New to this thread...
Dear Peter,
Just received my kit today (Rui Lourenco from Portugal), I have a big question about capacitors, read quite a few posts now, but still some doubts remain.
It seems that one of the best combinations is using 100uf N Black Gates near the chips and no caps on the rectifier, correct? Now it's quite impossible to get these BG caps at reasonable prices. I have quite sensible >95db speakers, and was thinking to use 100uF Elna Cerafines near the chip, and 2.200uF Nichicon Gold Tune on the rectifiers, any comments?
Would appreciate your feedback.
Many thanks and regards,
Dear Peter,
Just received my kit today (Rui Lourenco from Portugal), I have a big question about capacitors, read quite a few posts now, but still some doubts remain.
It seems that one of the best combinations is using 100uf N Black Gates near the chips and no caps on the rectifier, correct? Now it's quite impossible to get these BG caps at reasonable prices. I have quite sensible >95db speakers, and was thinking to use 100uF Elna Cerafines near the chip, and 2.200uF Nichicon Gold Tune on the rectifiers, any comments?
Would appreciate your feedback.
Many thanks and regards,
You can read my comments about caps here:
http://www.diyaudio.com/forums/digi...gate-caps-out-production-so-2.html#post574431
http://www.diyaudio.com/forums/chip...ut-any-comments-suggestions-8.html#post581230
BG N 100/50 alone produced the best sonics, although with certain limitations. While I was impressed by them initially, in a long run I was missing the bass and slight humming was noticeable. So later I started using additional BG STD 1000/50 at the rectifiers. And that's stiill my first choice. As to other caps, like Cerafines and old Tunes, I can't comment as I never tried them. They might be fine though.
http://www.diyaudio.com/forums/digi...gate-caps-out-production-so-2.html#post574431
http://www.diyaudio.com/forums/chip...ut-any-comments-suggestions-8.html#post581230
BG N 100/50 alone produced the best sonics, although with certain limitations. While I was impressed by them initially, in a long run I was missing the bass and slight humming was noticeable. So later I started using additional BG STD 1000/50 at the rectifiers. And that's stiill my first choice. As to other caps, like Cerafines and old Tunes, I can't comment as I never tried them. They might be fine though.
Hi there Peter.
I also got my kit on Thursday (LM4780) and I'm also from Portugal. Nice coincident. And I have a few questions.
Please excuse if they are so simple. But I'm trying to learn electronics while doing this projects.
1-The schematics say R6/R7 is 270R but the ones I got in the package are 222.
2-Is it possible to use a single PSU board with e single transformer and power to AMP boards? I wanted to use a 2*25V 300VA PSU to drive the two amp boards at 120w each. If the answer is yes how should I do the connections and star grounding? Can I follow the instructions you have for the LM3875 kit?
I hope to be enjoying good music with your fine kit soon.
Thanks
I also got my kit on Thursday (LM4780) and I'm also from Portugal. Nice coincident. And I have a few questions.
Please excuse if they are so simple. But I'm trying to learn electronics while doing this projects.
1-The schematics say R6/R7 is 270R but the ones I got in the package are 222.
2-Is it possible to use a single PSU board with e single transformer and power to AMP boards? I wanted to use a 2*25V 300VA PSU to drive the two amp boards at 120w each. If the answer is yes how should I do the connections and star grounding? Can I follow the instructions you have for the LM3875 kit?
I hope to be enjoying good music with your fine kit soon.
Thanks
R6/R7 values are not critical. I presently supply 220R.
With a single transformer, a single PS board is recommended, I described preferred wiring method here: http://www.diyaudio.com/forums/audi...-kit-building-instructions-4.html#post1518369
With a single transformer, a single PS board is recommended, I described preferred wiring method here: http://www.diyaudio.com/forums/audi...-kit-building-instructions-4.html#post1518369
I have finished the kit doing what I asked before.
The LM4780 is now working
But I have some questions.
1 - In my system ( LM4780+SqueezeBox V3+Celestion F20) I really like the sound. But when I tested at my fathers place ( LM4780+SB V3+Martin Logan Clarity) there was a distinct sound coming from the speakers. Something like gre gre gre gre. Any idea what the problem may be?
2 - It gets really hot. Today I left it just turned on for some hours and when I went to see the temperature with a IR thermometer the temp was 71 Celsius! Is this normal? If yes I really need to add some heatsinks to the side of the casing.
As you will see from the picture the holes that the case had where not in the best position. Do you guys think problem 1 may be related? I'm thinking of doing a back panel with holes in "proper" locations. Will that help improve the sound?
I really enjoy the amp. And in the last few days I have spent all my free time listening and reading Great product.
The LM4780 is now working
But I have some questions.
1 - In my system ( LM4780+SqueezeBox V3+Celestion F20) I really like the sound. But when I tested at my fathers place ( LM4780+SB V3+Martin Logan Clarity) there was a distinct sound coming from the speakers. Something like gre gre gre gre. Any idea what the problem may be?
2 - It gets really hot. Today I left it just turned on for some hours and when I went to see the temperature with a IR thermometer the temp was 71 Celsius! Is this normal? If yes I really need to add some heatsinks to the side of the casing.
As you will see from the picture the holes that the case had where not in the best position. Do you guys think problem 1 may be related? I'm thinking of doing a back panel with holes in "proper" locations. Will that help improve the sound?
I really enjoy the amp. And in the last few days I have spent all my free time listening and reading
Great product.Attachments
Can you record the gre gre gre and post?
If left on (presumably without a signal) it shouldn't heat up as you describe.
HF instability/oscillation?
Can you get a scope on the output with not signal? Should be dead quiet, if not, maybe the LM is thrashing away at inaudible frequencies? Do both channels heat similarly? Which part was at 71C?
Does it also get as hot if you disconnect the speakers? Try disconnecting just one, then just the other, then both - and see if there's a pattern. What about with different speaker cable or speakers.
Not the same part, but my LM3875 runs dead cold, and quiet.
Best of luck
rivets on aluminum stock: sufficient for ground?
I'm really captivated by the economy of using aluminum channel for a gainclone chassis. I've built two of Peter's kits so far, but I have to admit my case builds have been less than acceptable as far as "good looks". Aluminum channel offers a simplified build as per the instructions of the kit instructions supplied by Peter. My question is this: in building one of Peter's LM3886 kits with an aluminum channel (as per his build example), can I use aluminum rivets to finish off the amp with cheap aluminum stock that I can find locally at Home Depot? My concern is whether or not the rivets would provide the electrical connection necessary for grounding the outside of the case. Thank you for your help.
I'm really captivated by the economy of using aluminum channel for a gainclone chassis. I've built two of Peter's kits so far, but I have to admit my case builds have been less than acceptable as far as "good looks". Aluminum channel offers a simplified build as per the instructions of the kit instructions supplied by Peter. My question is this: in building one of Peter's LM3886 kits with an aluminum channel (as per his build example), can I use aluminum rivets to finish off the amp with cheap aluminum stock that I can find locally at Home Depot? My concern is whether or not the rivets would provide the electrical connection necessary for grounding the outside of the case. Thank you for your help.
give careful consideration to the atmospheric effects on aluminium and it's alloys. Alumimium oxide is a very good electrical insulator.
If the rivet to chassis corrodes to form a slightly more resistive electrical connection then what could be the repercussions?
Imagine a fault current of 1000Apk passing through a group of 10 rivets in parallel, each having developed one milli-ohm of additional resistance. The voltage rise/drop across the connection is only 100mVpk during the fault condition.
What if the insulation value was higher, say 100milli-ohms, then the voltage across the connection would rise to ~10Vpk.
Think of where the Safety Earth is located. How many rivet to chassis joints must the fault current pass across to get to Safety Earth?
This is an example of where it would be wise to secure all chassis components together with dedicated Earthing wires so that every panel is effectively connected to Safety Earth. You will find this inside commercial gear, particularly if one or some panels are loosely held in place.
If the rivet to chassis corrodes to form a slightly more resistive electrical connection then what could be the repercussions?
Imagine a fault current of 1000Apk passing through a group of 10 rivets in parallel, each having developed one milli-ohm of additional resistance. The voltage rise/drop across the connection is only 100mVpk during the fault condition.
What if the insulation value was higher, say 100milli-ohms, then the voltage across the connection would rise to ~10Vpk.
Think of where the Safety Earth is located. How many rivet to chassis joints must the fault current pass across to get to Safety Earth?
This is an example of where it would be wise to secure all chassis components together with dedicated Earthing wires so that every panel is effectively connected to Safety Earth. You will find this inside commercial gear, particularly if one or some panels are loosely held in place.
Thank you Andrew. I was worried about galvanic reactions so I thought I was ok since I was going to use aluminum rivets on aluminum stock. If I'm hearing you correctly, it is the oxidation I may have to worry about. Sounds like a simple grounding wire (copper wire to a non-reactive lug) to all pieces might do the trick. Thanks for your help.
My recent implementation
Just thought you would like to see my recent implementation of this amp.
Front and back panels are from Hifi2000, machined in the case of the back panel to allow connectors mounting.
Inside there is a big copper block that serves as heat sinking for the IC's, whish is then connected to the front panel via heat compound.
Connecting the front and back, 4 machined aluminum pillars. Laterals are 15mm polished 15mm acrylic boards.
Top and bottom are produced by Front Panel Design in Germany.
Separate power supply, using separate 225VA toroidal transformers and 2 rectifier boards. Caps under the boards are 15.000uF Gold Tune Chemicon's.
Cheers,
Just thought you would like to see my recent implementation of this amp.
Front and back panels are from Hifi2000, machined in the case of the back panel to allow connectors mounting.
Inside there is a big copper block that serves as heat sinking for the IC's, whish is then connected to the front panel via heat compound.
Connecting the front and back, 4 machined aluminum pillars. Laterals are 15mm polished 15mm acrylic boards.
Top and bottom are produced by Front Panel Design in Germany.
Separate power supply, using separate 225VA toroidal transformers and 2 rectifier boards. Caps under the boards are 15.000uF Gold Tune Chemicon's.
Cheers,
Attachments
Last edited:
Thanks Wlowes, never thought of using sand, and I have plenty here (leaving near the sea
). Nevertheless I use that black rubber compound you see in one of the photos, behind the boards. It's the same used in several hiend eq. On their chassis.As for the sound, it's really very good.
Cheers.
Dear Giantstairs,
Not really. I do DIY audio for my own private use (or friends), and it's not my intention to do what you propose, sorry.
Cheers.
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