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Chip Amps Amplifiers based on integrated circuits

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Old 25th October 2013, 03:06 PM   #61
udailey is offline udailey  United States
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Default Am I getting OT?

What about this? I cant find a real life version of this but I am unsure why it shouldnt work as long as we keep the phasing correct. Its a stepdown transformer that would help the amp perform at 20x gain. Yes its more expensive. Lets look past that.
Uriah
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Old 25th October 2013, 03:09 PM   #62
udailey is offline udailey  United States
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Quote:
Originally Posted by davym View Post
Interesting conversation this. When I suggested fitting expensive resistors to my Brian GT LM3886 boards a couple of months or so back, some members told me to save my cash because it would be a waste of time and money.

Anyway, I hope to have a couple of mono block My Ref FE's completed in the near future so that's where my limited funds are going. That and a DCB1 to go with them.

I will probably find another use for the Brian GT kit at some point though, it's good to know it can be improved further as it's pretty decent already.

I also believe it's a good idea to build in variable gain for power amp's but i was quite effectively dismissed by a certain Mr T when I suggested it
There are a lot of variable gain amps out there. My Haflers are variable gain and TI, Analog, NXP, THAT etc etc all make VGAs albeit in smaller packages.
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Old 25th October 2013, 03:46 PM   #63
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by udailey View Post
What about this? I cant find a real life version of this but I am unsure why it shouldnt work as long as we keep the phasing correct. Its a stepdown transformer that would help the amp perform at 20x gain. Yes its more expensive. Lets look past that.
Uriah
If that transformer doesn't get up to at least 4mhz, I suspect that you'll need to add some caps (probably RC's) that will work at least up to the highest pitch the amp may do.

There's open loop gain in that area, so it will take some care. For sure it will sound different. Just using a multi-turn cermet trimmer sounded better to me than a resistor on the negative input to ground leg of the gain voltage divider. This is a bit hard to explain, but I propose that it was the epic gain at that locale that has made resistor differences more noticeable.

Question: I notice that there's a little blue cermet trimmer on your LDR driver board. So, I wonder, ironically, if you've tried using that type of trimmer instead of the LDR??? It might not be as good as an LDR but it will probably beat a film resistor! I tried the 10 turn 1k model at the radio shack; and I connected one of the outboard pins to wiper to use it for a variable resistor. Sounds great and the thing is adjustable. That was. . . a bit easier.
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Last edited by danielwritesbac; 25th October 2013 at 03:53 PM.
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Old 25th October 2013, 04:21 PM   #64
davym is offline davym  Scotland
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I know at least one amp manufacturer who swears by cermet pot's although he fit's ladder type stepped attenuators to his most expensive pre amps.

udailey, I recon there are too many self appointed 'gurus' in this world and audio is no exception. It didn't even help when I pointed out that many pro audio manufacturers also supply variable gain power amp's. My understanding is that it's better to remove unnecessary gain at the power amp stage than at the source to limit the amount of unwanted noise being amplified at the final stage and this is why most sources output around 2v these days. I was effectively dismissed for making that statement and told I had it the wrong way round.

Maybe it's just as well I am quite a tolerant man eh

I dream of a better world where Chickens can cross a road without having their motives challenged.
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Old 26th October 2013, 11:05 PM   #65
udailey is offline udailey  United States
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Davey
Checked your profile and noted your question on Vishay foils. My suggestion (not that you asked me but I've been there) is to use
A: a foil as you wondered
B: Roll your own of manganin which will beat the foil
C: Use a resistor replacer which will also beat the foil and to me the jury is out versus the manganin. The manganin is really really good.
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Old 26th October 2013, 11:42 PM   #66
davym is offline davym  Scotland
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Thanks U

I was tempted to try Vishay Foils even though I had been advised not to bother. I believe the quality of components in the signal path matter but it depends on the situation, sometimes the cost outweighs the benefits.

I am interested in your suggestion of the manganin, that's a new one to me. Can you point me in the direction of some more info on that, I like the idea of rolling my own.

Cheers

Davy
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Old 27th October 2013, 12:16 AM   #67
davym is offline davym  Scotland
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I just found this supplier in the UK WIRES.CO.UK MANGANIN

Lots of diameters, bare or insulated. Which to use and what to use for a core, would a thick piece of solid copper wire do if I left the insulation on?

Also how to wind it accurately, would an electric drill do. Sorry if all this seems obvious, it's not something I have looked into before.
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Old 27th October 2013, 04:12 AM   #68
udailey is offline udailey  United States
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Try ebay. Manganin is hard to find at more than 350 ohms per meter. Must be insulated but you myst be able to solder through it.
You can get 100ft kits on ebay.
Wrap it on a dowel or tube or even just cardboard. Its dainty stuff. You need a magnifying glass and patience.
Get some copper wire to fab your leads. Solder the manganin to the leads.
There's a resistor thread around here where I got a bit more detailed.
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Old 27th October 2013, 11:06 AM   #69
davym is offline davym  Scotland
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I would have to get some sent over from the US, that can get very expensive.

If I can get some fairly cheap, I might have a go at winding some for low values but inductance issues could be a problem. I'll look into it a bit further.
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Old 31st October 2013, 03:59 PM   #70
udailey is offline udailey  United States
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In regards to the LDR based chipamp...
I have the board finished. I am wondering if there is interest in a small group buy. I think Silver Circuits at CustomPCB.com would do the trick in a few weeks for a very low price. I just want two for myself but figure I can defray cost by selling a few to you guys. Anyone in?
If we do 20 then they cost me a bit over 7 each and shipping in the US would be around 3 bucks each order plus my packaging so 4 bucks total shipping. Outside the US I think it would run around 7 dollars shipping.
We can talk about me supplying the entire BOM if there is interest. Cheap anyway. Entire BOM probably around 15 my cost.
So lets say that an entire kit including parts and board would run around 22 dollars. Its cheap.
I would build and test first of course. So I could set up a google page to run the buy and then if I get to 20 boards then I buy them and test them. If it works then I invoice you guys. We all win
If youre interested show interest here so I know if I should do the google spreadsheet.
Uriah
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