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Old 17th June 2004, 06:11 PM   #251
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It has been a while since I checked into these pages, but I have an X100 running and I am happy with it. I much prefer this design to the hothouse variants of the Aleph ilk which is why I did not participate much in those threads.

The problem with building the X series amp is getting it to "balance". You can easily spend a day thinking it does not work only to realize it actually was OK. Thus, my recommendation is to build a version that auto-calibrates. I started doing that but quit - perhaps I should take it up again

Petter
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Old 18th June 2004, 01:29 AM   #252
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First to mention a class D X amp? Hmmm. Maybe I should go back through my notes and post other ideas. To paraphrase what an older gentleman once said,"I've got more ideas than Carters' got liver pills." It's time and resources to follow through that I lack.
After all, it only took...what...one year? two? for me to go from concept to working prototype on Aleph-X. I'd like to move a lot more quickly than that.
For that matter, I thought of something while I was in the shower yesterday, but I haven't had time to puzzle it through yet. If only the folks here at work would let me bring in a soldering iron and a bunch of parts, I might get something done. Life's a bummer sometimes.
Petter,
Go for it, man. Is it the bias or the DC offset that you're wanting to calibrate?

Grey
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Old 18th June 2004, 03:36 PM   #253
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Sorry for my post earlier which was far to skimpy on the technology

Yes, it is the current sources for the input stage (4 on bottom and 2 on top) that need to "balance" in order for the output of that stage not to go completely bananas. It is not that bad once you have ironed out your design etc, but before that it is painful.

Now that I am at it, I still don't understand why somebody did not just build an X input stage as a ZenX. Using auto-adjust on the current sources and small sense resistors, it should be very easy, and you share the heat over a lot more transistors than for the original Zen. In effect, what one should consider would be a power version of the input stage of the X.

Petter
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Old 18th June 2004, 05:55 PM   #254
Clarkcr is offline Clarkcr  United States
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How do the read Xs balance the bias voltage? Trim POTs from the factory table?

Why go the extra effort to have a selfadjusting circuit (unless you want it to change while it's warming up??) when a single adjustment at time of assembly would work?

C
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Old 18th June 2004, 06:09 PM   #255
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Good question.

1. It will change with temperature
2. I fixed it by having a large drop across the current source - I had about 20V on the Zeners at the gates of the FET's so there was CONSIDERABLE degeneration. I assume half that would work as well - still over twice the value of the Vgs
3. The suggestion to use a factory tuned unit works.
4. For a high-power ZenX, you probably won't be able to afford the thermal loss of large degeneration.
5. For those not used to building circuits, the X is far too complicated to set up.

Petter
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Old 13th January 2005, 06:51 PM   #256
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Question Few Questions if may

Hi Petter,

I just discovered this thread by luck yesterday. I have spent a good amount of time reading the entire thread. I have a few questions if I may:

1) There was mention of a V2 and V3 in your postings. Is it correct to assume the circuirts and PCB you posed are for V1?
2) It seems you have made some refinements after posting the circuit and PCB re resistor values and added a Vbe. Any chance of posting or eMailing me those updates?
3) I like to see how you implemented the 10W Class A/100W AB and 50W Class A/100W Class AB so you can change via the external case switch you installed. Pic not needed just what points you tapped to, the values you used to switch between or add in parallel or series to enable the bias value change and method of value change as in did you just switch in different value or switched in a series or parallel value?
4) Is there a formula to determine different Class A/Class AB threshold points? If so what or where is this formula?
5) There seemed to be some reference to using output drivers in quadruplets? Is this a fixed requirement of this design that one has to use or can one choose to use 2 or one set of output devices per side of X? I realize this implies less power, that is ok, I am well aware that may be case.
6) Indication is this design scales well. What PSU or componet value calculations does one use to scale the design? For your implementation I cannot recall the Secondary Vac you used and resulting VRail of your supply design. I have a number of PSU based calculations, but seems the PSU calculations vary widely due to topogogy of the amp. Some topologies need certain key component values recalculated for different PSU rail voltages.
7) Any general thoughts on use of PSU chokes in terms or pros and cons that may be specific to this amplifier design?

I think to have a question or two more, but cannot recall now as my mind tries to review all that I read in thread in my head. Petter, If you have anything to add or is suggested to be commented or added upon due to my questions above, feel most free to do so.


Regards,

John L. Males
Willowdale, Ontario
Canada
13 January 2005 14:52


Regards
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Old 14th January 2005, 12:49 AM   #257
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Default Re: Few Questions if may

Quote:
Originally posted by keypunch
Hi Petter,

I just discovered this thread by luck yesterday. I have spent a good amount of time reading the entire thread. I have a few questions if I may:

1) There was mention of a V2 and V3 in your postings. Is it correct to assume the circuirts and PCB you posed are for V1?
2) It seems you have made some refinements after posting the circuit and PCB re resistor values and added a Vbe. Any chance of posting or eMailing me those updates?
3) I like to see how you implemented the 10W Class A/100W AB and 50W Class A/100W Class AB so you can change via the external case switch you installed. Pic not needed just what points you tapped to, the values you used to switch between or add in parallel or series to enable the bias value change and method of value change as in did you just switch in different value or switched in a series or parallel value?
4) Is there a formula to determine different Class A/Class AB threshold points? If so what or where is this formula?
5) There seemed to be some reference to using output drivers in quadruplets? Is this a fixed requirement of this design that one has to use or can one choose to use 2 or one set of output devices per side of X? I realize this implies less power, that is ok, I am well aware that may be case.
6) Indication is this design scales well. What PSU or componet value calculations does one use to scale the design? For your implementation I cannot recall the Secondary Vac you used and resulting VRail of your supply design. I have a number of PSU based calculations, but seems the PSU calculations vary widely due to topogogy of the amp. Some topologies need certain key component values recalculated for different PSU rail voltages.
7) Any general thoughts on use of PSU chokes in terms or pros and cons that may be specific to this amplifier design?

I think to have a question or two more, but cannot recall now as my mind tries to review all that I read in thread in my head. Petter, If you have anything to add or is suggested to be commented or added upon due to my questions above, feel most free to do so.


Regards,

John L. Males
Willowdale, Ontario
Canada
13 January 2005 14:52


Regards

A lot of questions - far too detailed to work in the middle of the night. In fact I might not be able to answer most of them but will do my best - probably next week, but some are a bit general. In the meantime: Item 6 - the design is inherently scalable. As long as the power ratings of each component is not exceeded all you have to do is to change the supply voltages. Note that the input stage needs higher voltage than the output voltage in order to be able to drive the output stage to full power. Watch out power dissipation, especially on input FET's.

I am currently on version 3. Considering doing version 4. The basic topology is essentially the same for all - the intial drawing was that good - with the exception of not needing any resistors to ground as per patent, and reduction of the "X" resistor - I have tried short-circuiting it with no issues.

Petter
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Old 14th January 2005, 02:49 AM   #258
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Smile Re[03]: Few Questions if may

Hi Petter,

Thanks for the reply. No hurry, I know you can be very busy. Some of us think better at night!

There was excellent infomation in this thread, not much diversion as the project proceeded and other inquiries and ideas evolved as progressed.

Excellent that can scale so easy, just what I need as well as not heaing up place in process.

Look forward to your reply when you have time.


Regards,

John L. Males
Willowdale, Ontario
Canada
13 January 2005 22:50
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Old 15th January 2005, 03:25 PM   #259
estman is offline estman  Estonia
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without current sources, haven't build yet. Any comments!
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Old 15th January 2005, 05:28 PM   #260
estman is offline estman  Estonia
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sorry, R25/74 for bias, DC 0V by adjusting potential of Bases Q5(4) and Q7(6). Biasing of CB Bases is the part I don't know how exactly to do. By the sim there is needed around 100pF to put on each to GND, for stability issues. Can they have bad influence on sound ?
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