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Old 16th April 2009, 03:14 AM   #361
njepitt is offline njepitt  United Kingdom
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Quote:
Originally posted by danieljw


Sorry i was not clear, I meant in the shcematic the "Y" might be a typo. because the normal (as you have seen) groupings for the j74/k170 is GR, BL and V. per the datasheet.

i think perhaps the original article has a type and Y should be V???

I have not yet tried the 2SA1186/2SC2837 combo.

currently you are running if i am not mistaken:

2SK170BL, 2SJ74BL
2SC2240, 2SA970
BC640, BC639
2SC5200, 2SA1943

this is what i think after briefly looking at the data sheets.

2SK170BL, 2SJ74BL should function well.
2SC2240, 2SA970 relatively similar if hfe is selected appropriately
BC640, BC639 hfe is much to low (in my opinion)
2SC5200, 2SA1943 should function well.

-Dan
I had understood differently; that really the "Y" grade, while available, was lower Idss than the others - only I can't remember (or find) where I saw this - can anyone clear this up for sure? If it's a typo, the same typo is repeated not only four times on the schematic, but again twice on the sketch of the pcb, which seems a little odd...

Actually I have switched 2SC5200/2SA1943 for MJW3281/1302, but other than that your list is correct. (I switched to eliminate the possibility of fake Toshibas... switiching back is relatively simple if indicated.) Any suggestion of easy-to-find drivers in place of B640/639? I have BC550/560 on hand, for instance, but the datasheets seem to give hfe for different input data, and I don't know how to convert...

Quote:
Originally posted by Lumba Ogir
Hi,
Idss classification GR=2.5-6.5mA, BL=6-12mA, V=10-20mA.
Lumba, I am not sure what you meant by the schematic you attached... Are you querying values of R1 and R2? and voltage across R3 and R4? Sorry if I'm being dense...

Cheers

Nigel
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Old 16th April 2009, 03:23 AM   #362
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Quote:
Originally posted by njepitt


I had understood differently; that really the "Y" grade, while available, was lower Idss than the others - only I can't remember (or find) where I saw this - can anyone clear this up for sure? If it's a typo, the same typo is repeated not only four times on the schematic, but again twice on the sketch of the pcb, which seems a little odd...
I agree and would like to know this also.

Quote:
Originally posted by njepitt

Actually I have switched 2SC5200/2SA1943 for MJW3281/1302, but other than that your list is correct. (I switched to eliminate the possibility of fake Toshibas... switiching back is relatively simple if indicated.) Any suggestion of easy-to-find drivers in place of B640/639? I have BC550/560 on hand, for instance, but the datasheets seem to give hfe for different input data, and I don't know how to convert...
BC560B (specifically "B" suffix) looks like the right hfe range
however the Pd looks a little low 500mW vs 750mW, Cob is higher also
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Old 16th April 2009, 03:32 AM   #363
njepitt is offline njepitt  United Kingdom
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Well it's too late tonight to try it out, but I can easily switch the BC550/560s in to see if they give an improvement... They don't seem to be graded, at least not visibly, so I'll have to check the Fairchild datasheet to see hfe and so forth.... Stay tuned...

Cheers

Nigel
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Old 16th April 2009, 03:47 AM   #364
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will do,

hope it works !!!!

-Dan
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Old 16th April 2009, 04:02 AM   #365
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Nigel,
try to get around 1mA current though the FETs by selecting R1/2. JFETs always need to be checked and matched for Idss, you could use 9V batteries.
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Old 16th April 2009, 04:14 AM   #366
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Dan,
my pleasure. Have you obtained any 2SC2837/2SA1186?
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Old 16th April 2009, 05:04 AM   #367
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i have some on the way, i have not tried them in circuit yet.....

still measuring parts....

-Dan
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Old 16th April 2009, 05:27 AM   #368
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Dan,
they are probably the very best power BJTs ever made.
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Old 17th April 2009, 01:48 AM   #369
njepitt is offline njepitt  United Kingdom
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OK, here's an update. I followed Lumba's suggestion first. Measuring voltages as suggested, I had about 2mA going through the jfets, so I fiddled the resistance values on the trimpot to get things in order. Of course changing this changed the bias current also, so I had to alter those values.... et cetera. (Lumba: your schematic didn't show the bjts between R3 and R4 and the jfets - but these don't make any difference, right?)

In the end I got to about 1.15mA through the jfets, with bias current of about 550mA, by choosing R3 and R4 at 980R, and R1+R2 (total trimpot value) as 400R. (I expected this to be lower, but that's the way it worked out.....

Sound was helped a bit, but still louder than expected.

Then I decided to switch out the BC639/640 drivers. Turns out that the diferent pinning on the BC550/560 gave a (non-interesting) poroblem given my board layout, so I decided to try out 2SA970/2SC2240 here. (Looking at the datasheet the hfe was supposed to be about the same as BC550/560, and they are claimed to be "low-noise"...) This made a nice albeit subjective difference to the sound. A little less "stressed".

Still, much louder than the first Monstre. Let me repeat a question I asked above... What's an easy way to estimate an amp's output? Maybe the first one is weaker than it should be?

I should add that I don't think there is anything grossly wrong any more - with help from you guys the sound overall is pretty nice, now, although too loud. (It's also not as good as my F5, or as good as I had hoped. Well, maybe that's the way things go...)

Cheers

Nigel
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Old 17th April 2009, 02:15 AM   #370
njepitt is offline njepitt  United Kingdom
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I've just been looking at a Le Monstre version at this site:

http://belinfabien.free.fr/amplifica...hema_ampli.png

In this circuit he has resistors R14 and R15 on the bases of the driver transistors. What would be the effect of this? Am I right in thinking it would reduce voltage at base, hence reduce current through the driver, hence reduce gain in the output transistor? (Sorry, I realise my grip on these things is weak at best... )

Cheers

Nigel
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