Sabbra Cadabra Vero help

[befey]

I thought I was getting the hang of this after a mostly successful breadboarding and then Vero build off the mastotron. But this one is stumping me again.

Here's pics of my board
Component side:
http://imgur.com/gallery/ElPM1at

Solder side:
http://imgur.com/gallery/7rdobQT

Here's the Vero layout I'm using:
http://1.bp.blogspot.com/-1BbOnDJyOsI/VQ8UQXiQxqI/AAAAAAAAGEs/RHBNhvkf3KE/s1600/Catalinbread-SabbraCadabra.png

Here's a schematic I found:
https://easyeda.com/arturman2002/sabbra-cadabra

The problem is the output is lower than unity even with all the knobs maxed. I've used an audio probe and found that everything sounds loud up until the 100k resistor after Q4 in that schematic. Then there's a pretty significant volume drop that basically persists through the rest of the circuit. I'm not sure if the volume is really as loud as it should be before that. It sounds basically unity to me, maybe just slightly louder up until that point, depending on which transistor I'm probing after.

Voltages at the transistors are:
BC184
C 9v
B 1v
E 0v

2n4393 1
D 9v
S 5.75v
G 4v

2n4393 2
D 4v
S 1.3v
G 0v

2n4393 3
D 3.5v
S 1.1v
G 0v

2n4393 4
D 9v
S 5.7v
G 4.2v

2n4393 5
D 9v
S 5.6v
G 3.9v

I did use 2n4393 instead of mpf4393. But I understand the pinout is different and I did move the leads to the right spots on the Vero.

I also didn't have a 250k pot for the output, so I soldered a 470k resistor across lug 1 and 3 of a 500k pot.

[PRR]

> BC184
> E 0v

E should not be zero. Maybe 1V or 2V. Suspect a short here.

[befey]

I'll check it out when I get home today, thanks!

Could that be caused somehow by the 47uF cap or the 47R resistor not being socketed correctly? I socketed them because some of the comments at tagboard suggested trying different values there.

But now I'm thinking that's a pretty likely point of failure.

Is it effective to try a continuity test from each lead of those components to the solder point for the socket?

[duck_arse]

Could that be caused somehow by the 47uF cap or the 47R resistor not being socketed correctly? I socketed them because some of the comments at tagboard suggested trying different values there.

those parts affect AC conditions - we are only doing the static, DC conditions at the moment. if they were shorting to something else, maybe they would mess, but a simple way to dis/prove is to pull that 47R outta the sockets, the DC voltages should not change.

I can't follow your fet numberings, from the circuit you show, Q1 and Q3 should have 0V on the gates, and Q2, 4 and 5 should be 1/2 +9V [but will measure less than half due to meter loading]. and as Paul says, T1 E should be higher, base should be about 2V and collector should be lower.

[that circuit diagram - it shows "22mF" for 22uF, and "2m2" for 2M2, as well as "1M" for 1M. that would put a crease in your sim outputs.]

[befey]

Would whatever's throwing off the voltage at T1 also cause the wrong voltages on the FETs?

I'm still trying to wrap my head around how the different errors can manifest. I'm sure the answer could be maybe... But is there some spot to look at that could in particular cause the variations I'm seeing?

[duck_arse]

here's a trick question - exactly what is the part number for the T1 you have fitted?

[befey]

It's this one from tayda:
https://www.taydaelectronics.com/bc184-bc184l-bc184lc-general-purpose-transistor-npn.html

Hmm.... Now it does look like I have it the wrong way around. But I swear I tried flipping it first thing and then I got no output. I will look at this again later too.

A geez... I'm an idiot. Flipping it won't get them in the right spot either.

[befey]

Ok, well after getting the orientation of the transistor right, it sounds much more like I expected.



Thank you, and I'll be checking my transistor orientations over and over from now on. And making sure I check the actual part data sheet and not just googling the pinout.

[duck_arse]

befey - well done! what are your voltages now?

the BC series transistors are pretty much all ebc pinout, EXCEPT when they are BCxxxL, which puts the base on the end, collector in the middle.

tayda really shouldn't have that part listed as

BC184 BC184L BC184LC GENERAL PURPOSE TRANSISTOR NPN

because the first named is different to the second and third named, and it will cause problems for most who purchase that part.

you've got a more leg bends there than a game of twister.

[befey]

 Voltages are now:

BC184
C 100mv
B .67v
E 54mv


2n4393 1
D 9v
S 5.75v
G 4v

2n4393 2
D 4.8v
S 1.3v
G 0v

2n4393 3
D 4.3v
S 1.1v
G 0v

2n4393 4
D 9v
S 5.7v
G 4.2v

2n4393 5
D 9v
S 5.6v
G 3.9v

So the FETs didn't change. And now the bc184 seems way off.

But I have plenty of gain now.

[befey]

And the range knob doesn't seem to have any effect now too. Maybe it didn't before either and I just couldn't tell because everything else wasn't really working.

[duck_arse]

something very wrong around T1. power off, pull that transistor out, and measure resistance from the socket pins:
- from collector to the +9V line [unpowered, obvs .....]
- from base to both +9V line and ground
- from emitter to ground.
also measure resistance between collector and base. then power on, and measure the voltages on the empty transistor socket.

[JustinSelf]

Ok, well after getting the orientation of the transistor right, it sounds much more like I expected.

Thank you, and I'll be checking my transistor orientations over and over from now on. And making sure I check the actual part data sheet and not just googling the pinout.

I've had this issue a few times myself, especially with old germaniums that aren't always marked very well or have conflicting datasheets.  Another issue I recently had was a transistor not fitting tightly enough in the socket and was giving very low output.  Luckily I've learned by now to check simple things like that first.  I just wiggled it around and it started working fine.  I once spent a good 20 minutes troubleshooting a fuzz that stopped working before I realized I forgot to put a transistor back in after swapping them out. Sometimes we learn the hard way. 

[befey]

Powered it up again and remeasured:

BC184
C 5.8v
B 2v
E 1.5v


2n4393 1
D 9v
S 5.75v
G 4v

2n4393 2
D 4.8v
S 1.3v
G 4.5v

2n4393 3
D 4.3v
S 1.1v
G 2.7v

2n4393 4
D 9v
S 5.7v
G 4.2v

2n4393 5
D 9v
S 5.6v
G 3.9v

So T1 seems normal now? And Q2 and Q3 both have a reasonable voltage on G now I think. I'm not sure what changed though.

[befey]

And the range knob is working. I think maybe a connection to the knob is not great and that might be causing the weirdness?

[duck_arse]

I don't mean to sound rude, but I'm starting to .... have doubts? .... about your measures. yes, T1 now looks like it is paying attention to those resistors around it, but your jfets are now not making sense.

Q2, Q4, Q5 all have one pin to +9V, and their gates should be measuring a little lower than 1/2 9V, due to those equal value resistors on their gates.

but, Q1 and Q3 both have thier gates tied to ground, so those gates should read 0V [vrrr close to]. they both have their Drains connected to the Source of another fet via a 1k, so their drain voltage should be a little lower than the source they connect to.

[I was going to post your circuit but lost patience w/ that site ....] a closer look at your circuit shows there is two SRPP stages, Q1&2 and Q3&4, which you can read about over at geofex.

[befey]

I'm was thinking of the numbers based on the Vero layout. I'm not sure if that schematic matches exactly. My numbers are

      T1     Q5
Q1       Q4
Q2       Q3

It looks like the schematic is actually
      T1    Q5
Q2      Q4
Q1      Q3

So that should make more sense if you swap my numbers for Q1 and Q2.

It looks like with that transposition, the only thing that doesn't quite make sense is the gates on Q1 and Q3 not being close to 0.

[duck_arse]

whelp. I dunno. more measures? pull the fets out, and measure the resistance from the gate pins to ground. pick one ground point and do all measure from that, it might show something. then measure from the first fets empty gate socket to the second fets empty gate socket, and then from the third to the fourth. there might be a connection out-by-one connecting the gates to a wrong point.

[befey]

BC184
C 5.8v
B 2v
E 1.5v


2n4393 1
D 4.8v
S 1.3v
G 0v

2n4393 2
D 9v
S 5.7v
G 4.2v

2n4393 3
D 4.3v
S 1.1v
G 0v

2n4393 4
D 9v
S 5.7v
G 4.2v

2n4393 5
D 9v
S 5.6v
G 3.9v

I checked the voltages again. I made sure I've listed them in the correct order this time, and I think they look like what we expect?

It sounds right to my ears, though I've never used the real one.

[duck_arse]

excellent. those look like a sane set of volts. and if you say it sounds good/ok as well, I think job done.