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Chip Amps Amplifiers based on integrated circuits

Beginner's Gainclone, HiFi LM1875, The Amplifier Board
Beginner's Gainclone, HiFi LM1875, The Amplifier Board
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Old 15th November 2017, 10:33 AM   #771
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by vj_audio View Post
Mr. Daniel

There are three pinouts on a 200R trimmer. How do I attach it to the schematic? Eagle has 3 pins for all trimmers.

1 Pin = Input

2 Pin = Ground

3 Pin = Output

Am I right?

Thank you
Vijay
For the multi-turn type you have shown there are two pin outs:
the inline version and the offset version.
The offset version has the wiper (pin2) offset to one side from the two outer pins. This prevents the VR being inserted the wrong way round.
The inline version can be inserted either way around.

Pin1 is connected to one end of the resistive track.
Pin3 is connected to the other end of the track.
Pin2 is connected to the wiper.
There is no "ground" inherent to any of these pins
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Last edited by AndrewT; 15th November 2017 at 10:35 AM.
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Old 24th November 2017, 04:50 PM   #772
Jishu is offline Jishu
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Would the Rod Elliott design work? It has no 1M ohm resistor in the input stage before the 2.2uF bipolar electrolytic capacitor. Could someone explain to me the importance of the 1M ohm resistor.
Thank you.

This project exactly:
Single Chip 25W Amplifier (Project 72)

Last edited by Jishu; 24th November 2017 at 04:52 PM. Reason: forgot to input link
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Old 24th November 2017, 05:34 PM   #773
cspirou is offline cspirou  United States
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Quote:
Originally Posted by Jishu View Post
Would the Rod Elliott design work? It has no 1M ohm resistor in the input stage before the 2.2uF bipolar electrolytic capacitor. Could someone explain to me the importance of the 1M ohm resistor.
Thank you.

This project exactly:
Single Chip 25W Amplifier (Project 72)
Main reason is to discharge the capacitor while powered off. The value is high enough where it shouldn't effect the circuit, but still provides a path to ground.

Not an issue if a potentiometer is part of your circuit.
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Old 24th November 2017, 07:12 PM   #774
AndrewT is offline AndrewT  Scotland
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Charge can build up on an open input.
If one were to hot plug, the sudden discharge is multiplied by the amplifier gain and comes out as an almost explosive pulse into the speaker/s
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Old 27th November 2017, 09:40 AM   #775
Clueless but avid is offline Clueless but avid  Germany
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Hey people,

I'm the new guy. My name is Jochen, I'm 48 years old an located in Germany. I got plenty of diy experience in building & repairing PC's, but I'm totally new to the audio thing.
I've built my first chipamps a few days ago and I love it. As I have no audio equipment at all besides my headphones and a few soundcards, the plan is to build 2.1 active speakers with the option to 5.1 surround for movies.
I'm always pretty broken and I love to repair or build technical stuff, so I deceided to create my own speakers and not to buy a kit. Dumb as I was, I thought just putting the TSP and some dimensions in a PC program would be enough to have my own speakers calculated and ready to build. Ok, its not as easy as I thought, but its fun, an even without the second, not yet complete, satellite and with just a 6db hi-pass capacitor as crossover, to me it sounds great .
Until now I've got two LM1875 for the satellites and one TDA7293 for the subwoofer. As source and active subwoofer- crossover I'm using a Asus Xonar D2X soundcard wich works really fine.
Right now painting is on the schedule, and this really sucks. Not much room, crappy tools, cheap paint ... but I've got time and its getting better. When the painting is done, I'm gonna build the crossovers.
The installation on the pics is just provisionally, but I really like how it sounds. More to come when everything is done.

Click the image to open in full size. Click the image to open in full size.
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Old 27th November 2017, 09:53 AM   #776
AndrewT is offline AndrewT  Scotland
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Clue,
please attach your pictures.
How to attach images to your posts.
the 1200x900 is probably OK when attached.
The 1726x3065 is going to be too big for most of our screens/monitors.
Crop and compress/resize before you attach.
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Last edited by AndrewT; 27th November 2017 at 09:55 AM.
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Old 3rd December 2017, 05:52 AM   #777
dannyjmf is offline dannyjmf  Malaysia
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Quote:
Originally Posted by vj_audio View Post
Can I use it for small subwoofer?
Depends on the subwoofer driver wattage rating ... but it is not recommended as if the LM1875 was overdriven into clipping it sounds nasty ... based on my past experience
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Old 8th December 2017, 07:01 PM   #778
kurtvisti is offline kurtvisti  Denmark
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Location: SorÝ
Hi Daniel

I’m in the process of building the amp according to your fine instructions.
As I understand there are 2 choices of schematics. The “original” one shown in post #1 and the Turbo II. Is that correct?
What are the differencies in sound between the 2 layouts?
In short: Which one should I build if best sound quality is wanted?

Regards Kurt
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Old 16th December 2017, 06:07 PM   #779
kurtvisti is offline kurtvisti  Denmark
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Hi folks

1. What is the purpose of the 1R 3w resistors in the power supply from post #1?
2. Which components "need" to be of good quality and which doesn't in order to make the amp sound its best?
3. What specs do you recommend for these better quality components (resistors, capacitors)?

Regards
Kurt
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Old 16th December 2017, 06:50 PM   #780
Mooly is offline Mooly  United Kingdom
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Beginner's Gainclone, HiFi LM1875, The Amplifier Board
As no one has spoken I'll give my thoughts:

The 1 ohm resistors increase the impedance of the supply as seen by the transformer and so help reduce the overall 100/120Hz ripple more effectively than if they were not present.

The downside is that they reduce the 'stiffness' of the supply meaning that the regulation becomes poorer i.e. the rails will sag more under sustained load. Its the designers choice to do it this way.

All parts should be of good commercial quality and (imo) exotic or boutique parts are not required.

The electrolytic caps should be a reputable brand and of 105C temperature rating. Resistors (unless specified otherwise) should be metal film types of 0.5 or 0.6 watt and 2% or 1% tolerance. The 1 ohms you asked about would typically be a small wirewound vitreous enamel type.

The 2.2uF input cap should be a film type.
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