| homer09 |
Brian's out of stock with the current REV B boards and is working on the REV C boards for shipping mid Jan (according to his site).
Any info on what changes the new revision is going to bring? I'm sure we're in for a treat as usual... |
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| grege |
Oh no homer09, I have both Rev A and Rev B now I'll have to buy Rev C to keep my collection of BrianGT PCBs complete. :D
BTW: What I'd really like is a experiementers PCB. Similar to the existing board as far as the LM3875 and caps are concerned but the connectors to the sides and a prototyping area in the middle. I wish I had a tenth of Brian's skills to design and make one. It would be nice if a LM3886 chip could fit as well. Hey, this is probably a good idea for digi01. |
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| m0tion |
| We could always turn this thread into a Revision C wishlist. Perhaps Brian and PD could get some ideas from it. I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about. |
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| steenoe |
| quote: | | I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about. |
That is easely done on the rev.B boards! You actually have four holes for the caps 'onboard'. The zobel network would in either case be mounted at the output of the PSU. Assuming you are talking about the 'high-cap' PSU. See the pic.
Steen. |
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| jackinnj |
| quote: | Originally posted by m0tion
We could always turn this thread into a Revision C wishlist. Perhaps Brian and PD could get some ideas from it. I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about. |
the snubber caps belong on the diode board -- |
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| widman |
| quote: | | That is easely done on the rev.B boards! You actually have four holes for the caps 'onboard'. The zobel network would in either case be mounted at the output of the PSU. Assuming you are talking about the 'high-cap' PSU. See the pic. |
steenoe,
What size/type cap did you use with the snubber?
widman |
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| jackinnj |
| quote: | Originally posted by widman
steenoe,
What size/type cap did you use with the snubber?
widman |
the size of the capacitor is related to the inductance of the secondary of the transformer, and the capacitance of the diode itself (this can be obtained from the manufacturer's data sheet).
when you measure the inductance make sure to short the primary leads. |
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| steenoe |
| quote: | | What size/type cap did you use with the snubber? |
The value of the caps is 100nF as recommended by CarlosFM.
It is generic polyesterfilm caps. You could ofcourse consider more excotic parts, but how much is gained by that?
It is the same type 1oonF caps used at the output of the psu for the Zobelnetwork, as well as for bypass for the 100uF electrolytics on the board. Hope this helps:)
The small caps are not at all implementet as diode-snubbers.
Steen. |
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| jackinnj |
| quote: | Originally posted by steenoe
The value of the caps is 100nF as recommended by CarlosFM.
It is generic polyesterfilm caps. You could ofcourse consider more excotic parts, but how much is gained by that?
It is the same type 1oonF caps used at the output of the psu for the Zobelnetwork, as well as for bypass for the 100uF electrolytics on the board. Hope this helps:)
The small caps are not at all implementet as diode-snubbers.
Steen. |
100nF is a number pulled out of thin air -- with any value this high you dissipate energy through the snubber according to E= 1/2 (C*V^2) -- (not that it's a lot of joules, it's just a pointless waste of energy).
here's a homework assignment: using 100 uH for the secondary inductance and 100pf for the diode capacitance of an MUR860 at 30V determine the correct value of a snubber --
http://www.hagtech.com/pdf/snubber.pdf |
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| homer09 |
| Well this thread just totally went off topic... back to the REV C boards if possible |
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| grege |
hi homer09,
Any post NOT from BrianGT or Peter Daniel are going to be off topic, including this one. ;)
and... I think BrianGT and Peter Daniel are now "smart" enough not to get involved in heated technical discussions that go round and round in circles. :smash: I use to love those threads. :bawling:
I'm sure they will deliver a good product. :angel: |
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| dw1narso |
Hi Greg,
>It would be nice if a LM3886 chip could fit as well.
actually with an effort, LM 3886 can be fit also to the current PCB (rev A or B)... from the datasheet you can see that the first 4 pins of both chip is the same:
- no problem for the first 4 pin
- un-used the pin 5 on 3886 (since it is exactly the same as pin 1, as V+).
- Pin 6 is the same on both chip.
- don't connect pin 7 on 3886 to the board. Bend it out then run a wire from it to the star ground point.
- don't connect pin 8 on 3886 to the board. Bend it out then run a wire from it through mute resistor to the V- (pin 4, or somewhere else the same V- referenced on the board)
- bend pin 9 of 3886 to the board hole position of pin 8 of 3875 (this is easy)
- bend pin 10 of 3886 to the board hole position of pin 7 of 3875 (this is a bit diffcult). OR, you can also bend it out and wire a jumper to the hole position of pin 7 of 3875, or directly to the meeting point of R1 & R2 on the board (solder directly to the meeting point... the resistor leg)
Sounds complicated :) but actually easier to do than write... :)
My real wonder is actually whether LM3886 in Non-inverted mode will sounds better than LM3875. (Just my curiousity, despite the difference in power and current output, I seems mostly see LM3886 configured in inverted mode while LM3875 mostly configured in NI mode. So I figure out those must be an optimal setup for both the chips.)
Regards,
---
David |
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| BrianGT |
Hello,
As for the revision 3 boards (last ones were called revision 2), the current idea is that the changes will be minor, but if you have suggestions, please post them in this thread, and I will consider them.
Here is the current ideas for modification:
- slight modification for placement of zobel resistor to maximize ground plane
- modification of signal ground -> output ground trace to optimize ground interactions
As for the snubber capacitors, they can be soldered directly to the pins of the diodes, on the bottom of the pcb.
As for the idea for the LM3886 compatibility, it would be easier to just make a new pcb for it. I actually worked on one quite a few months ago, but there didn't seem to be as much interest in the LM3886. I could revive the design in the same fashion as the LM3875 boards if people are interested.
Happy Holidays to all. I have caught with the US orders and all but 1 are not shipped out, and I have started working on the remaining International orders. I should be completely caught up by the end of the week.
Also, I was straightening up my parts bins last weekend, and found enough components for 5 LM3875 premium kits. If people are interested, I will sell them for $75 each + shipping (for stereo version). Drop me a mail if you want to get one of the last kits.
--
Brian |
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| peranders |
Good to change the ground, now it will be perfect. You might also add an instruction for patching the signal ground at the present pcb's. My simple calculation points to an increase of the distortion of 0.02%. It my not be that much but with this minor change you have done what it's possible to direct the ground currents where they should go and not go.
Brian, I think you should consider to add every part on the pcb's which needs to be there becasue it will be easier for the builder to have holes to put the parts in, less sources to problems.
I'm quite sure you can get an interest for LM3886 also. If you do, add the mute option! If digi01 make and sell LM3886 pcb's, so can you :nod:
Brian, please add good schematics for your projects also! |
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| digi01 |
Brian,another suggestion is the ability of bridging & parallel.do you mark out this performance in #3?
good wishs,happy holiday.
digi |
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| percy |
This is more of a question but it could be a suggestion too.
I haven't yet built Brian's GC but looking at the manual I noticed that PCBs come joined, but scored, so that they can be snaped apart. I am not sure how the optimal implementation is intended to be - in the sense that - is it better to just leave the boards joined and use small jumper wires going from the rectifier board to the amp board ?
Otherwise if you break them up then I wonder if the long snaky wires running from the transformer to the rectifier board and then from the rectifier board to the amplifier board have anything to do with the power supply decoupling issues that arise when using high value filter caps, and apparently can be taken care of by the new(Carlosfm) impedance compensation/decoupling arrangement.
In other words would it help to have everything - i.e the psu and amp - onboard as one unit ? |
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| Gerben |
Brian,
I would like to buy 2 premium kits for one stereo pair. Since e-mail tru this forum doesn't seem to get across i'm also posting my interest over here.
Please let me know if you have received my message?
Regards,
Gerben |
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| BrianGT |
I do have a few premium LM3875 stereo kits left. They will be $75 each, and include:
1 - revision 2 pcb set, containing 2 main boards and 2 rectifier boards
2 - LM3875TF chips
4 - Caddock MK132 21.5k resistors
2 - Riken 680ohm 0.5w resistors
2 - Caddock MK132 220ohm resistors
4 - Panasonic FC 1500uF caps
2 - Blackgate N 4.7uF non-polar caps (for rectifier board)
8 - MUR860 diodes (for rectifier board)
2 - 0.1uF polypropylene caps (for zobel network)
2 - 2.7 ohm resistors (for zobel network)
Shipping is $6 for US, and $11 for international. Drop me an e-mail if you are interested. I am not going to put up an order page, as I only have 4 kits left right now.
The bold entries indicate the upgraded components over the standard kits.
--
Brian |
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| Evilsizer |
| how many of the kits you have left brianGT? |
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| BrianGT |
Here is the the revised board so far:
changes:
- added zobel resistor to silkscreen (can be mounted on top or bottom of pcb)
- widened the pin spacing on the zobel resistor to allow for larger resistors and more continuity on the groun plane
- changed the connection for the signal ground (SG) and power ground (PG) connection [credit to PA's suggestion for this minor change]
- added chipamp.com to the silkscreen
Let me know if you have any more suggestions. The difference in this rev.3 from the last rev.2 design is quite minimal, mostly cosmetic.
Let me know if you have any more features that you would like to have added to this pcb, as I am looking to order some relatively soon.
I still have rev.1 and rev.2 boards left, and will put up a clearance page soon to get rid of my stock.
LM3886 board here:
http://www.diyaudio.com/forums/show...4825#post554825
Also, let me know if you have any suggestions for the LM4780 board.
--
Brian |
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| m0tion |
| Did you decide against the snubber then? |
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| BrianGT |
| quote: | Originally posted by m0tion
Did you decide against the snubber then? |
I haven't finalized anything yet. What would need to be added to allow for the snubber setup? I haven't made any changes to the rectifier pcb yet.
Also, would anyone be interested in premium kits again with the Riken/Caddock resistors?
--
Brian |
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| m0tion |
At the bottom is a link to Carlos' schematic. Looks like you could make all of the changes on the rectifier PCB, but it may require a slightly larger board. You'd need to add a place for the 2.2k resistor, then the 100nF cap, and the 2.2k->100nF cap. You would then replace the 1500uF Panasonic cap you're currently using with a ~10000uF capacitor, which may or may not require changing the footprint for the capacitors on the amp PCB. Heh, a pain I know, but this is now pretty widely accepted as an improvement that yields [B]significant[/B increases in sound quality.
Quote from Peter Daniel regarding sound quality improvements:
"...last week I tried Carlos' suggestion with regards to snubbers in GC supply (and big caps) and right away I liked the results. It is better even comparing to battery supply I was using up untill now. There is more bass slamm but at the same time the mids and highs are not veiled by anything (like it was in a case of regulators). There is more midrange presence and dynamics, but also what suprises me, more micro detail, something I wouldn't really expect."
I suppose it should also be noted that this would probably increase the price of a kit buy a few dollars ($5?). Possibly this Panasonic capacitor could be used in place of the 1500uF?
I personally think this would have a much larger improvement on over-all sound quality than the premium parts and is also a good deal cheaper. Just something to think about...
http://www.diyaudio.com/forums/attachment.php?s=&postid=533226&stamp=1103055025 |
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| BrianGT |
| quote: | Originally posted by m0tion
At the bottom is a link to Carlos' schematic. Looks like you could make all of the changes on the rectifier PCB, but it may require a slightly larger board. You'd need to add a place for the 2.2k resistor, then the 100nF cap, and the 2.2k->100nF cap. You would then replace the 1500uF Panasonic cap you're currently using with a ~10000uF capacitor, which may or may not require changing the footprint for the capacitors on the amp PCB. Heh, a pain I know, but this is now pretty widely accepted as an improvement that yields [B]significant[/B increases in sound quality.
Quote from Peter Daniel regarding sound quality improvements:
"...last week I tried Carlos' suggestion with regards to snubbers in GC supply (and big caps) and right away I liked the results. It is better even comparing to battery supply I was using up untill now. There is more bass slamm but at the same time the mids and highs are not veiled by anything (like it was in a case of regulators). There is more midrange presence and dynamics, but also what suprises me, more micro detail, something I wouldn't really expect."
I suppose it should also be noted that this would probably increase the price of a kit buy a few dollars ($5?). Possibly this Panasonic capacitor?
I personally think this would have a much larger improvement on over-all sound quality than the premium parts and is also a good deal cheaper. Just something to think about...
http://www.diyaudio.com/forums/attachment.php?s=&postid=533226&stamp=1103055025 |
Sounds like an interesting idea. I will definately look into it.
--
Brian |
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| SheldonD |
IF you are changing the PS and the chipamp PCB, why not combine them into one board. this way there is more flexibility
about the real estate and would still have a compact layout.
It would require then about the same space as current both PCBs
This would also reduce the number of solder holes
vote for mute function to have room for cap for delay, as well as snubber circuit, instead of expensive premium components, as was suggested.. |
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| BrianGT |
| quote: | Originally posted by SheldonD
IF you are changing the PS and the chipamp PCB, why not combine them into one board. this way there is more flexibility
about the real estate and would still have a compact layout.
It would require then about the same space as current both PCBs
This would also reduce the number of solder holes
vote for mute function to have room for cap for delay, as well as snubber circuit, instead of expensive premium components, as was suggested.. |
The reason that the rectifier board and amp board are seperate pcbs is so that they can be seperated from each other for better shielding, and also allow for a stereo configuration to be used with 2 amp boards per rectifier board.
I will work up a new rectifier board for the snubber setup.
--
Brian |
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| homer09 |
| I think keeping the rectifier boards separate from the amp board is the more flexible layout for people that want to either shield PSU from amp circuit or build PSU into a separate case. Joining them together would limit the possibilities this kit offers. |
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| SheldonD |
Homer09 and Brian:
You are so right about keepijng PS and amp PCB apart. Far more advantages than the other way.
It was not a good idea, at all. |
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| BrianGT |
| quote: | Originally posted by SheldonD
Homer09 and Brian:
You are so right about keepijng PS and amp PCB apart. Far more advantages than the other way.
It was not a good idea, at all. |
The option will still be there to keep them together as done by this person:
http://www.briangt.com/gallery/nigc-maarten/board
--
Brian |
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| m0tion |
| I'd have to agree, I think allowing the ability to seperate the boards outways the advantage of one consolidated smaller PCB. These amps are such a bargain I know I personally wouldn't mind chipping in a few extra dollars for the larger sized boards these modifications would require. That is, of course, only my personal opinion. |
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| BrianGT |
| quote: | Originally posted by m0tion
At the bottom is a link to Carlos' schematic. Looks like you could make all of the changes on the rectifier PCB, but it may require a slightly larger board. You'd need to add a place for the 2.2k resistor, then the 100nF cap, and the 2.2k->100nF cap. You would then replace the 1500uF Panasonic cap you're currently using with a ~10000uF capacitor, which may or may not require changing the footprint for the capacitors on the amp PCB. Heh, a pain I know, but this is now pretty widely accepted as an improvement that yields [B]significant[/B increases in sound quality.
Quote from Peter Daniel regarding sound quality improvements:
"...last week I tried Carlos' suggestion with regards to snubbers in GC supply (and big caps) and right away I liked the results. It is better even comparing to battery supply I was using up untill now. There is more bass slamm but at the same time the mids and highs are not veiled by anything (like it was in a case of regulators). There is more midrange presence and dynamics, but also what suprises me, more micro detail, something I wouldn't really expect."
I suppose it should also be noted that this would probably increase the price of a kit buy a few dollars ($5?). Possibly this Panasonic capacitor could be used in place of the 1500uF?
I personally think this would have a much larger improvement on over-all sound quality than the premium parts and is also a good deal cheaper. Just something to think about...
http://www.diyaudio.com/forums/attachment.php?s=&postid=533226&stamp=1103055025 |
Here is a quick workup of a rectifier board that you mentioned above. Let me know what you think.
The placements are for the 10000uF caps you mentioned, and the larger 30mm will fit as well, with replacement of R1 and R2 on the bottom of the pcb.
--
Brian |
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| BrianGT |
Here is how the boards would hook up to each other (LM3886 board shown here has the same side pinout:
--
Brian |
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| m0tion |
Brian:
You work quickly =). Looks very good, I think this would work very well. One possible concern is that this does make the rectifier PCB much larger and this would raise the cost of the PCB sets considerably I think (maybe I'm wrong here). I believe Carlos' design used the 10000uF capacitors as the only filtering capacitors, but your design seems to use them along with the existing 1500uF capacitors. I think a lot of space could be saved if you moved the 10000uF capacitors onto the amplifier PCB (making that PCB slightly larger) in the place of the 1500uF capacitors. I think the other components could still remain on the rectifier PCB. This would change the order in which the components appear in parallel (instead of R1->C1->C2->(C3-R2), it would be R1->C2->(C3-R2)->C1, if that makes sense), but I don't think that matters electrically speaking. Please correct me if there is some glaringly obvious reason why this won't work, but it makes sense to me and would make the PCB set much smaller. Also, if this post isn't clear please tell me and I'll try to make some sort of visual representation of my idea when I get home. Thanks for your great effort! |
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| m0tion |
| I just noticed that you changed the LM3886 PCB layout in that picture compared to the picture you posted earlier today in your LM3886 thread (in the upper right hand corner you moved a resistor and added a capacitor). Were these changes due to the snubber addition? I'm guessing not, but I thought I'd ask anyway. |
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| BrianGT |
| quote: | Originally posted by m0tion
Brian:
You work quickly =). Looks very good, I think this would work very well. One possible concern is that this does make the rectifier PCB much larger and this would raise the cost of the PCB sets considerably I think (maybe I'm wrong here). I believe Carlos' design used the 10000uF capacitors as the only filtering capacitors, but your design seems to use them along with the existing 1500uF capacitors. I think a lot of space could be saved if you moved the 10000uF capacitors onto the amplifier PCB (making that PCB slightly larger) in the place of the 1500uF capacitors. I think the other components could still remain on the rectifier PCB. This would change the order in which the components appear in parallel (instead of R1->C1->C2->(C3-R2), it would be R1->C2->(C3-R2)->C1, if that makes sense), but I don't think that matters electrically speaking. Please correct me if there is some glaringly obvious reason why this won't work, but it makes sense to me and would make the PCB set much smaller. Also, if this post isn't clear please tell me and I'll try to make some sort of visual representation of my idea when I get home. Thanks for your great effort! |
I didn't want to change the order of the components, but I did make the layout more compact after the initial layout:
| quote: | Originally posted by m0tion
I just noticed that you changed the LM3886 PCB layout in that picture compared to the picture you posted earlier today in your LM3886 thread (in the upper right hand corner you moved a resistor and added a capacitor). Were these changes due to the snubber addition? I'm guessing not, but I thought I'd ask anyway. |
The resistor and cap are for the muting circuit. The resistor sets the current for the mute pin, and the cap is for a turn-on/turn-off delay.
If I was to use the snubber rectifier board, I will be adding pads for the smaller decoupling caps, instead of the 1500uF. The design would allow for both,
--
Brian |
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| grege |
Brian,
Creating those red T traces for filter caps is bad. You'd be better off with bend traces instead.
BTW: Just an opinion from someone who have never made a pcb in his life. :D |
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| m0tion |
| Oh, really excellent. I hadn't thought about this, but I do think it's important that the snubber be optional. Good idea about the decoupling cap or the regular filter caps. Kudos on the PCB compression as well. |
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| BrianGT |
| quote: | Originally posted by m0tion
Oh, really excellent. I hadn't thought about this, but I do think it's important that the snubber be optional. Good idea about the decoupling cap or the regular filter caps. Kudos on the PCB compression as well. |
Here is what I referring to with regards to allowing both setups:
This way the .1uF decoupling can be installed along with a 100uF cap (100uF would fit stretched out to fit in the larger spacings). If the standard 1500uF setup is desired, than the extra holes would be ignored (or even stuffed on the bottom side for experimentation).
--
Brian |
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| BrianGT |
I updated the picture above a few posts of the 2 boards together to show the current LM3886 with the extra pads for decoupling caps. This should show what I am referring to. Here it is again:
The total size of the 2 boards together is 1.2" for the amp, and 2.4" for the rectifier board = 3.6", and for a 2 channel pcb, it would be 7.2", which is still reasonable. What do you think?
--
Brian |
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| m0tion |
Everything looks wonderful to me, I can't think of anything to make it better.
The LM3875 and LM3886 seem like pretty similar chips to me. With you doing your new LM3886 boards it seems redundant tohave an LM3875 board available as well. Perhaps you should pick the better of the two chips and simply focus on that, unless there is a big difference between them that I don't understand. I just don't think it makes sense to have two choices available that are so similar. |
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| BrianGT |
| quote: | Originally posted by m0tion
Everything looks wonderful to me, I can't think of anything to make it better.
The LM3875 and LM3886 seem like pretty similar chips to me. With you doing your new LM3886 boards it seems redundant tohave an LM3875 board available as well. Perhaps you should pick the better of the two chips and simply focus on that, unless there is a big difference between them that I don't understand. I just don't think it makes sense to have two choices available that are so similar. |
My plan is to get another batch of the standard LM3875 boards made with the small modifications made, and a new batch of boards made with the LM3886 and the snubber setup, and I will compare the two. With the board pinouts being the same for hooking up connections, the LM3875 boards will work together well with the rectifier board on the LM3886 pcb, so I can also try the new power supply setup with the LM3875.
--
Brian |
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| sbolin |
| Brian, is the LM3886 board the same size as the rev B LM3885 board? Just wondering if it will fit in one of Peter's chassis without modification. The PS board isn't the same, of course, but I think it should still fit in the chassis, just need to drill new mounting holes. Looks very nice to my untrained eye, can't wait to see/hear the final product. |
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| BrianGT |
| quote: | Originally posted by sbolin
Brian, is the LM3886 board the same size as the rev B LM3885 board? Just wondering if it will fit in one of Peter's chassis without modification. The PS board isn't the same, of course, but I think it should still fit in the chassis, just need to drill new mounting holes. Looks very nice to my untrained eye, can't wait to see/hear the final product. |
The LM3886 amplifier board is exactly the same size as the LM3875 board. The mounting holes are the same as well, so it will work in peter's chassis.
--
Brian |
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| sbolin |
| One last question, Brian. I am now confused a bit, I was thinking I was in the LM3886 thread. Will there be a LM3875 rev C board and the LM3886 board? So two separate boards? |
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| BrianGT |
| quote: | Originally posted by sbolin
One last question, Brian. I am now confused a bit, I was thinking I was in the LM3886 thread. Will there be a LM3875 rev C board and the LM3886 board? So two separate boards? |
I am going to handle the new LM3886 boards first, and then once I get the order placed and finalized, I will work on getting the LM3875 rev.3 boards done. The changes are quite minor for the rev.3 boards compared to the rev.2 boards, so I would like to see how the LM3886 boards work out first, and possibly build more features into the LM3875 rev.3 pcb set based on this. I still have about 50 rev.2 boards available, and I will take orders for them again soon.
In the end, there will be 3 pcb sets offered, each with 2 amp boards and 2 rectifier boards:
- LM3875
- LM3886
- LM4780
Let me know if you have any more questions.
--
Brian |
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| homer09 |
| If its not too much to ask, any estimates on time for each stage? |
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| sbolin |
Thanks for the quick replies, Brian.
If possible, I would like the rev C board to have the 'standard' PS (like the current rev B board). In the LM3886 thread you mentioned that the LM3886 would be where the new ideas and experiments take place, and I think that is a good idea. I like that board, but for the LM3875 think a simple design is best.
And yes, I'm with homer09...any time tables? |
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| homer09 |
sbolin, i side with you on the time tables, but i would like to see the snubbered power supply for the rev3 boards of the lm3875. and i think im far from being alone on that one. the complexity of the snubber isnt much greater either, only larger caps and extra pair of resistors... :rolleyes:
but anyway, correct me if im wrong brian, you're planning on desiging a rectifier board capable of a snubbered or normal supply right (up to the builder's preference)? |
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| BrianGT |
| quote: | Originally posted by homer09
If its not too much to ask, any estimates on time for each stage? |
| quote: | Originally posted by sbolin
Thanks for the quick replies, Brian.
If possible, I would like the rev C board to have the 'standard' PS (like the current rev B board). In the LM3886 thread you mentioned that the LM3886 would be where the new ideas and experiments take place, and I think that is a good idea. I like that board, but for the LM3875 think a simple design is best.
And yes, I'm with homer09...any time tables? |
The form factor of the LM3875 board will not change, and it will be compatible with new power supply board on the LM3886 set.
As for time frames, if people are interested in the LM3886 boards, I will order them Friday and start taking pre-orders for them.
As for the LM3875 boards, I will sell the remainder of my rev.2 inventory starting within a week, and work on ordering the boards for that after I get the LM3886 boards ordered.
All boards are ordered with a 2 week leadtime.
--
Brian |
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| BrianGT |
| quote: | Originally posted by homer09
sbolin, i side with you on the time tables, but i would like to see the snubbered power supply for the rev3 boards of the lm3875. and i think im far from being alone on that one. the complexity of the snubber isnt much greater either, only larger caps and extra pair of resistors... :rolleyes:
but anyway, correct me if im wrong brian, you're planning on desiging a rectifier board capable of a snubbered or normal supply right (up to the builder's preference)? |
To get the LM3875 with the new snubber power supply, you will have to order the LM3886 pcb set to get the power supply boards to go with the LM3875 amp boards. The snubber power supply boards will be compatible with all previous LM3875 amp boards, so if you already have a built amp, you should be able to swap the power supply boards, and swap the 1500uF caps for a 100uF/0.1uF combination (pads are there for it, see screenshot above in this thread).
The reason that the snubber supply boards won't be included with the LM3875 set is the extra board size, and extra components. If it is determined that this is clearly a better solution, then the board for the LM3875 can be redone again in the future for this, or a stand-alone snubber supply board can be offered, but I would like to take this one step at a time and see how the setup works with the LM3886 boards.
If you are interested in the LM3886 boards with the new snubber power supply, please indicate your interest in the Wiki that I created:
http://www.diyaudio.com/wiki/index....interest+survey
as I will reference this when placing my order for pcbs.
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Brian |
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| sbolin |
| quote: | Originally posted by homer09
sbolin, i side with you on the time tables, but i would like to see the snubbered power supply for the rev3 boards of the lm3875. and i think im far from being alone on that one. the complexity of the snubber isnt much greater either, only larger caps and extra pair of resistors... :rolleyes:
but anyway, correct me if im wrong brian, you're planning on desiging a rectifier board capable of a snubbered or normal supply right (up to the builder's preference)? |
I know adding the snubber isn't that complex, it is actually the size I am more concerned with. I can snubber the current PS board if I want AND have a small board. The PS board for the LM3886 is big whether I snubber it or not, that was all I was getting at. Of course, the boards are cheap, so I may end up ordering the rev B board along with the rev C kit...:confused: if that actually works. Or maybe just order one of the remaining rev B kits and one of the LM3886 kits, just to try it. Sheesh, I still have a LM4780 kit I haven't finished, maybe I better finish that first! :D |
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| BrianGT |
| quote: | Originally posted by sbolin
I know adding the snubber isn't that complex, it is actually the size I am more concerned with. I can snubber the current PS board if I want AND have a small board. The PS board for the LM3886 is big whether I snubber it or not, that was all I was getting at. Of course, the boards are cheap, so I may end up ordering the rev B board along with the rev C kit...:confused: if that actually works. Or maybe just order one of the remaining rev B kits and one of the LM3886 kits, just to try it. Sheesh, I still have a LM4780 kit I haven't finished, maybe I better finish that first! :D |
I will make it more clear when I get everything together. Now, my main focus is getting the LM3886 boards together.
btw: I put up a new LM4780 schematic that makes it clear what component values are which:
http://www.chipamp.com/lm4780.pdf
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Brian |
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| sbolin |
| quote: | Originally posted by BrianGT
I will make it more clear when I get everything together. Now, my main focus is getting the LM3886 boards together.
btw: I put up a new LM4780 schematic that makes it clear what component values are which:
http://www.chipamp.com/lm4780.pdf
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Brian |
Regarding the 4780 schematic: yeaaaa!
Sorry, I posted before I saw your post right before this, so everything is cool. 3875, no snubber, 3886 with snubber. Easy enough to mix and match, too, so that is just great. Thanks for the great goodies. |
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| homer09 |
there's probably an obvious reason why this isnt a good idea, but here goes anyway....
i was thinking, instead of always having PCBs made with 2 amp channels and 2 rectifiers, why not make PCBs with only rectifiers and PCBs with only amp channels? what i mean is, for example, you would order a set of PCBs which have 2x LM3886 channels and 2x LM3875 channels (no rectifiers). Then another set with 2x standard rectifiers and 2x snubbered rectifiers.
Since everything is scored, you could then easily mix and match. And now, a much larger number of possibilities become available (ex. dual mono snubbered LM3886, stereo standard LM3875, etc)
when ordering from Brian, one would have the following variables:
(LM3875 | LM3886) + (dual mono | stereo) + (snubber | standard) + (PCB only | stand. comp | premium comp.)
Or if larger PCBs are better for pricing (when Brian has them made), combine the two sets above (4 channels, 4 rectifiers). If smaller PCBs are better for pricing, separate everything... the possibilities are endless.
just a thought that could possibly better accommodate everyone. :angel:. i guess, the remaining question is: does it accommodate Brian better? |
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| BrianGT |
| quote: | Originally posted by homer09
there's probably an obvious reason why this isnt a good idea, but here goes anyway....
i was thinking, instead of always having PCBs made with 2 amp channels and 2 rectifiers, why not make PCBs with only rectifiers and PCBs with only amp channels? what i mean is, for example, you would order a set of PCBs which have 2x LM3886 channels and 2x LM3875 channels (no rectifiers). Then another set with 2x standard rectifiers and 2x snubbered rectifiers.
Since everything is scored, you could then easily mix and match. And now, a much larger number of possibilities become available (ex. dual mono snubbered LM3886, stereo standard LM3875, etc)
when ordering from Brian, one would have the following variables:
(LM3875 | LM3886) + (dual mono | stereo) + (snubber | standard) + (PCB only | stand. comp | premium comp.)
Or if larger PCBs are better for pricing (when Brian has them made), combine the two sets above (4 channels, 4 rectifiers). If smaller PCBs are better for pricing, separate everything... the possibilities are endless.
just a thought that could possibly better accommodate everyone. :angel:. i guess, the remaining question is: does it accommodate Brian better? |
For me, it is much easier having 3 complete boards on hand, than having to worry about mixing and matching 5 different boards. But, I can consider this for the future, after I get the initial boards done and shipped out.
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Brian |
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| m0tion |
| Great idea, it would allow for a lot more options, but it sounds like a logistical nightmare, especially considering this is a one man show. =) |
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| BrianGT |
| quote: | Originally posted by m0tion
Great idea, it would allow for a lot more options, but it sounds like a logistical nightmare, especially considering this is a one man show. =) |
And considering that I do this in my spare time and have a normal full time day job :)
I will see what I can do. My main focus now is to just get some new LM3886 boards out there, and then we can talk combining boards in different ways across the pcb sets.
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Brian |
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| homer09 |
Brain, im guessing you should split up the boards and split up the components into little bags (snubber rectifier comp., LM3875 amp comp. etc). A bit in the same way you do now. Then it would just be joining the baggies and PCBs in the right quantities for each order.
but then again, easier said than done. im not the one who's going to have to do this...
and everyone already appreciates your efforts Brian :up: |
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| BrianGT |
Here is what I am currently looking at for the rev.3 boards. It is similar to the new LM3886 board, which followed a similar form from the LM4780 board.
The only other modification that I am looking to do to this board is add more spots for decoupling caps for a setup similar to the snubber setup on the LM3875 board. This way, it can be implemented with the new power supply board in the same fashion as the LM3886 board.
Let me know if you have any comments. I am going to try to finalize the layout soon, and order more pcbs. I ordered the pcbs for the LM4780 boards yesterday and am accepting pre-orders again for them on the website.
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Brian |
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| sbolin |
| Looks good. I will order one of the LM3875 C boards when they come out, I'll wait until the rev 2 of the LM3886 board, in case anything comes up :cannotbe: |
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| BrianGT |
Here is an updated power supply, and I added an extra placement on the amp board for a decoupling cap (for using with the Carlos snubber power supply). I also added larger holes on the rectifier board for external components as requested.
I moved back to a similar power supply as the rev.1 boards, due to simplicity. The pads don't line up perfectly anymore for the V/PG pins for mounting the boards together, but the board layout is cleaner. This also allows the use of spades, which people missed not being able to be used on the rev.2 boards. Here is a rev.1 picture with spades:
http://www.briangt.com/gallery/nigc...T_GC_PS_800x600
Anyone have any other features desired for this board?
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Brian |
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| KT |
Brian,
I'll be interested in at least 4 boards for the LM3886 and snubber PS when they're ready.
I'm actually most interested in getting the snubber PS boards only, but I'll go with whatever's most convient to you.
Best,
KT |
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| BrianGT |
| quote: | Originally posted by KT
Brian,
I'll be interested in at least 4 boards for the LM3886 and snubber PS when they're ready.
I'm actually most interested in getting the snubber PS boards only, but I'll go with whatever's most convient to you.
Best,
KT |
Once I get the initial orders handled, I will have extra pcbs available for the snubber boards, and will sell them seperately. I can also sell a snubber power supply kit if desired.
I checked the status of the boards this morning, and the LM3886 boards are in the 65% complete - copper plating stage, while the LM4780 boards are in the 50% complete - drilling stage, so hopefully they will ship out early. :)
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Brian |
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| budwiser |
| So after reading this forum, I can assume that I won't have to make any modifications to my rev2 boards if I add the suberized power supply board (ie decoupling cap etc). Just unsolder wiring from old power supply board and resolder to new one. |
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| BrianGT |
| quote: | Originally posted by budwiser
So after reading this forum, I can assume that I won't have to make any modifications to my rev2 boards if I add the suberized power supply board (ie decoupling cap etc). Just unsolder wiring from old power supply board and resolder to new one. |
It will work this way, but you might also want to try removing the 1500uF caps on the amp board and replacing them with a 0.1uF cap and 100uF cap combination (they will fit on the rev1/rev2 boards).
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Brian |
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| homer09 |
Nice work Brian, i really the layout change (separating power connections from signal connections).
I dunno if this could help, but i was thinking maybe shortening the thick trace from the left side of the feedback resistor to the OUT pad (since this is a critical trace). this could be done by moving the OUT and OG vertically up by about a cm placing them to the left of the R3 resistor. The SG pad could then also be moved somewhat to shorten traces.
Or even simply removing the place for Rf (i dunno how many people actually use it, most just solder directly under board since it isnt much harder) and this would allow the OUT and OG pads to come even closer to the chip, maybe placing the OUT over the OG instead of side by side. |
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| Peter Daniel |
Brian didn't mention, but I had some input in designing that board. There is a certain harmony and order in placing the pads this way and I wouldn't be tempted to rearange them much, just to shorten connections by a fraction of an inch. It is still better than a previous version.
If you want the output trace to be really short, you can always solder your wire in a place of a feedback resistor (as you would be using it in other location anyway) or directly to pin 3. But placing Rf underneath is not the best choice either, as pin 3 of the chip extends the connection to the chip quite substantially. The best way is to mount it right beside the chip, in top layer as it was pictured in a manual. This way the feedback loop will be the shortest.
See page 10 of this guide: http://www.chipamp.com/nigc_kit-users_guide.pdf |
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| homer09 |
| quote: | Originally posted by Peter Daniel
If you want the output trace to be really short, you can always solder your wire in a place of a feedback resistor (as you would be using it in other location anyway) or directly to pin 3. But placing Rf underneath is not the best choice, as pin 3 of the chip extends the connection to the chip quite substantially. The best way is to mount it right beside the chip, in top layer as it was pictured in a manual. This way the feedback loop will be the shortest.
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Yeah that was my idea all along to solder directly on the top side, but soldering under is still a shorter path for people not willing to solder topside as compared to placing it in the Rf pads. in the end soldering on the pads is the longest path, thats why i was questioning even having it.
Harmony is a great word for the new layout, i definitely noticed the layout was much more elegant than rev.2. since im still new to this, and im definitely not questioning your choice. can you point out how my suggestion spoils the harmony? (attached) |
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| Peter Daniel |
| quote: | Originally posted by homer09
can you point out how my suggestion spoils the harmony? (attached) |
The holes are not in one line any longer and ground pad is more off center.
Now, you tell me what are you gaining by that? |
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| homer09 |
| quote: | Originally posted by Peter Daniel
The holes are not in one line any longer and ground pad is more off center.
Now, you tell me what are you gaining by that? |
only a shorter path :sad:
but more is lost lost and your right, not worth it. i withdraw my suggestion :smash: |
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| Peter Daniel |
Your suggestion was actually good, but it is also a matter of preferences. For somebody who does one off board this may be preferrable, but those boards sell in substantial quantities and besides presenting proper layout, they should also posses certain visual appeal ;)
Now, though output trace got shortened a bit, if you consider that power traces to the chip are still much longer, that the signal has to go through binding post (in most cases of not ultimate quality) those few hundreds mills of reducing the output trace is not that critical. At least this is how I look at that.
For best purist approach, I would again suggest soldering output wire directly to pin 3. |
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| Peter Daniel |
Here's the layout I was working on recently. As you see, it says SE, which stands for Special Edition.;)
I will offer again LM3875 Premium kits as those are still the best. The layout is made to accomodate Riken gain setting resistor, and also a special mounting pad for a feedback resistor.
While the usual location is still available, the board also utilizes the preferred location, right between the pins, close to the chip. One of the resistor pins has a dedicated hole (at chip's pin 8). This will allow placing resistor exactly where you want it, without need of using tweezers or any other special tools as we've seen it. The other resistor pin is bent and soldered directly to pin 3 of the chip. This provides for easy and repeatable mounting. I was recently putting together 20 sets of those boards and I know how hard it is to properly mount feedback resistor.
The rectifiers board allows direct power connection, as well piggy backing. I might add a big cap/snubber combo here, by either connecting a cap directly to rect. board, or with aditional board and both connected with standoffs for compact assembly. But I still have to experiment a bit more to see what really works well.
The best news is that all copper surfaces will be gold plated, as special edition would rightly deserve. ;)
PS: I was always unhappy with a way Zobel components butchered a ground plane in rev.2. This time they are discreetly on a side. However, Premium kit will be offered without Zobel parts, as they are not recommended. They could be added on special request;) |
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| BrianGT |
Here is my current version:
The power supply has extra holes for external caps, and will also accomidate a pair of 35mm caps (white outline is cap size, which would mount under board):
I also changed the input/output pads on the rectifier board to allow for spades or terminal blocks.
Peter and I have been going back and forth with the layouts, and I appreciate his input on the current board design.
As for the slightly shorter output setup, I don't think that it would make much of a difference, as the wire will still have a much longer run than the 0.25" extra length in the pcb trace. The current placement of the input pins allows the builder to also use terminal blocks if desired. Also keep in mind the size of the amplifier board, as it is only 2.9" wide by 1.2" tall.
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Brian |
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| sbolin |
| Kind of a dumb request, but any way to add a LED supply point on the PS board? Not a big deal at all if it can't be easily accommodated. Otherwise, looks very good, nice improvements over the rev B board. |
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| homer09 |
Are the extra holes (for the 35 mm caps) for the snubber setup? how does this differ from the other snubber board you designed for the LM3886?
PS. with the caps in place, how is one supposed to use the pcb mounting holes? |
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| Peter Daniel |
I guess in that case you treat the board as addition to the caps and mount the caps somehow. A good example of that can be found in Lyra Connoisseur PS.
And the LED supply point is a very good suggestion, something that escaped our consideration. |
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| jleaman |
nice picture peter : O )
Any word on some dac ideas ? |
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| BrianGT |
| quote: | Originally posted by sbolin
Kind of a dumb request, but any way to add a LED supply point on the PS board? Not a big deal at all if it can't be easily accommodated. Otherwise, looks very good, nice improvements over the rev B board. |
I will look into this. I don't know if there will be an easy way to add it to this board. One of the extra supply pads, which could also be used for additional capacitance could be used for the LED, wiring a 10k or so resistor in series with the LED. (this is assuming using the same supply). I added a separate supply (Carlos' idea) on the LM3886 power supply board, as there was additional space available.
| quote: | Originally posted by homer09
Are the extra holes (for the 35 mm caps) for the snubber setup? how does this differ from the other snubber board you designed for the LM3886?
PS. with the caps in place, how is one supposed to use the pcb mounting holes? |
The extra holes were added as a suggestion for additional pads on the board for an external cap bank. Since these pads were to be there anyway, I decided to make them the appropiate size for the larger 10,000uF low profile 35mm diameter caps. If they are used, an alternate mounting method will need to be used, such as using some sort of adhesive to the bottom of the caps and affixing to the bottom of your chassis.
The intended kit application and parts for the LM3875 kit will not change, and if a larger, snubberized power supply is desired, I will have extra pcbs for the larger power supply board, which includes and LED supply, and proper placements/mounting for the zobel components. The reasoning behind in adding the extra pads is that this is still a DIY project, and it seems best to allow more options for experimentation.
For the snubber setup on the new rectifier board, the snubber components (.1uF||(.1uF+1ohm)) will need to either be placed in the C1/C2 cap pads, or soldered to the capacitor leads coming through to the top of the pcb (preferred).
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Brian |
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| Peter Daniel |
Jason,
I will check in next couple days what I have there. |
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| jleaman |
Brian i must say your boards work great with my new speakers ill post pic's of them soon hold on a hour whyle i change the size's.
Jason.. |
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| BrianGT |
| quote: | Originally posted by sbolin
Kind of a dumb request, but any way to add a LED supply point on the PS board? Not a big deal at all if it can't be easily accommodated. Otherwise, looks very good, nice improvements over the rev B board. |
| quote: | Originally posted by homer09
Are the extra holes (for the 35 mm caps) for the snubber setup? how does this differ from the other snubber board you designed for the LM3886?
PS. with the caps in place, how is one supposed to use the pcb mounting holes? |
I handled both of these issues, and finalized the details for the new rev.3 LM3875 boards and put info on the product page here:
http://www.chipamp.com/lm3875.shtml
I ordered a batch of pcbs, and should receive them in 2 weeks or so from the board vendor.
Here is a pic of the new mounting for the cap, with the holes for standoffs on the edges of the board. The power supply board is now 2.9" x 1.5" instead of the previous 2.9" x 1.2"
Let me know if you have any questions.
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Brian |
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| jleaman |
| Look's good Brian. Keep it up. : O ) |
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| ransom peek |
Since the general conclusion is that adding a snubber circuit to the LM3875 improves the result noticably, why would one choose to not utilize this option?
What is the difference between the rev C version available now and the snubber version that will follow? Is the pcb the same, so one can build the basic kit now and easily add the snubber once the snubber parts are identified? |
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| BrianGT |
| quote: | Originally posted by ransom peek
Since the general conclusion is that adding a snubber circuit to the LM3875 improves the result noticably, why would one choose to not utilize this option?
What is the difference between the rev C version available now and the snubber version that will follow? Is the pcb the same, so one can build the basic kit now and easily add the snubber once the snubber parts are identified? |
The rev.3 pcb allows for both options regarding the power supply. I will refer the original 1500uF capacitor configuration as the legacy setup, and the snubber power supply as the new setup.
I will be offering upgrade kits (containing the new power supply pcb and snubber components) and LM3875 kits including the new snubber components soon on the website.
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Brian |
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| budwiser |
Will the future seperate snubber board come with upgrade parts to replace the 1500uf cap on the main board or will we have to find our own source for thos parts.
Thanks,
Pete |
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| ransom peek |
| Would really appreciate general clarification on what is different for the snubber version - electronically, as far as the pcbs are concerned, and in terms of expectged audio results... |
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| BrianGT |
| quote: | Originally posted by budwiser
Will the future seperate snubber board come with upgrade parts to replace the 1500uf cap on the main board or will we have to find our own source for thos parts.
Thanks,
Pete |
I will allow the kit to be purchased either way in the future. I will modify the website this weekend or earlier next week to allow orders to be accepted for both.
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Brian |
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| homer09 |
| quote: | Originally posted by ransom peek
Would really appreciate general clarification on what is different for the snubber version - electronically, as far as the pcbs are concerned, and in terms of expectged audio results... |
This has been coverred EXTENSIVELY in the forum. There are a few threads a couple of miles long about the snubber, the first of which was started by CarlosFM, the original starter of the idea.
But if you want a long story short, the snubber supply is basically a high capacitance power supply for gainclones. Before, power supplies for chip amps were always of small capacitance ~1500 mF/rail because of certain inheritent incompatibilities between the chips being used and large capacitance supplies. Carlos implemented a " snubber" as a fix for this incompatibility and now a high capacitance ~10 000 mF/rail power supply may be used successfully.
The difference electronically? I would refer to this page http://www.chipamp.com/lm3875.shtml and read the 3 links at the top.
The difference sonically? You should expect the advantages that higher capacitance supplies bring to amps in general. The amp will basically be able to deliver power faster and in larger quantities when needed. An overall improvement should be noticeable, and if you read diyers impressions, almost all are very favourable to it. |
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| ransom peek |
Now it is clear. Thank you Homer! My guess is that when Brian offers the snubber version of the LM3875 kit it will simply be the standard rev C board kit plus the extra snubber components.
So, if I'm correct, one could purchase the rev C kit and add the extra parts for the same result, as long as one knew how to choose audio grade parts, not just correct values and tolerances...
Is that correct? |
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| steenoe |
| quote: | | So, if I'm correct, one could purchase the rev C kit and add the extra parts for the same result, as long as one knew how to choose audio grade parts, not just correct values and tolerances... |
You are partly correct;) I am not sure at all, that so called audiograde parts are needed. Having built a few of the snubberred amp with generic parts, I can safely advice you to use standard parts. I have used generic MKT's for the snubber with good result. Just use whatever filmcap you have lying around. 100nF ofcourse;)
Steen. |
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| carlosfm |
| quote: | Originally posted by homer09
But if you want a long story short, the snubber supply is basically a high capacitance power supply for gainclones. |
Basically but not only.
But that would give another miles long discussion.:)
Good summary you made there.:angel: |
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| carlosfm |
| quote: | Originally posted by steenoe
You are partly correct;) I am not sure at all, that so called audiograde parts are needed. Having built a few of the snubberred amp with generic parts, I can safely advice you to use standard parts. I have used generic MKT's for the snubber with good result. Just use whatever filmcap you have lying around. 100nF ofcourse;)
Steen. |
Steen, you're revealing part of the secret.:D
Spot on. |
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| steenoe |
| quote: | | Steen, you're revealing part of the secret. |
Hey, thats what DIY is all about, isn't it :D
It makes me wonder though, if that was part of the secret,
what is the rest then:D :D Come on, Carlos, let us know if there is more to it:cool:
Steen. |
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| BrianGT |
Here is a picture of the one of the new power supply boards from the LM3886 pcb set. I will also sell these boards seperately as a kit for upgrading an existing amp.
I just got these boards tonight and took some quick pictures, and will post better quality pictures on my website in the next couple of days..
These are the components that will be offered with the LM3875 kits if an upgraded power supply setup is chosen.
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Brian |
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| jleaman |
| Look's nice.. i like the red back-ground LOL. |
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| BrianGT |
| quote: | Originally posted by jleaman
Look's nice.. i like the red back-ground LOL. |
red background = table I modified to make a poker table.
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Brian |
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| KT |
Brian,
Yes, thanks for offering the stand-alone snubberized PS board as an upgrade for the older kits.
Sorry if I'm rehashing a question (haven't had time to read through the whole thread), but have you had a chance to compare the 3875 to the 3886?
I'm very curious about the differences.
Best,
KT |
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| BrianGT |
| quote: | Originally posted by KT
Brian,
Yes, thanks for offering the stand-alone snubberized PS board as an upgrade for the older kits.
Sorry if I'm rehashing a question (haven't had time to read through the whole thread), but have you had a chance to compare the 3875 to the 3886?
I'm very curious about the differences.
Best,
KT |
I will make the comparison soon, as I have all the parts sitting out on my table, ready to assemble the new amp. I can compare it to each of my 2 LM3875 amps.
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Brian |
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| e.lectronick |
BrianGT
I just looked at the order page on your website, and I think I've found a typo where the you have listed the preorder option for the "Snubberized Non-Inverting LM3875 rev.3 Stereo Kit (item # NI3875-KIT-ST)"
It mentions that the kit comes with a single "rectifier board" (which I take to mean the original design). This is different from the dual mono kit above it which comes with two "Power Supply Boards" (which I take to mean the Snubberized PS with 10000UF caps).
Is the stereo kit supposed to say it comes with a single "Power Supply board"? If you're implementing the Snubberized PS, you don't actually need the "rectifier board" too, right?
Please forgive the dumb question, but I've been trying to catch up to speed on the new modifications and I want to make sure I'm not missing anything.
-Erik. |
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