Explendid amplifier designed by Michael Bittner, our MikeB

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#2,503
Thank you Mike,

For input I have the BC550B/philips ,think is good .

For recent days, I was reading this 251 pages "Great thread", my poor english really embarrassed me.


Grrrr...

P.S. I used to have a oral english teacher , a German lady who really give me good instruction to improme my english.

Thank her & Thank you

hoho
 
#2,505
MikeB said:
They should be both okay, i would use 2n5551, and the Toshiba for input ? Or do you have other plans for input ?

Mike
Click to expand...


in fact, I'd prefer 2SC1815 first, seems less cap(hidden) under less voltage torlerance, seems more clean.

haha

Really excellent design Mike, when research this sch, always have the bright spot came out.

Decent and serious-focus guy must you be !

haha
 
#2,508
anatech said:
Hi Mike,
I use XP Home. It was good until now and usoft doesn't know how to fix it.

Hi HBarske,
A/D is supposed to be 192 KHz. The published specs seem to look good, we shall see. The older card was in trouble at 18 KHZ, so this is an improvement. I saw it on sale for $134 CDN, so I picked it up. Also hoping a mjor change would shock XP into working. No such luck.

I do plan to buy a DSO with FFT functions, so this is good enough for quick things on the bench.

Mike,
Don't worry, I'll measure THD with my normal stuff and look at the residuals. Might actually send the residuals to the sound card. I'm sure that will extend the usefullness.

-Chris
Click to expand...

Can you check, is there any pop, crackling, oscillation from x-fi ?
there are so many issue with x-fi, and there is online petitions for creative.
 
#2,509
borys said:
MikeB
I have problem with 2pairs version. When I turn on my amp it has ("on thumb" - I don't know how it does name in English) "-" out voltege for aprox 0,5s, my speaker cone goes inside the box. Can you hepl me with this ?
Click to expand...


pardon me some words.

your situation must be actully like this:

when turn on your amp, there's a voltage offset occured,so it drivers your speaker "pong"
after about "0.5s", the voltage offset disappear because of the NBF ,and then there is nolonger a "pong"

to a conclution, all the criminal is the offset voltage,
and I think mostproberbly is because your unmatched MPSA18(if you used of course)

so may you simplely rematched them and soder them on you board.

good luck.

hoho
 
#2,511
Hi borys, that's really odd, i have no idea how the increased number of output devices should do that. Normally for symasym the turn on thump is not even audible.
I am not 100% familiar with the 2 devices version, is the only change the additional outputpair ? Which voltage supply are you using ?
What are you using as input devices (and their hfe) ? Have you changed the gain ?
Is the feedback DC-blocking cap (c19) too big / reversed ? Input cap ?
Can you measure polarity of the turn on thump ? It sounds like you get several volts.

You don't have that problem with the single pair version ?
I will take a look at the layout... Can you show pic of the actual PCB from below ? Maybe there is a routing error... Could be a grounding issue...

Mike

Edit: Does "wovo" has the same problem ? According to his pics he has also built the 2 pairs version, with self etched boards.
 
#2,514
Can you change input devices to bc546 or bc547 ? Maybe the mpsa42 has ugly low hfe at low voltages. Datasheet says hfe = 70 for 1.5ma. Interesting that it is rated at 10v, and not at 5v as usual. For comparison, the mpsa18 has hfe = 980 at 5v/1ma. (measured)
What hfe did you measure for mpsa42 ?
For high voltage types i recommend 2sc2240 as input device. (hfe=~500,BL type)
With hfe = 70 you get 471mv input offset, this gives 0.471x45=18v at at startup. (Until c19 is charged)

The DC-offset of 2.5mv is standard for symasym and shows that the input devices are perfectly matched.

Mike

My symasym measures 12mv input offset, giving hfe = 2750 at 35v. (mpsa18 rocks !) Can you measure your inputoffset ? (Voltage across r14, the 22k at input)
I might remember the 12mv wrong....
 
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