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Old 28th October 2008, 05:36 PM   #1691
nut_ty is offline nut_ty  Thailand
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this schematic can be made . how watt of this sch.
Quote:
Originally posted by noisefree
Hello,

hope there is any interest in this project – seems that I am the only one who tries it :-(

Here are some new details:

Have changed again some resistors with the result that the absolute and differential offset is very stable now:
I came to the decision to put in again the divider across the voltage reference and throw out the frontend loading resistors to ground – have found out that the divider only has the effect of a shifting ground (the supply voltages starts to become unsymmetric) in combination with this output to ground resistors (but I don’t know why this happened).
Also the trimmers have been scaled down: Abs. pot is now 20R and diff. pot 50R – both are 25 turn types.
I have implemented the resistor from FE to OS which I have also seen in the A75 article. (The A75 uses a combined feedback from output and front end.)
In the shown circuit below the feedback is not mixed and only comes from the OS. But mix mode can be realized when changing the 0R resistor to a higher value.
My main goal was to get a really good trimmable offset and this is done now and works very well - both offsets are adjustable to 1-3mV without a problem (but I can’t say if this resistor has a negative effect and how to dimension it!?) and the supply rails stay symmetrical.
The abs. offsets of the FE reaches values in size of +140 and +180mV - think that is acceptable (perhaps it can be reduced with a bit higher resistor value for the upper divider resistor)
Also new are the four resistors in the bias circuit connected to ground – it could be that they are not necessary - perhaps they bring a bit stabilization.
The two resistors which steal the voltage references some current in stand by mode are reduced to 270k which give a stand by output bias of only 26mA (2mA p-fet + 24mA SE-resistor)! That’s a consumption reduction to a tenth. The abs. offset goes down to -120mV and for diff. offset I get about 12mV.
However I need another possibility to throw away some open loop gain which is still to high.
Without the ugs output to gnd loading resistors the open loop gain raises again by 4dB.

Perhaps other people will try it out or have some ideas!???

Regards
Dirk
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Old 30th November 2008, 10:58 PM   #1692
Sander is offline Sander  Netherlands
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I am currently designing my enclosure. Still need the components though.

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Old 1st December 2008, 04:08 AM   #1693
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Those Rifa Electros for your ripple and power caps are rather bright - might consider some "fatter" caps as bipass or elsewhere in the cct to compensate. Cerafines, or perhaps Silmics, would do the trick - a suggestion only, as not sure if you're using u.fast diodes, too.
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Old 1st December 2008, 12:07 PM   #1694
Sander is offline Sander  Netherlands
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Quote:
Originally posted by jameshillj
Those Rifa Electros for your ripple and power caps are rather bright


What do you mean by this?


Quote:
- might consider some "fatter" caps as bipass or elsewhere in the cct to compensate. Cerafines, or perhaps Silmics, would do the trick - a suggestion only, as not sure if you're using u.fast diodes, too.
I have indeed some cerafines as bypasses in my orderlist. I am using the MUR3020 diodes. Thank you.

Actually I am looking for other capacitors. The voltage rating of these a rather high for my needs. But I can't find any reasonable caps.
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Old 1st December 2008, 06:51 PM   #1695
Sander is offline Sander  Netherlands
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I am currenltly considering a dual stereo setup with 2x15V 500VA toroids each supplying a symmetric capacitor bank of CC-CC-CC, with additional resistors in between. Maybe one or two resistors.

What do you think? Is a toroid per channel preferrable in a stereo chassis when we keep the rail capicitance the same for both single as dual toroid. The other option is a single 2x15V 800VA toroid with the same capicitance.

The two toroids are in the bottom.

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Old 1st December 2008, 10:28 PM   #1696
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Default caps and things

Sander'

Each brand and type of capacitor has it's own "sound", and as the power supplies are directly connected to the amp .....

The Rifa's, after a reasonable "break-in" time, (about 200hrs) are very accurate, fast, etc but still results in a "toppie" cap - I would use a Siemens or Mundorf as a ripple cap with the Rifa as a supply cap (the 2nd one) in a R-C-R-C (0.1R & 10,000uF)combination, (rather than the C-L-C), particularly if you are looking for an accurate, detailed and punchy A-X. [The 0.075R - 0.125R will be quite noticeable, particularly next to each diode bridge - adjust this "by ear", just like engines]

Suggest a single 500VA of better quality, rather than 800VA - this isn't fashionable today with dual mono setups but actually does give better results. (Put the money saved into those caps)

Silmics aren't as heavy, but clearer, than Cerafines, for sound (In My Opinion, that is!)

I haven't tried the MUR3020s, but did try the MUR410, 820c, 1620CT, etc (including those !SL9R8120P2 stealths) and ended up with the BYW29 and 8ETH08s - I think Jacco V. is also using the BYW family ( from memory, the 99s? not sure)Other Caps - Epcos B41550/70s, Mundorf M-lytic (?) Jensen 4pole, DNM Audio T-Networks or SlitFoils, etc, etc. (you have easy access to nearly everything over there)

Good amp, this.
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Old 2nd December 2008, 02:04 PM   #1697
Sander is offline Sander  Netherlands
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Default Re: caps and things

Thank you for your answer James.

Quote:
Originally posted by jameshillj
Sander'

Each brand and type of capacitor has it's own "sound", and as the power supplies are directly connected to the amp .....

The Rifa's, after a reasonable "break-in" time, (about 200hrs) are very accurate, fast, etc but still results in a "toppie" cap - I would use a Siemens or Mundorf as a ripple cap with the Rifa as a supply cap (the 2nd one) in a R-C-R-C (0.1R & 10,000uF)combination, (rather than the C-L-C), particularly if you are looking for an accurate, detailed and punchy A-X. [The 0.075R - 0.125R will be quite noticeable, particularly next to each diode bridge - adjust this "by ear", just like engines]


I am not inteding to use CLC because of the high price for the inductors. What is exactly the influence of the R next to the rectifier bridge, oher then burning of exessive voltage?

I have the 0.33F RIFA's in the first drawing available. But they are to big in my opinion. I can get some RIFA 0.22F which are a lot smaller (second picture)

Quote:
Suggest a single 500VA of better quality, rather than 800VA - this isn't fashionable today with dual mono setups but actually does give better results. (Put the money saved into those caps)
I am inteding to construct a dual stereo chassis. So two toroids in one chassis. Only the extra capicitance and rectifier will add in price. Two 500VA is as much as 1 800VA. The second RIFA's (0.22) allow me to give each toroid its own bank of capacitors. So in my opinion this is a better idea. Paralleling two toroids on the same bank will give surge problems i think.

Quote:
Silmics aren't as heavy, but clearer, than Cerafines, for sound (In My Opinion, that is!)
My goal is to first have the Aleph up and running. When everything is fine I will fine tune the amplifier with additional bypasses etc.
Quote:
I haven't tried the MUR3020s, but did try the MUR410, 820c, 1620CT, etc (including those !SL9R8120P2 stealths) and ended up with the BYW29 and 8ETH08s - I think Jacco V. is also using the BYW family ( from memory, the 99s? not sure)Other Caps - Epcos B41550/70s, Mundorf M-lytic (?) Jensen 4pole, DNM Audio T-Networks or SlitFoils, etc, etc. (you have easy access to nearly everything over there)

Good amp, this.
I have the MURs available. But I am going to buy some schottky's. De BYW99W-200 are obsolete. I think the MBR3045 or MBR2045 will be a good replacement. Iw ill use the MURs in a Gainclone or something.
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Old 2nd December 2008, 11:08 PM   #1698
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Default that first resistor?

Ah that one, eh, Sander.

Probably a better clearer explanations can be found on the DNM Audio website, but the gist of it is this ( according to me!) -

The requirements of the active amplifier stages are quite different from the behaviour of the charging capabilities of the fixed 100Hz (rect 50Hz) mains supply - (pretty basic, please excuse). When you look at the current fed to the caps via the diodes, it isn't a 1/2 sine wave at all but a series of pulses that occur when the diode voltage is higher than the retained voltage in the caps - this usually occurs only at the top part of the waveform (1/2 sine wave of diodes) when the voltage is near maximum and thus when the diodes now charge the caps up, there is a quite sharp current pulse (see "current charge behaviour" in literature) - now the first series resistor limits the spike of this current pulse and hence you find a quite noticeable reduction of "edge" in the sound.

There is a second part to this. When the diode "turns off" at the end of the half cycle, the residual charge left across the diode junction manifests itself as a "reverse current spike" that is most offensive " to the transformer (it's inductance) and this same resistor seems to act as a "damper" on the spike - this is why the u.fast diodes are smoother in the same circuit (I prefer the faster ones - lowest Trr - but others like med 35 nS devices - not much in it, really - "standard" diodes are unsatisfactory, IMHO.

Now when you do the sums about high pass filters, it doesn't seem to add up correctly, but it works very well. (1/2*pi*R*C = 1/ 2 x 3.14 x 0.1 x 10,000 x 10E-6 = approx 160Hz) ** Changing this value by about 15% has quite noticeable effect.

The second resistor acts , not only as a filter, but also as another "current surge damper" with similar effects with changes in resistance. The accepted design calls for twice the capacitance on the power cap (2nd one) - [ie diode- R.1- 10,000uF- R.1- 20,000uF (+ bipass on amp rails pcb) - This seems to give heavier base, but not too critical, I've found.

I agree with the idea of chokes being very useful between the 2 caps, but it doesn't seem to work for me - I do use chokes in high freq "hash" filters elsewhere, tho.

I expect to get some "static" from folks that know a lot more than I do about all this (not hard!) but, for me, the "stuffing about" is part of the fun and it sort of makes sense, particularly if you are all about accurate AND good sounding reproduction - I also use AKG k701 and Stax h.phones as references (easier to get things right)

*Hope this helps, sorry for the non-tech explanation, maybe someone can fill in the blanks and correct things.
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Old 3rd December 2008, 12:23 AM   #1699
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Quote:
Originally posted by jameshillj
BYW29 and BYW99
Both.

Quote:
Originally posted by Sander
BYW99W-200 are obsolete.
The reason why i bought 1200 of them.
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Old 4th December 2008, 11:09 PM   #1700
Sander is offline Sander  Netherlands
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Thanks guys. When my chassis is sortend out I will consult the theory regarding RC filters. My design relies on the RIFA 22mF capacitors. So my design is constraint on these capacitors. I will tweak the PS when everyhing is installed. This is how I try to avoid projects which take too much time. Just build it and tweak afterwards that is, when I am not satisfied.

I have slected the MBR1645 schottky's. I do not like the dual package MBR's and I really do not see any use of them when I need three for a fullwave rectifier. I ask myself why they are used that often at diyaudio.

This is my current and almost final design. I couldn't place the toroid anywhere else. I hope toroid coupling wil be minimal. When everything is installed I will consider PCB shieding etc. I have taken this into account on my design. The chassis will be plated with 5mm acryl/plexiglass.

PS. Those AREN'T donuts!

Front

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Upperpart

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Back

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BOTTOM

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