My Problem Amplifier And Symptoms...

[phatt]

@ JMF, Thanks for the correction. Where would we be without the sharp eyes of the experienced.  :dbtu:

As comparo
Woohoo,, Just found this pis of board,  I did take pics as well but forgot I had them. :duh

Yes obviously a little different layout but looks close to same.
Note the Ribbon cables they should be banned as they don't take kindly to much movement. A real pain to reconnect as very little trace is present and these often lift with too much heat. 

Re the big Yellow disc on the output might need explanation.
I don't trust the current limit stuff I find the poly switches are a god send and have tested these many times on My Amps which have NO Short Circuit protection and not once have I blown any active devices. Heck one simple part replaces a whole lot of fiddly bits which takes up real estate.
These PTC's (Poly Thermal Switches) can also be used to save speaker from over current.
The HiFi folks don't like them claiming all sorts of sonic impairment but for R&R guitar perfect.

[phatt]

I just had a thought???
We now have 2 pics for comparison.
Mine has the inductor on output,,, Hum?
Could the unit be going into supersonic Oscillation and be the cause of the initial problem? surely the zobel network (which seems to be there) should stop that?

Oh yeah,
I'd be interested in comment from someone who knows which way pnp transistors point,, 

Regarding that lone VAS (The voltage Driver or Voltage Amplifier Stage, I think is the term?)

There is often no heat sink on that transistor yet it's actually the only device that see's the Full Rail to Rail voltage?
On some Amps I've messed with I notice that it can run warmer that those 2 predriver.
just wondering? Headscratch?
Phil.

[J M Fahey]

Interesting to compare both.
One looks "more Pro" being fiberglass, silkscreened parts, fully tinned below, driver heatsinks, etc. ... although it lacks short protection and output inductor.
The Ozzy one has these, but no parts silkscreen and cheaper phenolic material.
Maybe Torque wanted to cut costs down and either got the lowest bidder or made them by themselves.
The basic schematic is probably the same ... what else?.
I have used output inductors in about 30% of my amps and none on the others.
Never found a difference.
I think layout and grounding is the *big* factor referring to stability, all others help.
Zobels *yes* are indispensable.

[noddyspuncture]

Hi again. I have an update... I *was* searching for shorts on this board... but I found two transistors (would be Q1 & Q2  on this schematic although they are numbered differently on mine...) that, when removed measure "open" all round with my meter on the ohms setting... however using the diode/capacitor setting they read 'open' (3volts) one way and 0.7volts the other between the three legs. Now, which should I go with? Are they suspect, would you say?

Yeah I found it  :cheesy:
Don't take it as gospel but it will likely be close to what is in front of you.

From memory give or take a few brain cells the rails where around 35 VDC.
Not a rock concert level of power but a big 12 inch driver makes it OK for a fold back Amp.

My guess at why it blew??  Likely someone added a dodgy external speaker jack and did not bother to check the internal speaker was already 4 Ohm and adding another driver would definitely blow it up.

The owner who knows me well has had no problems since we fixed it  and removed the ext socket.
(over a year ago now)
Phil.

[J M Fahey]

Transistors are always measured in the diode setting, that's what it's for.
Google how to measure transistors with a multimeter, as not to repeat the same time and again.
Good luck.

[noddyspuncture]

Yes, of course... my meter doesn't have a dedicated transistor tester, as some do. And I never really got out of the habit I developed on my old analogue meter which only had an ohms range... anyway here's an update - as of this afternoon the amp is fixed!

But I think there is more to this than meets (or met) the eye!

All I did was to remove those two transistors... then replace them, possibly swapping them around!? I also lifted all three zeners and checked those again...remember this is all treble checking as I have gone over and over this amp already. So I ran up the variac again - and there were zero volts on the output..! I monitored both rails and it all behaved beatifully. I next attached the speaker... no hum!  So it seems to have 'fixed itself'.

Now remember, this is an amp I already fixed once and after a couple of days use it blew again. I am expecting it to do the same as I haven't actually found anything definitely wrong. Maybe I 'disturbed' something - I might never know....

My next step will be to reattach the preamp section ribbon cable and feed some audio through it... but this begs another question... what would the recommended procedure be here?

Soak test it all via the bulb just in case the problem rears it's head again? Tap around (lightly) and see if I can 'force' the fault to reappear? I am going to have to put all my faith into this bulb to protect it should this be an intermittent problem...hehe!

Cheers,
Tom

Transistors are always measured in the diode setting, that's what it's for.
Google how to measure transistors with a multimeter, as not to repeat the same time and again.
Good luck.

[J M Fahey]

Yes, all analog meters had a single resistance setting for everything. Oh well.
Believe it or not, I sometimes still use my old analog (needle) meter , both to keep trained with it, and because some things are best shown by a wiggling needle than by rapidly changing numbers.

[noddyspuncture]

Well I think my Torque amp is now fixed... just on soak for a few days... and no issues yet, touch wood. I am attaching my revised circuit diagram - I slightly edited the one posted by (phatt) Phil, making it a circuit of the one I have here. A couple of changes... removed the protection circuitry, added a few components and moved one 'trace'... please let me know if it "looks about right", it's quite confusing as you probably know, trying to follow the path!

It might be useful to someone with this same model combo...!?

Thanks for all the help and advice.
Cheers
Tom

Yes, all analog meters had a single resistance setting for everything. Oh well.
Believe it or not, I sometimes still use my old analog (needle) meter , both to keep trained with it, and because some things are best shown by a wiggling needle than by rapidly changing numbers.

[phatt]

Hi Noddy,
Well done you worked that out well  :tu:
just need to flip Q5,, which was my booboo.

Others here will know more than myself ,, but I'd be a bit worried about that *220R* off the base on Q2.

In my real world testing Destruction of perfectly working transistors. :duh
I did realize that if that is set around 1k it seems to stay safe but depends on circuit/voltages and much other stuff which is mostly beyond my ability to understand let alone explain clearly.
One quick Q?
what is the DC voltage at the base of Q2?
Circuits like this are a very good learning tool for understanding DC coupled stages as they are very basic and in my experience can often sound better for guitar work.

From what I've understood (while blowing things up) the idea is to keep the base of Q1, Q2 and the speaker out should be all close to Zero Volts.
Phil.

[noddyspuncture]

Hi Phil,

Thanks for the reply and the comments. My redrawn cct does indeed have Q5's emitter amended! Also I'm pretty sure that the resistor is 220ohm... and as for the voltage on the base of Q2... well the amp is now all reassembled and I am loathed to open her up, in case I disturb something again. I was fixing this amp for a friend and have told them it's all done! Success...etc... Hahaha!

I wish you'd have asked these questions a little earlier, I could have checked it all for you. It has been quite a learning curve for me... and I have now also built a Variac/Light Bulb station which I shall be using more in future, I get the feeling...;c)

Can anyone else comment... about the 220ohm... or even what volts there 'should' be on Q2's base...?

Cheers
Tom

Hi Noddy,
Well done you worked that out well  :tu:
just need to flip Q5,, which was my booboo.

Others here will know more than myself ,, but I'd be a bit worried about that *220R* off the base on Q2.

In my real world testing Destruction of perfectly working transistors. :duh
I did realize that if that is set around 1k it seems to stay safe but depends on circuit/voltages and much other stuff which is mostly beyond my ability to understand let alone explain clearly.
One quick Q?
what is the DC voltage at the base of Q2?
Circuits like this are a very good learning tool for understanding DC coupled stages as they are very basic and in my experience can often sound better for guitar work.

From what I've understood (while blowing things up) the idea is to keep the base of Q1, Q2 and the speaker out should be all close to Zero Volts.
Phil.

[J M Fahey]

1) The voltage on Q1's base will be a few mV DC, because its base current flows through R2 to ground.
The voltage on Q2's base *should* be the same, because it also flows through a 10K resistor to ground : R7 .
And where is that ground connection?: through the speaker.
I didn't even mention its value because 4 or 8 ohms are *nothing* compared to 10000.
In fact it won't be *exactly* the same because Q1 and Q2 do not have the exact same current gain, but anyway they will be only a few mV from each other.
So , in a nutshell, Q2's base will also be a few mV (less than 100mV ) from ground.
Exactly what Phatt said from his considerable experience, only I added the *why*.
2) those 220 ohms shown are necessary so the amp has gain, otherwise you would need to hit it with over 20V RMS.
The AC (signal) gain is= (R7/220)+1=(10000/220)+1=46.5 ... call it 50.
Which in practical use means , since it can put around 20V (20000 mV) into that speaker, it will need to be driven with = 20000mV/50=400mV .
Easy for any preamp, even a 9V battery powered one.
The 47uF capacitor in series with the 220 ohm resistor blocks DC, so the amp has AC gain around 50, but DC gain of 1 , which is good because otherwise any DC at the input would produce a speaker burning disastrously high DC voltage at the output.

This amp uses a classic design, time tested and used by the Millions , basically for one reason: it works ... and very well.
Long live SS !!!!!!  :dbtu: :dbtu: :dbtu: :dbtu: :dbtu: <3)

[phatt]

Hi Phil,

Thanks for the reply and the comments. My redrawn cct does indeed have Q5's emitter amended! Also I'm pretty sure that the resistor is 220ohm... and as for the voltage on the base of Q2... well the amp is now all reassembled and I am loathed to open her up, in case I disturb something again. I was fixing this amp for a friend and have told them it's all done! Success...etc... Hahaha!

I wish you'd have asked these questions a little earlier, I could have checked it all for you. It has been quite a learning curve for me... and I have now also built a Variac/Light Bulb station which I shall be using more in future, I get the feeling...;c)

Can anyone else comment... about the 220ohm... or even what volts there 'should' be on Q2's base...?

Cheers
Tom

Hi Noddy,
Well done you worked that out well  :tu:
just need to flip Q5,, which was my booboo.

Others here will know more than myself ,, but I'd be a bit worried about that *220R* off the base on Q2.

In my real world testing Destruction of perfectly working transistors. :duh
I did realize that if that is set around 1k it seems to stay safe but depends on circuit/voltages and much other stuff which is mostly beyond my ability to understand let alone explain clearly.
One quick Q?
what is the DC voltage at the base of Q2?
Circuits like this are a very good learning tool for understanding DC coupled stages as they are very basic and in my experience can often sound better for guitar work.

From what I've understood (while blowing things up) the idea is to keep the base of Q1, Q2 and the speaker out should be all close to Zero Volts.
Phil.

Well excuse me while I go bang my head against a wall :loco

I've now taken the prize as I've achieved boobooing my own booboo,, a double booboo :lmao: :lmao:

Yes you did fix the upside down transistor :tu:
Phil.

[phatt]

1) The voltage on Q1's base will be a few mV DC, because its base current flows through R2 to ground.
The voltage on Q2's base *should* be the same, because it also flows through a 10K resistor to ground : R7 .
And where is that ground connection?: through the speaker.
I didn't even mention its value because 4 or 8 ohms are *nothing* compared to 10000.
In fact it won't be *exactly* the same because Q1 and Q2 do not have the exact same current gain, but anyway they will be only a few mV from each other.
So , in a nutshell, Q2's base will also be a few mV (less than 100mV ) from ground.
Exactly what Phatt said from his considerable experience, only I added the *why*.
2) those 220 ohms shown are necessary so the amp has gain, otherwise you would need to hit it with over 20V RMS.
The AC (signal) gain is= (R7/220)+1=(10000/220)+1=46.5 ... call it 50.
Which in practical use means , since it can put around 20V (20000 mV) into that speaker, it will need to be driven with = 20000mV/50=400mV .
Easy for any preamp, even a 9V battery powered one.
The 47uF capacitor in series with the 220 ohm resistor blocks DC, so the amp has AC gain around 50, but DC gain of 1 , which is good because otherwise any DC at the input would produce a speaker burning disastrously high DC voltage at the output.

This amp uses a classic design, time tested and used by the Millions , basically for one reason: it works ... and very well.
Long live SS !!!!!!  :dbtu: :dbtu: :dbtu: :dbtu: :dbtu: <3)

Arrh,, Mr Fahey you are very kind about my experience :lmao:
Thanks for the maths as it does help explain all those transistors that sacrificed there guts to help an Amateur learn.
Re discrete Pwr Amps,, I have one of my first ever attempts at hand drawn PCB somewhere in the shed and the schemo from a Electronics mag, So I'll try and find it,, might be an interesting exercise to analyze the merits or lack off.
Oh Yes the first one did actually work but the second one blew instantly.
Oh Well 50 % success for a beginner was not bad ay?
Cheers, Phil

[J M Fahey]

That's what the lamp limiter was invented for 

[noddyspuncture]

Thanks guys... glad I joined this forum, you're a great bunch of friendly and knowledgeable chaps. Who'd have thought this little problem amp of mine (well, my mates...) could have provided this much debate...;c)

Looking forward to my next problem/project...haha!

Stay good!
Tom

1) The voltage on Q1's base will be a few mV DC, because its base current flows through R2 to ground.
The voltage on Q2's base *should* be the same, because it also flows through a 10K resistor to ground : R7 .
And where is that ground connection?: through the speaker.
I didn't even mention its value because 4 or 8 ohms are *nothing* compared to 10000.
In fact it won't be *exactly* the same because Q1 and Q2 do not have the exact same current gain, but anyway they will be only a few mV from each other.
So , in a nutshell, Q2's base will also be a few mV (less than 100mV ) from ground.
Exactly what Phatt said from his considerable experience, only I added the *why*.
2) those 220 ohms shown are necessary so the amp has gain, otherwise you would need to hit it with over 20V RMS.
The AC (signal) gain is= (R7/220)+1=(10000/220)+1=46.5 ... call it 50.
Which in practical use means , since it can put around 20V (20000 mV) into that speaker, it will need to be driven with = 20000mV/50=400mV .
Easy for any preamp, even a 9V battery powered one.
The 47uF capacitor in series with the 220 ohm resistor blocks DC, so the amp has AC gain around 50, but DC gain of 1 , which is good because otherwise any DC at the input would produce a speaker burning disastrously high DC voltage at the output.

This amp uses a classic design, time tested and used by the Millions , basically for one reason: it works ... and very well.
Long live SS !!!!!!  :dbtu: :dbtu: :dbtu: :dbtu: :dbtu: <3)

Arrh,, Mr Fahey you are very kind about my experience :lmao:
Thanks for the maths as it does help explain all those transistors that sacrificed there guts to help an Amateur learn.
Re discrete Pwr Amps,, I have one of my first ever attempts at hand drawn PCB somewhere in the shed and the schemo from a Electronics mag, So I'll try and find it,, might be an interesting exercise to analyze the merits or lack off.
Oh Yes the first one did actually work but the second one blew instantly.
Oh Well 50 % success for a beginner was not bad ay?
Cheers, Phil