Fitting "Pentawatt" and similar "staggered leg" chips in perfboard - diyAudio
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Old 1st May 2014, 09:41 AM   #1
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Default Fitting "Pentawatt" and similar "staggered leg" chips in perfboard

Hi all. A lot of chipamps have very non-standard leg spacing, where the legs are "staggered" into two rows. The legs in the two rows don't line up with each other, and the between-leg spacing is not the standard 2.5mm you see with DIP/SIP chips. I'm thinking in particular of the TDA2050, but it's by no means the only one, this is actually very common.

Has anyone tried to get one of these to fit in to perfboard/stripboard/etc? Judging by the datasheet measurements, this is not an easy task. Rod Elliot says "These ICs are a cow to wire on Veroboard - it is possible, but results are unpredictable". I've found at least one nice close up photo where someone seems to have made it fit very neatly.

If someone has done this successfully - or, actually, better yet, if someone has tried to do this and either snapped a leg off or given up in frustration - I'd like to hear about it. I'm thinking of building an amp with one of these chips, but I'm not really interested in rolling my own PCB for it. And I know I can buy kit PCBs off eBay, but where's the fun in that?
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Old 1st May 2014, 02:15 PM   #2
johnr66 is offline johnr66  United States
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Not really a problem. Just twist the outer leads out a bit and spread the back two leads slightly and it will fit. Avoid stress where the leads enter the package and bend them a few mm away from that point.
Click the image to open in full size.
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Old 1st May 2014, 04:53 PM   #3
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Here's my old project for that:
Beginner's Gainclone, HiFi LM1875, The Amplifier Board
For use as monoblocs with 18+18vac 36va 1 ampere transformers.
The project uses copperless phenolic perfboard.
Click the image to open in full size.


However, this schematic works better:
Click the image to open in full size.
For use as monoblocs with 18+18vac 36va 1 ampere transformers.


It does still need a DC power board:
Click the image to open in full size.
The power board can be assembled on copperless phenolic perfboard.
When used with the newer schematic that has the 1n5405 series diodes on the amplifier board, and a transformer not more than 36va, then, in that case the power board can be built simply, without the 0.33R (3x1R) CRC filtration. Then a smaller power supply can be built with just 3 of 3300u caps (9900u) per rail and the 35v caps are a nice small size.
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Old 1st May 2014, 05:37 PM   #4
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Suggested by someone in the forums who is stunningly practical.
45 degree rotation fits.
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Old 1st May 2014, 10:50 PM   #5
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Thanks everyone, I'm very much encouraged by all the good photographic evidence that this actually isn't all that hard.

Daniel, the close-up, step-by-step construction photographs a few pages into your LM1875 thread are a huge help. It's reassuring to see how much space is available between the legs!

ricortes, I never would have thought of the 45 degree option, hats off to whomever first realised that! The only downfall I can think of is that if you want two chips mounted to one heatsink (as shown in jonhr66's photo) you end up having to basically build your whole circuit at that angle, which may be a little wasteful of board. But if you wanted separate heatsinks you could easily do the whole circuit as normal and just have the two chips at 45 degree angles, in opposite directions (i.e. with a 90 degree angle between the two chips), and that would end up quite neat.
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Old 3rd May 2014, 02:56 PM   #6
jcx is offline jcx  United States
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you don't even need perf for simple enough circuits: Mick Feuerbacher Audio Projects
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Old 6th May 2014, 07:55 AM   #7
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The copperless phenolic perfboard will also cut at 45 degrees and you can still make squares then if you want to. This will require a slightly larger board; however, 5-pin chips make very small size amplifiers anyway, so a small amount of wasted board is not a concern.

P.S.
The Parallel LM1875 doesn't use a board at all since the twin chips have already enough support. The board on the solo chip amplifiers is only there to prevent the chip from rotating free of the insulating pad. That problem doesn't happen with tandem chips. An especially cheap stereo amp could be made by following the parallel lm1875 construction technique, although when the power decoupling caps are shared by a stereo pair, the stereo width could suffer slightly (or at least would not be enhanced at all).
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