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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 6th March 2012, 10:37 PM   #7381
dimkasta is offline dimkasta  Greece
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Thanks a lot
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Old 10th March 2012, 10:18 PM   #7382
Djinn is offline Djinn  Norway
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Wink Thank you for your answer. :-)

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Originally Posted by Salas View Post
Set each at 150mA and supply channels individually. To keep the power output impedance low.
I am now gathering and matching parts for the riaa 43db version, and I am using a Tonghui TH2821A 10KHz LCR meter with kelvin test probes and a Fluke 87V and a Fluke 73II for testing and matching.

I am using russian silver mica caps for the riaa circuit. The caps are spot on 47nF and 15.330 nF (I soldered several together to get it these values).

Regarding resistors I have followed the posts and bought Shinkoh resistors. What about the 1M resistors as I have not fund any Shinkoh in this value, what about Amtrans amrg? Are there any other resistors that will match the Shinkoh, Z foil, Caddock maybe as the 47K input resistor?

I will post some photos as the work evolves.

With kind regards and thanks once again for all the help this forum has given me

Martin
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Old 10th March 2012, 10:42 PM   #7383
Salas is online now Salas  Greece
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Simplistic NJFET RIAA
Since you are going towards the more ''organic'' flavored parts, use Amtrans 1M. For the load resistor Shinkoh and all you mention give subtle results of their own, its more about cooking them parts for some favorite overall flavor than finding equivalents. The more neutral and informative of all those is Z foil. Important is the 47K bridge resistor between input stage and RIAA too.
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Old 10th March 2012, 11:31 PM   #7384
Djinn is offline Djinn  Norway
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Quote:
Originally Posted by Salas View Post
Since you are going towards the more ''organic'' flavored parts, use Amtrans 1M. For the load resistor Shinkoh and all you mention give subtle results of their own, its more about cooking them parts for some favorite overall flavor than finding equivalents. The more neutral and informative of all those is Z foil. Important is the 47K bridge resistor between input stage and RIAA too.

It is not so easy to chose parts and I assume I will be testing and changing resistors quite a bit in the months to come, but that is also some of the fun with DIY . The cost of it all is the down side, and since the Shinkoh 47K is not so easy to come by in 0.5W I really would like an alternative (I have them in 1watt but the matching is not good). Maybe the Z-foil will be the way to go, I am really are not certain? regarding interstage cap that will be an russian FT-3 100nF. And since I allready have some K75-10 2.2uF caps and some FT-3 220nF, maybe I will use these for output cap. Any oppinions on what would be the right way to match components will be appriciated. Are these components maybe to "soft" sounding?
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Old 10th March 2012, 11:46 PM   #7385
Salas is online now Salas  Greece
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Simplistic NJFET RIAA
The bridge 47K resistor needs have best tolerance so use Z foils there. The input load puts no particular tolerance demands so use the 1K Tantalums there. Mixing the Teflons and the Z foils which are clean but not harsh with the ''mellower'' ones produces some balance. Never go one sided in total because it gets boring tonally.
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Old 11th March 2012, 12:45 AM   #7386
Djinn is offline Djinn  Norway
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Default components and matching

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Originally Posted by Salas View Post
The bridge 47K resistor needs have best tolerance so use Z foils there. The input load puts no particular tolerance demands so use the 1K Tantalums there. Mixing the Teflons and the Z foils which are clean but not harsh with the ''mellower'' ones produces some balance. Never go one sided in total because it gets boring tonally.
I am really looking forward to testing the riaa I can hardly wait. But what about the 6.8k resistors should these be z-foil as well or maybee somthing completly different. I have heard and read that the Shinkoh to is on the top shelf, but as you say it is all about getting a balanced sound.

With kind regards

Martin
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Old 11th March 2012, 08:13 AM   #7387
vgeorge is online now vgeorge  Greece
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If I could, I would put z-foils. What I did was to put some 2.2M resistors in parallel to bring the Shinkohs down to 6.8K, as they were measuring a bit high.
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Old 11th March 2012, 07:57 PM   #7388
Djinn is offline Djinn  Norway
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Smile resistors and capacitors

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If I could, I would put z-foils. What I did was to put some 2.2M resistors in parallel to bring the Shinkohs down to 6.8K, as they were measuring a bit high.
Yes getting resistor value spot on by connecting them in parallel is smart, I will be doing this with 2.4k to get the 1.2K value that I only can find in 1W when it comes to Shinkoh. I will try to keep values matched between the two channels. And if I get it right, the 47k, 6.8k and 1M regarding riaa is important to get in dead center. Well there will be many resistors that will be surplus stock after I am finished.

Is there anyone that have other recommendations, and what about output capacitor? I have both the 220nF and the 100nF FT-3 that could be used, along with K75-10 and K73-16. Any recommendations and suggestions is greatly appreciated.


With kind regards

Martin
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Old 11th March 2012, 08:06 PM   #7389
Salas is online now Salas  Greece
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100n will be enough for bypass.
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Old 14th March 2012, 05:27 PM   #7390
atupi is offline atupi  Romania
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I have received today one nice aluminum box for my RIAA preamp. How to proceed with grounding the case ? My pcb's (preamp, shunt) and RCA connectors will be isolated from the case but i think will be good to have the case connected to ground. Also where to connect the ground wire that comes from TT ?
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