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Old 8th November 2008, 02:23 PM   #1
thuur is offline thuur  Belgium
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Thumbs up Fix my RIAA

Hi there,

Just bought an nice small preamp for my recently (back from the basement) installed turntable. Hooked it up to my Arcam and it sounds great I've installed a new Ortofon cartridge Link to specs.

The problem however is that on loud recordings (last few years of mostly dance/club and pop records) the pre-amp starts clipping.

Another minor problem is that the power supply isn't filtered or anything. I've installed a separate fuse group in my house for the stereo, but I can even hear the neighbour's refridgerator turning on with this thing

I've been soldering for almost 20 years now and have a higher degree in Electronics, however actually never did anything with it. I can read schematics and solder it together, but with phrases like 'add another stage' I'm lost

I would really love to attach my schematic and two pics, but somehow there is a problem with uploading them? Yes, they are <100kb.

So, the question is simple: what must I change to make this this el cheapo preamp fit my system and sound great?

If I can provide more info, just shout.


PS: I know I can buy an expensive phonostage, or create a brandnew one, but the WAF factor plays and important role as well
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Old 8th November 2008, 05:00 PM   #2
thuur is offline thuur  Belgium
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Still cannot upload...

Here are the links then.

Schematics
http://www.imagebam.com/image/1e20a317774400

Top
http://www.imagebam.com/image/2d00d117774401

Bottom
http://www.imagebam.com/image/e2a72a17774402



Thanks in advance!
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Old 8th November 2008, 06:50 PM   #3
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You can increase R8 220 -> 470 ohms

or

Reduce the R7//10n + R4//2n7 to half the impedance = connect the same network in parallel.
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Old 9th November 2008, 11:30 PM   #4
thuur is offline thuur  Belgium
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Thanks!

I'm about to place an order for all sorts of components, so I'll order a bit more.

Does the impendance match the phono cartridge better with adding a parallel network?


It's best to use metal film resistors, right? And polypropylene for capacitors?
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Old 12th November 2008, 11:01 AM   #5
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Default Isolation AMp

Hi.
I have a setup in my home where i have an Isolation Transformer. Being in Australia iwe have 240Volt at the mains. I got 2 stepdown transformers (240 to 120 Volt) and use a pair of them to form a balanced 240 Volts bycombining the 120 V outputs from the stepdown trannys) Depending on the current draw of your amp and therefore the watts needed, could you try this with say a 120 to 12 volt transformer. Then connect the 12V out of the first transformer to the 12Volts tapping of the second identical transformer to get 120 Volts isolated out (in other words the second tranny is connected the opposite wayand assuming you are in the USA and that you only want to power the preamp in this way)... I have noticed a big difference in the crud that comes throught the mains.
Of cousre if you arent confident with mains volatges, then dont do it and all the other usual high volt caveats
Nick
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Old 18th November 2008, 04:51 AM   #6
kevinkr is offline kevinkr  United States
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Play with this for a while, but based on what I've just seen you really either ought to invest in a better phono stage (one of the Project models comes to mind) or better still build one of the many mentioned here.
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Old 18th November 2008, 06:09 PM   #7
thuur is offline thuur  Belgium
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Ok, thanks!

I'll just slighty modify it and start saving for something better then.
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Old 24th November 2008, 02:48 PM   #8
thuur is offline thuur  Belgium
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Why can't I find any 2n7 capacitors?

All the shops have to offer is 2n2 or 3n3...


Thanks again
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