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Old 27th September 2010, 07:25 AM   #5011
Salas is online now Salas  Greece
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Reduce the output capacitor's value if you ever buy an Obbligato down to 2.2-3.3uF if your next stage isn't lower input than 20K Ohm. Not having to pay for 10uF that will allow more infrasonic rumble on top of the expense. Maybe your carts are already loaded well with what the TT cables and residual input capacitance provide. In any case for an MM two things can help you nail the final system best HF balance. One is to substitute the Rload input resistor to ground with a 100k trimmer wired with its middle pin and low pin together to ground. By tweaking that, the cart's HF change. Another way is tweak C3, is the HF riaa cap. If you will feel too much treble, add value, if you feel soft treble reduce value. 15.3-16.1nF play should give enough trends. Maybe there is more in the TT and carts to tune and listen to even better although it may be ''wow'' already. Hum is normal in a non boxed phono. Buzz could be a loop. Use shielded coax for signal and keep the trafo outside. You got a tight perfboard layout and that is good.
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Old 27th September 2010, 07:48 AM   #5012
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Thanks for the input Salas, very much appreciated. I had the 10.0uF caps from another project and had ordered some 3.3uF Soniq's from ebay, but only 1 arrived!!! (I'm still chasing that... grrr). I'll try the input trimmer as that's the easiest to change first, and I'm sure the hum will disappear with an enclosure.

I'm also glad that you consider the tight layout a positive... it was more like building mini-models than soldering. :-)
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Old 27th September 2010, 07:55 AM   #5013
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Its not trivial. Omnipresent 47k and some pF load isn't the best answer for what an MM can give. Look what paying attention can do.
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Old 27th September 2010, 08:28 AM   #5014
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Great read. Certainly makes me wonder if I should build some a variable input loading device to wire any pre-amp under test through, minus the Rload & Cload of the amp itself of course. It looks like the loading alone could be enough to wrongly turn me off a given circuit if it weren't optimum. Thanks for the further insight. The learning continues.
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Old 27th September 2010, 08:35 AM   #5015
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The preamps don't vary significantly for residual input capacitance in most cases. And they all got 47K for MM. If there is no purpose added pF parallel to their input of course. The carts differ a lot in needs. Best tactic IMO for those who want to be checking best MM loading is to use no extra cap no matter what the manufaturer says, use a 100k trimmer, hunt high to low, and when settled after enough records, subtitute the arrived at value with a good resistor.
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Old 27th September 2010, 09:47 AM   #5016
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Of course... it's cartridge loading, not pre-amp loading... silly me. I'll apply this method and see what I come up with. Given it is unlikely that I'll be changing carts too often, I could fix this value once decided. Are there any pots or trimmers that are good enough to remain in this location for future adjustments for cart changes?
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Old 27th September 2010, 07:06 PM   #5017
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Those look good. http://www.texascomponents.com/pdf/5_reasons.pdf
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Old 27th September 2010, 07:57 PM   #5018
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Quote:
Originally Posted by Salas View Post
The preamps don't vary significantly for residual input capacitance in most cases. And they all got 47K for MM. If there is no purpose added pF parallel to their input of course. The carts differ a lot in needs. Best tactic IMO for those who want to be checking best MM loading is to use no extra cap no matter what the manufaturer says, use a 100k trimmer, hunt high to low, and when settled after enough records, subtitute the arrived at value with a good resistor.
My friend Chris is using the Hagerman Piccolo MC (without RIAA) togheter the Puresound P10 MM (with RIAA), now is time to upgrade the MM & the question is: it's necessary also the 100K trimmer when is connected before the MC phono preamp?
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Old 27th September 2010, 08:03 PM   #5019
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Default Balanced Simplistic NJFET RIAA

One photo my Balanced Simplistic NJFET Phono RIAA just for fun:

Click the image to open in full size.

To finish only needs the 15nF RIAA caps.
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Old 27th September 2010, 08:32 PM   #5020
Salas is online now Salas  Greece
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Quote:
Originally Posted by merlin el mago View Post
My friend Chris is using the Hagerman Piccolo MC (without RIAA) togheter the Puresound P10 MM (with RIAA), now is time to upgrade the MM & the question is: it's necessary also the 100K trimmer when is connected before the MC phono preamp?
No way for MC carts. This is for MM carts only that have high inductance and react with hundreds of pF and tens of Kohm. The pre pre loads the MC and expects 47K MM input.
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