Lemonade Drive report

[Mark]

Great report, where did you get the real deal J201’s from?

I noticed PedalPCB has the small boards to use SMD components but are out of stock.

I was listening to the Lemonade Drive and wondered if having the bias off a bit was part of the pedals charm?

What did you find.

Regards

Mark

 

[music6000]

Great report, where did you get the real deal J201’s from?

I noticed PedalPCB has the small boards to use SMD components but are out of stock.

I was listening to the Lemonade Drive and wondered if having the bias off a bit was part of the pedals charm?

What did you find.

Regards

Mark

This is my own Eyelet Board design.
I have 7K6 at 4.75v
My input cap was increased from 4n7 to 8n2 & 3n3 was increased to 4n7.
The Red Led is Bypass & Green is On :

 

[Mark]

I love the way you finish your pedals, I’m reading Chuck’s articles at the moment.

 

[Mark]

I measured around my JFET today. The gate was 0VDC as you’d imagine, the source was 0.145vdc and the drain was 4.17vdc with the 20K drain resistor.

Doing a simple bit of maths, if I am to have VCC/2 on the drain, the Id would have to be 661uA with the 1K source resistor.
This means the Vgs would have to be .661vdc.

Regards

Mark

 

[Mark]

This diagram does confuse me a bit. It is very much like a thermonic valve where lower Vgs means more current flow.

If I have 0VDC on the Gate and 0.145VDC on the source I have a Vgs of 0.145VDC. According to the common drain source diagram. I should be seeing 3mA with that Vgs. This doesn’t make sense as if I had 3mA going through a 1K resistor I would have 3V on the source resistor.

If there is s simple error in my logic, please point it out to me.

Regards

Mark

 

[Mark]

View attachment 14039

This diagram does confuse me a bit. It is very much like a thermonic valve where lower Vgs means more current flow.

If I have 0VDC on the Gate and 0.145VDC on the source I have a Vgs of 0.145VDC. According to the common drain source diagram. I should be seeing 3mA with that Vgs. This doesn’t make sense as if I had 3mA going through a 1K resistor I would have 3V on the source resistor.

If there is s simple error in my logic, please point it out to me.

Regards

Mark

 

[Mark]

I decided to have a go at measuring Vgs (off) and Idss.

I used a power supply that supplied 9.3VDC, the 10M resistor on the source that measured 10.1M, and a 1K resistor on the Gate which measured 996 ohm.

I have five 2N5457 JFETs this are Vgs and Idss figures.



(1) 0.543V, 1.57mA

(2) 0.506V, 1.95mA

(3) 0.509V, 2.19mA

(4) 0.464V, 1.7mA

(5) 0.471V, 1.46mA

Is that what you would expect to see from 2N5457’s?

I suspect not.

Regards

Mark

 

[Mark]

I have two quite old J201’s which I measured.

(1) 0.881vdc, 0.553mA
(2) 0.856vdc, 0.550mA

From what I’ve read these are good values, not sure why yet, but they are bound for the Boogie Monster.

Regards

Mark

 

[Mark]

I decided to take the measurements a bit further today. I used the simple FET tester to check the Vgs(off) and Idss, then I put the FET into the circuit on my breadboard.

Basically, I found the higher the Vgs(off) and Idss the closer the 2N5457 was to operating in the desired area.

2N5457 Power Supply = 9.36VDC

Vgs(off) Idss Vgs (in cct) Vd

0.466v 1.7mA 0.18v 8.12VDC
0.511v 1.5mA 0.20v 7.97VDC
0.538v 1.9mA 0.19v 8.05VDC
0.452v 1.4mA 0.16v 8.25VDC
0.530v 2.2mA 0.21v 7.95VDC

J201.

Vgs(off) Idss Vgs(in cct) Vd

0.885v 0.553mA 0.257v 7.61VDC
0.858v 0.550mA 0.253v 7.64VDC

I thought the J201’s would have had a lower voltage on the Drain than they did. Mind you, I have seen circuits using J201’s using 100K trim pots on the Drain.

It seems with 2N5457 JFET’s in this circuit, the higher the Idss the better fit the FET is.

Thoughts?

Regards

Mark

 

[Mark]

Still reading up on FET’s, the calculator implies the source resistor is too large to have the Vd at 4.5vdc. With the data I had it states the Rs would need to be 390 ohms.

JFET calculator

 

[HamishR]

I don't know if this helps but I just remembered I built a few of these on vero a while back, and the advice then was to make Q1 have an hfe of around 270-300, with bias at 4.5V. It could be a 2N2222A, a BC108 or a BC183 - probably others too. I always used a 2N5457 as Q2 with 4.6V on the drain. Whenever I've built them like this they have worked beautifully. Cool pedal.

 

[Mark]

Thanks Hamish R for your reply, much appreciated.

As seen in my attachment, the difference between the Fairchild 2N5457's and the Motorola 2N5457's is night and day.

A huge thank you to Phil for supplying with the Motorola 2N5457's, having the right part makes a huge difference. There is one JFET which is perfect for this circuit.

Regards

Mark

 

[Mark]

One thing that I have noticed is if the battery gets down to 7vdc the pedal sounds like the bias is off.

I think this pedal is better off being run from a power supply.

Regards

Mark

 

[flexoffset]

Like Tayda, Pedal Parts Australia get supplies from China, they have Good components & they have bad components.
If I see a 2N5457 with BC27 code, I would guantee it's a Fake!
About the only safe 2N5457 now is the Mouser Lead free version!

Apologies for waking up this thread but I think I too have some counterfeit 2N5457 at $1 ea. (I only bought 10 fearing the worst so it's not like I'm going broke on the deal). They have the f logo followed by BC27 and when I test it against ones I know are real, the curve tracer display goes crazy. Strangely (or not) the Idss values appear in line with the spec ranging from 1.7 to 2.7mA with 9V supplied.

What is it about the BC27 code that makes these guaranteed counterfeit transistors?