V zener? (i dont like light sources in my room)
Q2: Pinout for coil on G5LE is 2 and 5, not 1 and 2? Wrong pinout (presumably) on schematic doesnt matter i guess since its correct in function.
Q3: BC546A safely substituted by BC550B?
I have a couple of questions about FE, if its not a problem..
I am looking at July 2020 schematic, i assume that one is latest.
It is frankly impressive how much evaluation you did on the board for each component, and how much incremental improvements, so it is not obvious to me what can be "safely" altered..
Q1: Red LED1 can be replaced by 2.5V zener? (i dont like light sources in my room)
Q2: Pinout for coil on G5LE is 2 and 5, not 1 and 2? Wrong pinout (presumably) on schematic doesnt matter i guess since its correct in function.
Q3: BC546A safely substituted by BC550B?
The heart of my amplifier will be intelligent softstart + remote On/Off
Until the pcb on my_ref arrives, I'll start slowly building.
I plan to fit MY_REF with 15.000 or 22.000 uF main filters. What voltage should I buy these filter caps for? 40V or better for 63V? My toroidal is 2x25V.
Thank You!
Until the pcb on my_ref arrives, I'll start slowly building.
I plan to fit MY_REF with 15.000 or 22.000 uF main filters. What voltage should I buy these filter caps for? 40V or better for 63V? My toroidal is 2x25V.
Thank You!
The voltage rating should be 50V minimum, with 37V rails 40V does not have enough margin...
10000 uF is plenty for the amp, I would not deviate much from that value.
A1: you can simply omit it without problems.
A2: The Eagle component has different pin numbering, don't mind about that.
A3: BC546 supports higher voltages than BC550, I would not swap them. BC546 is available from Mouser for pennies.
Oh, I didn't think about a LCF filter - I just have a momentary switch+softstart . Any improvement over sound or safety?
Hello gentlemen, trouble
After assembling everything, i turn it on, after 2 seconds or so solenoid activates, i see very low DC offset and think im good to go.
Voltage on opamp rails is +-15v exactly as it should be. Main power is +-23v, a bit on the low side but should technically at least function right?
So for testing i plug in a sine wave of 0.560v AC. On output i read 0.017v AC. No matter the volume of input, output always shows 0.017v.
I thought maybe because of special configuration of feedback, a load is required to show voltage on output, so i connected a 100w 4 ohm resistor simulating a speaker and nada, still the same. The LM3886 is not heating at all, about skin temperature, maybe slightly more.
So i went around the board to troubleshoot, and here are the values i recorded, all in AC
What do you think it could be? i assume 11.2v AC on output of LM318 is not normal.
It's also interesting as i vary the input voltage the output of the opamp (pin 6) is like, nothing 0v, nothing 0v, a little bit 0.5v, a little bit 1v, and then in just a few more clicks its 11.2v, so what im trying to say very non linear. Is it a sign of oscillation? Feedback network shows 0.273v on pin 8.
But also, even when i keep the input very low, and on pin 6 of opamp is like 1v or so, the output of lm3886 is still, always, 0.017v AC.
Do you have any hints perhaps what to do, or what nodes to check?
Thank you
After assembling everything, i turn it on, after 2 seconds or so solenoid activates, i see very low DC offset and think im good to go.
Voltage on opamp rails is +-15v exactly as it should be. Main power is +-23v, a bit on the low side but should technically at least function right?
So for testing i plug in a sine wave of 0.560v AC. On output i read 0.017v AC. No matter the volume of input, output always shows 0.017v.
I thought maybe because of special configuration of feedback, a load is required to show voltage on output, so i connected a 100w 4 ohm resistor simulating a speaker and nada, still the same. The LM3886 is not heating at all, about skin temperature, maybe slightly more.
So i went around the board to troubleshoot, and here are the values i recorded, all in AC
What do you think it could be? i assume 11.2v AC on output of LM318 is not normal.
It's also interesting as i vary the input voltage the output of the opamp (pin 6) is like, nothing 0v, nothing 0v, a little bit 0.5v, a little bit 1v, and then in just a few more clicks its 11.2v, so what im trying to say very non linear. Is it a sign of oscillation? Feedback network shows 0.273v on pin 8.
But also, even when i keep the input very low, and on pin 6 of opamp is like 1v or so, the output of lm3886 is still, always, 0.017v AC.
Do you have any hints perhaps what to do, or what nodes to check?
Thank you
The relay subsystem seems to be working fine, all PS voltages are nominal, so it must be something in the main circuit
I think it really must be the LM318 just because of the massive and non linear output for a given input voltage (goes up very fast with small input increments, and then caps out at some value and doesnt budge). im not sure how its supposed to behave though.
When i touch it, it doesnt react at all.
i noticed with no input at all there's 0.15v ac on input terminals if the mains cord is plugged in, and 0v if i connect ground to case...
Now when nothing is plugged in, output (pin6) of lm318 is perfectly at 0.00mv. But connecting the ground to case didnt fix the problem.
I also fully replaced the LM318 for a new one, but same thing.
Checked all solder joints, all fine.
One interesting thing i found out!
Measuring AC of power rails, shows they're dead quiet. But then measuring after the BD140 and BD139 (opamp power rails), there's is apparently 223mV RMS of AC on the positive, according to the multimeter (but it only shows it in V mode, not in mV mode which i never understood). Negative -15v is clean.
So i put a large cap on the positive rail of the opamp, but same thing, didnt even budge a microvolt. I wonder what's causing it, oscillation of opamp?
So my theory for now is, the LM318 oscillate for unknown reasons, and then LM3886 self protects by shutting off or something? I cant explain why there's nothing on the ouput no matter what i do.
All components used are high quality, c0g or PPS smd caps, smd thick film 20ppm resistors, etc...
I think it really must be the LM318 just because of the massive and non linear output for a given input voltage (goes up very fast with small input increments, and then caps out at some value and doesnt budge). im not sure how its supposed to behave though.
When i touch it, it doesnt react at all.
i noticed with no input at all there's 0.15v ac on input terminals if the mains cord is plugged in, and 0v if i connect ground to case...
Now when nothing is plugged in, output (pin6) of lm318 is perfectly at 0.00mv. But connecting the ground to case didnt fix the problem.
I also fully replaced the LM318 for a new one, but same thing.
Checked all solder joints, all fine.
One interesting thing i found out!
Measuring AC of power rails, shows they're dead quiet. But then measuring after the BD140 and BD139 (opamp power rails), there's is apparently 223mV RMS of AC on the positive, according to the multimeter (but it only shows it in V mode, not in mV mode which i never understood). Negative -15v is clean.
So i put a large cap on the positive rail of the opamp, but same thing, didnt even budge a microvolt. I wonder what's causing it, oscillation of opamp?
So my theory for now is, the LM318 oscillate for unknown reasons, and then LM3886 self protects by shutting off or something? I cant explain why there's nothing on the ouput no matter what i do.
All components used are high quality, c0g or PPS smd caps, smd thick film 20ppm resistors, etc...
And of course Joseph you were right!
I was thinking the same thing last night, after i wrote "I cant explain why there's nothing on the ouput no matter what i do."
It was an obvious hint to myself that it must either be broken or muted, assuming the former is less likely.
What a stupid mistake, so much messing around, but it was the 10K. Plays perfect now
I disconnected the board from the case though, because i get very audible mains hum, it is injecting some sort of current into the board ground. And the case is earthed to the plug, and the PSU is earthed as well, so i dont know..
C9 is bypassed, only 1.5mv of DC offset, still <10mv when playing music.
Also why is the gain so high? The max i dare to go is like 30%, and my dac is R2R with simple resistor I/V, pretty low Vout.
Is it worth changing out some resistor (the 12K?) to bring it down or would it mess with the compensation (i assume not)?
You mean OPA 627BP..
there are available versions of OPA627, in SOIC packaging..
I am afraid it's a bit 'brutal', to try insert a Dip socketed chip into an FE board.
I have tried, even used for some time a pair of FE equipped with SOIC OPA627. I think a search in this thread would reveal the results. It can be made to work. Sounds ok.
I use almost exclusively everywhere the OPA828 lately. It just works, for me in these configurations.
It would be interesting to do an apples to apples comparison, where two boards equipped with different chips could be compared..
There is a little bit of problem, that the FET input opamp setup permits different options to adopt: like no C9, not even input 1uF C13, + different compensations.
These are integral part of the opamp choice, and so maybe a more coherent comparison would be to confront these two configurations. (original BOM <> opa828)
Also, presently I have a completed scheme of compensation with OPA828, and decreased gain (like 12kohm/ 750ohm feedback)
all the best, George
there are available versions of OPA627, in SOIC packaging..
I am afraid it's a bit 'brutal', to try insert a Dip socketed chip into an FE board.
I have tried, even used for some time a pair of FE equipped with SOIC OPA627. I think a search in this thread would reveal the results. It can be made to work. Sounds ok.
I use almost exclusively everywhere the OPA828 lately. It just works, for me in these configurations.
It would be interesting to do an apples to apples comparison, where two boards equipped with different chips could be compared..
There is a little bit of problem, that the FET input opamp setup permits different options to adopt: like no C9, not even input 1uF C13, + different compensations.
These are integral part of the opamp choice, and so maybe a more coherent comparison would be to confront these two configurations. (original BOM <> opa828)
Also, presently I have a completed scheme of compensation with OPA828, and decreased gain (like 12kohm/ 750ohm feedback)
all the best, George
Ah i see, so it would affect the compensation. Im courious to play with other opamps, im reading a lot of the posts here now.👍
I am using my version of this amplifier with half gain. Though that is not exactly your configuration, and I did not check yet the all the necessary compensation steps for this, base LM318 config.
Looking at the schematic im guessing double the 390 to half the gain?
Also i think im very lucky to get 1-2mV DC offset with C9 shorted and also bypassed the input caps, because my DIY flat foil cables have like...50nf capacitance and probably very low inductance just for the 3m length. And plugged this into the speaker, and played music, and absolutely nothing got warm at all, but i think im pushing my luck...
yes, 50nF cable capacity is quite nasty..
though the standard BOM should be capable to deal with that. (original gain!!)
So yes, please do not take it light hearted, the only tried and trusted configurations are the classic BOM & and gain configuration.
I take responsability for my configuration/ opamp suggestions.
though the standard BOM should be capable to deal with that. (original gain!!)
So yes, please do not take it light hearted, the only tried and trusted configurations are the classic BOM & and gain configuration.
I take responsability for my configuration/ opamp suggestions.
I did not like the sound with OPA627. I went with ADA4627 in one build and OPA828 in another. 4627 is dynamic and has very good attack. 828 is very delicate and sweet sounding. I can't say which I like better. Eliminating any cap at C9 free the beauty of the music (IMHO). Dario's design is extremely versatile and I have had no issues with Joseph K's compensation designs using alternative op-amps.
Cheers, Pete
I would not hold anyone responsible if i make a modification and bust something , every time i connect something to my speakers i treat it as my responsibility as its my own decision to acquire it and plug it in the first place. I appreciate the comment to not take it light hearted and its very fair of you George to even offer informal "warranty" for your configurations, though i would never blame you
. Im plugging them in speakers i can afford to lose currently, for me things are things and main thing is knowledge and experience, life is just play.3886 has minimum closed loop gain of around 11 or so, but gain is currently 12k/390 = ~30 so it should still have sufficient margin for a higher 390 or am i understanding that wrong? But i guess it changes the overall compensation. That's why im trying to build a working LTspice model now but LM3886 is giving me trouble, model from TI doesnt work for me. I want to understand it better, maybe play around with values (in sim), and really understand what goes on, so i can participate in the thread better. And maybe build a compensation around OPA1655 in the future.
P.S Seems like input cap is redundant if preceeding dac already has output caps. i.e it is electrically equivalent? I guess this cant be guaranteed for everyone's system so better safe than sorry kind of thing.