Parallel LM1875, 2 chips per channel, in 5 minutes ea? Can bridge if 8 ohm speakers. - Page 3 - diyAudio
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Old 22nd December 2011, 06:17 PM   #21
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by danielwritesbac View Post
Please replace that with +-27.5vdc or less
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Originally Posted by AndrewT View Post
Can't you read english?
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Originally Posted by danielwritesbac View Post
You said +-30 abs max. I said +-27.5 abs max.
Now I know, you can't write english.
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regards Andrew T.
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Old 22nd December 2011, 10:12 PM   #22
Einric is offline Einric  United States
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Alright Andrew there is no need for that!!

I appreciate Daniel's assistance and I'd like him to keep writing.
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Old 22nd December 2011, 11:49 PM   #23
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Originally Posted by AndrewT View Post
Now I know, you can't write english.
That wasn't a secret, but would you help me out with the PI filter safety current limit idea? I wish to rob power from clipping and block some noise at the same time. Apparently, the CRC with the bigger "R" can do it for very durable LM1875 guitar amplifiers to improve clipping performance, such as less noise. What is an estimated ballpark value for "R" if I didn't want LM1875 to be the weakest link?
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Old 22nd December 2011, 11:56 PM   #24
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Originally Posted by Einric View Post
Alright Andrew there is no need for that!!
I appreciate Daniel's assistance and I'd like him to keep writing.
I like Andrew a lot, and I understand that his negative responses are usually in proportion to and related to the severity of an error that I have made. In this case, anything vague or inexact, when it comes to power and current, is indeed a potentially hazardous sort of error in writing. I can't argue with that at all. Therefore, please validate any of my posts, by comparing with other sources, prior to building the circuits.
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Old 23rd December 2011, 06:28 AM   #25
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One popular source is Decibel Dungeon and here's a link to it: Building a Gainclone chip amp power supply. <--link

On that page you find this: "Somebody wrote to me suggesting that the 1875/6 chip will last longer with the following settings:"

Those are my long term test findings for real LM1875 chips. They didn't include highly reactive loads as severe as double 10" woofers or 15" woofers or extraordinarily difficult to drive crossovers; because, I didn't have such things during the long term test. AndrewT's post #6 indicates the need for triple parallel LM1875 for such highly reactive loads. For large/difficult speakers, Parallel TDA7294 is also a contender and it can be built with the point to point method in post #18, resulting in a very similar audio performance, actually imitating the LM1875. I'm actually saving the larger amp for later, for after I have the bridging adapter up and running.
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Old 23rd December 2011, 08:05 AM   #26
Grega is offline Grega  Australia
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nice one dwb - thats a good page on DD. must read up on it.
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Old 23rd December 2011, 12:48 PM   #27
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Originally Posted by tweakk View Post
Got a good link for building your LM3886 kit?
Not me. I do not have a high fidelity LM3886 kit, design, or project demo. However, a high fidelity LM3886 kit exists. . . The MyRef C is a unique fully optimized support circuit for LM3886. I am not the designer, but there is no need to design it. The boards are currently available.
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Originally Posted by tweakk View Post
Thanks for the reply Daniel.. . . I've built your 1875 amp and thought the parallel implementation would be something that would use your PCBs.
I have PCBs? Okay, that's fine. Several people have the rights to produce my two LM1875 designs. But I really don't have any PCB's personally.

With a circuit board or the absence of a board, most of that difference is merely visual. When the performance and layout are good for a single amplifier, you can use it for parallel amplifiers if you like. You'll need to add the 0.22R ballast resistors to the outputs. You'll need to measure all resistors to make sure that the two amplifiers are exact copies (resistor matching). Some extra review of star grounding may be necessary. Grounding follows a general "Once met" idea to avoid ground loops.
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Originally Posted by tweakk View Post
It's interesting that you mention using an array of smaller caps for the power-supply. I was trying to figure out a way to do that with my 1875 amp yesterday!
Transformer and rectifier is one easy section:
Check Mark Houston's Synergy Gainclone.
Check the datasheet for KBPC2504 or KBPC1604
Check Decibel Dungeon transformer explanation

Example power smoothing board another easy section:
12 caps (2 100nF polyester dip caps, 10 pack of 35v 2,200uF ecaps) on copperless phenolic perfboard (no pads, just non-conductive board with holes), and it has this arrangement.
v+, 100nF, 2,200uF, 2,200uF, 2,200uF, 2,200uF, 2,200uF, rectifier +
0v---------------------------------------------------------- CT
v-, 100nF, 2,200uF, 2,200uF, 2,200uF, 2,200uF, 2,200uF, rectifier -
The rectifiers that we are using have clearly marked polarity--KBPC1004 on Mark Houston's example is even better in that respect. The power smoothing section is easier and faster to assemble on a board. I cannot give you a great deal of advice on power supplies, but I can provide photos. Please look up the relevant materials on the Decibel Dungeon website and also Rod Elliot's website.

Here are some power supply photos:
Attached Images
File Type: jpg Ladderback Row.jpg (327.2 KB, 359 views)
File Type: jpg ladderbackds10.jpg (82.8 KB, 346 views)
File Type: jpg ladderback_schematic.jpg (67.2 KB, 293 views)

Last edited by danielwritesbac; 23rd December 2011 at 01:05 PM.
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Old 23rd December 2011, 01:06 PM   #28
tweakk is offline tweakk  United States
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Oops...

I thyought you has a hand in this:
Finally made a LM1875 amp

Thanks for the links. I have some research to do.

Mark Gilbert of Blue Circle is powering a preamp with energy stored in caps only.
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Old 23rd December 2011, 01:34 PM   #29
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Originally Posted by tweakk View Post
Oops...
I thought you has a hand in this:
Finally made a LM1875 amp. .
That amplifier is not one of my designs. It is the datasheet example in LM1875.pdf by National Semiconductor. <--links The chipamp.com LM1875 is a highly usable kit that many people like. Most often they use the board and then simply transplant a favorite design onto the board. There's a couple of threads here on diyaudio.com about enhancements and upgrades for that kit.

The chipamp.com LM3886 kit, which was produced much earlier, is most definitely not an optimized support circuit for LM3886, but rather a low components count model with many omissions. So, if you wanted a hi-fi LM3886, I would suggest using the MyRef materials instead. The cost is similar, the results much different. The tone of the MyRef is same as the source. The sound field cast of the MyRef is both deep and wide, which is a characteristic of a high end amplifier.
Resources:
My "audiophile" LM3886 approach
The new "My Ref" Rev C thread
MyRefC build guide
MyRef_C with Ultimate BOM

Last edited by danielwritesbac; 23rd December 2011 at 02:01 PM.
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Old 23rd December 2011, 01:47 PM   #30
tweakk is offline tweakk  United States
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Ahhh...

I've been looking for a way to buy the MyRef PCBs the past few days but I've searched the threads until my eyes were bleeding and could not find them ready to buy. I did learn who to PM for info.

Twisted Pear Sympatico looks interesting.

Last edited by tweakk; 23rd December 2011 at 02:07 PM.
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