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Leach Amp pcb group buy interest

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#422
I am going to place my order with Digikey in the morning. Does anyone have anything they would like me to add and ship to them. Most of what I am getting is the resistors and silver mica caps. I am going to try and find some Cerafine or better for the small on board electrolytics.
I found a great price on the output resistors at Pridmore on Ebay. They look like quality items. I am going to use the 0.47 that Jens recommended to help with stability even though it might rob some power. If after I do some measurements I need to change then so be it. I will try an implement the voltage regulator's that Bob Ellis and Jens collaborated on some years back for the frontend.

If anyone finds a really good price on the output devices 3281 or 4281 please post a note. These guys are expensive if you need 48 units. Ouch. A lot worse if you are going to match.

I am waiting for a reply from a fellow member on 100 volt Kendeil power supply caps from Istanbul. He seems to have a good source if shipping does not eat up the savings.

Tad
 
#423
Luke,
C1=1uF sounds right.
C12=470uF seems completely wrong.
Rin=22k. An input cap between 1uF and 10uF should allow sufficient unattenuated bass for all music and sound effects lovers.

C15&C16 are the NFB blocking caps. These should never have any AC signal across them. The value for C15>=1.414*[C1+C12]*R43/R40
if the input caps are 1uF then C15+C16>=31uF
if the input caps are 10uF then NFB caps >=310uF

C4 & C22 are discussed in Leach's Lo Tim paper.
I hope you already have a copy and know it off by heart. Print it out and keep it close by.
 
#424
Tad,

My components supplier is EPCOS authorized dealer here in Brazil. I bought 10.000uF/80V capacitors at about U$6,00 each. If you want some, I can buy it for you and send you. My pleasure! Those caps are 35mmX50mm snap in types (10mm spacing).

And if anybody else wants those caps, I can send you.

80V capacitors is fine if using +/-65VDC supply.
 
#427
Hi Ed,

Yes, they have the GigaElco capacitors (those with screw terminals).

I don't know if they have it in stock, but the price is:

22.000uF/100V = U$29,00 (B41874 series - 50mm diam X 116mm tall)

They also have 10.000uF/100V snap-in, but the price isn't good: U$18,00.

If you want any of those, let me know, so I can call them and see how many they have in stock.
 
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#430
Toshibas

I can now follow up my reference to Toshiba output transistors in post #301 with the following:

I have 2 quads of them in 2 channels of AAK's DTV Symassum playing right now. Just fired them up.

They work well in his boards, providing 4 & 8 mV DC offset @ 40 mV bias.
 
#434
AndrewT said:
Luke,
C1=1uF sounds right.
C12=470uF seems completely wrong.
Rin=22k. An input cap between 1uF and 10uF should allow sufficient unattenuated bass for all music and sound effects lovers.

C15&C16 are the NFB blocking caps. These should never have any AC signal across them. The value for C15>=1.414*[C1+C12]*R43/R40
if the input caps are 1uF then C15+C16>=31uF
if the input caps are 10uF then NFB caps >=310uF

C4 & C22 are discussed in Leach's Lo Tim paper.
I hope you already have a copy and know it off by heart. Print it out and keep it close by.
Click to expand...

thanks Andrew, the 470uF input cap is on all of Jens boards, I dont get it and would rather use a film cap.

Ill leave c15 and 16 as per the BOM.

Have read parts of the Lo Tim paper but will revisit before building.
 
#436
just reading Dr Leaches papers and he states that the cascading resistors Q5 and Q6, (Jens latest diagram T10 and T19) drop the voltage by about 18V. I dont understand this, if the zeners put 40V at their bases then wont they drop 40V plus Vbe of 0.6V?
 
#438
Tony said:
0.6 is very very very small compared to 40 volts don't you think? so that it can be ignored.....😎
Click to expand...

yes very very very close🙂 I wanted to show how I calculated the voltage on the input pair. But it all makes sense now, I think he used 58 v rails so 58-40 is 18 dropped across the cascade. I was thinking of 80 v rails which is what Im planning so I thought he was wrong;-)
 
#439
would 2sc5171 and 2sa1930 be a good substitute for for the mje15032 and mje15033?
They have the same pinout so that makes it easy.
I worked out that if my outputs have a minimum hfe of 25, for an 8 amp output, the driver would need to deliver about 320mA I think. This device is good for 18V and 2amps Ic. What's the verdict, will it work?
 
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