2N5952 matched pair

[Artcool]

  Hi there,

anyone with a matched pair of 2N5952 for sale? Just did one P45 and i'm having trouble finding this JFETs , just did the thing trying some equivalences (not matched) and not geting any sweep, or, getting some sweep only when messing with the trimpot , but it makes only one sweep loop and keeps steady... i'm in Portugal.

cheers!!!

[G]

http://www.banzaimusic.com/2N5952-matched-transistors.html

[Processaurus]

With unmatched transistors it should still work, just the tone won't be as good as with the matched set.  There should still be audible sweeping, maybe your LFO isn't functioning?  Do you have a multimeter to test it with?  You can put set the LFO to its slowest, and the meter to DC volts, and be able to read the voltage rising and falling.  What circuit and schematic are you using?  Phase 45?

[Artcool]

thanks for the link!!!

[Artcool]

Hi Processaurus !

well, i'm using the P45 schematic which have two ways (DOD 201 and MXR P45), but using a PCB made from a copy of a real P45... i can read some voltages rising and falling in the JFETs gate pins so i presume the LFO is working, but i'm using the BF245A not matched.. any known voltages i should read in the board?

cheers!

[Processaurus]

Sounds like the LFO is working, so maybe it is your initial instinct, the transistor choice, causing the lack of phasing.  The one DC voltage I can think to double check is that there is about 4.7v at the cathode of the 1n5230 zener diode.  That is the Vref voltage everything is referenced to, so double check that.

There unfortunately won't be DC voltages being amiss if the FET's aren't turning on and off at the right time of the LFO's sweep, and in sync with each other.  There's the Geofex FET matcher circuit for testing the VGSoff of FETs out of circuit:
http://www.geofex.com/article_folders/fetmatch/fetmatch.htm

Question of my own, could the FETs be tested in circuit with an Ohm meter across the source and drain, to verify they are turning off and on?

[Artcool]

Thank you very much for your tips.

I will relook all the components/values tonight and check those voltages..i love the P45 sound (i will use it with my Rhodes piano ) and can´t wait to have it working

cheers! i will probably  order 2 pairs of matching 2N5952 since here where i live can´t find them, and if i will i bet they will be expensive so the way of buying 20 or 30 units to match is out of question..already spent almost 10 EUR in four J201 just for trashing them ...

thank you again!!

[Govmnt_Lacky]

Aren't there equivalant FETs available over there? 2N5485 or BC264??

[Artcool]

Hi,

2N5485 i can't find it either ... will try today the BC264 which i wasn't aware of..

thank you very much!!

[Galego]

Thank you very much for your tips.

I will relook all the components/values tonight and check those voltages..i love the P45 sound (i will use it with my Rhodes piano ) and can´t wait to have it working

cheers! i will probably  order 2 pairs of matching 2N5952 since here where i live can´t find them, and if i will i bet they will be expensive so the way of buying 20 or 30 units to match is out of question..already spent almost 10 EUR in four J201 just for trashing them ...

thank you again!!

If you buy from Musikding, you can get them matched. Anyway, if you don't want to order anything right now, I can sell you a matched pair. I have 3 matched quartets, but i'm building a Phase 45 as well sometime soon, so it's no problem. I'm in Loures.

Envia-me uma PM se os quiseres.

[Artcool]

Just did some voltage reads in the board and there's something i dont understand, the Vref at cathode is about 3.8v ... when it should be around 4.7v ... the 9 volts from battery just pass the 10k resistor and after this drops to 3.8 and this is the voltage at cathode...what's wrong here?

[frequencycentral]

Just did some voltage reads in the board and there's something i dont understand, the Vref at cathode is about 3.8v ... when it should be around 4.7v ... the 9 volts from battery just pass the 10k resistor and after this drops to 3.8 and this is the voltage at cathode...what's wrong here?

That vref is normal for a P45, and to be expected from a 10k resistor/4.7v zener. Nothing wrong.

[Artcool]

Hum, thanks FrequencyCentral! i will redo the circuit in a test board (my fault going directly to soldering in board...) and see what's going wrong here... just dont want to give up on this...

[raulgrell]

Huzzah! Another portuguese guy! Yeah, JFETs are annoying to get over here, you have to do everything online basically...

Good luck in your quest! Whereabouts in portugal do you live?

[Artcool]

Hi Raulgrell!

estou em Aveiro....


cumps

[Artcool]

Ok..finally i made it working with unmatched FETs for now, until a matched pair come my way. I just made another pcb (this time from Tonepad ... ) and jumped (again) to solder everything in the board , worked as soon as i powered it  ... damn ...these Tonepad layouts are so small with all the components literally in top of each other..very dificult to solder but it seems my soldering skills are ok

the first pcb board was made copying a photo from a real P45 i saw online (before i knew of Tonepad layouts), and after a better look of schematics i saw some diferences .... the real P45 pcb have [P45 b] printed on it...could it be a B version from the factory , somehow diferent of online schematic ?? oh well... its working now..thanks to all who helped me with this!!

cheers!

[Artcool]

hi

decided to take a look to my first P45 board (which i coudnt make work ) and this PCB/schematic is diferent from the tonepad one . I did this PCB looking a web photo and making a layer from it (with Gimp) so it is the same , this one have P45 b written on the copper , is this a B version ? How can i link to some pictures in this forum?

basically the phase is working , if i shunt the 10uF cap which is connecting  the Speed pot to Ground, discharging it , it starts a sweep, but it will give only one sweep cycle and stops . I think the LFO isn't working , and LFO part is where i see some diferences against Tonepad layout and schematic... any clue?

[Artcool]

SOLVED! two resistors were misplaced!

thank you...