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Need help with Triple Parallel LM1875 dynamics amplifier.
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Old 20th December 2011, 07:18 PM   #101
Grega is offline Grega  Australia
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yes of course, will dig it up.
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Old 26th December 2011, 04:17 AM   #102
danielwritesbac is offline danielwritesbac  United States
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Default Overrun conditions detected--please stretch to a Quad parallel

In regards to the photo in post #71, please add another LM1875 chip to the center, stretching it out to a Quad Parallel.

This is necessary to enhance the usefulness of the amplifier. Too many of the applications put triple LM1875 into overrun condition. It must be a Quad Parallel, to be more worthy of PCB design efforts and support a wider variety of speakers.

With post 71, you may need to size most of the resistor pads for 1/2w resistors (especially those that jump over traces); however, it should be fairly easy to pop another chip right in at the middle. Considering the current, the power rails and 0v need to be thickened when possible.

Last edited by danielwritesbac; 26th December 2011 at 04:25 AM.
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Old 27th December 2011, 11:26 AM   #103
Grega is offline Grega  Australia
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you're going to need a fairly beefy trafo to run that (600va springs to mind)
i am not sure i can fit 4 as the boards i can do are limited to a 100x100 size
i will see what i can figure out as i need a bit of down time to get my brain doing a bit of thinking. has been nice being on holidays.
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Old 27th December 2011, 12:21 PM   #104
AndrewT is offline AndrewT  Scotland
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No,
the standard recommendation for a Power Amplifier Transformer is
VA is from 1times to 2times the total maximum output power.
Paralleling does not increase the output power. Paralleling increases the current capability.
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Old 27th December 2011, 11:46 PM   #105
Grega is offline Grega  Australia
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indeeed - thanks for the correction
question :
sqrrt of (2x8)x20 or sqrrt of (2x8)x80 for vopeak?
similiarly for iopeak
sqrrt of (2x20)/8 or (2x80)/8
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Old 27th December 2011, 11:50 PM   #106
danielwritesbac is offline danielwritesbac  United States
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It seems to work to calculate at 48 watts per board times 1.5.
For a bridged monobloc, that's a low cost 4 ampere transformer.
This seems workable for a nice big stereo amp: http://www.antekinc.com/details.php?p=614

Last edited by danielwritesbac; 27th December 2011 at 11:56 PM.
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Old 28th December 2011, 12:02 AM   #107
Grega is offline Grega  Australia
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think i've answered my first vopeak question, as 17v vs 35v seems somewhat more consistent
2.2a vs 4.4a
i guess where i'm headed is i calculate each of the LM power requirements individually, then, multiply by a factor of (x) being the number of modules used (which for 4 would be 8.8 and 3, 6.6 respectively.
the voltage requirement though I would expect to remain at 17v across all modules

so a 300va supply would suffice here - ie 8.8x17/0.6 = 250va
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Old 28th December 2011, 12:04 AM   #108
Grega is offline Grega  Australia
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dwb - i wish we got antek toroids over here. 36 bucks is a bargain. the local electronics place here is 84 bucks for the same thing!!!!!!!
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Old 28th December 2011, 10:47 AM   #109
Grega is offline Grega  Australia
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ah daniel-san
i didn't think this was possible

some caveats ;

in your original post theres a couple of errors which i have worked around - however there are still things to be added to this so, its by no means complete.

i have omitted the 100nf 'filter' caps - they can be soldered direct under the board
there are resistors on the feed to the line out --> these would be wire 'bridges'
most of the resistors - are still to be determined values.
NOTE the overlapping parts when the board is build would NOT overlap - they are 'oversized' in eagle for larger pin spacing.

Click the image to open in full size.

please note this is a first cut - and needs bits and bobs before it is in any way shape or form usable - its taken me MANY hours to get it sorted though.

oh i reckon another pair of capacitors would balance the board out too
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Old 28th December 2011, 01:17 PM   #110
Grega is offline Grega  Australia
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ok so went a bit mad
- managed to get the snubbing capacitors (100nf) on the leads of the radial capacitors - tight fit but there.
- also managed to provision space on the input for a DC blocking cap from the line input - with multiple vias for different types of capacitors
- re-arranged things and moved radial capacitors around to accomodate spacing
- added an additional 2 x radial capacitors (so 6 x 220uf) instead of 4 x 330uf

i'll put the board images up later today, need to get some shuteye.

oh - we also need to decide on some values for resistors. plus i remember andrewT suggesting diodes inverse on the resistor joining the audio ground from the power ground. the resistor is bottom left next to the line out
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