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Chip Amps Amplifiers based on integrated circuits

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Old 25th January 2013, 09:06 PM   #11
Sjef is offline Sjef  Netherlands
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No it's like setting 220V on the case of your washing your washing machine and stating it's not lethal because the mains has a earth leak switch (DC protection diodes)

Now no one would think this is normal practice.

It's like saying is that you should walk around the streets in thick rubber bump suit because there are cars driving around that might hit you. It's your responsibilty, not the drivers.

Why on earth would you design a piece of equipment that relies it charging of the output caps on the input resistor of the next stage. Well in lots of cases this all goes pretty well, in some cases it means pure disaster. It's a design flaw. The first time ever I have seen this in a ac coupled amp. This is a commercial vendor who should pay attention to safety.
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Old 25th January 2013, 09:38 PM   #12
dmills is offline dmills  United Kingdom
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One should IMHO design outputs to be conservative in what they generate, AND inputs to be very liberal in what they will accept, to do other is to invite reliabilty problems.

That means ESD and transient protection, it means bleed resistors, it means RFI filters and limiting input bandwidths to someting sane, it means not passing ultrasonic energy from a DAC to its output, and designing inputs to deal with it if it is present, it means design tradeoffs, and possibly a little thermal noise, but that is the nature of engineering.

73, Dan.
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Old 26th January 2013, 02:27 PM   #13
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Quote:
Originally Posted by Sjef View Post
DC protection is not needed if the preamp has a coupling cap AND A BLOODY CHARGING/BLEEDING RESISTOR. That's the place where it belongs. Even with dc protection on the input of the poweramp this could lead to serious problems.
I have a ebay chinese gainclone, and can you tell me where to solider the bleeding resistor?
I'm new to gainclones, som can you tell me; what does this resistor do, and where should I solider it?
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Old 27th January 2013, 02:24 AM   #14
redjr is offline redjr  United States
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Taking a broad brush swing at the Asian eBay vendors is unfair. They're not all 'crap'. I'm sure there are many reputable companies. I know of a couple I deal with, and I can unequivocally state they offer first parts, kits and other DIY audio sub assemblies.
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Old 28th January 2013, 05:33 PM   #15
Mykk is offline Mykk  United States
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Please forgive me uneducated question here. I realize you deal with alot of newbs here, I'm afraid I'm just adding to the toll.

I have a chinese 6n3 tube buffer I was planning on using in a home sound system. Do I need to worry about the same bleed resistor issue? If so, what value should I add and where. I am not new to electrical, fabrication, soldering/wiring. I have a career in automotive electronics. I am however new to the world of home/commercial audio electronics.

This is the buffer I have:

Buffer 6N3 Tube Preamp Amp Matisse Kit with Transformer | eBay
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Old 3rd February 2013, 01:24 PM   #16
Sjef is offline Sjef  Netherlands
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A capacitors with a DC voltage on it needs a reference to ground so that the cap can charge up.

In this exemple, when you have an output stage wich is capacitor coupled between the cathode of a tube and the cathode resistor htere will be a voltage on that side of the cap wich is equal to the voltage on the cathode resisitr (if it is refered to ground that is) The cap has to charge up to this voltage wich it can only do if it has some kind of ground reference. The ground reference can be a simple resistor of several tens of kiloohms. The value doesn't matter much. This value only set the time in wich the cap charges up. If fully charged the voltage on the other side of the cap equals zero. If it cannot charge up the voltage on the other side is exactly the same as on the input side. In that case, when you connect the buffer 'live' to an amp ther wuill be a sdden charge up via the input resistance of the amp wich means there will be a considerable amount of DC at it's input for some time.

I will see if i can draw a simple schematic of it. It's really very very simple, it's just one tiny little resistor, that's all. But it is of great importance.

In the mean time I have ordered a new lm3875 chip to repair my amp. Can't wait. Still listening to the tripath amp now wich is really pretty bad, almost unlistenable bad. Music never sounded so uninvolving, boringly flat, undynamic, veiled, undetailed and truncated on every note than with this amp (also with every other Tripath I have tried, really don't now what people like in them) Got other amps in the house wich sound a bazillion times better but being lazy I just wait for the Gainclone to be repaired. My advise still stands. Run don't walk away from cheap chines Hifi
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