(AK) classA HA/Preamplifier.

[Deleted]

Jan 6, 2011 3:12:16 GMT XTRProf said:

Jan 5, 2011 20:04:40 GMT Will said:

Found this link to a dc protection delay pcb for headphones, courtesy of the link that Mike posted in the panda thread

www.aliexpress.com/fm-store/705243/210789324-392489674/HeadphoneAMP-protection-KIT-for-2-channel-.html

Might be just the thing for a couple of you.

x


Yeah, just great! But any idea what dc mv it protects?

Chong
Both you and Friedrich are a pain in the arse on this subject !
Why do you both keep going on about anything less than 600mV, which is the conduction threshold of transistor based voltage detectors ?
There will always be some kind of limiting resistor in this design, and even with 30 ohm headphones and NO series resistor, if you had 600mV DC into them , it's still only 12 milliwatts dissipated in them ! Obviously, with higher resistance headphones, and a series output resistor, the power dissipated when there is 600mV of DC will be far less again !
You simply do NOT require anything more sensitive than can be obtained using a simple DC detector circuit with a 600mV threshhold !
If you are THAT concerned, then use .25W MF output resistors.
In the event of the output going to full supply rail voltages under a fault condition when using with a 120 ohm .25W series resistor and 30 ohm headphones , there would be >2W briefly dissipated in the 120 ohm resistor before it went open circuit !

[Deleted]

+1.24V and -1.04V

It might be a wise decision to swap out the 2 smaller electrolytics for NP electro's of a higher value (220uF/6V to 470uF/6V).
They appear to be 100uF polar types.
Since there will probably never be a DC voltage on them (and if there is it will be a small one) the polar types will survive though.

there is a DC servo in the amp isn't there ?

In this case the only protection you will need is when the amp goes to the power rail.
or..when playing the devils advocate, in case the DC servo gives up there might be a DC voltage lower then 1.2V.
When using low Ohmic headphones it is adviseable to use 120 Ohm output resistors anyway (lowest value 68 Ohm)

In this case a 32 Ohm HP (68 Ohm series resistor) will dissipate 12mW max.
with a 10 Ohm series resistor 29mW max (if + 1.23V is present which is unliky).
with 0 Ohm series resistor 37mW max.
is DC power and heat up voicecoils higher/faster and unnoticed contrary to AC power which create a lot sound.

But the chances an amp creates a fault by which it has a voltage just under the activation voltage of the IC is extremely unlikely.
Sometimes you have to take chances in life...

I think using it is very safe, safer for sure as when you didn't.
It also provides slow-on delay but probably NOT fast-off.

You could create a pretty fast turn off by modifying this circuit.
The 12V relay should be replaced by a high sensitivity 5V relay and the resistor in series with the voicecoil by a strategically value 3W zener diode and the relay must be fed from the DC voltage directly behind the rectifier and before the voltage regulator of the amp.

[Deleted]

It may be a wise decision to swap out the 2 smaller electrolytics for NP electro's of the same value. there is a DC servo in the amp isn't there ?

Frans
There are no capacitors in the signal path or the Feedback network.
Yes , there is a DC servo with this HA/preamp.
Alex

[Deleted]

I was talking about the capacitors on the relay board ..

[Deleted]

Hi All

Just off topic

Has anyone had any contact with our friends from Queensland? looking at the new it's pretty bad up there and it would be nice to know all is OK with them.

take care

[Spirit]

Shaun,

This topic might be of interest:
rockgrotto.proboards.com/index.cgi?board=general&action=display&thread=6253

My house won't flood, which just leaves Jeff - I can't see any major waterways near his place. Brisbane hasn't had that much rain anyway.

Cheers,
Phil

[Deleted]

Hi Phil

Good to know

thanks for pointing me to the thread

i just hope things can get back to normal ASAP

take care

[Deleted]

Brisbane hasn't had that much rain anyway.

You feel wet through up there, even when it isn't raining !

P.S.
I had a visit yesterday from a friend in Sydney who will be building the HA. He will now also be converting his for preamp use as well.
Alex

[Deleted]

I'm just about to start the process of getting all the bits together for my build, as I feel the boards may be imminent.

The resistors are termed as "MRS25". Will standard metal film 0.5w do the job as well? Or is the extra, special coating important?

Cheers,

Chris

[Deleted]

Jan 6, 2011 23:52:25 GMT @cjarchez said:

I'm just about to start the process of getting all the bits together for my build, as I feel the boards may be imminent.

The resistors are termed as "MRS25". Will standard metal film 0.5w do the job as well? Or is the extra, special coating important?

Cheers,

Chris

Chris
Standard 1% .5W will be fine.Although there could be a minor advantage to using those .1% MF resistors that Mike linked to for the current mirror and LTP emitter resistors .(4 x 100R, and 4 x 150R) See what Will thinks, as they would remove the need to match those resistors, as well as suffering less from changes due to soldering. If I lived in the U.K. I would get some for my personal stocks.
Alex

[Deleted]

Jan 7, 2011 0:07:26 GMT @sandyk said:

Jan 6, 2011 23:52:25 GMT @cjarchez said:

I'm just about to start the process of getting all the bits together for my build, as I feel the boards may be imminent.

The resistors are termed as "MRS25". Will standard metal film 0.5w do the job as well? Or is the extra, special coating important?

Cheers,

Chris

Chris
Standard 1% .5W will be fine.Although there could be a minor advantage to using those .1% MF resistors that Mike linked to for the current mirror and LTP emitter resistors .(4 x 100R, and 4 x 150R) See what Will thinks, as they would remove the need to match those resistors, as well as suffering less from changes due to soldering. If I lived in the U.K. I would get some for my personal stocks.
Alex

OK,

Thanks Alex.

Chris

[XTRProf]

Jan 7, 2011 0:07:26 GMT @sandyk said:

See what Will thinks, as they would remove the need to match those resistors

Err, I don't think so. If you want on the dot matched values, it's still better to measure those high precision 0.1% MF resistors. I have some of them, and not the complete list, for this HA as the diy shops doesn't carry all values.

[Deleted]

Jan 7, 2011 3:33:57 GMT XTRProf said:

Jan 7, 2011 0:07:26 GMT @sandyk said:

See what Will thinks, as they would remove the need to match those resistors

Err, I don't think so. If you want on the dot matched values, it's still better to measure those high precision 0.1% MF resistors. I have some of them, and not the complete list, for this HA as the diy shops doesn't carry all values.

Chong
What you don't seem to understand is that very few DMMs have sufficient accuracy to match that closely. I have 2 DMMs, one of which has far greater accuracy than the other.(+-.3% resistance scale vs .8% to 1% typical) That is the one I use for matching resistors.Even then ...
Alex
P.S.
Also, with 50PPM 1% MF resistors, the values change a small amount due to soldering.

[XTRProf]

Jan 6, 2011 7:38:31 GMT @solderdude said:

+1.24V and -1.04V

It might be a wise decision to swap out the 2 smaller electrolytics for NP electro's of a higher value (220uF/6V to 470uF/6V).
They appear to be 100uF polar types.
Since there will probably never be a DC voltage on them (and if there is it will be a small one) the polar types will survive though.

there is a DC servo in the amp isn't there ?

In this case the only protection you will need is when the amp goes to the power rail.
or..when playing the devils advocate, in case the DC servo gives up there might be a DC voltage lower then 1.2V.
When using low Ohmic headphones it is adviseable to use 120 Ohm output resistors anyway (lowest value 68 Ohm)

In this case a 32 Ohm HP (68 Ohm series resistor) will dissipate 12mW max.
with a 10 Ohm series resistor 29mW max (if + 1.23V is present which is unliky).
with 0 Ohm series resistor 37mW max.
is DC power and heat up voicecoils higher/faster and unnoticed contrary to AC power which create a lot sound.

But the chances an amp creates a fault by which it has a voltage just under the activation voltage of the IC is extremely unlikely.
Sometimes you have to take chances in life...

I think using it is very safe, safer for sure as when you didn't.
It also provides slow-on delay but probably NOT fast-off.

You could create a pretty fast turn off by modifying this circuit.
The 12V relay should be replaced by a high sensitivity 5V relay and the resistor in series with the voicecoil by a strategically value 3W zener diode and the relay must be fed from the DC voltage directly behind the rectifier and before the voltage regulator of the amp.

So in the end, your opinion to have the dc and delay relay or not for this AHA build? Even if good to have and not must have, I will buy a few from the Will's link. But I'm not sure at what mv it will kick in though and how fast it will turn off. Thanks.

[XTRProf]

Jan 7, 2011 3:38:18 GMT @sandyk said:

Jan 7, 2011 3:33:57 GMT XTRProf said:

Err, I don't think so. If you want on the dot matched values, it's still better to measure those high precision 0.1% MF resistors. I have some of them, and not the complete list, for this HA as the diy shops doesn't carry all values.

Chong
What you don't seem to understand is that very few DMMs have sufficient accuracy to match that closely. I have 2 DMMS, one of which has far greater accuracy than the other. That is the one I use for matching resistors.Even then ...
Alex
Also, with 50PPM 1% MF resistors, the values change a small amount due to soldering.

Actually, it doesn't matter as the resistors are going through the same DMM at about the same instance. The same inaccuracy coefficient applies or whatever. What we need is on the dot matched resistors, to at least qualify as a nut , and not same value as the resistor bands indicate. The latter will qualify as super nut . Anyway, when in circuit and powered up, the resistor values will change somewhat as they heat up. For sure, it will go up and not down but by how much each resistor will depend on their individual change coefficients. All matching on the dot will go somewhat depending on the heat produced when powered up. So are we going to matched resistors under dynamic condition as what we are doing now is static and cool condition.

As to soldering, that will be an individual's skill and nobody can help in this. So far, those I had soldered retain the same value thru the same DMM after cooling down.

[Deleted]

Chong
Get into the real world of DMMs where the resistance value doesn't stay rock steady when being measured. Especially in the lower ohms ranges.
To get REAL accuracy below 200ohms you need to use an accurate current source, and use the DMM on a voltage range.
What are the specifications of the DMM that you are using ?
Note also, that many DMMs have improved markedly in accuracy during the last 2 years.
Alex

[Deleted]

Jan 7, 2011 3:39:03 GMT XTRProf said:

So in the end, your opinion to have the dc and delay relay or not for this AHA build? Even if good to have and not must have, I will buy a few from the Will's link. But I'm not sure at what mv it will kick in though and how fast it will turn off. Thanks.

it kicks in at + 1240 mV and - 1040 mV

and yes it's much prefferred over just a delay.
Yes you can modify it to have reasonably fast turn off that is fast enough to prevent a 'plop'

and I recommend to change the 2 100uF caps for at least bipolar types as explained above.

[Deleted]

My preferred option would be to use the attached which is more versatile, and could be used to switch to either headphones or RCA Output sockets IF the constructor felt the need to use such a device.
This circuit is also designed to operate when > +-600mV is detected at the output of the amplifier, as against >1,000mV of the online module.
As Chong will be keeping his voltage regulators inside an external PSU case, he will not be able to use this unit .
It is available in kit form from Altronics.
www.altronics.com.au/index.asp?area=item&id=K5124

[Will]

Jan 6, 2011 23:52:25 GMT @cjarchez said:

I'm just about to start the process of getting all the bits together for my build, as I feel the boards may be imminent.

The resistors are termed as "MRS25". Will standard metal film 0.5w do the job as well? Or is the extra, special coating important?

Cheers,

Chris

Hi Chris,

It's pretty much as Alex says, that any decent MF 1% 0.5W resistor type will do. I do think that the idea of going for 0.1% types for emitter duties might help.

The only reason I mentioned the MRS25 is that they are a good quality GP resistor, available in quantity. From the Jaycar kits, their MF resistors are nice as well.

Resistor lead pitch on the PCB is 10mm, so a body length of 6-8mm, plus lead bend, will fit perfect.

[XTRProf]

Jan 7, 2011 8:45:40 GMT @sandyk said:

As Chong will be keeping his voltage regulators inside an external PSU case, he will not be able to use this unit .
It is available in kit form from Altronics.
www.altronics.com.au/index.asp?area=item&id=K5124

Really, how come? This is supposed to operate with DC instead of AC right? I still have spare DIN pins, for any future expansion purpose, for this if I wanted to as my DIN plug is 5 pins instead of 3 pins.

[Deleted]

Jan 7, 2011 9:57:19 GMT XTRProf said:

Jan 7, 2011 8:45:40 GMT @sandyk said:

As Chong will be keeping his voltage regulators inside an external PSU case, he will not be able to use this unit .
It is available in kit form from Altronics.
www.altronics.com.au/index.asp?area=item&id=K5124

Really, how come? This is supposed to operate with DC instead of AC right? I still have spare DIN pins, for any future expansion purpose, for this if I wanted to as my DIN plug is 5 pins instead of 3 pins.

Chong
To use the SC delay and protection unit, you would need to supply it with lpw current AC, so that the fast turn off feature can be implemented. It's basically the same method as I mentioned in the explanation of my simple delay unit.
Alex

[Will]

If anybody wants some of these 0.1% resistors for the emitters of the LS devices, as mentioned above, please contact me, as I'm placing an order at the end of the month.

[Deleted]

Jan 7, 2011 8:45:40 GMT @sandyk said:

My preferred option would be to use the attached which is more versatile, and could be used to switch to either headphones or RCA Output sockets IF the constructor felt the need to use such a device.
This circuit is also designed to operate when > +-600mV is detected at the output of the amplifier, as against >1,000mV of the online module.
As Chong will be keeping his voltage regulators inside an external PSU case, he will not be able to use this unit .
It is available in kit form from Altronics.
www.altronics.com.au/index.asp?area=item&id=K5124

This kit does NOT disconnect at +/-600mV but more in the neighborhood of +/- 1.5V which is higher then the very small one Will referred too.

For headphones small signal relays are usually better then bigger relays.
The bigger relays are more suited for LS.

The small PCB can be modified to have fast off too (even without an extra AC signal)

[oohms]

Surely it would be possible to build an offset detector with a BJT differential amplifier, and adjust the gain to make the difference 0.7v at much smaller voltages?

[FritzS]

Jan 7, 2011 12:54:10 GMT @solderdude said:

This kit does NOT disconnect at +/-600mV but more in the neighborhood of +/- 1.5V which is higher then the very small one Will referred too.

For headphones small signal relays are usually better then bigger relays.
The bigger relays are more suited for LS.

The small PCB can be modified to have fast off too (even without an extra AC signal)

AMB use one of this
Omron G5V-2-H1-DC12
Omron G6A-234P-ST15-US-DC12
Omron G6A-274P-ST15-US-DC12
Fujitsu RY-12W-K
Fujitsu RA-12W-K
Tyco C93402

www.amb.org/audio/epsilon12/