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Old 15th October 2012, 02:07 AM   #11
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Cool Boozehound Break-Down Part 1 - JFET psu & gain control...

Hi again A M

Just another thought...
...This circuit is one that pays dividends...through experimentation...so...
Buying in costly & fancy parts from the get-go...might well back-fire...
...and you end up finding they need value changes to optimise.

The gain resistors, for example, can be replaced with a fixed value...later...
...But in the mean while, a 5K 20 turn mini-pot would be a smart move !

Measure & set it to the schematic value to begin with...
...can optimise later...depending on cartridge output & JFET current draw.

A good thing to do first off as well...is measure the current draw of your JFETS to see if they are any good...ie well matched...if not ...you might want to get some more & test them as well.
About 99% more important than a $1M resistor !


Si.
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Old 15th October 2012, 02:30 AM   #12
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Si, thanks again for your help, this is starting to get fun.

The Ayre is $2500 not $25,000 but it is still very quiet, uses jfets and is going to be my reference pre to compare to the home made jfet pre's. I keep any transformer away from gain stages, orient them properly and shield them.

A little trick I found is to hook up a microphone to a simple mixer with a mic pre and listen on some headphones, then move the mic in the air around the transformer (while transformer has power running through it but no need to touch transformer, be careful) The mic allows you to hear where the worst transformer radiation noise is coming from. This can help you build a really good shield.

There are a lot of R core tranny's coming from China of questionable quality, this may have been the case. i will ask my friend next time I talk to him.

Also thank so much for posting all the schematics in one place to see how many variations there are on these things. I love the second one down all the way on the left (Pacific with RiAA mod). It is so elegant, I already have all the resistors to get it working and it gives me the peaceful feeling like looking at a really nice vintage tube schematic and knowing I can solder it up point to point in a very short amount of time.

The only problem I see is that I bought a bunch of 2sk170 BL jfets instead of the GR, that may give me some issues with the gain as you mentioned above. I don't know enough about circuit design to address this. Guess I need to read up on the threads to find every detail as you mentioned.

I can drop a few bucks on the 27k resistor because it is the only one in the signal path!
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Old 15th October 2012, 02:35 AM   #13
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Agreed, very wise advice to build and optimize circuit before dropping any dough on pricey resistors that may not be the right value.
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Old 15th October 2012, 02:38 AM   #14
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Yes I know it's only a cheap one at $2500...
...I just added the extra ZERO to wag you !
( no typo ! )
Could have added 000000000 !!!!!!!!!!!

Anyhow...
....you could get your Boozehound to sound better !!!

Si.

EQ section info coming up next...
...stay tuned ( no pun intended ! )
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Old 15th October 2012, 02:45 AM   #15
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The BL ( blue ) grade JFET's I'm sure will be just fine...
...measuring them is easy & will tell you if they are OK.

Have you got a meter that measures 'capacitors' ?

Don't spend on the 27K ( no not $27000 ) resistor...until you have checked out the online RIAA calculators...& measured your capacitor values...you may wish to change the value.

Have you got the PIO caps or any others already ?
What have you got ?

Si.

Last edited by The Space Egg Corp; 15th October 2012 at 02:47 AM. Reason: Sorry...I meant BL not GR...JFET grade now corrected !
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Old 15th October 2012, 03:03 AM   #16
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Arrow My $25 000 000 phono-pre with 0.01% accurate RIAA equaliser ( yeah...right ! )

Here's the RIAA equaliser section.
A million-dollar series resistor...
+
Capacitors ( need to measure them )

Could be...
PIO
Teflon
Polypropylene

Values can be 'bumped-up' to the desired value by soldering small value...
Polystyrene ( NOT 'syroflex' TM ( TRASH ))
or
Silver Mica...
...across the main big capacitor.

Tip Here...
...measure the big ones first ( optimise with online RIAA calculator )...
...then order your Polystyrene or Silver Mica's in whatever smal pF or small nF values are needed to make up the correct value.


Si.
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Old 15th October 2012, 03:30 AM   #17
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Yes i have a cap meter and all the caps I received are very lose to spot on their stamped value, nice!

No I won't buy that expensive $27,000 dollar resistor yet. I am going to build whatever pre I decide on first with the cheap Radio shack resistors on hand until I finalize.

I am not so sure what I am going to build at the moment. I started out planning to build the Boozehound and bought all the jfet 2sk170 BL versions and the Russian PIO caps .1uf, .033, .001 and 1uf. I also have large selection of larger pio and other sized output and coupling caps laying around.

Although after seeing the Pacific "RIAA MOD" schematic second down on left on your list I think I am going to build that or a slight variation as it has 6 resistors as opposed to 12 on the BHL and I have plenty of .1uf and .47uf's laying around as well as the .033uf needed.

(Actually I bought enough parts to build two Boozehounds) just in case I needed a second one to pretend I am a DJ for a party here and there, so I a may just build a Boozehound anyway for kicks to compare with Pacific.

I also just read an quite lengthy interesting "Words of Wisdom" paper by John Curl talking about the many aspects of solid state design and he recommended not using a resistor before the gate on a jfet as it just adds noise. With my limited knowledge of circuit design I am taking very carefully John C advice and his legendary experience. I guess am going to be learning about circuit design as I build these and listen

http://www.q-audio.com/johncurl.pdf

Last edited by audio mind; 15th October 2012 at 03:58 AM. Reason: typo/grammar
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Old 15th October 2012, 04:11 AM   #18
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Yes...
...Mr Walter's original 'L' Pacific' is VERY minimalist.

Less resistors = Less NOISE...
...whether in practice, rather than theory, you will notice this is another matter...
...well worth bearing in MIND though.

As you see...
...the 100R series & the ones from JFET's to ground are not in the original...
...However...
...The ones from JFET's to ground could be a good move...
...I would loosen the purse-strings here and spend $0.50c on a pair of 100R 3watt 5% wire-wounds, for least theoretical circuit noise & super theoretical stability.
5% tolerance is fine...not a critical value really...Match per position per channel if possible though.
Just to say you did it, if nothing else !
Conrad Johnson...eat yer heart out !

Si.

Another EQ scheme coming up...
...this time a ZERO CAPACITOR option...Very Expensive...Very 'Audiophile'
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Old 15th October 2012, 04:19 AM   #19
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My favorite 3watt wire-wounds BTW are...

...the green-round type 5% 0.50p each
( of course the tolerance is only in manufacturing, once measured, the value will not change EVER !!!...so go figure...6 of these for cost of 1 0.1% type...Z-Foil...get outta here ! )

People don't seem to like the 'square white type' much...never used 'em myself so can't comment.

or
...the black ( Vishay, I think ) 0.1% for more critical apps. 3.00p each

Si.
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Old 15th October 2012, 04:48 AM   #20
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I believe the majority is correct, the square white sand resistors are harsh sounding low fi to me, I would avoid those at all costs for critical designs. Wire wound always in place of white or beige square sand resistors is the way to go if possible.

I don't mind adding the resistor to ground off the jfet if needed.

You mentioned a zero capacitor design, does it use a +- supply? I would like to see that schematic.

Next is the power supply design to think about, I am wondering if a really stiff supply with chokes might sound better than a discrete regulator?
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