Hi,MBK said:
that would explain why Mike has adopted 100pF.
The low pass filter RC is really [Rs+R]*100pF.
If 5k5 & 2k0 are used as source resistance then the RF filter is really 0.75uS, right inside the more usual recommended range.
But, Mike has already confirmed
Hi AndrewT,
I thought the gain of the amp are set high so that no active preamp are neccessary.
Thanks.
I thought the gain of the amp are set high so that no active preamp are neccessary.
Thanks.
The problem is not the gain but the added impedance in front of the amp. At second thought it's really better to stick with Mike's values. For instance, if you must use your 33p caps, simply double them up on top and put one on the bottom (all parallel). Then you're back to Mike's values.
Basically modifying these caps without properly knowing the potential effects and for really no good *technical* reason is just asking for trouble. I substituted some parts on mine after a lot of handwringing, consulting all threads, Mike's site, Pavel's site, chose the best recommended config, thinking it all through with good technical reasons, and *still* got into trouble because my input transistor batch had low hFE... so, save yourself a lot of trouble and buy those $0.50 100 p caps
When I say I got into *trouble* I mean, desoldering and resoldering approx. 30 to 40 parts total (I built 6 channels), countless measurements, a broken PC and soundcard due to the oscillations the amp produced when I did my countless measurements, and all in all 8 weeks of labor, till I found out what was wrong and fixed it.
I say, stick to Mike's values.
Basically modifying these caps without properly knowing the potential effects and for really no good *technical* reason is just asking for trouble. I substituted some parts on mine after a lot of handwringing, consulting all threads, Mike's site, Pavel's site, chose the best recommended config, thinking it all through with good technical reasons, and *still* got into trouble because my input transistor batch had low hFE... so, save yourself a lot of trouble and buy those $0.50 100 p caps
When I say I got into *trouble* I mean, desoldering and resoldering approx. 30 to 40 parts total (I built 6 channels), countless measurements, a broken PC and soundcard due to the oscillations the amp produced when I did my countless measurements, and all in all 8 weeks of labor, till I found out what was wrong and fixed it.
I say, stick to Mike's values.
That's part of the problem.
In the UK, mica are around £0.90 (~$2) each.
If an inventory of values are stocked for debugging stability problems, that is a big investment.
Silver mica caps ratings
According to the BOM :
C2,C7 100pF/300V
C3,C4 330pF/500V
C14 10pF/300V
May I use lower voltage ratings caps ?
And which absolute minimum ? Sum of rail supplies : 50+50 = 100 V should be enough in any case, right ?
For instance I have a lot of cheaper 100pF/100V silver mica ...
Alternatively, may I use Wima film caps instead of mica and will I lose quality doing that ?
TIA, Hervé
According to the BOM :
C2,C7 100pF/300V
C3,C4 330pF/500V
C14 10pF/300V
May I use lower voltage ratings caps ?
And which absolute minimum ? Sum of rail supplies : 50+50 = 100 V should be enough in any case, right ?
For instance I have a lot of cheaper 100pF/100V silver mica ...
Alternatively, may I use Wima film caps instead of mica and will I lose quality doing that ?
TIA, Hervé
Andrew,
that's quite expensive, but still, in this case there shouldn't be much experimentation needed. Also, I used silver mica only for C14.
To Herve,
100V should be fine, the higher ratings may be better built (dielectrics) which may be an advantage but I don't believe it's a must.
that's quite expensive, but still, in this case there shouldn't be much experimentation needed. Also, I used silver mica only for C14.
To Herve,
100V should be fine, the higher ratings may be better built (dielectrics) which may be an advantage but I don't believe it's a must.
Hi Ipanema,
The PC based item may give you ground loop noise, plus all the switching noise from the computer.
The inputs to a sound card are easily damaged and present around a 10 K impedance normally. Not great performance and you will probably damage it at some point. The THD meter will properly condition the input signal for you and presents a higher input impedance. That and HP units will respond to signals out past 1 MHz, many sound cards cut off around 20 KHz. You can also remove the ground reference on the HP THD meter input. 😀
What you can do that will be intelligent is to route the THD meter monitor out into your sound card. This will extend the dynamic range of your PC instrument greatly.
One last thing to consider. The THD meter is real time and easy to decipher. Your PC "meter" will be much more valuable examining the residuals.
The other MJW series parts should work well. The last time I looked, Digikey still had those parts in stock. They are not expensive.
I'm not sure what your bias should be. Differ to MikeB's suggestions until you are able to set with a THD meter. Real time is king here!
-Chris
Not really, for a couple reasons.
The PC based item may give you ground loop noise, plus all the switching noise from the computer.
The inputs to a sound card are easily damaged and present around a 10 K impedance normally. Not great performance and you will probably damage it at some point. The THD meter will properly condition the input signal for you and presents a higher input impedance. That and HP units will respond to signals out past 1 MHz, many sound cards cut off around 20 KHz. You can also remove the ground reference on the HP THD meter input. 😀
What you can do that will be intelligent is to route the THD meter monitor out into your sound card. This will extend the dynamic range of your PC instrument greatly.
One last thing to consider. The THD meter is real time and easy to decipher. Your PC "meter" will be much more valuable examining the residuals.
Now, there's a course! Experience is the best teacher. I don't know of any books, but app notes from HP or Tektronix would be good. Owner's manuals from Leader or Kenwood might be helpful.
Yes. Look at the zero crossings for input vs. output. You will need to look at lower frequencies to properly figure out where you are, then go to higher frequencies to get a more accurate figure. I never do this.
The ones I used were discontinued.
The other MJW series parts should work well. The last time I looked, Digikey still had those parts in stock. They are not expensive.I'm not sure what your bias should be. Differ to MikeB's suggestions until you are able to set with a THD meter. Real time is king here!
-Chris
Hi,
AAk, are the two resistors R35/36 1W ?
On picture in post 61, they seems to be very short...
Mine are to big for the board, i've to fold them.
Thanks.
JF.
AAk, are the two resistors R35/36 1W ?
On picture in post 61, they seems to be very short...
Mine are to big for the board, i've to fold them.
Thanks.
JF.
Hi JF,
Yep, one watt they are. Your larger ones will do. For all others you can find them at mouser. Here's the BOM.
Regards,
Al
Yep, one watt they are. Your larger ones will do. For all others you can find them at mouser. Here's the BOM.
Regards,
Al
anatech said:
The ones I used were discontinued.
-Chris
Chris,
You may want to use only the transistor from NJL0302/0281 😉
That part is the same as MJL or MJW0302/0281.
Or, if you want to design symasym with different bias circuit you may want to include NJLs diode ...
Anatech quote:
The ones I used were discontinued. The other MJW series parts should work well. The last time I looked, Digikey still had those parts in stock. They are not expensive.
-Chris [/B][/QUOTE]
Onsemi calls them obsolete.
Digikey list the MJl/w but they do not stock them, but the minimum order is in $100s. either 360 @$1.75 or 300 # $1.88
I have looked around and the scalpers have them but there have minimum orders of $200 /$300 USD and i do not know how many you can get for this as you would have to get a quote.
At Digi-Key 2sc5200 and 2SA1943 are $2.28
mjl3281 etc are $4.25
So the prices have really jumped for what are equivalent devices.
If there was enough interest to do a Groupbuy to total 300 pieces
but this is more than double the number of AAK boards out.
The ones I used were discontinued.
The other MJW series parts should work well. The last time I looked, Digikey still had those parts in stock. They are not expensive.-Chris [/B][/QUOTE]
Onsemi calls them obsolete.
Digikey list the MJl/w but they do not stock them, but the minimum order is in $100s. either 360 @$1.75 or 300 # $1.88
I have looked around and the scalpers have them but there have minimum orders of $200 /$300 USD and i do not know how many you can get for this as you would have to get a quote.
At Digi-Key 2sc5200 and 2SA1943 are $2.28
mjl3281 etc are $4.25
So the prices have really jumped for what are equivalent devices.
If there was enough interest to do a Groupbuy to total 300 pieces
but this is more than double the number of AAK boards out.
roender said:
The pricing problem again thenjl0302 ar not in stock and Digi cant give a lead time ad they need 225 units min order
SheldonD said:
Did you try to order samples from ONsemi?
They send you max 5 peers per order. In my experience, you can use them all in the same amp without sorting them for hfe or Vbe. All are very tight factory matched which denote a very good manufacturing process
roender said:
Roender
No, I did not. But am attempting this while I type $15 for 5 units.
Thanks.
Ryssen said:
You can order more stuff for same price..
Ryssen Good Point!
Actually I did: got both the 0821 0302 could not find any other samples that I was interested in. so that is $1.50 each.
I will have tto do more research to see what else I may like.
The stuff I wanted was not on samples.
No,I got the MJW0302/0281 audiokit in last minute,now they have taken it away..before they had MJL21193/94 as sample not any more,hmm wonder why?..