adjusting current gain for Aleph30 necessary?

[h_a]

Hi!

I read quite some about the importance of having 50% current gain on the current source, but - please excuse my lacking knowledge - there's no hint which resistor is to change?

I read about Aleph-X, Aleph5, even Aleph2, but not the Aleph30...

I'm sure you have already the feeling that with my lacking knowledge it would be smarter to use the stock values from the schematic anyway, so how much deviation of the 50% I have to expect when using well matched parts (9610er input pair matched to within 2mV@20mA)?

Would be great if one could help me here! I really don't want distortion!

BTW when does the amp start to clip? Given a 3V source, a 25k log pot as preamp, does the Aleph30 clip at full throttle?

How many watts@8Ohm has the Aleph30 with stock rails really?

Thanks a lot for helping me out!

Cheers, Hannes

 

[Zen Mod]

Hi!

I read quite some about the importance of having 50% current gain on the current source, but - please excuse my lacking knowledge - there's no hint which resistor is to change?

I read about Aleph-X, Aleph5, even Aleph2, but not the Aleph30...

I'm sure you have already the feeling that with my lacking knowledge it would be smarter to use the stock values from the schematic anyway, so how much deviation of the 50% I have to expect when using well matched parts (9610er input pair matched to within 2mV@20mA)?

Would be great if one could help me here! I really don't want distortion!

BTW when does the amp start to clip? Given a 3V source, a 25k log pot as preamp, does the Aleph30 clip at full throttle?

How many watts@8Ohm has the Aleph30 with stock rails really?

Thanks a lot for helping me out!

Cheers, Hannes

30W/8E
40W/4E

for AC current gain ,vary resistor in series with 220Uf connected from output rail to base of bjt in output CCS
hehe
your searches are lousy

and-yes-if you stick with stock values,you'll be in ballpark of everything

 

[h_a]

So...R21 with 820 Ohms?

Well...you know..if some terms yet mean nothing to you, it's a bit hard. The specific number of the resistor in the schematic helps a lot.

But being not even 2 months in the DIY business I think I do quite well

Concerning current gain:
Sorry, but being in the ballpark is not enough for me - I would greatly appreciate a more numerical guess, something like 45-55%?

Thanks a lot! Hannes

BTW I thought the 30W is a rounded number? I read Pass' gear is underrated powerwise, so I expected something like 35Ws?

Don't forget, this info is added to the wiki so your chances are good, nobody has to ask that again ;-)

 

[h_a]

Ah...and by the way: what about clipping?

 

[Nelson Pass]

If you build from my stock designs, you will get accurate enough
results from the specified parts.

Any yes, they can be clipped.

 

[wuffwaff]

Hi,

clipping will occur at max current (two times the bias current at 50% ac-current-gain) or at max. voltage (about 4-5V under the rail voltage) depending on the load.

There are quite a few threads on setting ac current gain. Replacing the ac-c-g resitor with a pot, setting the amp at 50% ACCG and then replacing it with a fitting resistor seems the easiest way to do it. There´s quite some tollerance in the bjt´s and fets so sometimes you will need different resitors for both channels.

William

 

[h_a]

Thanks for all your replies!

However I'm a bit worried clipping wise...

The A30 has a gain of 26dB for unbalanced input, that means input voltage is multiplied by a factor of 20, right?

So a 2V source (connected directly) drives the amp into the wall?

Consequently I can turn up the volume only to half of the max position (0.5x2V=1V times 20 gives 20V, 5V below rail)??

Turning it up further the A30 clips?!

This would practically mean that I can only turn up the volume to half of its maximum?!

Sorry for a truly stupid question, but at that position (half of max) do I get then already the full 30Ws?

Maybe somebody could take the time to reply to my little calculation?


Please help me out of this!

Thanks a lot!

Cheers, Hannes

EDIT: position half of max would mean roughly 2/3 for a log pot.

 

[wuffwaff]

Hi,

yes that is true but only if the 2V source puts out 2Volts. Normal CD´s are recorded with a peak value much lower than 2V.

So if the max output is -6dB the CD player will "only" put out 1V and your A30 won´t clip.

And since your volume pot is logarithmic half of the voltage will occur when it is almost in the 5 o clock position.

I´m not shure I understand what you are afraid of. This will happen with every 30 watt ampifier.

William

 

[h_a]

Oh yes I know.

I was just wondering wether I get the whole 30Ws before clipping or not?

Cheers, Hannes

 

[Babowana]

I don't need to worry about
the distortion,
the current gain rate,
and the clipping
when I don't build it.

Why worry . . . ?

 

[h_a]

Because I don't want to build a nice Aleph30 just to realize that I need an Aleph5!

I love to DIY but I love to do it in a way that's so expensive that I cannot afford building unused amps!

Have fun! Hannes

 

[Babowana]

Because I don't want to build a nice Aleph30 just to realize that I need an Aleph5!

Bad mouthing the nice A30,
promote yourself A5 . . . ?

Ahrrrr . . . o my Papa!

 

[h_a]

C'mon! Never! I don't want to say anything bad about the A30!

I just remember Grey Rollins saying he's going to build the Aleph5 to have some headroom.

So what about the wattage?

Do I get 30W right before clipping?

I guess this is related with the loudness of the source? So only the loudest peaks are clipped whereas the average loudness gets below 30 Watts?

So it depends entirely on the source?

Heavy compressed dynamically - no clipping up to nearly full volume, great dynamics - possibly clipping before even 4 o'clock?

Any grain of salt in that?

Thanks! Have fun! Hannes

 

[Zen Mod]

C'mon! Never! I don't want to say anything bad about the A30!

I just remember Grey Rollins saying he's going to build the Aleph5 to have some headroom.

So what about the wattage?

Do I get 30W right before clipping?

I guess this is related with the loudness of the source? So only the loudest peaks are clipped whereas the average loudness gets below 30 Watts?

So it depends entirely on the source?

Heavy compressed dynamically - no clipping up to nearly full volume, great dynamics - possibly clipping before even 4 o'clock?

Any grain of salt in that?

Thanks! Have fun! Hannes

sometimes you need to read between the lines.....
you certainly read somewhere that Aleph series is sorta toob sounding........that means something softer clipping behavior than usual neighbor's amp.......
and- you really need more than 30W of pure SE classA?

you just split hair here .........
Aleph 5 isn't twice costlier than A30 ......


or-give us more data......room,average listening level you prefer,spks you have .......and somebody will answer you precisely on precise question

 

[GRollins]

I just remember Grey Rollins saying he's going to build the Aleph5 to have some headroom.

So what about the wattage?

Do I get 30W right before clipping?

I guess this is related with the loudness of the source? So only the loudest peaks are clipped whereas the average loudness gets below 30 Watts?

So it depends entirely on the source?

Heavy compressed dynamically - no clipping up to nearly full volume, great dynamics - possibly clipping before even 4 o'clock?

I don't recall ever saying that I was going to build an Aleph 5. I've got two pairs of Aleph 2s, an Aleph 3 (courtesy MikeW, though I've been slowly modifying it), and a veritable army of Mini-A variants. Can't remember ever wanting a 5, though.
I confess that I'm not clear as to why this clipping thing is worthy of so much angst. Thusly, I will draw my Gordian sword and cut the knot. If you're that worried about clipping, build a bigger Aleph. The Aleph 60 (technically a Volksamp) would be the logical choice. Next up would be the 100W versions, the 2 & 5. Then the 200W. You can also build any arbitrary size Aleph you want--the topic has been discussed to a fare-thee-well.
Swoosh! Whack!
Done.
See?
Simple.

Grey

P.S.: Trying to determine an arbitrary point at which clipping will occur involves so many variables (recording level, preamp gain, volume knob setting, amp gain, and speaker efficiency for starters) that it is a topic best left to those who debate the number of angels that can dance on the head of a pin.

 

[h_a]

Thanks for all your replies!

Indeed I think I will be more than happy to build an Aleph30! Or maybe spice it up to 40W...that should be surely enough...I'll see.

@Grey: sorry I'm sure I mixed that one up! I remember you wrote that somewhere in the eternal depths of the AlephX-thread, so maybe you build an 50W AlephX?

However, don't worry about me guys! I'm just notoriously curious about every detail and I love to inform myself a bit!

Thanks for your patience!

Have fun! Hannes

PS: one reason I cannot immediately build the A30 is that I've to finish my Pearl first - such a great phono design!