Eeeh, it's soldered to the 3-Pin Camac (fem) input chassis part ?
Choosing between single-ended or balanced operation meant installing the FB-parts or not.
(the balanced operation compensation C is the green Wima cube smack in the middle of the 4 heatsinked TO-39s, the 1pF CD15 silver mica is on the other side of the 0.68uF pink Roederstein foil cap)
Choosing between single-ended or balanced operation meant installing the FB-parts or not.
(the balanced operation compensation C is the green Wima cube smack in the middle of the 4 heatsinked TO-39s, the 1pF CD15 silver mica is on the other side of the 0.68uF pink Roederstein foil cap)
Jacco,
you need to put two beads in series because they are also used as standoffs for the resistor, one on each leg.
Please see:
http://www.fotop.net/TheFabFour/CelloEncoreAmplifier
picture IMG_2603 clearly shows a resistor (R1, R18?) mounted on ferrite beads (close to where the input signal cable is connected on the PCB).
Regards
you need to put two beads in series because they are also used as standoffs for the resistor, one on each leg.
Please see:
http://www.fotop.net/TheFabFour/CelloEncoreAmplifier
picture IMG_2603 clearly shows a resistor (R1, R18?) mounted on ferrite beads (close to where the input signal cable is connected on the PCB).
Regards
i'll be damned, there they are, i thought i checked every sqr mill of those pictures.
Picture 2587 shows the ferrite bead on the other resistor lead.
Probably means the beads for the compensation network R are under the TO-39 heatsink and consequently not visible.
Explains the input resistors thing in the schematic, doesn't make much sense to remove them for either mode of operation.
Good show, S.A.G.
(poor schematic drawing btw, there's a dedicated symbol for a ferrite bead)
Picture 2587 shows the ferrite bead on the other resistor lead.
Probably means the beads for the compensation network R are under the TO-39 heatsink and consequently not visible.
Explains the input resistors thing in the schematic, doesn't make much sense to remove them for either mode of operation.
Good show, S.A.G.
(poor schematic drawing btw, there's a dedicated symbol for a ferrite bead)
It's only used with balanced inputs, otherwise it should be grounded.
Regarding the negative feedback: I think I could have been more clear on that.
The Cello Encore does not have global negative feedback at all. All the connections from the VAS back to the LTP (input differential) are only frequency compensation. The small pF caps act as a filter well above the audible range somewhere in the lowish MHz-band.
All the best, Hannes
Most of it is not that complicated. At least the frontend (input differential+VAS) is quite easy - I posted the links earlier where Steve posted explanations.
The output stage is still not fully understood. I still cannot offer help on the output stage since I've been away lately and still don't have time currently to look at it.
The question is, do you want to clone it 1:1 with these ancient, hard-to-get parts, like the 2N5416, 2n6718? They're really old, ancient parts, by the way I agree to the old law
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2357&highlight=
However if you start substituting with new parts, you will have to look at getting back stability. No way around this, so better get a scope. This is also the reason why I didn't post my pcb-layout yet, I still want to incoporate some more compensation features.
However, please let me (us) now what became of your amp! I would be very interested in the results!
Of course feel free to also mail me, if you wish.
All the best, Hannes
The output stage is still not fully understood. I still cannot offer help on the output stage since I've been away lately and still don't have time currently to look at it.
The question is, do you want to clone it 1:1 with these ancient, hard-to-get parts, like the 2N5416, 2n6718? They're really old, ancient parts, by the way I agree to the old law
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2357&highlight=
However if you start substituting with new parts, you will have to look at getting back stability. No way around this, so better get a scope. This is also the reason why I didn't post my pcb-layout yet, I still want to incoporate some more compensation features.
However, please let me (us) now what became of your amp! I would be very interested in the results!
Of course feel free to also mail me, if you wish.
All the best, Hannes
HKC,
my post was not exactly aimed at you.
The 2N5566 is "comparable" with the Toshiba 2SK389 dual JFET.(Nelson Pass used S-loads of 2N5566s in his Threshold gear of the 1980s, early '90s)
The K389 is also obsolete and it's price level has stepped way beyond the $3.50/100 of the Siliconix dual JFET.
my post was not exactly aimed at you.
The 2N5566 is "comparable" with the Toshiba 2SK389 dual JFET.(Nelson Pass used S-loads of 2N5566s in his Threshold gear of the 1980s, early '90s)
The K389 is also obsolete and it's price level has stepped way beyond the $3.50/100 of the Siliconix dual JFET.
h_a said:
Hi Hannes
I have searched the parts which indicated on the schematic and Mouser has all of them except U403 so that was why I asked if this component can be replaced by 2N5566.
According to Mouser 2N6718 is selling @ $0.50 & 2N5416 @ 0.90. Mouser also has the other parts of this circuit.
I would like to clone the amplifier exactly same as the original schematic therefore your comment and advice on the output stage will be helpful and of highly appreciated.
Best Regards
syn08 said:
Very important & good points, syn08
It may not come as news for John Curl. He has optimized for these things.
He has made sure to get the optimal COMPLEMENTARY in his amplifiers.
Almost before we were born.
Same for Nelson Pass. I can see he is aware and adjust to best performance for complementary JFET pairs.
--------------------------------------------------------
I have found out .. on my own.Because I do not read technical literature about transistors.
2SK170 + 2SJ74 are almost complementary.
At least there is a 'sweet spot' where they cancel even harmonics.
I have found this spot is Not at same VGS for the N-FET and P-FET.
More closer to when the N and P works at same current I-DS.
The practical choice of making Practically this means making both source resistors equal value.
And run this complemntary at same current level.
This also means, that using a potentiometer as divider between such pair, in a 'wrong way',
can create even order distortion of considerable magnitude.
It is easier if I post some figures from my simulation works.
Here is first.
There circuits to demonstrate this fenomena.
And the one to the right, is one solution I use,
to compensate and make them N-JFET and P-JFET work in
Complementary Harmony.
I post the harmonics difference in next post.
Regars Lineup
Attachments
Here is my comparing FFT analys.
Before and after my Capacitor Compensation.
As I call it.
In this case was a difference of -32 dB for 2nd order harmonics!.
But quite often there are improvements at like -10 to -20dB level.
These are very high magnitudes, People!
My CapComp Trick.
This allows for ZERO DC-offset adjustment
and still cancels out even order dsitrtion.
Making the 2SK170 / 2SJ74 Complementary input/pair
work at as low distortion as possible.
A hookup is, that you probably need some distortion measurement device.
Unless there are some mathematical way, by just measuring VGS or whatever.
ESP has a project to build a THD harmonics analyser.
Bob Cordell has the definitive THD analyzer building project at his website.
Links:
--------------------------------------
Distortion Analyser
Rod Elliott (ESP)
Updated 23 Dec 2007
http://sound.westhost.com/project52.htm
Before and after my Capacitor Compensation.
As I call it.
In this case was a difference of -32 dB for 2nd order harmonics!.
But quite often there are improvements at like -10 to -20dB level.
These are very high magnitudes, People!
My CapComp Trick.
This allows for ZERO DC-offset adjustment
and still cancels out even order dsitrtion.
Making the 2SK170 / 2SJ74 Complementary input/pair
work at as low distortion as possible.
A hookup is, that you probably need some distortion measurement device.
Unless there are some mathematical way, by just measuring VGS or whatever.
ESP has a project to build a THD harmonics analyser. Bob Cordell has the definitive THD analyzer building project at his website.Links:
--------------------------------------
Distortion Analyser
Rod Elliott (ESP)
Updated 23 Dec 2007
http://sound.westhost.com/project52.htm
