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Old 26th December 2008, 05:04 PM   #491
jcarr is offline jcarr  United States
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Mihai: Thank you for the kind words. And thanks also for the acknowledgement that you gave me at the beginning of this thread. That was wholly unexpected, and I appreciate and respect you the more for it.

I haven't so much experience with using Li Ion batteries (I've experimented with video-cam batteries) with audio gear, but my experience with other types of batteries is that there are marked differences in sound, depending not only on the technology employed but also the manufacturer and type. Experiencing this can be a dismaying surprise at first, and a decided nuisance subsequently. For one's own purposes, you can test different batteries and settle for the one that pleases your ears the most, but when it comes to specifying a build specification for other RMI-FC100 builders, I think it would be best if you specified a type of battery that is available in as many countries as possible.

To mention an alternative to batteries, you may like to try your hand at some type of "never-connected" power supply, similar to the circuit that I posted years ago, or the one that EC Designs has come up with recently for his DAC project. Based on personal experience (as well as listening feedback from dealers and customers), I can vouch that, in terms of sonic benefits, this is a worthwhile area for development effort - possibly more so than the amplifier circuit itself.

As you probably know, I normally don't like to swap resistors in for CCSs, because there is too much chance for current modulation. The exception would be if you have a lot of voltage headroom, and even then it would be a "maybe I'll think about it" situation (^o^). Voltage sag and back-EMF generated due to the fluctuating current demands of the circuit acting upon the inductances of PCB traces can be a problem in any situation, and IMO it is better to keep the circuit in a configuration that allows it to reject conceivable ill-effects as much as possible. The LTP pivot is a sensitive node which has direct consequences on the CMRR, and so at least I would not replace the CCS here for a resistor. If you are worried about the effects of Q8's capacitance, you could try inserting a series resistor.

OTOH, I certainly make use of JFET CCSs (and one-piece JFET CCSs from the likes of Siliconix and Ishizuka-SemiTec) in my own designs. For non-demanding locations, I may simply choose to use the JFET CCS as is. But for more critical locations, I prefer to shield the CCS with a bipolar or MOSFET cascode (thereby fixing the voltage and therefore the operating point). Also I will select the cascode voltage to keep the CCS in the most linear part of its curve, so that power supply variations or voltage reference modulations have as little effect on the current as possible.

To feed Q13 and Q11 with a JFET CCS will be no problem at all, since Q13 and Q11 will keep the operating voltage across the JFET CCS constant. FWIW, this alteration would be fairly close to how the 4-2SE preamp is designed.

IME, making the design simple from the signal point of view often means that it physically gets more complex rather than less. I believe in attempting to envision everything that could possibly be going on, and arrange the design (schematic and board layout) so that as many factors as possible are accounted for.

To accomplish this and yet keep the design simple and elegant is undoubtedly and always the most difficult thing to do. I'd suggest that you first get the total functionality for RMI-FC100 MkII where you want it to be (almost regardless of complexity), and then work on streamlining it over time.

So you want to develop a Mk II? That feeling sounds rather familiar (^o^).

Let me know if I can be of any help.

regards, jonathan carr
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Old 26th December 2008, 06:48 PM   #492
Sheldon is online now Sheldon  United States
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Mihai,

I got four sets of boards from the recent buy. I'll probably build later this spring. A couple of questions:

I may have missed it, but is there an image of the main board with the parts labeled that I have missed? No problem, if not, as the schematic and pictures here should do.

I will probably use one front end supply for each stereo pair of power amps. But I'd like to use the two extra for other projects. Any limitations on reducing the input voltage and reference zener for other applications?

thanks,
Sheldon
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Old 27th December 2008, 06:21 AM   #493
roender is offline roender  Romania
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Jonathan,

Thank you for your thoughts. A lot of information to digest.
Very interesting idea with never connected PSU, I definitely try it.

Best regards,
M
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Old 27th December 2008, 06:39 AM   #494
roender is offline roender  Romania
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Quote:
Originally posted by Sheldon
Mihai,

I may have missed it, but is there an image of the main board with the parts labeled that I have missed? No problem, if not, as the schematic and pictures here should do.

thanks,
Sheldon
Hi Seldon,

Sorry for no PCB component label layer ... it is so difficult to do that in EAGLE.
This is all I can do for you:
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Old 27th December 2008, 06:40 AM   #495
roender is offline roender  Romania
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PSU
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Old 27th December 2008, 06:47 AM   #496
roender is offline roender  Romania
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Quote:
Originally posted by Sheldon


I will probably use one front end supply for each stereo pair of power amps. But I'd like to use the two extra for other projects. Any limitations on reducing the input voltage and reference zener for other applications?
It is possible to use other output voltages by putting other zener values but don't forget that this is a shunt PSU. You have to modify CCS current in order to keep at least 10-15mA through PSU output transistors (MJL15034/35).

Happy Holidays,
Mihai
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Old 27th December 2008, 12:13 PM   #497
pooge is offline pooge  United States
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Quote:
Originally posted by roender


Hi Seldon,

Sorry for no PCB component label layer ... it is so difficult to do that in EAGLE.
This is all I can do for you:
Could you drop the red. blue, purple and black colors, and just leave the green vias? That's a LOT of printer ink, and not really helpful to visualize parts layout.
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Old 27th December 2008, 12:22 PM   #498
pooge is offline pooge  United States
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What is the maximum voltage drop the PSU regulator can do, so we can know the voltage range for acceptable transformers. Also, what is the minimum and maximum difference acceptable between the PS voltage delivered to the input stage and that to the output stage?
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Old 27th December 2008, 12:47 PM   #499
roender is offline roender  Romania
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Quote:
Originally posted by pooge


Could you drop the red. blue, purple and black colors, and just leave the green vias? That's a LOT of printer ink, and not really helpful to visualize parts layout.
It is better now?
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Old 27th December 2008, 12:51 PM   #500
m2003br is offline m2003br  Brazil
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Default layouts

Hope this may help:

edit: deleted atachment. too bad quality.
I posted better one in the post 504
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