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Old 24th May 2003, 04:08 PM   #11
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Default Pacific

Hi all,

just finished my version of the pacific (some pics are here I guess you will need an yahoo-account, for i have no own webspace)
It has an additional MC-Pre Stage. Thorsten is right, it has lots of gain (acutally a bit too much)
As a friend stated, it sounds that 'you miss nothing'.
(Same night we tried the blue amp phonostage, well, there is still a lot to improve...)
It is a good value for money, but, on the other hand, no 'beats everything, costs nothing'. Of course, other implementations may sound different.
Rudiger
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Old 25th May 2003, 12:26 AM   #12
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Default Re: Pacific

Koinichiwa,

Quote:
Originally posted by Onvinyl

(Same night we tried the blue amp phonostage, well, there is still a lot to improve...)
Nice work in general, but the ouput coupling cap is a little prosaic.

You can reduce the Drain Load resistors of all stages to reduce gain. This will also allow you to "tune" the sound somewhat. Just as with Pentodes, the J-Fet is more linear into lower loads.

However, the biggie (if you ask me) is to add a third battery and to cascode the two J-Fets with a nice bipolar transistor each, base connection directly to 12V, +V 36V. This makes the drain load of the J-Fet almost zero, maximising the linearity of the circuit.

You may be able then to increase the Gain further by adding the +V up to 48V and doubling or even trippling the load resistor, which may allow you to remove the MC Pre-Pre stage.

Sayonara
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Old 25th May 2003, 01:06 AM   #13
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Hi,
Quote:
... , but the ouput coupling cap is a little prosaic.
Quiet true




Quote:
You can reduce the Drain Load resistors of all stages to reduce gain.
At least the drainres of the stage before the riaa is part of the network, if I understood it right, so tuning might outtune things...

Quote:
However, the biggie (if you ask me) is to add a third battery and to cascode the two J-Fets with a nice bipolar transistor each, base connection directly to 12V, +V 36V.
That may be worth a try.

thanks,
Rudiger
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Old 3rd October 2003, 05:56 PM   #14
Marinos is offline Marinos  Greece
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Default Pacific RIAA - final touches/questions

Hi all,

Some months ago I have built a copy of Pacific and I really like it. The gain is more than enough for my high output VDH MC2.

I used parts from my stock ( beyschlag mf 0.6w resistors, ICL MKP capacitors, SCR tin foil 100n, 2 SLA 1.2Ah // a Mallory 12000uF ) , and I must tell you that this little thing really sings..

Later I added a 470uF decoupling capacitor + 10R carbon film isolation resistors per fet , 100R carbon film "gate stoppers" and finally stacked a 110R resistor on the 30n RIAA capacitor (hidden tc).

All of these changes improved the sound especially the decoupling capacitors.

Now I'm finishing a second build using better parts ( Maplin M mf resistors, SCR tin foin caps, silver mica 30n, Elna Starget 470uF )and better layout but I have two questions.

- The prototype plays ok with the 100K input resistor but the recommended loading for my cartirdge is 47K. Should I change it to 47K or I'm altering anything important for the operation of the 1st stage ?

- The correct position of the resistor for the hidden tc is on top or at the bottom of the 30n cap ?

Any other suggestion/advice is welcomed.
I'm learning but slowly......
Thanks in advance for your help

Marinos
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Old 16th October 2003, 09:51 AM   #15
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Hi,
never heard about adding a resistor for time constant.
But another thing: I recently wrote, the pacific didn't reach the awaited sonic level. Meanwhile I replaced the accus with big panasonics (7,2Ah each) -- it is a completly different thing now.
Sound is deep, tight and sweet at the same time. Not bad, really!
Rudiger
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Old 16th October 2003, 01:56 PM   #16
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Default Pacific preamp??????

Yuk. Built one once for someone. The RIAA accuracy was poor. Some may like its "harmonic structure", but I didn't. A better solution would put a follower in between stages.

Jocko
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Old 17th October 2003, 06:18 PM   #17
Marinos is offline Marinos  Greece
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Hi Rudiger,

Adding a resistor to the HF part of the filter you stop boosting the HFs at around 50KHz (3.18 ìS). This has been referred as the 4th or hidden time constant. See this link for more information.

http://www.klaus-boening.de/html/tim...#time constant

Experienced guys, like Werner in this forum, have mentioned the difficulty of making a suitable PSU for pacific. I started with batteries and from the beginning I have really good sound from it.

Using 7,2Ah SLAs you start with a clean supply, with an internal resistance around 20 mOhm, and capable of huge transients.
I think that this is what you hear now.... Do you bypass the batteries with a BIIIG capacitor ?

Sorry but what do you mean with 'accus' ?

Marinos
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Old 17th October 2003, 07:02 PM   #18
Marinos is offline Marinos  Greece
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Default Pacific Yes..

Hi Jocko,

I also think that something is wrong with RIAA values. With 27K, 3K, 100n and 30n the sound is bass heavy and a little splashed highs. I checked the values with TCJ's RIAA calculator and I came to the following better sounding values 24K9, 3k2, 100n, 35n.

These values are very close to Werner's Pacific variation (see attachment). What values did you use?

For the Pacific "as is" I will only check if moving the 470n coupling capacitor after RIAA sounds better.

For a "modified" Pacific I would like to implement Thorsten's suggestion (see this post, BJT cascode....). Sorry but I don't have the background... to understand the " ...a follower in between..". Could you please explain this in more detail ?

Any better RIAA pre suggestions ?
Marinos
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Old 19th October 2003, 12:37 PM   #19
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Hi Marinos,
with accus I meant batteries, and yes, these are bypassed by huge amounts of uF...

from my limited experience I might add the following:
1) If you use 1.8K Drain-Resistors instead of the mentioned 2.4 K, you change the riaa network as well! Lowering the 27K might cure this. You will as well get lower gain with 1.8

2) I really made a big effort to decouple the very first stage (head for MC-pickup) (choke, Res, couple of caps). That paid!

3) what's the point of the 2.2megs?

Suggestions for better? Currently, I'm building la bohème, we'll see...
Thorsten's suggestions seem to be inspired of klaus boening's design, I think...

Rüdiger
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Old 19th October 2003, 02:10 PM   #20
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Konnichiwa,

Quote:
Originally posted by Onvinyl
Thorsten's suggestions seem to be inspired of klaus boening's design, I think...
I think not.

We added cascoding Transistors to the Pacific long before Mr. Boening published his design.... I have liked using Cascodes in Solid State Circuits for a long time as they allow to combine devices to achieve normally conflicting performance items.

The simplest way to add the cascoding is to use good (Low Noise High Ft, High Beta, good Beta Linearity) NPN Transistors like BC239 and use a stack of 3pcs 12V Batteries for the Supply. The BJT's are added between FET Drain and Drain resistor with the Emitter to the Drain and the Collector to the Drain resistor.

Simply connect the Base of the Transistor(s) to the top of the first Battery (+12V) and apply +36V (nominal - in reality over 40V) to the +B Line. Worked a treat for us. BTW, the Drain Resistor should drop around 12V and the 2SK170 MUST be selected for identical currents for the two channels plus should have Idss of 4 - 6mA....

If one wants to implement Jocko's suggestion to place buffers simply add another BC239 Transistor with another BC239 as CCS. The Base of the first BJT goes to the signal takeoff Point, Collector to +B and the signal is taken of the Emitter. The RIAA needs re-calculating then.

I have done this and attached what I would suggest in this case.... Not as simple as before, but still a minimal number of components per gainstage (6components) and all the transistors can be glued together and hardwired so that hardwiring the circuit in air is still a perfect possibility. And each such gainblock offers a very low noise level with a gain of around 36db and pretty decent (thanks to cascode) linearity.

Another Idea, the schematic as posted here would be usable with the S&B 600R RIAA Module.

Simply connect a 600R resistor between the output of the first stage and the RIAA Module Input and remove all the other RIAA components. As the RIAA is input terminated the RC combo coupling to the next stage can remain just as shown....

Sayonara
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