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Chip Amps Amplifiers based on integrated circuits

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Old 27th July 2009, 02:05 PM   #831
udailey is offline udailey  United States
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I test for DC while playing music from my speakers.
Uriah
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Old 27th July 2009, 04:10 PM   #832
troystg is offline troystg  United States
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jonclancy

Exactly what Uriah said... My you have nice..... Toriods..
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Old 27th July 2009, 04:16 PM   #833
AndrewT is offline AndrewT  Scotland
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Default Re: DC Offset

Quote:
Originally posted by jonclancy
Clarification gratefully sought,
check the output offset of the amplifier alone. To do this you should short the input hot (Signal flow/line) to the input cold(signal return).

Now disconnect the short and connect the source.
Check the offset again.
It should be the same but sometimes it changes. Do check for each source if you have a number of pre-amps or intend to direct drive from music sources.
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Old 27th July 2009, 05:33 PM   #834
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Lightbulb Thanks!!!

Thanks everyone - that's all perfectly clear now!!

BTW, the Grounding / Safety Earth thread has changed my attitude towards mains-powered projects entirely. It should be made compulsory reading on joining the forum!

understanding star grounding

Cheers

Jon
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Old 28th July 2009, 06:16 PM   #835
jERiCOh is offline jERiCOh  Canada
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Just a head up...

Finally I fixed my bad channel. Replacing the LM3886 stopped that noise.

Thanks guys for your help. Now I can work on the enclosure.
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Old 1st August 2009, 09:43 PM   #836
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Cool Another fine pair.....

... or MyRefC amps!! Same toroids, though!

Click the image to open in full size.

I finished these this morning and they tested absolutely fine. DC offset is 0.9mV - must be bouncing off the accuracy limits of my DMM to be honest.

Hooked up to the big speakers, I get the same HUGE soundstage and MASSIVE bass. These amps are only half the power of my Arcams, but seem to have a synergy with my system.

This pair were built completely stock - no sockets (apart from the LM318) or substitutions. As I have the other pair socketed, it'll make rolling easy. Sounds so good, I don't know if I can be bothered!! I might bung them on the scope and see if there's anything to see (dual window) between them, and I still have one of the first pair to have a look at (decided to reduce power output on its own).

My plan is to install the trafos (all 4) in a separate case with umbilicals to the amp box. Safety earth will be fed back to the power box. Signal ground will be starred and linked to safety earth with a Safety Loop Breaker circuit. As far as I see it, there is no power common (4 boards, 4 trafos).

Comment and suggestions gratefully recieved!

All in all, a great deal learned, fun had, and at Bank/Mrs-friendly cost!

Thanks again, guys!

Jon
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Old 2nd August 2009, 12:53 AM   #837
udailey is offline udailey  United States
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Nice Job Jon!! So glad you are thrilled with their performance.
I do guarantee increase in sound quality with the removal of the input caps. I also guarantee increase in sound quality with the Lightspeed. So you have minimum two things to look forward to.
Now with regard to opamp rolling... I would read the original thread. It was very frowned upon for the most part. The opamp has a great slew rate and THATs what makes it the opamp for this circuit, not whether or not its a BurrBrown or LM4562 or other hot shot opamp So I just suggest searching the original thread first.
Have fun!
Uriah
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Old 2nd August 2009, 03:15 AM   #838
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Jon,

Glad to see you're up and running with 3 out of 4.

Rolling opamp is not advised. There is nothing to be gained and possibly something to be lost, according to the designer and experimenters in the original thread. Mauro was no dummy, and he used the BEST sounding opamp for this circuit. These are amazing little amplifiers.

Putting trafos in a separate box probably won't provide any improvements, either. The amps should be dead silent, even with a transformer only inches away. If not, there is something else wrong. Unless you're doing it for practical reasons such as space or enclosure availability, long umbilicals may very well contribute more problems.

The single most critical area to be improved sonically is the input cap. It's really that simple. If you want to experiment and make your amps sound better, spend as much time and money as you can on optimizing that single component with polypro or teflon caps, either high quality metalized film, or actual film and foil. They do not need to be mounted on the actual PCB. Or as Uriah suggests, eliminate them, but understand the risk.

Peace,
Tom E
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Old 2nd August 2009, 03:24 AM   #839
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Default Re: Another fine pair.....

Quote:
Originally posted by jonclancy
This pair were built completely stock - no sockets (apart from the LM318) or substitutions. As I have the other pair socketed, it'll make rolling easy. Sounds so good, I don't know if I can be bothered!!
...
Comment and suggestions gratefully recieved!
I can assure you, Jon, that it could sound even better

C13, C9 and C21 have the biggest impact but also others components swap are clearly audible.

In Rev A LM318 can be swapped with others opamps but in Rev C it is not advised because one of the mods is related to the compensation network of the LM318...
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Old 2nd August 2009, 04:11 AM   #840
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Also C32 swap had a big impact on my setup...
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