Mad Professor - Amber Drive

hopdybob · Post by **hopdybob** » 07 Oct 2016, 17:50

i don' t have the battery part on the board, only what is on this layout.

but did some test
new Q4 bf256 placed housing like on the board layout i
D= 3.29v
S=2.52v
G=2.53V
Mirrored, whit the connections like most off the data sheets show to this fet
D=3.05v
S=2.92v
G=0V

Q1
C= 4.01v
B=0.64v
E=0.03v

Q2
C=4.3v
B=.67v
E=0.02v

Q3
E=0v
B=0.51v
C=9.01v
don't know if this is what had to be suspected

hopdybob

Posts: 9
Joined: 18 Aug 2016, 15:26
Has thanked: 2 times
Have thanks: 0 time

BJF · Post by **BJF** » 07 Oct 2016, 18:15

Hi there,

Transistor should be faced according to data sheet and gate should rest at 0V

(because there should be no current flowing through or if there is the transistor converts to a diode.)

Your measurement suggests that the transistor either is shorted or drawing too much current as in IDSS or UP being too high.

To get it working adjust Source resistor, that is now 6K8 to a higher value.

Here’s a fun thing you can do connect a potentiometer in series with the 6K8 resistor and watch on your meter or DVM what happens with the Voltage at Source.

Have fun
BJ
BJF Electronics
Sweden

hopdybob · Post by **hopdybob** » 08 Oct 2016, 06:38

thank you BJF four your help
what voltage does the Source needs to have to work correctly?

hopdybob · Post by **hopdybob** » 09 Oct 2016, 08:01

yesterday i gave it another try.

with a fine sawblade and stanley knife i cleaned op all the space between the copper lanes, and heyyyy it worked

but than i noticed that when the sustain was turned down complete, volume on max there was a volume loss in compare with the volume of the amp itself after switching.
i then put a 10 k pot in series with the 6k8 resistor.
sustain turn down complete, volume complete up and then turned the 10k pot slowly to a volume level that was just as loud as the amp without the effect.
measured the total of 6k8 with the 10k pot in series and came to about 11k.

is there something i have to check now ore can i replace the 6k8 with a 10k ore 12k?

BJF · Post by **BJF** » 10 Oct 2016, 21:17

hopdybob wrote:yesterday i gave it another try.
with a fine sawblade and stanley knife i cleaned op all the space between the copper lanes, and heyyyy it worked
but than i noticed that when the sustain was turned down complete, volume on max there was a volume loss in compare with the volume of the amp itself after switching.
i then put a 10 k pot in series with the 6k8 resistor.
sustain turn down complete, volume complete up and then turned the 10k pot slowly to a volume level that was just as loud as the amp without the effect.
measured the total of 6k8 with the 10k pot in series and came to about 11k.

is there something i have to check now ore can i replace the 6k8 with a 10k ore 12k?

Hi there,

Try 12K and if all's good then there's no need to fix things

11K is otherwise a standard E24 value not too hard to get even in 5% should you ever need that value.

At your service
BJ

hopdybob · Post by **hopdybob** » 14 Nov 2016, 18:40

been a while but i have some good news.
i bought on ebay some 2N5485 en tried it again
measurment with BF256c
D =2,98v
S= 2,85v
G=0

with 2N5485
D= 5,30v
S= 1,80v
G= 0
the amount off fuzz was better in control but soundwise i still had the money for nothing sound that i did not like and could not get rid off.
on a dutch site someone gave me the tip to change this

bring back R12 to 22K, en C7 to 4,7nF,and you get a more useful tone control

and this works fine for me.
so all i can say is thank you all for helping and don' t change the 2N5485 with a BF256C

Mad Professor - Amber Drive [traced]