Yes they will usually smell of the resin when they are new.
If the laminations are not perfectly smooth, IE 😀 they have very small gaps between the plates - this can induce eddy currents in the transformer. This heats the transformer and may even induce mechanical hum in the transformer. It also reduces the efficiency of the transformer.
If the laminations are not perfectly smooth, IE 😀 they have very small gaps between the plates - this can induce eddy currents in the transformer. This heats the transformer and may even induce mechanical hum in the transformer. It also reduces the efficiency of the transformer.
safetyman asked:
This is a question your local electric provider should answer. Some systems are better than others in regulating supplies and demands. You might consider using the 260V tap on the transformer.
This is a question your local electric provider should answer. Some systems are better than others in regulating supplies and demands. You might consider using the 260V tap on the transformer.
Byrd, therefore when you refer to the laminations, are you refering to the resin dip?
Ed, if I use the 260V tap, when the incoming mains drop to 220V or 240V for that matter, and my primaries are 22V, would there still be enough to power the amp?
Thanks for the quick response.
Ed, if I use the 260V tap, when the incoming mains drop to 220V or 240V for that matter, and my primaries are 22V, would there still be enough to power the amp?
Thanks for the quick response.
Sorry - I should have been more clear 
.
"Laminations" actually describes the construction of the core - it is made out of many very thin sheets of steel all stuck (laminated) together. The thing that has to be smooth to ensure no gaps is the thin sheet of steel
It is difficult to describe a technical specification to get a good construction. Maybe look at weight to power (VA) ratio. As long as the manufacturer is truthfull about the power rating, the ones that are lighter per VA are the ones that are going to create less heat. NB This is pure conjucture on my part and may be a bunch of b.....
."Laminations" actually describes the construction of the core - it is made out of many very thin sheets of steel all stuck (laminated) together. The thing that has to be smooth to ensure no gaps is the thin sheet of steel
It is difficult to describe a technical specification to get a good construction. Maybe look at weight to power (VA) ratio. As long as the manufacturer is truthfull about the power rating, the ones that are lighter per VA are the ones that are going to create less heat. NB This is pure conjucture on my part and may be a bunch of b.....
safetyman asked:
I wish you were blessed with a steady power source. It is something I take for granted.
You could expect your secondaries to change in proportion to the incoming V divided by 260V. The same is true for the other tap. It would result in a change in output from your amp. I think your amp will still work, though 24-25V rails is preferred by many.
How hot is the transformer? Don't touch any live contacts...or unplug it first...how long can you leave your finger in contact with it?
The switch to the 260V tap may have the effect of lowering the transformer temperature. That is the reason for my suggestion.
I wish you were blessed with a steady power source. It is something I take for granted.
You could expect your secondaries to change in proportion to the incoming V divided by 260V. The same is true for the other tap. It would result in a change in output from your amp. I think your amp will still work, though 24-25V rails is preferred by many.
How hot is the transformer? Don't touch any live contacts...or unplug it first...how long can you leave your finger in contact with it?
The switch to the 260V tap may have the effect of lowering the transformer temperature. That is the reason for my suggestion.
hmm I thought I posted this yesterday but it seems it didn't work... Anyway I have (almost) finished my ref-c, my first amp project ever. No pics yet because my sister has stolen the camera... So I'll have to go steal it back off her. Besides this amp is too much of a mess internally for me to post pics 🙂
anyway a couple of other newbie questions that I should have asked BEFORE I built it, one of te resistors was 220ohm on the pcb and a 47ohm was supplied, was it r42 maybe? Is this correct... secondly which of the c10? capacitors should I have used, 22pf or 100pf... I think one of them is rev-a and the other is rev-c.
My main problem is unfortunately I am getting a bit of hum. I'm not really surprised by this, because I was not planning on using having a volume control in the amp, then I changed my mind and added a stepped attenuator. Problem was there was no room left in the enclosure so its right next to the transformer. I got a lot of hum earlier, but then I seperated the input grounds (they were connected at the stepped attenuator), and most of it dissapeared, only a bit left in the left channel... By moving the leads from the attenuator to the left board input I change the amount of hum, so it appears that this is where most of the hum is occuring.
edit: I also noticed now that now the hum increases as I increase the volume, wereas before it was constant.
I am not if there is much I can do about this as by the enclosure design it has to pass over or right next to the transformer and all the power leads... unless i route it externally... any tips Ive never dealt with this kind of stuff before. Is there anyway I can shield this lead? My last resort is to remove the stepped attenuator (good excuse to make a preamp I guess 🙂 ) but I want to try everything else first.
anyway a couple of other newbie questions that I should have asked BEFORE I built it, one of te resistors was 220ohm on the pcb and a 47ohm was supplied, was it r42 maybe? Is this correct... secondly which of the c10? capacitors should I have used, 22pf or 100pf... I think one of them is rev-a and the other is rev-c.
My main problem is unfortunately I am getting a bit of hum. I'm not really surprised by this, because I was not planning on using having a volume control in the amp, then I changed my mind and added a stepped attenuator. Problem was there was no room left in the enclosure so its right next to the transformer. I got a lot of hum earlier, but then I seperated the input grounds (they were connected at the stepped attenuator), and most of it dissapeared, only a bit left in the left channel... By moving the leads from the attenuator to the left board input I change the amount of hum, so it appears that this is where most of the hum is occuring.
edit: I also noticed now that now the hum increases as I increase the volume, wereas before it was constant.
I am not if there is much I can do about this as by the enclosure design it has to pass over or right next to the transformer and all the power leads... unless i route it externally... any tips Ive never dealt with this kind of stuff before. Is there anyway I can shield this lead? My last resort is to remove the stepped attenuator (good excuse to make a preamp I guess 🙂 ) but I want to try everything else first.
So i'm round at my sisters place at the moment to take pics. I ask, "do you have a screwdriver"? I get the reply "no, we keep them in my husbands car". Doh
So no inside pics at the moment, maybe tomorrow.
http://img516.imageshack.us/img516/3692/amp33yr.jpg?
http://img516.imageshack.us/img516/2996/amp27js.jpg?
http://img516.imageshack.us/img516/2897/amp10fp.jpg?
So no inside pics at the moment, maybe tomorrow.
http://img516.imageshack.us/img516/3692/amp33yr.jpg?
http://img516.imageshack.us/img516/2996/amp27js.jpg?
http://img516.imageshack.us/img516/2897/amp10fp.jpg?
MegaMe-
RevC uses the 22pF cap (100pF is for RevA and mounts differently). The R42 issue was discussed a bit in a previous post, but Mauro recommended a switch to something under 100ohms after the boards were in production. So the 47R replaces the 220R.
As for the noise, I think it's either you have the input leads backward where they attach to the board (just possible) or you are getting hum from your trafo (likely). You can try using shielded signal cable, but the better solution would be to keep the signel wires away from the trafo and power wires.
RevC uses the 22pF cap (100pF is for RevA and mounts differently). The R42 issue was discussed a bit in a previous post, but Mauro recommended a switch to something under 100ohms after the boards were in production. So the 47R replaces the 220R.
As for the noise, I think it's either you have the input leads backward where they attach to the board (just possible) or you are getting hum from your trafo (likely). You can try using shielded signal cable, but the better solution would be to keep the signel wires away from the trafo and power wires.
Hi MegaMe, can you shoot a PIC or two of the guts. 🙂 Might be able to help you out with your hum that way. 🙂 Good work getting as far as you have, especially for a first amp. Very ambitious, I think in the end you will be happy.
okay so I took some more pics... having said that though I am pretty sure that I will have to remove the stepped attenuator, and that will remove the hum. I did a quick test where I bypassed the stepped attenuator and there was no hum... I knew I was bieng a bit optimistic trying to put it in in the first place. Only problem with that is that I will have to come up with a badge or a big led or something to fill in the hole drilled in the front. I might try rewiring the transformer though to get the power a bit away from the attenuator to see if that makes a difference.
pics: (sorry about the size)
http://img509.imageshack.us/img509/618/amp50ol.jpg?
http://img509.imageshack.us/img509/6870/amp41uk.jpg?
http://img509.imageshack.us/img509/2498/amp63yn.jpg?
if there is anything in particular you want to see i can easily take more pics.
edit: btw I cant really comment about the sonics yet as the only speakers I've used with it in testing so far really need a "sub" to fill in the low end (and most ofthe middle as well 🙄 ), except to say I'm hearing big problems with my (temporary) pc soundcard at the moment, which was something I previously only noticed significantly with my headphones.
pics: (sorry about the size)
http://img509.imageshack.us/img509/618/amp50ol.jpg?
http://img509.imageshack.us/img509/6870/amp41uk.jpg?
http://img509.imageshack.us/img509/2498/amp63yn.jpg?
if there is anything in particular you want to see i can easily take more pics.
edit: btw I cant really comment about the sonics yet as the only speakers I've used with it in testing so far really need a "sub" to fill in the low end (and most ofthe middle as well 🙄 ), except to say I'm hearing big problems with my (temporary) pc soundcard at the moment, which was something I previously only noticed significantly with my headphones.
Hi MegaMe,
Fisrt you did not do a bad job for your first amp. 🙂
Now some things to fix:
1) Your signal wire are way toooooo loooooong. 🙂 They should take as short and direct rout to the PCB as possible, also twist the in GND and in SIGNAL wire togther 5 or 6 turns per inch at least as from the input jack to the PCB.
2) You are running low volatge signal wire right next to high voltage mains wires which sort of relates to #1. Keep all of your Trafo wire as far from signal wires as possible.
3) (related to #1 and #2) You are running you signal wires too close to the trafo itself and running them through a spot where they could be influenced by the magnetic leakage and EMI from the trafo.
All of the above are likely factors as to why you are getting your humm.
My recommendation since you case is so small is that you keep the signal wires as short as possible by not using any sort of preamp, attentuator or potentiometer inside that case. Instead build a seperate active or passive preamp and run your wires outside the amp. 🙂
Something else to try. See if you can find some shielded wire, or fashion a shield for your signal wires from foil with the foil conneced to GND. It also wouldn't hurt to use a bit heavier gage wire for your signals, though its not a huge deal as long as they are short.
Keep at it. It will be singing sweetly soon. 😀
Cheers!
Russ
Fisrt you did not do a bad job for your first amp. 🙂
Now some things to fix:
1) Your signal wire are way toooooo loooooong. 🙂 They should take as short and direct rout to the PCB as possible, also twist the in GND and in SIGNAL wire togther 5 or 6 turns per inch at least as from the input jack to the PCB.
2) You are running low volatge signal wire right next to high voltage mains wires which sort of relates to #1. Keep all of your Trafo wire as far from signal wires as possible.
3) (related to #1 and #2) You are running you signal wires too close to the trafo itself and running them through a spot where they could be influenced by the magnetic leakage and EMI from the trafo.
All of the above are likely factors as to why you are getting your humm.
My recommendation since you case is so small is that you keep the signal wires as short as possible by not using any sort of preamp, attentuator or potentiometer inside that case. Instead build a seperate active or passive preamp and run your wires outside the amp. 🙂
Something else to try. See if you can find some shielded wire, or fashion a shield for your signal wires from foil with the foil conneced to GND. It also wouldn't hurt to use a bit heavier gage wire for your signals, though its not a huge deal as long as they are short.
Keep at it. It will be singing sweetly soon. 😀
Cheers!
Russ
Yeah I agree with all of that, which is why am considering removing the stepped attenuator... With the rca's where they are, it should make the signal wires much shorter and away from any power stuff. However, just messing around with the placement of the signal wires I have been able to get the hum pretty much an acceptable level . Now my head has to be right next to the speakers for me to hear any hum. I did this by running one of the signal wires through the hole in the transformer... No idea why this reduced the hum so much, but it did...
I plan to use this an amp for pc speakers which I plan to build in the new year, looking at the modula mt for their apparent performance and that the dayton drivers are shielded. At the moment though, the noise from the pc fans completely overwhelms the hum, so the hum is not really a big issue for me any more. Its actually pretty rediculous, I have power wires 3mm away from the top of the stepped attenuator, the signal wires touching the insulation of the power wires, and touching the transformer, and I think the hum is acceptable 😱
Its a pity though I don't currently have any speakers able to do this amp justice... Timeto get back to building I think
I plan to use this an amp for pc speakers which I plan to build in the new year, looking at the modula mt for their apparent performance and that the dayton drivers are shielded. At the moment though, the noise from the pc fans completely overwhelms the hum, so the hum is not really a big issue for me any more. Its actually pretty rediculous, I have power wires 3mm away from the top of the stepped attenuator, the signal wires touching the insulation of the power wires, and touching the transformer, and I think the hum is acceptable 😱
Its a pity though I don't currently have any speakers able to do this amp justice... Timeto get back to building I think
I have to say , I was very surprised that my amp ended up quiet, as before I boxed it, it was quite hummy...
Not sure the boxed helped as much as the proper sized power wires I used in the box, both channels of REV C fitted in 12 x 13 x 14 cm, including the heatsink, with 2 pots (couldn't get dual at the time) and power switch, and then take into acount that it is constructed of 16mm oak as well... there was only enough space to route the wirering past the edge of the PCB. Its kinda the same size as one of Franz's valve GC's.
Only thing that changed between prototype rev c and boxed one, was that I used the nice RG58 signal cable and 2mm copper wire he sent me for power cables, that Rudi sent me.
Not sure the boxed helped as much as the proper sized power wires I used in the box, both channels of REV C fitted in 12 x 13 x 14 cm, including the heatsink, with 2 pots (couldn't get dual at the time) and power switch, and then take into acount that it is constructed of 16mm oak as well... there was only enough space to route the wirering past the edge of the PCB. Its kinda the same size as one of Franz's valve GC's.
Only thing that changed between prototype rev c and boxed one, was that I used the nice RG58 signal cable and 2mm copper wire he sent me for power cables, that Rudi sent me.
Hi folks,
This is probably a dump question. Can LM3875 be used in this schematic (minus the mute) instead of LM3886? Will there be any changes to the component values? As a matter of fact, can other 'gain chips' be coupled with LM318 this way to improve the sonic performance?
Regards,
KK
This is probably a dump question. Can LM3875 be used in this schematic (minus the mute) instead of LM3886? Will there be any changes to the component values? As a matter of fact, can other 'gain chips' be coupled with LM318 this way to improve the sonic performance?
Regards,
KK
Hi Nordic,
Yes. What I don't know is if there would be any changes in component values, given that the 3875 and 3886 specs are not identical.
Regards,
KK
Yes. What I don't know is if there would be any changes in component values, given that the 3875 and 3886 specs are not identical.
Regards,
KK
Well, been toying with the idea too, can't see why it wouldn't work, but then, I'm not the best qualified to give you an answer...
I see both chips used with interchangeable feedback setups, so that part I'm sure will do... of course you will be limited to driving 8 ohm loads.
I also prefer the 75 to 86... in fact I just picked up another 2 at RS 10 minutes ago.
I see both chips used with interchangeable feedback setups, so that part I'm sure will do... of course you will be limited to driving 8 ohm loads.
I also prefer the 75 to 86... in fact I just picked up another 2 at RS 10 minutes ago.
pwr_aux
Hi
This is my first post on this forum. I have built the amp and it looks real nice, well at least the pcb does but I cannot figure out what connects to the pwr-aux pins. I have built many amps but am baffled by this. Crumbs of information much appreciated. noob Q, sorry
thanks in advance
Hi
This is my first post on this forum. I have built the amp and it looks real nice, well at least the pcb does but I cannot figure out what connects to the pwr-aux pins. I have built many amps but am baffled by this. Crumbs of information much appreciated. noob Q, sorry
thanks in advance
Re: pwr_aux
Those pins exists on the original REV A Stereo PCBs and exist to drive optional things like various LEDs and such. They do not need to be connected to anything. 🙂 Just leave them open.
flodge said:
Those pins exists on the original REV A Stereo PCBs and exist to drive optional things like various LEDs and such. They do not need to be connected to anything. 🙂 Just leave them open.
BTW I'd just like to thank Russ and Brian for their great kit... seems great value to me and the individual labels on all parts and the time consuming way its all packaged together made it easy for newbies like me to put together... I cant help wondering if it would be faster for you to just build the boards yourselves rather than putting on all those labels 🙂
An update to my amp more fiddling has removed all the hum, at least with these lowish efficiency speakers. Its sounding great even with these bassless speakers and terrible source... So I think at the moment I'll leave it as is and wont bother removing the stepped attenuator... I'm just going to listen to the music 🙂 (and build speakers and search the digital forum for dacs 😀 )
An update to my amp more fiddling has removed all the hum, at least with these lowish efficiency speakers. Its sounding great even with these bassless speakers and terrible source... So I think at the moment I'll leave it as is and wont bother removing the stepped attenuator... I'm just going to listen to the music 🙂 (and build speakers and search the digital forum for dacs 😀 )