Jens Rasmussen Leach clone group buy

[pooge]

Are the Dale resistors you guys are using non-magnetic? If so, are they NOS or recent purchase, and where purchased?

[clm811]

My non-magnetic Dales were ordered online from Surplussales back east. I guess you could say that they are "NOS", because the package said "February, 1957!"

Again, speaking of resistors- on Jens' BOM R1/R23 are specified as 100ohms

I only have 91ohm/1Watts on hand(9% less than spec)-

Since these appear to set the voltage/current to the VAS, is there any forseeable problem using them?
(Bob, Tad, Jens, anyone?)

-Chas

[BobEllis]

Chas,

Don't sweat it - 91 ohms is close enough. The real purpose is to form an R-C filter with C1,C2, C14, C15 for the front end supply, removing output stage induced ripple.

Bob

[clm811]

Cool.
Thanks, Bob.

NEXT QUESTION-

How true are the following:

"Output transistors have to be matched for optimum performance..."

and

"there are quite a few parameters that should be matched to get true matched pairs. The situation is made a little harder when you have PNP and NPN (or N-Channel and P-Channel) devices."

-?
And what is a simple method for measuring/matching outputs?

Thanks as usual!

-Chas
little harder when you have PNP and NPN (or N-Channel and P-Channel) devices[/QUOTE]

[BobEllis]

The basic match is accomplished fairly easily by scaling Prof. Leach's input device matching scheme to your target idle current. Just change the load resistor to an appropriate value. You also need to adjust the base resistor since output devices have much lower current gain than the inputs. Calculate the current gain by comparing base current to output current.

Yes, output matching is supposed to improve sound quality, but my Leach amps sound great without. Vertical MOSFETS need matching to ensure reasonable current sharing.

Chances of getting the Ns to match the Ps are slim.

[tryonziess]

It sounds like a few of you are enjoying your little projects. The end result is real nice!!!
If anyone was paying attention I do not believe you will see any really audiophile type parts on Jens boards. He assembled quite a few and had very good results. Just standard quality parts and attention to detail. Dr. Leach in his assembly document specs 5% parts and mostly run of the mill or even cheaper. I think the real quality is in the design and layout.
When I was researching this project I got many nods for the Leach build from some of the most respected members of our forum. Do not sweat the minutae just take your time. Nothing is wrong with soldering in one little part at a time and closely checking it as you go. Remember the chassis will take about 10 times as long to build.
It is nice during the shut in winter months to have a project at hand.
Tad

[rob3262]

Originally posted by brutepuppy
I've had problems soldering the my 330 Ohm resistors. Some of the problems I have had : They take an extraordinary amount of heat to stick; Some take so much heat that they burn the pad; The leads are too large; They refuse to "wick" the solder;

BP - I've resorted to using a no-clean low solids liquid flux for improved flow. Like Chas, I'm using an 800º tip to get the heat in quickly.
I have touched up some pads on top, where i didn't flux.

I am just days away from testing the front end of my first PCB. Heat sinks due within the week (I WONT hold my breath though).

Matching zeners was as bad as small signal transistors. I'm beginning to think that 5% is useless! My reference voltages range between 19.2 and 19.8V Maybe I'm anal but I was hoping to exact match 6 boards!

[clm811]

Like Chas, I'm using an 800º tip to get the heat in quickly.

Speaking of which-

My trusty old WTCP just died. I loved that thing!

Anyone here have an extra (working) Weller #201 pencil to sell/trade? I can't find one locally.

I still need to finish soldering my set of boards...

-Chas

[tryonziess]

Doesn't anyone use a cheap 8.00 dollar 40 watt iron anymore. I never did enough soldering to justify spending 80.00 dollars for a decent station. When the little guy dies I just buy a new one.

Tad

[BobEllis]

I used throwaway irons until I bought my cheap $40 temperature controlled station. Results are worth it and the tips last a >10X longer than the cheap irons.