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Leach Amp pcb group buy interest

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#441
2sa1930/c5171 is usually looked at as a driver. It could be used as a pre-driver in a very high power amplifier.
Do not use it as a VAS.

Look at the SOA curves.
At 80Vce the device can only pass 35mAdc when it is cold.
It is not suitable for high current when high voltage is present.

I would suggest this device should only be used as a driver on amplifiers using <=50Vdc on the supply rails.
 
#443
I was comparing the 10 output version with the 12 output version and the 470uF input capacitor appears in both, so it was no typo.

Just like Luke, I don't get it either. A 10uF film capacitor seems best suited there, as already said earlier.

I also noticed that Jen made provision to bypass the input cap, by feeding the signal to the pin labeled "3" on the schematic. Very nice.
 
#445
Loboone said:
Luke,

Re:would 2sc5171 and 2sa1930 be a good substitute for for the mje15032 and mje15033

Farnells reference - MULTICOMP|MJE15032|TRANSISTOR, NPN, TO-220 | Farnell New Zealand and ON SEMICONDUCTOR|MJE15033G|TRANSISTOR, PNP, TO-220 | Farnell New Zealand

Not that expensive really!

Ian
Click to expand...

if they handled the demand then yes, better ft and hfe. Nelson talks about semis as being where you should look for better performance not expensive caps and resistors. If I can find a better transistor for less then I would use it, wouldnt you?
BTW I dont use farnell typically, its easier and cheaper to order from ebay and mouser.
 
#446
Miguel Nabuco said:
I also noticed that Jen made provision to bypass the input cap, by feeding the signal to the pin labeled "3" on the schematic. Very nice.
Click to expand...
Yes a beautiful bit of engineering.
Put in 3off 0.1inch pitch pins.
Use a 0.1inch pitch shorting plug (computers use lots of them and retailers sell them very cheaply).
Connect the signal input leads to AC Signal pin and to Signal Ground pin.
Short Ground to AC signal for testing and setting up.
Short DC to AC for running as a DC coupled input. This is particularly useful when the source already has a DC block or has a DC servo on it's output and DC detect to force a mute on fault.
Leave the shorting plug on the DC pin alone when using the amp in AC coupled mode. As I said Brilliant. I soldered the to the pins on the underside to leave the 3 connector parts clear of added solder.
I wish EVERY power amp PCB that gets posted on this Forum adopted this extra pin. It costs almost nothing to implement.
 
#449
BTW,
MCM electronics has a pretty good assortment of Sanyo and Toshiba transitors and there prices are somewhat better than Digikey and Mouser on small lots. They did not even charge shipping on the back ordered delivery.

What is the point of using extremely fast transitors in an audio device where the signal is ten thousand times slower? Is there a possiblitiy of undetectable oscillation with these parts? My scope only reads to 20 mhz. Some of these new transitors, which we can use, are approaching one gig. A decent digital scope is a little pricey.

I was using the web calculator and the input cap alone will pass about 40 hertz. Two in parralel, which the schematic shows, will go to 20 hertz. Seems reasonable enough.

Has anyone who paid not gotten there boards?

Tad
 
#452
Luke said:
if they handled the demand then yes, better ft and hfe.
Click to expand...
comparison of driver transistor parameters
params . . . 2sa1930 . 2sb649a . mje15034
Vce0 . . . . . 180 . . . . 160 . . . . . . 350
fT . . . . . . . 200 . . . . 140 . . . . . . 30
mA @ 80V . . 35 . . . . .100 . . . . . .350
hFE @ 10mA .100 . . . . 100 . . . . . .80

Give priority on a single parameter and one must compromise on the other parameters. Select what is adequate to good for all parameters and decide which suits the build.

the 6pair is intended for high power, either via high current and/or high voltage.
35mA is a non starter for the 6pair driver.

There are dozens of suitable driver devices between the extremes listed above.
Look for suitable candidates.
A 100W to 150W output device (To247) might even be suitable as a driver for a very high power 6pair, particularly if one takes advantage of it's inherent power dissipation by biasing it to achieve good fT and good hFE. The To220 mje15034 biased to 100mA improves both gain (hFE>100) and speed (fT>60Mhz)
 
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#456
Rob_S said:
For the BOM that Jens posted what are the rail voltages. I ask as I assume that moving away from these voltages would require some changes in values?

Also I assume this is for AB config?

Thanks
Rob
Click to expand...

Hi Rob,

go to Dr Leaches website. You need to change R4=R7=V-40/8.2. You will also need to determine how much power you will allow before your protection circuit will cut in. I havent done this part yet, but its on his website.
If you understand ohms law this shouldnt be too hard.

Leach Amp Plans - Part 1
 
#457
tryonziess said:
AndrewT,
The website address Speaker Crossover Chart and Capacitance vs. Frequency Calculator(High-pass) is the calculator I used. Input 470 microfarads at 8 ohms.
If per chance I have something wrong PLEASE let me know. I am still figuring a lot of this out. This is not my professional field or even close.

Thanks Tad
Click to expand...

Hi Tad, its a low pass filter to prevent DC entering the amp. Fc=1/2*pi*r*C Your input impeadance 22k set by resistor R43. Your calculator is for speakers with an R of 8 not 22k.
If you make Fc say 10Hz the cutoff frequency then C is 0.7uF
Use this spreadsheet if you like. The first calculation sets the input impeadance and cutoff frequency and gives you the capacitance. Move decimal 6 places to the left to get uF.
Try this spreadsheet out it gives you some idea how it works without getting your calculator out🙂
The second calculation gives you a Fc for a given R and C. Again the C is Farads, move decimal 6 places to give uF.
You could just use 1 or 2 uF and leave it at that.
 

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#459
It is truly strange that using the 470uf cap in the Leach clone with 10 transistors produces window rattling bass. What am I too expect if I change this to say 2uf? The EQ for this amp in a bi-amp system is set to 250 and below. I had built that amp exactly from the BOM.

Thanks for the heads up here. And Andrew most of the math I do these days is set aside for counting money and making sure peoples merchandise arrives correctly. That is where the toys and food come from. And thanks to you and Luke I have some knew knowledge to use.

Now, Which resistor values do we change on the Leach 12 to adjust the protection circuit? I would like to get this HIGH dollar monster correct. Leach states that installing all of the circuitry and leaving out the 2 transistors will eliminate protection all together. Not too good.

Tad
 
#460
tryonziess said:
It is truly strange that using the 470uf cap in the Leach clone with 10 transistors produces window rattling bass. What am I too expect if I change this to say 2uf? The EQ for this amp in a bi-amp system is set to 250 and below. I had built that amp exactly from the BOM.

Thanks for the heads up here. And Andrew most of the math I do these days is set aside for counting money and making sure peoples merchandise arrives correctly. That is where the toys and food come from. And thanks to you and Luke I have some knew knowledge to use.

Now, Which resistor values do we change on the Leach 12 to adjust the protection circuit? I would like to get this HIGH dollar monster correct. Leach states that installing all of the circuitry and leaving out the 2 transistors will eliminate protection all together. Not too good.

Tad
Click to expand...

Hi tad, your welcome, I studied this stuff along time ago, but most of its never been used for over 20 years. I should really brush up, but Ive made lots of stuff with no failures yet. Oh apart from one amp that oscilated and caught fire on the lounge floor, ya think that impressed the wife🙂
you should go with what works for you. The 470uF cap has a -3db point
0.105Hz, from the spreadsheet. I'm not sure if thats actually blocking any DC 😀 I expect the amp has a really good bass response.
I did some more work on my UGS today, its slowly coming together. Still planning this one but hope to make it after the UGS is finished.
I would love to see someone here get theres together. Any builders in here apart from Tad?
Ill take a look at the current limiter later, but from memory you need to know your rail voltage. I'm pretty sure its in Dr Leaches paper.
What voltage are you using BTW?
 
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