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Old 23rd February 2013, 03:05 PM   #191
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Default 1875 board pictures

Here are the pictures of the board.
Attached Images
File Type: jpg LM1875 - pcb.jpg (82.1 KB, 437 views)
File Type: jpg LM1875-components.jpg (84.9 KB, 424 views)
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Old 24th February 2013, 12:12 AM   #192
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Wow, excellent use of inductive series elements as noise filters, for both power and small signal.

Especially noteworthy is the inductive series element between the inverting input and the feedback-shunt resistor, which may drop the gain on RF. Personally, I would have installed a good brand of 1/2w carbon film for feedback-shunt resistor, but, it looks like your layout got the job done.

You might still enjoy a variable RC from "~" to "~" of the bridge rectifier.
The could be a 2u polyester cap and a 50R variable resistor.

P.S.
There's a bit of fun to be had with that board. We'd need to flip the output RC's polarity so that it is resistor first (resistor at amp, cap at ground, is normal) and install a more compact cap. Now, at the output RC, the midpoint between cap and resistor has "Dr. Cherry tap" available. We could cable from there to a resistor added at the other channel's inverting input to install a stereo width effect. To avoid bass reduction, it probably needs a series cap (series with the new cable) and that cap located pin2pin with the output RC's cap (right at the Dr. Cherry tap, of course). Both channels done the same. Now, you have a slightly bass boosting stereo width effect. It is desirable to have the effect so tiny that it is transparently not obvious, so the added resistors would be very high value. Personally, I'd use only enough effect to make it sound like monoblocs, in which case, we may have cancelled some stereo build power circuit crosstalk. This prospect may require an amp that has an NFB-shunt cap present (and perhaps a tiny little polyester cap for treble helper). Adding the NFB-shunt cap would give you a dynamics, safety, power output and midrange boost, and you could set the stereo width effect to conquer the midrange boost. (Adding a rail2rail cap helps too, such as one 250v 4.7u from v+ to v- probably at the two big caps.)
Anyway, it is actually possible to redeploy a very small amount of a popular stereo width effect as a useful compensation on stereo boards. I'd estimate that the effect may remain reasonably transparent up to about 12% of the gain factor or less than that much. It will reduce crosstalk gain by as much and therefore sound slightly quieter (you may need a small amount of regular gain boost to recoup). The circuit tells each chip "don't do what your neighbor does" and a little tiny bit of that can have it sounding like Monoblocs. Generally, negative feedback is responsible for power noise reduction, and I believe it is possible to use a tiny bit of width expander negative feedback on stereo board for stereo crosstalk reduction as well. That board looks particularly well able to do this. The bonus is making leeway in midrange ear tolerances so that you can re-install your NFB-shunt caps for more safety and more dynamics power.
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Last edited by danielwritesbac; 24th February 2013 at 12:15 AM.
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Old 26th February 2013, 09:27 AM   #193
pra3718 is offline pra3718  India
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@danielwritesbac : Is your schematic post # 1 would work with LM1876 ? ( Assume LM1876 has two LM1875)
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Old 1st March 2013, 01:00 AM   #194
prezden is offline prezden  Canada
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Default getting started

Hi guys- just placed my order with DigiKey Wish me luck
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Old 1st March 2013, 01:39 AM   #195
gychang is offline gychang  United States
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Quote:
Originally Posted by Bluto View Post
Hey Gychang -

Hear that??!!

Famous!!

Someday I'm gona be famous too!

Bluto
I just realized it is me!!!, I usually hang around fullrange and class D amp section. I hear you and appreciate danielwritesbac's efforts, thank.

of course I will try this.

gychang
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Old 12th March 2013, 01:11 AM   #196
fortney is offline fortney  United States
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Hi folks,

I recently built a K-50 (LM1875) mono kit following Danielcallsbac instructions except that I did not have a variable resisitor for R1 and use the 1K. It sound real good and I can understand the lyrics of the songs! That may be due to the Infinity Primus 153 speaker of course.

I am writing this because I used two Jameco regulated wall transformers, 12V, 2.5A, wired to make +12, 0,-!2V supply. This works very well. At maximum volume it is loud and also clips, but when backed off a bit it is just fine for private listening. This is a light weight and inexpensive solution. Would I prefer 15 or 18 volts? Probably, but this is very satisfactory.
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Old 12th March 2013, 11:45 PM   #197
prezden is offline prezden  Canada
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Hey Daniel- Can this amp be built with regular breadboard with copper? I know you specified board without copper but I accidentally ordered the wrong board.
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Old 13th March 2013, 01:18 AM   #198
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Yes it can. The layout shown is very roomy. Dodging copper dots and avoiding shorts will make the build take only slightly longer. No problem.
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Old 18th March 2013, 08:02 PM   #199
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Default output cap question

Can i use polarized caps in the output section, or must they be non polarized? Im having a hard time finding non polarized in that value.

I have gotten my board layout done and parts in. whoo hoo!!
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Old 20th March 2013, 10:45 AM   #200
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So I found the post regarding caps. As a noob im just learning about some of the search tools on the forum. Please disregard my question in post 199. I will build the amp out this weeks and see how it goes.
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