BrianDonegan said:
That's a really interesting comment Brian. I say this because yesterday I discovered a noise problem. With a pot in circuit and speaker attached it began close to halfway of the pots travel, increased a little then died off (not entirely) towards the end of the pots travel. Source or no source the result was the same.
I removed the pot, active pre and it's PS from the circuit which left only the amp, switch and attached speaker. The result was noise (uncertain if it is hum or buzz :/ )
I scratched my head for the longest time then finally used a alligator lead to attach the PGND on the amp to the Chassis ground. This cured the problem entirely :O
Has anyone any thoughts on what happened?
Cheers
Kendal
BrianDonegan said:For the fuse, I would put a 5A or so on the AC line coming into the amp, ahead of the transformer, as close to the entry as possible....
Hope this helps. These are not dumb questions. They would be dumb if you were asking just after electrocuting yourself.
I agree with Brian, but I used 2A slo-blo....
Brian-
Thanks for helping and watching out for the beginners... Someone did it for me when I was new and now I love this hobby instead of being fustrated or worse, dead!.
I've had that experience as well. It all depends on the circumstances. More often then not, it's the other way around. Depends on the case, the amp, etc. I didn't mean it as a hard and fast rule.
You can also run into issues if you connect a chassis-grounded amp to another chassis-grounded device, and create a ground loop. It's always experimentation that teaches us best.
Burn in is going nicely.
That "annoying upper mid" is now gone. I have never heard such a huge difference from burn in before. It now sounds alot smoother & more relaxed. Just to alay anybodies suspicions that it might be some sort of psychosomatic effect - the burn in was done with power resistors and I was NOT expecting much of a difference.
Do all chipamps change this much?
That "annoying upper mid" is now gone. I have never heard such a huge difference from burn in before. It now sounds alot smoother & more relaxed. Just to alay anybodies suspicions that it might be some sort of psychosomatic effect - the burn in was done with power resistors and I was NOT expecting much of a difference.
Do all chipamps change this much?
Hi Ross
I have the same scepticism as you. But after a week it sounded, well actually rather nice. When I build the first one I was messing around trying to change the signature.
I wish I had an explanation for the burn in period. One thing I still want to try is to crayo treat the entire amp after building it. (Maybe not much in it but I have access to the service so why not)
If the chip shows improvement form burn in, the crayo treatment might also work
maybe you can convince one of your friends to try my design and compare it with the TP version
R
I have the same scepticism as you. But after a week it sounded, well actually rather nice. When I build the first one I was messing around trying to change the signature.
I wish I had an explanation for the burn in period. One thing I still want to try is to crayo treat the entire amp after building it. (Maybe not much in it but I have access to the service so why not)
If the chip shows improvement form burn in, the crayo treatment might also work
maybe you can convince one of your friends to try my design and compare it with the TP version
R
Hey Byrd, I have only built the 3875, and noticed the same effect... it wasn't an expected thing, as this was my first amp... I kinda expected it to sound the same every time I listened to it... boy was I wrong, after about a week it was like listeing to angels compared to the amps I have had access too these last few years.
Appart from component burn in, if you use thermal paste, the first few times you heat the sinks by running the amp, it flows the paste which hardens again when you switch it off. In other words the paste works a little better with every run in in the beginning... but, some people are are using thermal pads... no idea what is hapening there.
My 86 would have been finished by now, if the post office could figure out what happened to the van with my parcell. Oh well car being broken, I had to walk from the post office and walked past one of these scrap dealers springing up everywhere... which impulsively had me walk in and ask if they have heatsinks... man what a find.. got some nice ones, and the guy says they get heatsinks in all the time... he will keep em now for me...
So if you got one of these places nearby (hopefully not too near) give em a check out.
Appart from component burn in, if you use thermal paste, the first few times you heat the sinks by running the amp, it flows the paste which hardens again when you switch it off. In other words the paste works a little better with every run in in the beginning... but, some people are are using thermal pads... no idea what is hapening there.
My 86 would have been finished by now, if the post office could figure out what happened to the van with my parcell. Oh well car being broken, I had to walk from the post office and walked past one of these scrap dealers springing up everywhere... which impulsively had me walk in and ask if they have heatsinks... man what a find.. got some nice ones, and the guy says they get heatsinks in all the time... he will keep em now for me...
So if you got one of these places nearby (hopefully not too near) give em a check out.
Received my RevC kit. Only 10 days from placing order to arrival, to a remote area of Australia. First class kit that will guarantee a successful project. Thanks Russ and Brian.
Regards the burn in. I'll use a dummy resistor too. Only after the burn-in will I make an ssessment.
What about Protos's discovery? He solved the problem in the mid/highs that requires a long burn-in to correct, by simply changing R1 and R4 resistors from 1k to around 600/620 ohms.
This resistor change would have an effect on the zeners.
As a consequence of this, is it possible that the 12v supply to LM318N is affected, resulting in the slight initial problem in the mid/treble?
If the resistor change really solves the long burn-in need, there must be a reason for it.
Audie.
Regards the burn in. I'll use a dummy resistor too. Only after the burn-in will I make an ssessment.
What about Protos's discovery? He solved the problem in the mid/highs that requires a long burn-in to correct, by simply changing R1 and R4 resistors from 1k to around 600/620 ohms.
This resistor change would have an effect on the zeners.
As a consequence of this, is it possible that the 12v supply to LM318N is affected, resulting in the slight initial problem in the mid/treble?
If the resistor change really solves the long burn-in need, there must be a reason for it.
Audie.
billabong said:
Audie, I cannot explain protos findings. But I can tell you that the amps in my HT and living room are all biased per the schematic and they sound simply stunning, absolutely nothing like the problems with the mid/trebel protos was finding. So I don't know how to explain his findings, but I can tell you I have found no such thing.
I have tried biasing all the way down to 2 x 1K(for 500R) and there is no difference at all, except that now the amp draws about double the idle current.
You have to remember that even biased at 1K the PS for the LM318 can deliver something like 3-4 times the needed current up to clipping voltage, also the 318PS is well bypassed, with ample storage caps(100uf).
I am not sure what to say about burn in. I think it can have a real effect, but it is likely on the passive components like the caps more then the active devices.
Anyway, enjoy the kit, I hope you have a very enjoyable project.
Cheers!
Russ
Hi Byrd,
Nice pics! Its good to seee the amp come together like that.
One note. Your resistors and zeners are flush with the PCB. That is not optimal, it is better to raise them up about .5" or so for the resistor and about .25" or so for the zeners. This will allow them to dissipate more heat.
Great work!.
EDIT: I was referring only to the power resistors of course. The other resistors should sit flush as you have them.
Cheers!
Russ
Nice pics! Its good to seee the amp come together like that.
One note. Your resistors and zeners are flush with the PCB. That is not optimal, it is better to raise them up about .5" or so for the resistor and about .25" or so for the zeners. This will allow them to dissipate more heat.
Great work!.
EDIT: I was referring only to the power resistors of course. The other resistors should sit flush as you have them.
Cheers!
Russ
Thanks Russ.
Your information changes things for me.
I will not change R1 and R4 . Should the sound not be perfect at first, I know it will be before long.
Found a beaut piece of timber for the front panel. It's 20mm thick dark Teak with a nice grain. ( it was my wife's chopping board, that she only used a few times).
Audie.
Your information changes things for me.
I will not change R1 and R4 . Should the sound not be perfect at first, I know it will be before long.
Found a beaut piece of timber for the front panel. It's 20mm thick dark Teak with a nice grain. ( it was my wife's chopping board, that she only used a few times).
Audie.
- but they are not brown / black yet
Yup. Looking at the top of the board, there is a big trace from the ground to the center pin of the relay on the 3-pin end. There is also a big trace from one of the pins on the opther end to the output (nearest the edge of the board). You can jumper between those to holes. Basically connecting the star ground to the output ground connector.
Rudi suggested I remove D2 and D3 before shorting the relay, is this neccessary? I don't realy wan't to desolder anything, it is looking so pretty... Once again special thanks to Rudi, you won't belive how many times he has phoned me long distance now allready, to help me out and see if I need any asistance etc...
Omiting the relay and shorting the two pins is not a good idea, unless you are using cheap speakers.
You will not get the turn on delay which is needed while the amp is stabilizing.
If you choose to do it with good speakers, do ot connect the speakers until the amp is on, and disconnect them before you turn the amp off.
You will not get the turn on delay which is needed while the amp is stabilizing.
If you choose to do it with good speakers, do ot connect the speakers until the amp is on, and disconnect them before you turn the amp off.