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Old 7th December 2008, 09:25 AM   #11
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I have never tried Auricap actually.
Up till now i was content with Zen caps.
Unfortunately they don't have values suitable for RIAA applications.

Nevertheless from the multiple researches i have done so fare Auricaps are the best, reasonable priced speaking, film caps on the market.
They are widely used on all kinds of modifications/tweaks and so on.

They are not as good as Dynamicap or others, of course.

I would use dynamicap actually, but i can't find any source for the 2700pF RIIA cap and i don't like to use 2 brands for the RIAA network.

If you wish you can tell me what is the best film cap accordingly to your experience that canbe found on the value required from the network in exame.

Speaking of BG: yes, I am sure they are good, but i don't mind taking more space on the board Vs having eletrolytic, although good ones, on the RIAA network or on signal path in general.
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Old 7th December 2008, 09:41 AM   #12
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Sorry, didn't realise this was about riaa caps. BG are obviously inappropriate. I like the cheap polystyrene Relcaps for riaa. Their teflons are probably much better.
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Old 7th December 2008, 09:59 AM   #13
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alright, not a problem

I didn't read great things about Relcap though! Still more inclined toward Auricap that are cheaper than Teflon Relcap.
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Old 7th December 2008, 11:23 AM   #14
MRupp is offline MRupp  Germany
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Default Bootstrapped cascode

Excuse my ignorance, and maybe I do not understand differential pairs well enough, but I do not see that you are really bootstrapping the common base transistors. You are referencing the cascode to the connection of the common sources with the current source. However, this point should have a more or less fixed voltage - in other words the effect would be the same as referencing the cascode to ground. If one side of the K389 is conducting less the CCS is just forcing more current to the other half, but their voltage should remain fixed.

Secondly, the signal voltages are so small that the capacitance of the K389 should not really change, besides it should be too low to make any differences in the load. So I do not "buy" this explanation either.

My last comment before I shut up: I believe the 5 Volt reference is setting the drain to source voltage too low. As a minimum I would try 2 references in series to get 10 Volts, that is if you must use them in the first place.
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Old 7th December 2008, 04:56 PM   #15
GaryB is offline GaryB  United States
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Quote:
Originally posted by Stefanoo
With regard to resistors i am planning on using Naked Vishay S102 that are premium resistors. For cap, still premium one, with Auricap Film Caps. Electrolytic will be Black gates STD for the smoothing caps and F for the RIAA 2 X 220uF (which i will replace with just one 470uF).
I've never listened to naked Vishay resistors but I suspect they will be fine. Regarding the RIAA capacitors, I don't think that Auricaps come in the right values. I was looking at the Partsconnexion website and see that Relcap has Teflon 0.01uf and 0.033uf 200v caps that would be excellent. They are expensive but I would recommend that expense. If budget is limited then I'd spend money on the teflon caps before the expensive resistors.
For the 2x220uf caps, I agree with Analog-sa that the Black Gate 220uf 6.3v NX capacitor is a much better choice.


Quote:
I am planning on using the 5V reference voltage AD586 (it's 2ppm with an extra low residual noise) on both current mirror and bootstrap.
- if you want to comment this last modification i don't know if you tried to replace the led with a good voltage reference-
The voltage of the LED is much less than 5v, so you will need to adjust the values of the resistors in the emitters of the current mirror transistors to get the right currents. I don't think this is worth the trouble since LEDs are already low noise.
In the bootstrap cascode, you can not use the AD586. You need to use a two terminal device such as a zener diode and the LM336 that I used is a very good low noise zener. Don't change this.


Quote:
One question:

you said you had to change the bias resistor R3 (ok) and R7 (? did you change this one? did you mean to say R67?
Yes, that is a typing error. It should have been R67.

Regards,
---Gary
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Old 7th December 2008, 05:05 PM   #16
GaryB is offline GaryB  United States
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Default Re: Bootstrapped cascode

Quote:
Originally posted by MRupp
. . . I do not see that you are really bootstrapping the common base transistors. You are referencing the cascode to the connection of the common sources with the current source. However, this point should have a more or less fixed voltage - in other words the effect would be the same as referencing the cascode to ground. If one side of the K389 is conducting less the CCS is just forcing more current to the other half, but their voltage should remain fixed.
Martin,
Thanks for the comments.
I respectfully disagree. If the current is changing between the two halves of the differential pair then the voltage of the common sources has to change. It changes less than the signal level since currents in jfets have a square law dependence on the voltage change, but it does change. We can argue whether or not this effect is significant or not but my experience has been positive with the use of the bootstrap cascode configuration so my experience is that this effect is important.


Quote:
My last comment before I shut up: I believe the 5 Volt reference is setting the drain to source voltage too low. As a minimum I would try 2 references in series to get 10 Volts, that is if you must use them in the first place. [/B]
I never experimented with this. The datasheet of the 2SK389 shows that even 5v is plenty to put the transistors into the saturation region, which is the goal. But they can handle higher voltage and it would not hurt. I suspect the effect won't be significant.

---Gary
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Old 7th December 2008, 05:43 PM   #17
GaryB is offline GaryB  United States
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Default photos

Here is a photo of my ONO in it's final configuration. Originally I stacked the power supply directly below the ONO as shown in the photo but this caused problems. Even with toroidal transformers, I got enough magnetic coupling between the units that there was an unacceptable hum. I found that the power supply needs to be at least 1 foot (30cm) away from the amplification circuits.

---Gary
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Old 7th December 2008, 05:44 PM   #18
GaryB is offline GaryB  United States
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And another.

---Gary
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Old 7th December 2008, 10:16 PM   #19
ungie is offline ungie  Canada
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Quote:
Originally posted by GaryB

My main phono stage is a highly modified NYAL Super It tube phone stage. It uses an FET/tube input stage, passive RIAA, followed by another FET/tube gain stage, and a MOSFET source follower output stage. It sounds slightly better than the ONO but the difference is small.
---Gary
Hi Gary,

I'd love to learn some details of the SuperIt mods you have performed.
I have a mint unit here that blew the main power supply cap some years ago.
I have been thinking of pulling it out of storage and making some upgrades.
Thanks!
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Old 8th December 2008, 08:37 AM   #20
MRupp is offline MRupp  Germany
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Quote:
If the current is changing between the two halves of the differential pair then the voltage of the common sources has to change.
Gary, you are off course right, the voltgage should change. As I said I did not understand this quite properly. Since this is the summing point of the input and the feedback signal it should somehow be the differential. I might try and sim this to better understand what the combined signal looks like.
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