ampeg scrambler problems

[lowstar]

hi,
i´m having trouble with an ampeg scrambler clone. i followed the veroboard from dragonfly, and the signal at the output is very tame and kind of starves. i used bc517s and one bc549c. audioprobing, i find that the first transistor does not amplify the signal. the bc549 does, the last two again do not amplify. any sugestions ?

thx,
lowstar

[Dragonfly]

hi,
i´m having trouble with an ampeg scrambler clone. i followed the veroboard from dragonfly, and the signal at the output is very tame and kind of starves. i used bc517s and one bc549c. audioprobing, i find that the first transistor does not amplify the signal. the bc549 does, the last two again do not amplify. any sugestions ?

thx,
lowstar

well, after i saw this thread, i decided to build one up this morning using my layout. i can tell you that the layout itself is verified and correct. i had to sub a couple values, and use mpsa13's for the darlingtons (instead of mpsa14s or the recommended ones) so it wasnt quite as fuzzy as it could be, though it was still very fuzzy....it also lacked the octaving, but once again i attribute that to using lower gain transistors and some resistor subs....

so....have you looked closely for any solder bridges ? double and triple checked that all components are placed properly ? all trace cuts in the proper location ? all jumpers in place ? what are your voltage readings on the trannys ? etc, etc, etc...

andy

[lowstar]

hi dragonfly,
thnx for your reply. i have a question concerning q4: from what i see in the veroboard layout, the base of q4 looks like "in the air" with no other connection - is it supposed to be like that ?
thnx,
lowstar

[lowstar]

and my transistor readings are:
Q1 - E:3.39 B:4.25 C:8.99
Q2 - E:0.31 B:0.95 C:2.24
Q3 - E:2.11 B:3.19 C:2.59
Q4 - E:2.11 B:3.22 C:8.54

looks like the last two are way off ?!?

[lowstar]

those measurements were taken with 2 jumpers in place that i installed to connect the signal from the diode 5 to the base of Q4. i de-soldered those jumpers (so it is like in the veroboard layout) and now i read:
Q3 - E:0.13 B:1.22 C:8.99
Q4 - E:0.13 B:0 (-0.1) C:8.98

so now the base of Q4 is definitely in the air
anybody else checked this layout ? Q4 has tracecut before and after base (if i interpret the symbols for the transistors right) so there cannot be any signal for base ?

cheers,
lowstar

[Ge_Whiz]

Most likely cause of no gain from first transistor: (i) base, not collector, is coupled through to next stage; (ii) chosen transistor has base and collector leads reversed at package; (iii) base-collector short.

[Dragonfly]

lowstar...
 im gonna try to check thru the layout tonite...i'll get back to you on it.
  andy

[R.G.]

Pinout???

[Elektrojänis]

I have no idea whats wrong on those but...

The first transistor in the scrambler is used as a unity gain buffer. So... It doesn't amplify the signal voltage at all and that is how it is designed to work.

I used 2n3904 for Q1, Q3 and Q4 on my unit and 2n2222 for Q2. I tried some others especially for Q1, Q3, and Q4 but the 2n3904 sounded best to me... Weird. I might try to change them some day again to see if I still feel that way.

It sounds a bit milder than the samples on tonefrenzy but I suspect that they had it feeding an amp that was not totally clean... At least I get a lot closer to that sound when I plug another distortion after the scrambler or turn the gain up on the amp. Hmmm... The tonefrenzy sample was probably recorded with a better guitar than mine also.

[lowstar]

thnx everybody that answered so far,
your help is really appreciated.

@ elektrojänis, did you do the pcb or veroboardversion or just perfboard it ?

cheers,
lowstar

[lowstar]

hi guys,
the ampeg scrambler problem is solved!
the veroboard layout is faulty in 3 points.
1. trace cut between d5 and resistor 4M7 on bottom righ of layout should not be there
2. base of Q4 is in the air, make a jumper to connect to signal
3. collector of Q3 is not connected to + , make a jumper to top

dragonfly wrote:
well, after i saw this thread, i decided to build one up this morning using my layout. i can tell you that the layout itself is verified and correct.

?!?

cheers everybodybody,
lowstar

[Dragonfly]

dragonfly wrote:
well, after i saw this thread, i decided to build one up this morning using my layout. i can tell you that the layout itself is verified and correct.

?!?

cheers everybodybody,
lowstar

that would explain the "lower fuzz" level i described when i built the tester the other day, though i'd attributed it to lower gain trannies...

i'll make the necessary changes...

andy

[Dragonfly]

hi guys,
the ampeg scrambler problem is solved!


1. trace cut between d5 and resistor 4M7 on bottom righ of layout should not be there

actually, it DOES need to be there...but moved toward the right hand side a bit more. the 4M7 is the pop filter to ground, and in no way connects to D5 on the schematic....

2. base of Q4 is in the air, make a jumper to connect to signal
3. collector of Q3 is not connected to + , make a jumper to top

the layout now reflects these changes...thanks for your help !  i'm sure that others wishing to build this will appreciate it too

andy





cheers everybodybody,
lowstar[/quote]