Sorry Nelson, but I have found an error ...

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... in the Aleph ONO schematics drawn by Wayne.

Correcting this error should solve all problems concerning the Ono mute circuit in cloned PCB's. Perhaps other problems too ...

Q25, labeled as "9610" in the original schematics of Aleph Ono service manual is wrong.

First it has to be a "610" and second, Drain and Source have to be swapped.

Only then, Q25 works as a simple voltage regulator with an output rail of about 24V to drive a 24 Volt-Relay.

Nelson, or do you work with 40V-Relays ??? :Pinoc:

The rest of the mute circuit is ok. The need of any additional components like shunt resistors (pquadrats PCB's) isn't required.

Best regards
toshiba with small "t"

P.S.
Nelson I'm sad, that you haven't answered to my quote
 
diyAudio Retiree
Joined 2002
Uh Oh another expert.........

The circuit looks fine to me........

From page three of the ALEPH ONO SERVICE MANUAL
REV 0, 1, 2, 3 9/30/1997 :

"Q25 and Q26 are used to power the mute relays."

How it appears to work to me:

The Mosfet act as switches they are low impedance when the gate to source voltage is greater than about 4 volts. This circuit is to short the outputs to ground until the supply comes up and the circuit stabilizes. R77 (750K) and C40 (220uF) provide a delay as the cap charges up and Q26 turns on. Q25 is already on when the 40 volt rail comes up. D11 clamps inductive voltage spikes across the relay coil and D10 provides hysteresis so the relay switches cleanly and does chatter during the switching.

The gate to source voltage for Q25 is about 12V after the 40 V rail comes up. You want to output to mute quickly when the power goes off and Q25 will go high impedance quickly while Q25 will still be swicthed on. You want to unmute after a delay when powering on and to mute quickly when powering down. 48 relays are very common for telecom use and should work for this circuit.

See anything wrong with the audio circuit you want to tell us about?
 

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I can only agree with Fred as it seems fairly straight-forward and the description Fred gave matches my understanding of the circuit for the Aleph P which I am currently building and which is the same and which in that case also would be faulty. Funny nobody has mentioned it since so many built these? Even more funny that I remember threads about it as well as reading the service manual where it is explained.

Personally, if I did not understand a circuit at all and wanted to I would probably ask how it works first and then claim it is incorrect...but that is just me.
 
toshiba said:
... in the Aleph ONO schematics drawn by Wayne.

Correcting this error should solve all problems concerning the Ono mute circuit in cloned PCB's. Perhaps other problems too ...

Q25, labeled as "9610" in the original schematics of Aleph Ono service manual is wrong.

First it has to be a "610" and second, Drain and Source have to be swapped.

Only then, Q25 works as a simple voltage regulator with an output rail of about 24V to drive a 24 Volt-Relay.

Nelson, or do you work with 40V-Relays ??? :Pinoc:

The rest of the mute circuit is ok. The need of any additional components like shunt resistors (pquadrats PCB's) isn't required.

Best regards
toshiba with small "t"

P.S.
Nelson I'm sad, that you haven't answered to my quote


They should put this post in the dictionary as the meaning for the word _dork_

I am sure looking forward for your next 'critique' of Nelson's work since I am about to build an aleph :rolleyes:
 
AX tech editor
Joined 2002
Paid Member
Re: Uh Oh another expert.........

Fred Dieckmann said:
The circuit looks fine to me........

From page three of the ALEPH ONO SERVICE MANUAL
REV 0, 1, 2, 3 9/30/1997 :

"Q25 and Q26 are used to power the mute relays."

How it appears to work to me:

The Mosfet act as switches they are low impedance when the gate to source voltage is greater than about 4 volts. This circuit is to short the outputs to ground until the supply comes up and the circuit stabilizes. R77 (750K) and C40 (220uF) provide a delay as the cap charges up and Q26 turns on. Q25 is already on when the 40 volt rail comes up. D11 clamps inductive voltage spikes across the relay coil and D10 provides hysteresis so the relay switches cleanly and does chatter during the switching.

The gate to source voltage for Q25 is about 12V after the 40 V rail comes up. You want to output to mute quickly when the power goes off and Q25 will go high impedance quickly while Q25 will still be swicthed on. You want to unmute after a delay when powering on and to mute quickly when powering down. 48 relays are very common for telecom use and should work for this circuit.

See anything wrong with the audio circuit you want to tell us about?

Fred,

Sorry, but your explanation still doesn't help me. Most of us know that we need to mute quickly and unmute fast. Why the need for two mosfets, complementary at that, when one could do the trick? toshiba might have been wrong, but nobody yet has proven that or even argued against him. I think it isa a bit cheap to say "...Mr Pass knows what he does...". Hell, we ALL know what we do, don't we? Let's try to keep this discussion intelligent.

Jan Didden
 
Re: Re: Uh Oh another expert.........

janneman said:

Why the need for two mosfets, complementary at that, when one could do the trick?
I suspect it has to do with PassLabs having a lot of leftover FETs that failed the hand-selection for matching.

When someone like toshiba comes out with an arrogant-sounding thread title and even refers back to his own earlier post pointing out another supposed error ("I'm sad you haven't answered..."), they can count on a few flames.
 
Re: Re: Uh Oh another expert.........

janneman said:


Fred,

Sorry, but your explanation still doesn't help me. Most of us know that we need to mute quickly and unmute fast. Why the need for two mosfets, complementary at that, when one could do the trick? toshiba might have been wrong, but nobody yet has proven that or even argued against him. I think it isa a bit cheap to say "...Mr Pass knows what he does...". Hell, we ALL know what we do, don't we? Let's try to keep this discussion intelligent.

Jan Didden

Reading a bit more carefully I see that Fred possibly made a small mistake in his explanation. The sentence:

"You want to output to mute quickly when the power goes off and Q25 will go high impedance quickly while Q25 will still be swicthed on. You want to unmute after a delay when powering on and to mute quickly when powering down."

Should probably read:

"You want to output to mute quickly when the power goes off and Q25 will go high impedance quickly while Q26 will still be swicthed on. You want to unmute after a delay when powering on and to mute quickly when powering down."

So essentially the circuit switches Q25 on quickly at power up (since it's gate voltage is presented at the same instant) and Q26 will be switched on when C40 is charged to the right level (it's gate voltage is presented with the delay of the charging of C40) and thus both FETs are switched on and the relay is activated. When power is switched off then Q25 will switch off quickly (as the gate voltage disappears at the same time) and the relay will be deactivated. Q26 still remains switched on (as C40 is still charged) but since Q25 is switched off then the relay can not be activated. This provides slow muting off at power on and quick muting on at power off.

Could you explain how to do it with just one FET?
 
diyAudio Retiree
Joined 2002
No flame in my game

paulb beat me to the punch. The circuit is neither overcomplicated
nor expensive. It appears to me to be a clever and reliable way to do it using parts that he is buying in large quantities. (read volume discount) Telecom relays are very inexpensive and very reliable also.

"Could you explain how to do it with just one FET?"

I kind of like the two fet circuit. I'll bet you can tell us how to do it since I think you understand the circuit as well as I do. Go for it. I need to go get ready to go to the doctor about my blood pressure (again..... it's getting to be a real pain)

I came not to flame but merely to try to shed some light on the circuit. "See anything wrong with the audio circuit you want to tell us about?" was gentle barb comparded to some I have handed out this week. Somehow I think Mr. Pass was probably amused and not offended by toshibas post. I seem to remember Mr. Pass
getting second guessed on audio circuits several times without getting ruffled. He is a gentleman and a scholar while I am a trouble maker and provocateur. Many of my post seem to arose the response one would expect from one who's car had just been keyed.

"What do you know? See an ordinary person spend his life avoiding tense situations. Repoman spends his life getting into tense situations."
 

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Hello,
here is a quick simulation of the timer's behaviour.
The top ("ps", blue) is the power supply trace, about 40V when I power-on the preamplifier at 0 seconds, then about 0V after 20 sec., when I decide to turn-off the power switch.
The "output" (red) trace is the relay contacts' trace, monitored with a pull-up resistor.
The other two traces are the relay coil's pins.
There is a little oscillation, I don't know if it is a parasitic phenomenon, or maybe an effect due to the rushed simulation:
these graphs are only to see the operating behaviour of the circuit.
Marcello
 

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I would not agree with toshiba - the circuit would work fine just as Fred described, thought with some overvoltage on the relay (it will see about 35-36 V - most 24V relays will survive it. I personally would add a resistor in series with the relay to drop the voltage down to 24V.

However I would be a bit critical from another point of view. I did use a very similar circuit in a production amplifier and found few years later that relays did not really like "soft switching" where the relay voltage rises relatively slowly, as FET just amplifies the input voltage. As a result of it the relay contacts did deteriorate somewhat over the time. So later I did switch to a Schmitt-trigger kind of circuit shown on the picture (sorry for a poor quality, as I only could use USB camera to get it in here). We didn't have any relay problems since.

Al
 

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diyAudio Retiree
Joined 2002
48 relays

48 volt relays are as common as dirt in the USA due to their wide use in telecom. You can get them pretty cheap since they are manufatured for hign volume use in telecom. We used about 12 million a year on one type of line card that I worked on a few years ago. The assembly plants for many Japanese relays are in China to reduce labor cost. They will operate at lower voltage than 48 since the is the nominal value for talk battery and it's range goes to a lower voltage to allow for battery discharge. You don't need series resistors in you use the right relay for the right supply voltage the coil resistance is fairly high to keep power dissapation low. I would be be willing to bet that Passlabs cound build the entire circuit for less what you our I could by one 24 volt relay in small quantities. I could probably do a cost model of what they spend for the circuit to within a 10% to 20% window. I guess designing a relay circuit for relability and cost is harder than most people thought. By the way what high volume electronic devices use 24 volts? Cars use 12 V, most logic circuits use 5 V, and telecom uses 48 V, I don't think I have ever seen a 24 volt relay although I am sure they make them. I'll bet you you would pay more for them than 48 V relays.
 
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