PASS A40 - bias

[lumanauw]

C3 (bias capacitor) changed from 220uF to 2200uF.
Upper and lower diode different position. Upper diode before base stopper 68R, lower diode after base stopper 68R.

 

[Babowana]

Upper and lower diode different position.

?!?!

The diodes look like two one-way bridges
from the output to the +/- of the cap. . .

 

[herodote]

NPass answer re "bias & kill the turn on thump"

Image http://www.diyaudio.com/forums/attachment.php?s=&postid=969953&stamp=1153941051 are worth a thousand words (for dummies like myself for sure). Thanks

Diode can be a a zener like 1N4148 ?

 

[Babowana]

Re: NPass answer re "bias & kill the turn on thump"

Diode can be a a zener like 1N4148 ?

Zener? No, no, no!
Diode. IN4004 would work.

 

[Nelson Pass]

Any diode will work.

 

[herodote]

In rush limitation

So 1N4148 would be fine ?

(Sorry I'm not fluent enjough to understand the difference between a diode and a zener) I reckon Zener Is a Diode but there are diodes that are not zener. I was a bit suprise by the 1N4004 - seems oversized (maybe Babowana JH wanted to have a good time) Thanks anyway

 

[Nelson Pass]

a zener diode is just a diode with a low breakdown voltage.
In this case you could use some 5.6V zeners easily enough.
There are diodes you wouldn't use, like a 100 amp rectifier.

 

[Babowana]

Re: In rush limitation

(maybe Babowana JH wanted to have a good time)

I just wanted to have normal diodes as on the drawing, safely
avoiding my ignorance. I casually thought about 1N4004, which
I use most time.

Anyway, thanks to Nelson, you have full answer. . .

 

[herodote]

DIode

Thanks to all for their contribution.

What could be the cause, now that the DC offset trimmed down by the R6 values is set to +1mv -1mv and the bias via R11 is set to 1.55A, after an 1.5 hours the amplifier start giving a hum, like a ground loop in the speaker.

 

[ggrovlanson]

A40 amplifier - who could help ?

Hello,
In the early eighties a firend built an amplifier which he viewed as state of the art at that time for its schematic. Unfortunately he passed away and recently the amplifier did the same. I ended up opening the box and searching the web to find where / how this amplifier (which I like the sound very much) could be brought back to function. (ok this is almost pathetic..since i know little to nothing about electronic) Searching the web I found the passdiy and this forum sites which are full of all information I needed to get the amp fixed (almost). I'd like to thanks Mr Pass as well as all others who by their questions and answers have teached me a lot and fix the amp.

Beeing far far having a good understanding, one issue remained unsolved yet and even after several searches, I haven't found how to address it. Maybe some of you would have the answer, please be thanked again. Here it is :

There is some hum in the speaker.

I've removed the transformer away to no results.
I've applied Eric (http://www.facstaff.bucknell.edu/esantane/movies/a40.html) recommendations as well as Mr Pass (http://www.diyaudio.com/forums/showthread.php?postid=969953#post969953) although there i haven't found 2200uf tantalum so far (car we use electrolitics instead ?) But to no avail.

Here are the measurements (if that helps)
Right channel
+DC 31.20; -DC 31.20
DC offset 2.8mv
Bias 1.56Amp per trail
Voltage drop
- D1 - D2 1,270V
- R7 0.642V
- R6 0.592V
- Q7 - Q9 emitter 1.089V
- R10 0.636V
- start up thump 0.184V
- light hum yes

Left channel
+DC 31.46; -DC 31.46
DC offset 0.1mv
Bias 1.64Amp
Voltage drop
- D1 - D2 1,286V
- R7 0.656V
- R6 0.589V
- Q7 - Q9 emitter 1.026V
- R10 0.649V
- start up thump 0.343V
- light hum yes

1°) What can be the cause of the hum in the speaker ?
2°) I don't understand why the difference in the start up thump.

The only difference I'm able to noticed with the schema on passdiy is the transformer. It is a secondary 1kVA at 24Volt DC with 8 wires 4 are connected to two rectifier of 50Amp 600V and the 4 other a fixed on the ground. I don't know if that makes a difference. Many thanks anyway.

 

[Babowana]

Re: A40 amplifier - who could help ?

Ahh. . .

There is some hum in the speaker.

Hmm. . .


Right channel
+DC 31.20; -DC 31.20
DC offset 2.8mv
Bias 1.56Amp per trail
Voltage drop
- D1 - D2 1,270V
- R7 0.642V
- R6 0.592V
- Q7 - Q9 emitter 1.089V
- R10 0.636V
- start up thump 0.184V
- light hum yes

Left channel
+DC 31.46; -DC 31.46
DC offset 0.1mv
Bias 1.64Amp
Voltage drop
- D1 - D2 1,286V
- R7 0.656V
- R6 0.589V
- Q7 - Q9 emitter 1.026V
- R10 0.649V
- start up thump 0.343V
- light hum yes


Err. . .

If you do not mind my ignorance, I would recommend you to change your speakers.

 

[ggrovlanson]

Hum and speakers

How could the speaker affect the amp and make it produce a hum ?

If the speakers are responsible for the hum, shall I consider changing some pieces of the passive filter ?

 

[Babowana]

Err. . . I do not know exactly.

A friend of mine told me to use low SPL speakers. And, she said
that listening point to be away enough from the speakers.
I wanted to further consult her. But, she already left for her
summer vacation, alone. I think she is on the way to London
with her MP3. Sorry. . .

By the way, is this yours?
If so, welcome back. . . stay home. . . don't leave. . .

 

[ggrovlanson]

Humming in Pass A40

A friend of mine told me to use low SPL speakers. And, she said that listening point to be away enough from the speakers. I wanted to further consult her. But, she already left for her summer vacation, alone. I think she is on the way to London with her MP3. Sorry. . .

Sorry you lost me ! My own limitations most likely .

What do you mean with

By the way, is this yours?

I thought providing the A40 measurment could help someone to let me know wich part I have to substitue.

 

[Babowana]

. . . my friend was right.
Before she left thru London for Norway,
said: "His measuring techniq is a professonal. More advanced than you."

Papa's diodes/cap cured the bump, but leaving the hum.
Papa, your diodes seems to be spoiled.

Remove the spoiled diodes, and live with the bump.
The bump is merely one small shot at the start while the hum goes all time.

Probably, you need to invite another expert. . . shhhh. . . no papa. . . gotit. . . ?

 

[ggrovlanson]

Humming / light rumble in A40

Babowana : do you mean when you wrote this http://www.diyaudio.com/forums/showthread.php?postid=970416#post970416 and N.Pass suggested this http://www.diyaudio.com/forums/showthread.php?postid=970757#post970757 thas indeed your solution maybe correct.

I did read the question from Herodote (http://www.diyaudio.com/forums/showthread.php?postid=970408#post970408) and the schema proposed by Pass to upgrade the capacitor from 220up to 2200uF but I haven't done it so far because I could not find a tantalum this value. So in the circuit there is still the 220uF.

I still have no idea how to get rid of this light noise

PS by the way how do you do when you quote someone to have it in a frame ?

 

[Babowana]

I thought mathematically Herodote=ggrovlanson.
My math is very poor, tho.

I have some idea only with very basic simple things.
We need experts for help with complicated things.

How to quote. . .?
Umm. . . I could answer this question. . .

Step one: go to the post you like to quote. Step two: look at the bottom-right corner of that post. Step three: find letter "quote" and small white empty square box beside it. Step four: tick-off it.
Step five: find the letter "post reply" at the bottom-right corner of the thread page. Step six: click it. Done!

Try. At first, it could be somewhat difficult. . . but, do not give up.
Repeat from Step one to six till you manage.

Goodluck!

 

[ggrovlanson]

A40 humming and start noise

I thought mathematically Herodote=ggrovlanson.
My math is very poor, tho.

I have some idea only with very basic simple things.
We need experts for help with complicated things.

How to quote. . .?

Thanks, excellent teacher... but poor matematician . I actually found the site because of the threat posted by this Herodote about BIAS and DC offset. I didn't know it before. Some of the answers were usefull for me.

Have you build a A40 yourself ?

I fummed yesterday on of the Lambda TO-3, so I guess I will have to change all for the other one. Which one would you suggest : motoroal or insemi ?

Regards

 

[Babowana]

Re: A40 humming and start noise

Have you build a A40 yourself ?

No.
I just studied the spirit of the design.

yea . . . . . . . . . . . i a poor MARS . . . . . . . . . . .


Best Regards

 

[gpsmithii]

Re: A40 amplifier - who could help ?

Hello,
In the early eighties a firend built an amplifier which he viewed as state of the art at that time for its schematic. Unfortunately he passed away and recently the amplifier did the same. I ended up opening the box and searching the web to find where / how this amplifier (which I like the sound very much) could be brought back to function. (ok this is almost pathetic..since i know little to nothing about electronic) Searching the web I found the passdiy and this forum sites which are full of all information I needed to get the amp fixed (almost). I'd like to thanks Mr Pass as well as all others who by their questions and answers have teached me a lot and fix the amp.

Beeing far far having a good understanding, one issue remained unsolved yet and even after several searches, I haven't found how to address it. Maybe some of you would have the answer, please be thanked again. Here it is :

There is some hum in the speaker.

I've removed the transformer away to no results.
I've applied Eric (http://www.facstaff.bucknell.edu/esantane/movies/a40.html) recommendations as well as Mr Pass (http://www.diyaudio.com/forums/showthread.php?postid=969953#post969953) although there i haven't found 2200uf tantalum so far (car we use electrolitics instead ?) But to no avail.

Here are the measurements (if that helps)
Right channel
+DC 31.20; -DC 31.20
DC offset 2.8mv
Bias 1.56Amp per trail
Voltage drop
- D1 - D2 1,270V
- R7 0.642V
- R6 0.592V
- Q7 - Q9 emitter 1.089V
- R10 0.636V
- start up thump 0.184V
- light hum yes

Left channel
+DC 31.46; -DC 31.46
DC offset 0.1mv
Bias 1.64Amp
Voltage drop
- D1 - D2 1,286V
- R7 0.656V
- R6 0.589V
- Q7 - Q9 emitter 1.026V
- R10 0.649V
- start up thump 0.343V
- light hum yes

1°) What can be the cause of the hum in the speaker ?
2°) I don't understand why the difference in the start up thump.

The only difference I'm able to noticed with the schema on passdiy is the transformer. It is a secondary 1kVA at 24Volt DC with 8 wires 4 are connected to two rectifier of 50Amp 600V and the 4 other a fixed on the ground. I don't know if that makes a difference. Many thanks anyway.

Hello not sure if you have resolved the hum problem stated in your post. Back a few years ago several people went about building the A40 and had problems with low levels of 60Hz hum. If the amplifier is not gounded per NP's specs it will do just what I think you are describing. I had forgotten about the subtle grounding nuance for this gem until latley when I completed mine. When implemented correctly the input shield is connected to power supply ground, and is 10 ohms above chassis ground. Many neglect the connection between the shield side and the power supply i.e. circuit ground.Hope this helps....