I have posted several times about specific audio output relays. The one I use has an initial 100A tungsten contact, bridged by a gold plated contact for low R. When opening, first the gold plated one opens, then the 100A tungsten.
Seems like a non-issue for me.
jan
"At max signal...? Maybe. Care to find out?" Already did. Not for as long as it took to blow the rail fuse. Further testing needs to be done with much cheaper transistors.
Thanks for the part number tips. I see the thought of the slower crowbar protecting the amp better, but with the assumption the amp is already toast, then a fast crowbar, like a tirac, may protect the speaker better. Tweeter being DC blocked, it is the woofer at risk. One would want to be quick enough for it not to bottom out. 15ms seems long for a light weight 6 inch. On the other hand, it think that is within the power rating of all my woofers, so they might survive a few milleconds.
I have been searching for reasonable output disconect relays. Best I can find so far without ordering 500 of them is the Tyco RP821012. DP, SiNiO, 8A. I would use both contacts for a channel to lower the static resistance. This is for SMALL amps. I can see how this gets really difficult for big amps. I can also see where corners are cut in commodity amps.
More on sound quality. I tested the matching of the transistors I took out of my Hafler. Clearly matching was not done at that price range. I found over 20% difference in Ic in a simple fixed rig at 2mA. for both the input pair and the current mirror pair.
Thanks for the part number tips. I see the thought of the slower crowbar protecting the amp better, but with the assumption the amp is already toast, then a fast crowbar, like a tirac, may protect the speaker better. Tweeter being DC blocked, it is the woofer at risk. One would want to be quick enough for it not to bottom out. 15ms seems long for a light weight 6 inch. On the other hand, it think that is within the power rating of all my woofers, so they might survive a few milleconds.
I have been searching for reasonable output disconect relays. Best I can find so far without ordering 500 of them is the Tyco RP821012. DP, SiNiO, 8A. I would use both contacts for a channel to lower the static resistance. This is for SMALL amps. I can see how this gets really difficult for big amps. I can also see where corners are cut in commodity amps.
More on sound quality. I tested the matching of the transistors I took out of my Hafler. Clearly matching was not done at that price range. I found over 20% difference in Ic in a simple fixed rig at 2mA. for both the input pair and the current mirror pair.
Thread topic?
here's another thread that may be useful about amplifier protection relays
http://www.diyaudio.com/forums/solid-state/120365-loudspeaker-relays.html
Jan probably refers to this.
And here's the parts list for Jan Didden's paX protection board that uses that relay. Appears the boards are still available, and it use the UPC1237
Protection system for power amplifiers - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement
kit here
Pilgham Audio - paX Protection unit
Won me a Variac cheap, so one more piece complete. I am holding off on the super relay as FEDX makes it expensive. Can't find them here. Probably smart though, as Jan says "solved".
I'll look over Jan's board and article. Next to check the details on Bosch auto relays. I know from experience in my cars, they are tons more reliable than others. $5 relay, not the $2 will get you to town.
I'll look over Jan's board and article. Next to check the details on Bosch auto relays. I know from experience in my cars, they are tons more reliable than others. $5 relay, not the $2 will get you to town.
Jan probably refers to this.
Yes.
BTW The board has been updated since the article, Pilgham Audio has the updated one.
jan
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Hi,
Based on my experiences in Pro-Audio I would question if this relay can reliably interrupt the rail voltage of an amp from an inductive load (speaker) where current has been flowing for a certain number of milliseconds.
Past that, for upgrades of relays in existing gear where it fits this relay is likely cost effective, however for a new design it would be trivial to combine a gold contact signal relay and an automotive relay with greater interruption capacity for something that works the same.
Still, if my object was to maximally protect the speaker from a defective amp (which I consider it is when I am an Amp designer), I would choose a crowbar, as this will reliably interrupt any current flow in the speaker and we need not to worry about arcing welding the contacts. If it did it would only do what we want anyway.
I can see why some designers may be reluctant to employ this "mute and crowbar" protection scheme, but in reality there is nothing to worry whatsoever. If the Amp is not broken it will not be damaged by the protection engaging in error if minimal care is take during implementation.
If the Amp is already broken I seriously doubt the crowbar will add to the silicone carnage that has already happened.
I had recent (a few years) occasion to test the effectiveness of this circuit when an amplifier circuit under development would blow out the outputs reliably every time I dropped the needle on the record with the volume at "are we having fun yet" after turning over the record to the other side (which I am very quick at).
The subsonics of the record warp had heated the outputs up so much that needle drop transient simply blew them, despite being operated well within datasheet limits (it turned out the manufacturer of the particular three legged fuse in use had not been totally inclusive and candid with information in the datasheet).
When this first happened with the amp driving around 3K USD field coil drivers, rated at 20 RMS, which I had on loan, I was mortified that the drivers would be toast (the Amplifier used BTL output with 35V rails), but the protection engaged and the drivers never suffered the slightest damage, nor did they on repeat occasions.
Until we finally got behind the underlying problem of this I got used to particular sound this made when the dropped needle transient would suddenly fly to one rail and then would be cut off by the protection relay and the subsequent disassembly of the prototype and change of the power module...
But to each their own. My way you never worry about damaged speakers and you never loose sleep that your speaker relay may mess up the sound (as it is not in series with the speaker).
BTW, as the response time of the DC detector is usually worse than that of the relays, I would not worry that we need to use a triac, though I know at least one company (Etalon of Hungary) who did that. I instead use a monostable circuit that locks the protection once engaged, until the output stage power gets disconnected...
Ciao T
Jan probably refers to this.
Based on my experiences in Pro-Audio I would question if this relay can reliably interrupt the rail voltage of an amp from an inductive load (speaker) where current has been flowing for a certain number of milliseconds.
Past that, for upgrades of relays in existing gear where it fits this relay is likely cost effective, however for a new design it would be trivial to combine a gold contact signal relay and an automotive relay with greater interruption capacity for something that works the same.
Still, if my object was to maximally protect the speaker from a defective amp (which I consider it is when I am an Amp designer), I would choose a crowbar, as this will reliably interrupt any current flow in the speaker and we need not to worry about arcing welding the contacts. If it did it would only do what we want anyway.
I can see why some designers may be reluctant to employ this "mute and crowbar" protection scheme, but in reality there is nothing to worry whatsoever. If the Amp is not broken it will not be damaged by the protection engaging in error if minimal care is take during implementation.
If the Amp is already broken I seriously doubt the crowbar will add to the silicone carnage that has already happened.
I had recent (a few years) occasion to test the effectiveness of this circuit when an amplifier circuit under development would blow out the outputs reliably every time I dropped the needle on the record with the volume at "are we having fun yet" after turning over the record to the other side (which I am very quick at).
The subsonics of the record warp had heated the outputs up so much that needle drop transient simply blew them, despite being operated well within datasheet limits (it turned out the manufacturer of the particular three legged fuse in use had not been totally inclusive and candid with information in the datasheet).
When this first happened with the amp driving around 3K USD field coil drivers, rated at 20 RMS, which I had on loan, I was mortified that the drivers would be toast (the Amplifier used BTL output with 35V rails), but the protection engaged and the drivers never suffered the slightest damage, nor did they on repeat occasions.
Until we finally got behind the underlying problem of this I got used to particular sound this made when the dropped needle transient would suddenly fly to one rail and then would be cut off by the protection relay and the subsequent disassembly of the prototype and change of the power module...
But to each their own. My way you never worry about damaged speakers and you never loose sleep that your speaker relay may mess up the sound (as it is not in series with the speaker).
BTW, as the response time of the DC detector is usually worse than that of the relays, I would not worry that we need to use a triac, though I know at least one company (Etalon of Hungary) who did that. I instead use a monostable circuit that locks the protection once engaged, until the output stage power gets disconnected...
Ciao T
It appears calculating output power from psu voltage is a moving target around here ...
( just saying )
Keeping on measurements vs sound , i would like to hear comments regarding the two graphs below, causes, good/bad, expected sonic signature ...?
Graph 1 : spectrum of 50Hz sinewave, DC–10kHz, at 201W into 8 ohms (linear frequency scale).
Graph 2: HF intermodulation spectrum, DC–24kHz, 19+20kHz at 401W peak into 4 ohms (linear frequency scale).
Attachments
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Hi,
It appears so.
A nice solid regulated +/-50V supply suffices normally for 150W/8Ohm, as it allows 35V RMS output...
We MAY have to allow some losses and voltage drop under full load if we use an unregulated supply and this was not included in the calculation, true
But the losses would be small enough for the kind of output stage suggested (12 pairs of output transistors with 0.1 Ohm emitter resistors) and the voltage drop, well we are talking 50V rails under load....
Ciao T
It appears calculating output power from psu voltage is moving target around ...
It appears so.
A nice solid regulated +/-50V supply suffices normally for 150W/8Ohm, as it allows 35V RMS output...
We MAY have to allow some losses and voltage drop under full load if we use an unregulated supply and this was not included in the calculation, true
But the losses would be small enough for the kind of output stage suggested (12 pairs of output transistors with 0.1 Ohm emitter resistors) and the voltage drop, well we are talking 50V rails under load...
.Ciao T
Hi,
Maybe. You snuck those in 12 minutes after I replied, so maybe I'll sneak my answer in later, maybe not....
Ciao T
OK
Maybe. You snuck those in 12 minutes after I replied, so maybe I'll sneak my answer in later, maybe not....
Ciao T
....................
Your post says:
"Last edited by a.wayne; Today at 08:02 PM."
Mine says:
"Today, 07:50 PM"
As for the graphs, I am unsure they show anything particulary relevant to sound quality.
I have heard amp's that had better measured performance than that in these test that sounded very bad and I have heard amp's that had worse measured performance in these tests and sounded rather good.
Ciao T
relays
When I was in the early phases of design of a cost-no-object switching system for amplifiers and loudspeakers, I specified mercury displacement relays. After the client discovered how expensive they were, cost became an object!
They are not fast and I wouldn't recommend them for speaker protection, but (if not ridiculously abused) they form new metallurgically pure contacts with each descent of the plunger down into the Hg bath. The larger ones are good for 100A, with a contact resistance of about 1 milliohm. I believe they still find use in certain high-rel switching applications.
As a proof-of-concept demonstration, I contemplated running a MC cartridge output through the relays to a preamp, to show how free from "dry-contact" intermittencies they were.
Brad
When I was in the early phases of design of a cost-no-object switching system for amplifiers and loudspeakers, I specified mercury displacement relays. After the client discovered how expensive they were, cost became an object!
They are not fast and I wouldn't recommend them for speaker protection, but (if not ridiculously abused) they form new metallurgically pure contacts with each descent of the plunger down into the Hg bath. The larger ones are good for 100A, with a contact resistance of about 1 milliohm. I believe they still find use in certain high-rel switching applications.
As a proof-of-concept demonstration, I contemplated running a MC cartridge output through the relays to a preamp, to show how free from "dry-contact" intermittencies they were.
Brad
Your post says:
"Last edited by a.wayne; Today at 08:02 PM."
Mine says:
"Today, 07:50 PM"
As for the graphs, I am unsure they show anything particulary relevant to sound quality.
I have heard amp's that had better measured performance than that in these test that sounded very bad and I have heard amp's that had worse measured performance in these tests and sounded rather good.
Ciao T
Hello T,
This is what i'm trying to get a grasp on, what is good, what is bad , what is absolute ..? I mean the soulution amplifiers measured immensily low ..... sonics..?
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