Ground planes and solidstate?

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I must have made like 5 PCB's now for the same circuit.... Nuuk's (Les Sarge) class-A buffer....

Invariably, there is noise from one channel...sometimes it seems to sound a bit better but the noise comes and goes, which leads me to think it could be oscillation...

Now the big question this morning.
were ground planes on the PCB's a bad idea for solidstate....? with chips they normally make things better.. no idea about stupid transistors... I just want to throw all of mine away... :hot:


I can't figure out if the problem is related to the sharing of the PSU or the ground plane....think I swapped enough transistors around to exlude ttransistors as the culrpits....
 
Sorry to avoid confusion... it was a single sided pcb with groundplane....there is about 4cm/almost 2" diffirence in trace lenghts connecting v+ and v-... one being very close to the connector...and regulator (maybe 3cm)

I have not seen too many transistor pcb's (compared to all the chip based stuff I learned from...), so its pretty foreign territory to me...

I think what I will do is start from scratch..., yet again! maybe try some stripboard and use 2 equal length power cords to the connection points.

I never knew transistors will be so hard to implement... being able to read te schematic here is of negligible importance it seems.
 
Would this layout be ok on veroboard?

the original circuit is this one;

An externally hosted image should be here but it was not working when we last tested it.
 

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Hi,
are the protoboard component numbers the same as the schematic numbers?
The bypass goes from Q1 collector to load return.

What current & dissipation is Q3 running at? Why use a medium power device?

What currents/dissiaption are Q1 & Q2 running at? What impedance are you intending to drive?

It looks like you intend this to run @ 5mA and 100mW why use medium power at all. Most signal transistors are happy at 25% to 30% of maximum dissipation. 100mW is well within that limit )650mW*25%=160mW)
 
Also, 'ring of two' current source can sometimes self-oscillate. The usual cure is a small capacitor in parallel with C-E of Q3 (100pF, say).

If you don't have local decoupling caps and make even a small error in groundd routing, a follower can oscillate due to hook-up wire inductance.
 
Many thanks for the tips, please keep em comming...

Yes I kept original component names..

The reason I used those were becasue it created the best sounding combination out of the npns I had on hand (they were from destroyer's headphone amp).

I tried bc639, bc547, bc550, BD135, and BD139...

I still have no real idea what diffirentiates a medium power transistor form others... I am aware, of current rateings etc.. which I know is pretty high considering the project.

Biasing is still a grey area for me... I left the resistors as is, as I am trying to learn hands on, and didn't want to just start changeing things, without knowing what I'm doing.

I experimented with voltages from 12V to 21.5V, sounded better towards the latter....is the biasing resistor the 22k one?, which would mean I got just shy of a milliamp there and the current over the bottom resistor must be in the 4 to 6 mA region.

Andrew should I measure the current or just calculate or sim it?
Nothing is getting hot.

Q2 got silly hot when I tried Q1 BD135 Q2 BD139 Q3 BD135... luckily I could quickly pull output plug and power and they werent killed.


Now about those lead lenghts?
 
Hi Nordic,
look at the schematic, V+ is conected to R2 and collector of Q1,
Now look at protoboard, using labels at the top V+, in, V-, 0v, the V+ is connected to collector=OK, and to r4!.
0v is is connected to R2 and R10, but on schematic 0V is connected to r4 & r6.
The protoboard numbering IS NOT the same as the schematic.

This is nonsense.
 
Hi Andrew aorry for the confusion... yep the two don't match... I didn't capture part names for the veroboard, that post was refering to my first try designs...

I did capture the resistor values, so I can still figure my way out, using the colour bands...

Lol man relax... I am in such a state after 4 days worth of pianfull experimenting with preamps... my valve buffer is still laughing at all my attempts.

I even tried 3 chipbased preamps but non of them have the life of the bloody transistor based buffers...

I am SOOOOOOOOOOOOOO frustrated.

To add to my damaged ego, finger one whole tip was purple from kickback on table saw, cutting too small blocks of wood.
Tip 2 and 3 sepperate soldering iron burn wounds, also have a gash on the back of my hand, from shocking myself, and ripping my hand the hell out of the case.... electric shoch therapy works well... every time I want to test, I find the lead magicaly plugged out now...
 

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So sorry about your wounded fingers. But you will have war scars to show to your children!...;)

Nice move about the medium power transistor use. If I remember well Les Sage original articles, he liked these transistors.

Besides the bypassing, which you should definitely add on board, there are two things:

1) If you did not, try an LM317/337 regulator. Batteries might do too. At least to see if what's happening is supply related.

2) Add a small series resistor at the input. Buffers need some sometimes.

Have you put it inside some kind of metal isolation box? Even if there's no gain to justify RFI, the grounding may not be enough.

What do you mean by ground plane on a single side pcb? I don't think there's such a thing, or at least working as such.
 
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