I'd greatly appreciate a direct comparison AJ to AB100 !! 
Honestly I do miss bass precision on my Aleph.
could I go?
Unfortunately I have just some transformers on spare with either +/-18 V
(giving ~24 V rails) or +/-42 V (58 VDC). Power is not any concern to me.
Thank you again for all the effort !!
Honestly I do miss bass precision on my Aleph.
Nelson, any idea what an appropriate voltage range would be? How low
could I go?
Unfortunately I have just some transformers on spare with either +/-18 V
(giving ~24 V rails) or +/-42 V (58 VDC). Power is not any concern to me.
Thank you again for all the effort !!
G'day,
AB100 bottom end is better between the two, suffers in the mids compared to the J. Is that any help doubt it though lol.
Original had fitted 1K pot fitted but bias at start up runs away, so threw in 5K.
Regards
AB100 bottom end is better between the two, suffers in the mids compared to the J. Is that any help doubt it though lol.
Original had fitted 1K pot fitted but bias at start up runs away, so threw in 5K.
Regards
Love your AB100! What problems has mine?
Hi guys, I'm pretty new in the audio diy but I'd like to get better, and I could really use a help from you all, please. I've been trying to build a class AB amp myself with TIP 142/147 Darlingtons, so I saw the AB100 and I found it great and not so different from mine.
Here is the schematic, I tried some simulations on Spice and it seems to work fine: but when I built it, I had (and still having) tons of problems. For instance, when I try it with no load it actually works pretty fine, but then I try a 15 Ohm resistive load or a 4 Ohm speaker and it starts ringing like there's no tomorrow (around 4-6 MHz). Ringing kinda decreases a little when I bias more the output stage (slightly higher values for R7), but nothing good anyway. Do you have any advice for me? Some changes to be made? Or would it be better to start over with a new schematic?
Thank you very much!
Giovanni
Hi guys, I'm pretty new in the audio diy but I'd like to get better, and I could really use a help from you all, please. I've been trying to build a class AB amp myself with TIP 142/147 Darlingtons, so I saw the AB100 and I found it great and not so different from mine.
Here is the schematic, I tried some simulations on Spice and it seems to work fine: but when I built it, I had (and still having) tons of problems. For instance, when I try it with no load it actually works pretty fine, but then I try a 15 Ohm resistive load or a 4 Ohm speaker and it starts ringing like there's no tomorrow (around 4-6 MHz). Ringing kinda decreases a little when I bias more the output stage (slightly higher values for R7), but nothing good anyway. Do you have any advice for me? Some changes to be made? Or would it be better to start over with a new schematic?
Thank you very much!
Giovanni
An externally hosted image should be here but it was not working when we last tested it.
Layout, grounding and signal returns can be crucial on designs like this.
I don't see any Zobel network on the output.
It might be worth looking at adding a small (10pf or less) across R18 and see if that changes things.
Also add a small cap across the vbe multiplier (say 4.7uf or 10uf)
I don't see any Zobel network on the output.
It might be worth looking at adding a small (10pf or less) across R18 and see if that changes things.
Also add a small cap across the vbe multiplier (say 4.7uf or 10uf)
In addition to what Mooly said, I wonder about C4 and R20. I would think 47pF and 22 Ohms would be more typical values.
Using a resistor load (R5=1k5) is unusual.
Have you considered and rejected the usual options of Bootstrapped and Active (current sink)?
You have matched the collector load currents of the LTP.
But ignored the current injected by the VAS.
The LTP currents end up not being matched.
C4 (Miller compensation) is unusually large. With only 1.1mA available to charge it, slew rate will be severely curtailed.
Consider where local decoupling can be added to maintain performance at HF.
Have you considered and rejected the usual options of Bootstrapped and Active (current sink)?
You have matched the collector load currents of the LTP.
But ignored the current injected by the VAS.
The LTP currents end up not being matched.
C4 (Miller compensation) is unusually large. With only 1.1mA available to charge it, slew rate will be severely curtailed.
Consider where local decoupling can be added to maintain performance at HF.
Thanks for your answers, first of all. Well, I didn't thought of a Zobel network actually, but I'll try. I imagine that I'll have to measure the series inductance of my speaker: given that I haven't got an impedance-meter, should I measure it manually with a sine wave at different frequencies or is there a simpler method?
Then I'll add a few caps where you told me and I'll tell you...just a few questions for AndrewT: can you provide an examples of what you call "Bootstrapped and Active (current sink)"? A resistive load was the simplest solution that came to my mind and no, I did not think of the usual solution (maybe I didn't even know...)! One more thing: what do you mean by VAS? Because if you mean the gain stage (Q8 with its R19) I thought I could neglect that base current...what should I do to match the currents correctly?
Then I'll add a few caps where you told me and I'll tell you...just a few questions for AndrewT: can you provide an examples of what you call "Bootstrapped and Active (current sink)"? A resistive load was the simplest solution that came to my mind and no, I did not think of the usual solution (maybe I didn't even know...)! One more thing: what do you mean by VAS? Because if you mean the gain stage (Q8 with its R19) I thought I could neglect that base current...what should I do to match the currents correctly?
A 0.1uf cap and a 10 ohm will be fine for the zobel. Its purpose is to provide a defined load for the amp at hf, your speaker doesn't really affect the values.
AB100 Boards
Hi Guys,
I want to build a Class AB power amp for a friend that's turning 70 this year.
Maybe should build a 70w amp to be symbolic. 😉
A class A amp might be too much for her in terms of weight and heat.
Was thinking about the ACA, but then would need high efficiency speakers.
Might be hard for me to build/find high efficiency speakers in a small package.
I did read that the AB100 runs cool, which is a step in the right direction.
Then I could get her whatever speakers fit her style and sound.
She loves classical, operas, orchestras, etc. So, I think some power is needed.
I consider her an audiophile, because I don't know too many women who record
classical broadcasts to a digital tape recorder, although I'm sure they're out there.
I want to make something for her that sounds really good.
I'm also curious as how this amp would sound for me, so...
Does anyone have PDF or Gerber board files for the AB100?
Thanks,
Vince
Hi Guys,
I want to build a Class AB power amp for a friend that's turning 70 this year.
Maybe should build a 70w amp to be symbolic. 😉
A class A amp might be too much for her in terms of weight and heat.
Was thinking about the ACA, but then would need high efficiency speakers.
Might be hard for me to build/find high efficiency speakers in a small package.
I did read that the AB100 runs cool, which is a step in the right direction.
Then I could get her whatever speakers fit her style and sound.
She loves classical, operas, orchestras, etc. So, I think some power is needed.
I consider her an audiophile, because I don't know too many women who record
classical broadcasts to a digital tape recorder, although I'm sure they're out there.
I want to make something for her that sounds really good.
I'm also curious as how this amp would sound for me, so...
Does anyone have PDF or Gerber board files for the AB100?
Thanks,
Vince
Have you considered the diyaudio store AB amp? It has quite a following, pcb and instructions easily available and fits the 4U chassis. Not a Pass design though, not sure if that's a deal breaker.
I have. I've looked at it a few time and thought it was overly complex. I was hoping to find a 2 stage ab amp, but haven't seen any, except maybe the X100.
I'll look at it again.
I'll look at it again.
ZM, that's what I thought. I think the DIYAB is 4 stages, maybe three if omitting the cascode stage. I could be wrong either way. Usually am. 🙂
I've look on the net for a simpler design, but keep coming back to the AB100.
That said, the DIYAB look fun to build, if that's what you're after. It's nice to have all that support on a project.
I'll just have to learn Eagle PCB software. 😀
I've look on the net for a simpler design, but keep coming back to the AB100.
That said, the DIYAB look fun to build, if that's what you're after. It's nice to have all that support on a project.
I'll just have to learn Eagle PCB software. 😀
Couldn't you run a FW push/pull such as F5 or F6 with lower bias and let run mostly class B with smaller heat sinks and power supply? Or is that just sacriledge?
Thought about doing an F5T v2 that way, since it's already at 50w. I just don't know what the distortion and sound quality penalty would be. I have a spare set of boards for it.
Any comments on the potential of the output stage of the F5t v2 in class AB?
Any comments on the potential of the output stage of the F5t v2 in class AB?
naah
those switching mosfets aren't so blissful when current starved
though - there is a way (tried oomphteen times ) - use laterals and bias them to 100mA
eenyweeny famous amps from Yore England had them biased even to just 15mA
those switching mosfets aren't so blissful when current starved
though - there is a way (tried oomphteen times ) - use laterals and bias them to 100mA
eenyweeny famous amps from Yore England had them biased even to just 15mA