First Watt B1 Buffer Preamp

[Born2BeWired]

http://beavishifi.com/projects/JFET_preamplifier/

I read the original article with the provided link, and was I tempted to make some devilish remark to several of the original author's conjecture. But I feel like a saint tonight, kaya behave muna ako.

Let me just suggest some mild additions to the circuit to improve one's chance of making it work in a more predictable way:

1. Add at least >100uF capacitor to decouple the power supply. Better still, add another 0.1uF in parallel with the 100uF. This becomes even more important if you use battery with the circuit as the author strongly recommends. The reason is, the battery effective series resistance, which goes up as the battery ages, will create an unwanted signal path between the output and the input. Without power supply decoupling, there is a likelyhood the whole circuit will oscillate (i.e. motorboating and/or HF oscillation). For sure you do not want this to happen in your circuit.

2. Add input coupling capacitor, even when the author says it is not necessary.

3. It seems the author picked an RF JFET only for reasons of availability. In fact, it is primary designed as a switch as per datasheet.  If you want a preamp with low noise floor and good linearity, an RF device (or switch) is not exactly an excellent choice. If you could get hold on one (JFET) that is designed for audio, the added inconvenience of experimenting with the bias may well be worth it.

 

[efren]

well said sir Born, if i were to build this project i will implement a cap multiplier since i'll be utilizing an AC power suppy, unfortunately, I've given away my last of mpf102 originals, so building this circuit is unlikely, i still got a lot of original gold plated pins Nfets more suitable for audio duty, anybody interested to build this Beavis linestage, just ask for it you can have it gratis, it's up to you to find the best operating points
one more thing is i'm  more into tubes now which i found more suitable for my pair of ears

[n0th1n6]

Hi sit efren, i am still interested to build thisas guitar preamp. Thanks

[tony]

http://beavishifi.com/projects/JFET_preamplifier/

I read the original article with the provided link, and was I tempted to make some devilish remark to several of the original author's conjecture. But I feel like a saint tonight, kaya behave muna ako.

Let me just suggest some mild additions to the circuit to improve one's chance of making it work in a more predictable way:

1. Add at least >100uF capacitor to decouple the power supply. Better still, add another 0.1uF in parallel with the 100uF. This becomes even more important if you use battery with the circuit as the author strongly recommends. The reason is, the battery effective series resistance, which goes up as the battery ages, will create an unwanted signal path between the output and the input. Without power supply decoupling, there is a likelyhood the whole circuit will oscillate (i.e. motorboating and/or HF oscillation). For sure you do not want this to happen in your circuit.

2. Add input coupling capacitor, even when the author says it is not necessary.

3. It seems the author picked an RF JFET only for reasons of availability. In fact, it is primary designed as a switch as per datasheet.  If you want a preamp with low noise floor and good linearity, an RF device (or switch) is not exactly an excellent choice. If you could get hold on one (JFET) that is designed for audio, the added inconvenience of experimenting with the bias may well be worth it.

 

good advise......

napasin ko ang title ng thread ay "First Watt B1 buffer preamp" i know this was a Nelson Pass design so this is the proper link: http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm

and scheme:

[Engr. Dacuycoy]

good advise......

napasin ko ang title ng thread ay "First Watt B1 buffer preamp" i know this was a Nelson Pass design so this is the proper link: http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm

and scheme:

tama sir tony... side dish lang yong beavishifi.com/projects/JFET_preamplifier.. i thought kasi mahirap hanapin yong 10uF na Caps, eh naglipana naman pala hehe  

@sir efren
gagawin ko pa din yong jfet as mobile preamp.. de-baterya  

[Engr. Dacuycoy]

reduce size 100MM x 82MM using EPCOS 10uF/63V/100V capacitor



http://www.4shared.com/office/ZReYH5Gd/B1_PREAMP_Small_Landscape.html
http://www.4shared.com/office/jlxpioyn/B1_PREAMP_Small_Layout.html
http://www.4shared.com/photo/kWOiDIMs/B1small.html

[THXneo]

MPF102 marami sa alexan nito,nagamit ko na ito before sa amp ng line(tone) tester

[THXneo]

heto check mo po dito:

[Engr. Dacuycoy]

+1 tnx 

[efren]

would you believe this costs USD1000.00 as a finished product as per Pass B1 site? 

you can build several cathode follower tube pre-amp using premium "audiophile" grade tubes and boutique parts with that amount, i never thought hand picking & closely matching to-92's JFET's would be that costly on the brighter side, it's nice of them to share the design, so DIY'ers have nothing to complain about

matching of jfets is the major reason why i shun away from this type of design, once i built Hiraga "Le Monstre" 8W class A uses jfets as differentials, the jfets i bought in a local electronics store despite bearing the same batch number were a total mismatch, figures were way off as much as 45-60%, the result is a total disappointment on my part, boards find their way in the trashcan

[efren]

But Eng'r. Dacs don't worry, the jfets you're about to get were premium, i got those from an importer of used Australian military surplus, so more or less you have an idea what you're gonna get i'll also throw in another value also Nfets maybe more than ten, also gold plated pins, i'll just split it between you & sir noli

[TinTopHack]

You can use 2N5457 which I think is still available locally.  Its typical Idss (zero-gate voltage drain current) of 3mA will give you approx 8V at the drain terminal - very near the ideal 9V. Of course you can play around with the drain resistor values if you like. Its Idds range is from 1mA to 5mA - much narrower than the 2mA to 20mA of MFP102. This means you will have a better chance of getting closely matched 2N5457's than MFP102's.

I have been using 2N5457's for my guitar preamps which I derived from Don Tillman's Discrete FET guitar preamp which has been used as reference by the author/designer of this buffer preamp as shown at the bottom of the article (link provided by Born).

In the post of THXNeo above where he shows a list where MFP102 is included, 2n5458 is also included. This belongs to the same family as 2N5457 but has higher Idss - typically 6mA. If you want to use 2n5458 you might need adjust the drain resistor value and maybe the source resistor too.

[TinTopHack]

I read the original article with the provided link, and was I tempted to make some devilish remark to several of the original author's conjecture. But I feel like a saint tonight, kaya behave muna ako.

The human side of Born2BeWired talking... hmm you have a carbon-based side after all.


By the way the 8V i mentioned in my previous post and the ideal 9V refers to the circuit when power by 18V, NOT 9V as in the test circuit.

Why is Idss important? For the drain and resistor values in the circuit, higher Idss means lower drain voltage and higher source voltage. Too low Vd and too high Vs will cause your preamp's output to clip easily -> distorted sound.

[Engr. Dacuycoy]

try ko muna yong original design.. then goes to modification using sir TTH recomendation.

here is the initial layout.



i was planing to incorporate a shunt regulator from esp.. any suggestion?

[tony]

there is a mistake in the drawing, C1 and C2 is just 1 cap and connects to the + and - terminals of the bridged diodes....
16volts ac input means an unloaded rail of 22.4 volts, as it is, zener current is about 22mA without anything connected to the psu terminals, actually less if we consider the dc resistance of hte power traffo...

D3,R4,Q1 can be replaced with just a single 5watt zener diode.....

[macky]

there is a mistake in the drawing, C1 and C2 is just 1 cap and connects to the + and - terminals of the bridged diodes....
16volts ac input means an unloaded rail of 22.4 volts, as it is, zener current is about 22mA without anything connected to the psu terminals, actually less if we consider the dc resistance of hte power traffo...

D3,R4,Q1 can be replaced with just a single 5watt zener diode.....

you mean D5, R4, Q1 sir?

[tony]

^yes....but there will be those who will say that the circuit as designed contributes to better sounds....

[Engr. Dacuycoy]

sir tony namisslook nyo ata... full wave voltage doubler yong input nya.

[efren]

here they are, I added some "freebies" among the free i hope you two find them usable, one man's trash could be another man's treasure, but they are not trash for sure .

those AC 132 are Germanium PNP trannies, they can make a nice fuzz tone for guitar, just search the net plenty of 'em.

then there's 2N5458 sir TinTop mentioned about.
Those 2N5401/2N5551 needs no further explanation

I'll try monday or tuesday if time & schedule permits i'll drop off these goodies at sir tony's place for pick up.
 

i have some other trannies for RF duties up to 450mhz military grade gold pins if somebody is interested...

[Engr. Dacuycoy]

wow   maraming salamat uli sir efren  

sakto yong ac132   hidden treasure yan sir efren hindi trash