Heathkit TA-28

[col]

I recently built this from the schematic at muzique.com to see what a 1.5v fuzz sounded like and it sounds fine apart from the lack of volume. I have tried several different transistor sets in it and they don't seem to make much difference. For the pnp I have tried 2N3906 and BC557B and even a germanium as I couldn't find any info on the one in the schematic.
Is this loss of volume normal? The battery is fully charged and using 3v makes it sound terrible.
i would welcome any suggestions.

Col

[petemoore]

  You noticed the second transistor is an 'upside down' PNP and the first is an NPN?
  BTW Here's the schematic link...
  http://www.muzique.com/schem/heathkit.gif
 

[markm]

I've seen those upside down trannies in some schems.....it's treated no different than "normal" is it?
Why are they drawn that way? Just to fit in the schem easier??

[Paul Marossy]

I've seen those upside down trannies in some schems.....it's treated no different than "normal" is it?
Why are they drawn that way? Just to fit in the schem easier??

No, the "upside down tranny" is indicating a PNP transistor. The easy way to remember which is which is to look at where the arrow is. On an NPN, the arrow will be pointing downwards on the emitter. On a PNP, the arrow will be pointing downwards from the collector.

[RedHouse]

Sometimes easier to remember as:

NPN - arrow points AWAY from the Base
PNP - arrow points INTO the Base

[markm]

Okay what about here;



Why is the bottom tranny facing the opposite way??

[markm]

I just realized I hi-jacked this thread......my apologies.

[Stephen]

these are all npn trannys arrow away from base ...it is just positioned from right to left rather than left to right........makes you think HUH

Here is another catch ..this is negative ground but if you wanted you could change the position of the caps and make it positive ground

Than they would all be pnp.
.. you would need a fet to match,,,,
...also reposition the diodes

[markm]

Very interesting.....
Now ya got me thinkin' 

[col]

I have put the transistors in as shown on the schematic but whichever ones I try the volume level is less than bypassed which is a shame as the circuit sounds good and has great sustain. Has anyone else built one?

Col

[petemoore]

  I'd guess other people have built it...
  Starting with a 1.5v supply, the guitars output may be near the headroom limited by the supply, I would check the bias on the transistors as an approach to 'is it workin' right'..I don't know what the output level of a 1.5v circuit should be expected as, but it can't be alot.

[Dragonfly]

here's a "quickie diagram" showing how PNP and NPN are represented in schematic form....


AC

[markm]

why are the sometimes drawn backwards in schematics......convenience?

[petemoore]

  I think so...
  If a transistors position in the schematic has all the input webbed to it's right and the output can go up...flipping the transistor so the input is on the right makes the schematic smaller and easier to read in a linear fashion.
  All the connections being the same, you could move all the input schtuff to the left side of the transistor...and flip it back to 'normal' so the input is on the left.

[Gladmarr]

Sometimes easier to remember as:

NPN - arrow points AWAY from the Base
PNP - arrow points INTO the Base

Here's the way I always heard it:

PNP = Pointing iN Putz.
NPN = Not Pointing iN

[tiges_ tendres]

NPN - Not Pointing North

[jmusser]

I built one awhile back. I don't think it was anything spectacular. When I get home, I'll look and see what transistors I used in it. I believe they were originally RCAs.