Hiraga "le monstre"

[danieljw]

Originally posted by neazoi
>and its best to select good quality potentiometers suitable for the >the bias circuitry............

To talk about specific items, how about these trimmers?

http://cgi.ebay.com/75H-100R-TRIMMER...arms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1| 294%3A50

http://cgi.ebay.com/3386F-1-101-TRIM...arms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A0|293%3A1| 294%3A50

And how about the precision ones?

http://cgi.ebay.com/10pcs-3296-101-1...arms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1| 294%3A50



>*however i used matched transistors (and jfets for the le monstre)

Tantalums of 1-2% should be pretty matched already, shouldn't they? I have bought 0.5W audio note tantalums but I am not fully aware of their performance, although they should be much better than the metal film ones..?

Soon I will have 100 resistors of 1 ohm 5W metal oxide 5% so I can match them. The problem is when they heat up their values could change differently, couldnt they?



Will it be so much problem if the input fets are not matched? I am not aware if a disaster in sound could occur by using not matched fets, any thoughts?

the first pot looks ok based on spec cant speak fort heother two

-Dan

[audiomanics]

Originally posted by neazoi
As long as I have the MOX resistors I will let you know.

Are Multi-turn trimmers fine?

What is the size of you MOX?

Multiturns are basicly the same as the single-turns... with the singleturns, the wiper is connected to a piece of plastic with a slot (where you put your screwdriver)
In a multiturn this plastic is a gear. A screw on the side is merely a worm that drives that gear (wormwheel), so only a mechanical solution. So it depends on how stable your hand is..
In this a trimmer is different from the multiturn helical potentiometers which contail a real physical coil shape of resistive material.

If you decided about your trimmer (i think a cermet type is fine) i can easily add another soldering-island in the layout, so you don't have to bend the legs of it.

Kees

[ericfe1975]

hello,

what if.... instead of the jfets at the input, i use the bc560/bc550 ,taking care to chose high gain types....this should improve the stability of the amp.

it will surely lower the input impedance but this should not be an issue since the output of cd players are able to drive such loads.

is the warm sound of the le monstre a legacy of the input jfet sound?
in this case, will the le monstre built only with bipolar transistor sound colder?

thx for your advice.

[danieljw]

if you use bipolars on the input then you will need to build or sym or calculate the amp operating characteristics and adjust resistance values to suit.

I cant comment on the change it will have on the sound... you would have to build and compare...

-dan

[ericfe1975]

thanks for the answer, i will do the simulations in a next future.

[danieljw]

hope it works well, i think a few people would like to see the results !

much easier to get newer parts !

-Dan

[ericfe1975]

well jfets easily picks up rf , bipolars dont do it as easily, but jfet have a warm sound, i am not too convinced , because even if the amp will probably be more stable, the warmness of its sound will be gone (may be may be not :P )

i was looking at the schematic, and in fact i am not sure at all wich resistors have to be changed, and how...
i guess almost every small resistor should be changed...help is much apreciated so it wont be necessary to do some "blind" simulation trying to choose the resistors value as some people choose lottery numbers..

thanks.

[danieljw]

perhaps you can start with the normal values which are listed for Le monstre and see the results, and then I can help you pick different values after, if the source of jfets is a problem i think i know where to get some:

http://ampslab.com/components_fets.htm

I have dealt with Michael from Ampslab before (see my signature line) he is a nice person to deal with - there are also quite a few interesting parts on the components section of his site.

-dan

[ericfe1975]

thank you very much i will do my best.
thanks for the link too.

[ericfe1975]

hello i replaced the input jfets by 2 bc550 in darlington and 2 bc560...it does not work at all.
the amp doesnt give any gain and there is a big offset at the output. any suggestions? i am using the second schematic in :

http://www.kk-pcb.com/hiraga.html

i have tryed a lot of changes, but the amp has no gain...help is much apreciated.
I use SIMetrix tu simulate the circuit , if someone wants it i can put it in a site and a link to it.