Simplistic NJFET RIAA

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#2,901
Hi Salas

After much twisting and repositioning of the two TX, I finally got an acceptable compromise minimizing hum.

There is a sweet spot were I can hear the image focus.

The true double mono setup also brings improvements in detail and speed.(It is very difficult to reach because turning only one TX will reduce noise in one channel and increase on the other so you need to turn the other TX to compensate..... All this with power on !!! )

I guess using only one TX is the way to go. Choosing this configuration I will use only one winding + one rectifier bridge to avoid rectfiing currents to loop inside the TX.

After that I am not sure if I can use two smoothing caps (one per channel) to feed the separate shunts or if I must use only one smoothing cap after the rectification to feed both shunts.

🙂
 
#2,902
You can branch out with RC or LC to channel filters most certainly. Counting on your experience, that is why I got in to the hassle and high price of bringing in the R-Core so to avoid as much as I can since I fancy one box too.
 
#2,903
Already have most of the parts for my next 57dB riaa including the case.

I chose a 80mm high case before experimenting with TX positioning so now I have this issue:

Minimum hum happens with the toroid on it´s side and I can not find an R core with 80mm... can I expect the r-core to be as good positioned flat inside the case ?
 
#2,904
It is supposed so, but I will have more info when I get all the parts and build. Another line of thought would be for the boards to be made short enough so they go vertical in your case? Thus keeping the toroids base down.
 
#2,905
I will have to review the p2p layout to acomodate the bypass cap over R2 and make space for the DIP Switch so I will try to make it slimmer 🙂

After installing the second toroid, I lost the hum coming from the rectifiers loop and gained a lot of definition.

This produced a subjective shift on the tone producing a slightly thin edgy sound.

To regain the fullness of sound I replaced the 470u35v Pana FM over the voltage reference resistor in the shunts by a much bigger 470u50v Nichicon Muse 🙂🙂🙂🙂

Now I am again rewarded by a full bass with detail and smooth highs.

My Voicing results are finally spot on with my previous thoughts.

Ricardo
 
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#2,909
RCruz said:
To regain the fullness of sound I replaced the 470u35v Pana FM over the voltage reference resistor in the shunts by a much bigger 470u50v Nichicon Muse 🙂🙂🙂🙂
Ricardo
Click to expand...

This again confirms the importance of what capacitor is in that position. Ricardo, did you bypass that capacitor with a film cap as well? Some people have reported very good results with two parallel caps, one of them a good film cap.
 
#2,911
Muse caps alone give very good bass but the sound seems "muffled / veiled" so I bypassed them with 4.7nF radial styroflex.

While keeping the good bass, a good quantity of "sparkle" and "space" was added.

Fingered strings are much more lifelike now.

I will let it burn for a while but IMO it is a keeper...🙂

Ricardo
 
#2,914
Hi Iko..... quite glad to be of help...... Happy new Year 🙂

Yesterday I had a good listen and left the riaa on during the night (remenber my previous issues related with spitting noises on power on ?.... All gone ! The fault was in the zeners 🙂).

The bypass on the muse proved a very good match and the sound presents now good bass presence allied with detail and attack.

My next mod will be the bypass cap on the first jfet to increase gain on the 48dB riaa.

Hi Salas

Can I use higher value caps there.... In your 0.2mV riaa I see you used 4700u... Would you elaborate in the resistor bypass tech so I can better understand it ?

Ricardo
 
#2,917
Please help, could somebody recommend me heatsinks types from Mouser or Digikey neededs for IRFP9140, with part number will be better🙂?

I ready matched all the 2SK170 bought to Spencer, also all the BC550C.

Finally I have all parts except:
-The heatsinks.
-The Shinkoh resistors for NJFET RIAA, today I will order to PCX.
-The Panasonics caps AI TSHA 10.000uF/63V, instead the Pan's next friday will get these Epcos Sikorel 10.000uF/63V:

R190891-01.jpg


Thanks
 
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