Tony I know you're electronics maintaining in the medical care industry has been rewarding and beneficial, but I can't help thinking that you would've been or could be upon retirement an excellent physics professor.
Very informative Tony, and thanks for taking the time to go through this. I haven't had the need to work on a failed protect circuit yet, but I've also avoided really looking at them because I didn't understand how they worked. After watching this video, I will pay more attention to the protect circuit when I refurb an amplifier. As always, I never watch one of your videos without learning new information.
One circuit that I like to use for my DIY " prototype projects is a combined soft-start / speaker protect circuit that uses an external 24 VDC "wall wart" (or external) PS. The power to the 24 VDC can be switched using a pole from the amps main power switch. You can easily modify the turn-on / turn-off delay by changing the size of the "timing" cap. Both circuits use the same type of basic DC RC charge pump. I also like to use 5-8 amp "robust" 24VDC relays. Most relays included in these "pre-fab" kits are only good for low power amps.
if you want an intellectual exercise, take a look at the Marantz 18 power amp. No relay, but a soft start that starts very early in the in the power amp that also detects DC offset. However if an output device is shorted there would be no joy!. Another funny one was the Marantz 15, it used two car brake lamps as the current limiter and overload indicators. For total torture look at the Marantz 500. One discrete diff pair feeding to two more diff pairs driving their respective positive and negative drives. You needed four edgewise volt meters side by side to get all three diff pairs balanced. I worked there as an engineer there after the 15 and 18 was designed so I never got an explanation of why this was done. Steve
Amplifiers in car audio systems often have an overdrive/limiting circuit. The system in my 2013 Kia Optima does, and there is a setting to enable/disable it.
12:25 ACC 260 (Acoustic Control Corp) has a AGC cirucuit. Picks signal off speaker output cap on one side, uses two 2N2926 in series from E-C with a few caps and a 2N4360 Jfet, and signal from input emitter side of a 2N3391, reduces overall gain by 6db when peaks get high.
Thank you Tony. Just helped me solve a problem on a Rotel multi channel. The time base is located on a separate board which acts like the timers for all 5 protection circuits. That’s why I scratched my head when I was looking for something missing on the amp board. I love it when you go into theory. More please sir, can I have some more?
I needed this theory Thanks I really love your videos, especially where you explain and share some Details about amplifier or just you talking about anything else. Love you Sir
on the Marantz 140 there are also thermistors - could you explain their role also in a follow-up video. the 140 has a protection circuit that is used in many Marantz amps - like 2325
Do you want to see a FUN protection circuit? Look at the schematic for a McIntosh MC5100 Integrated amp. On the "Output Monitor PC board 043-821, It has, 2 separate protect circuits, 1 for each channel, consisting mainly of a Triac and a "SBS" , or "Silicon Bilateral Switch" ( Which is basically a Diac with a gate lead, and in this case the "G" lead has no connection) (SBS201-202). How it seems to be engineered is, if the channel suffers a failure that passes a high amount of DC to the output, the voltage is shunted through the T1-T2 connection to ground, once it also is high enough to charge a 10uF capacitor in a R-C time constant circuit, and then get past the SBS junction breakdown voltage , it will trigger the Triac, which, should blow whatever 4 Amp fuse, F201~204 that is supplying the fault, to ground, and killing power to the fault, protecting your valuable speakers without inline fuses or relay contacts. It seems to be a logical, low maintenance design that does not add any mechanical contacts ( and the issue of resistance issues due to dirty contacts or higher resistance in general) to the circuit, and since the circuit is sitting idle and unpowered until needed, it should have a longevity factor that surpasses most of the other signal and power circuit components, but it will cause a owner, or tech, to open it up and investigate the issue, as it is not "self resetting" like a relay circuit.
FYI, they call it '' McIntosh's power guard circuit. '' It's a optocoupler attenuator that lowers the input drive signal below a 0.1% distorsion rate ( if memory serves ). Great tutorial and keep up your fine work. Oh BTW, would be nice to see how a crowbar work in detail. Cheers !
33:16 In the video This is the case I talking about, You did something like limiting the ac output signal by different values of Bipolar capacitor, Again my question is, 33uF 50V MUSE BP Nichicon or 220uf 35v BP Panasonic Which capacitor is more suited for 50W 60W amplifier Please share Details about it
El amplificador Sansui AU-717 usa ese circuito de sobrecarga. y de verdad es muy efectivo, por mas que quieras hacer distorsionar el amplificador no lo logras porque se auto ajusta solo.
Forgive me if I missed it in the video or comments but I didn't hear any discussion about the fact that the protect circuit is putting another component into the signal path at a critical point just before it goes to your speakers. I'm sure the impact is negligible to the sound. However I would think the quality of the relay is an important consideration. I have a Realistic SA-1001 intergrated amp without a protect circuit and I often argue that the simplicity of the design contributes to its wonderful sound. As few components as necessary in the signal path. I guess how important the protect circuit ultimately is depends on how much you love the particular speakers your using and how replaceable and available the drivers are 🤣.
I wonder: why do they use a BJT for Q2 ? Why not a thyristor, e.g. BRX45. Much faster and more definitive switching, and you need that for a relais. It has a hold current under 5 mA, so if you stay under that, say 2mA through C-A and LED, the LED will still light up OK, but the thyristor will un-latch when the Voltage on the gate goes under .6V in respect to the cathode.
Quality content and a pleasure, as always. Just one quick clarification; for the circuit presentation beginning at 21 minutes. Wouldn't shorting the outputs to ground be unnecessarily destructive ? If the final stage output connects to pin 7 and is coupled to the posts on pin 14, then we get a big badda boom. Perhaps it's the other way around ? Output is on J1/J2 and speaker terminals are represented by J3/J4 and J5/6 ?
Hi Tony. I'm going to assume that "short circuit protection" (driver failure or sloppy speaker wiring) is covered under the excessive current portion of the protect circuit. Is the protection circuit dependent on the impedance of the speaker (ie: 4 ohm draws more current and causes the circuit to trip before excessive clipping occurs)?
So basically the circuit takes a sample with a high enough impedance to not affect the amp output and uses large enough capacitance to shunt pretty much any freq over around 20 hz to ground then converts whats left to dc as well as directing the dc thats at that point to turn on the transistor to control relay?
Just saw your McIntosh videos. Love the board reproduction. I have a couple audio research solid states. Are you interested in taking a look into the mysterious “analog module” they famously put on these old pieces?
Love your video's Tony! A question about the Soft-start Power Circuit, isn't the limiting component placed on the other (mains) side of the transformer?
-"maybe you have dementia" -"shut up, i don't recall anyone asking you" you just explained to me on another video about adding a soft start that the thump i get on my bass guitar amp powering up is from a temp dc offset, thanks again for the reply, so now i'm going to watch this although yt says i've already watched it.. talking about dementia and i'm 40yo :}:}:}
Where are all these nasty comments? I don't remember coming accross many. Thats just life on the internet. You have to ignore or sift through the nonsense.
Thank you for making this video! I have Ad Com GFA 555 hooked up with B&W speakers. Should I add a speaker protection circuit to my amplifier or not? Also, I have heard that protection circuit clamps the power and reduces sound sonic and dynamics
Hi Tony, the circuit you've shown, would it handle left channel sitting at -5V and right channel at +5V DC? will combining them with 10k resistor equals to 0V or it's a rare condition and it's what it is?:)
Each individual amplifier will see a 10K input impedance. But, the signal at the bridge rectifier input will be halved since the ”other” amplifiers output impedance is low. The two 10K resistors will create a voltage divider.
Each channel passes though its own 10k resistor and is also isolated by the 10k resistor on the other channel. It will appear as a 10k input impedance to each channel, however, the two signals will be summed at the tie point. Out of phase signals will cancel/attenuate one another. Equal signals will not affect one another.
@@andersjohansson8588 yes, that divider of two 10k's - from the perspective of the capacitors looking back at the sources - appears as a 5k ohm impedance. Standard circuit analysis will short the sources, and the two 10k become one 5k on the hand-drawn simplified circuit diagram
I like your videos I like the way you explain the Theory the principles of the circuit nicely made. I also have a Pioneer A-70 Non-Switching Integrated amplifier that I bought non-working I did restore it back. Needed pretty much all the electrolytic replacing apart from the main filter caps. Had some resistors that were open-circuit due to that stupid glue that they use from factory. Give me your thoughts on this particular model what do you think is a good design. The only issue that I have I have to retake a look at the safety circuit which is the relay. Either than that the bias was adjusted very well maybe I adjusted it slightly higher than the factory spec. The amplifier sounds amazing has a very clean sinewave and both channels.
How can two polarized caps in series create one bipolar cap? Assuming both are equal, with identical leakage, one of them will always be reverse polarized.
using LT Spice - even using extended Capacitor models (with Rp, Rs, Rl) - it clearly requires a protection diode on each part... One think I did find looking at some datasheets the leakage (Rp) is very non-linear with reverse bias. The current will ramp up very quickly and damage the capacitor. Of course the 10k on each terminal (5k input impedance) creates an RC with a 0.3Hz corner frequency. That strongly attenuates signals >20Hz, so really it will only cause capacitor failures when there's a very low frequency or DC bias (which ironically is what we are supposed to detect and prevent)
@@xraytonyb Thanks for the response. Do you know of a protection circuit that will work in this situation? I have two class D amps with power on/off thump noise that I want to eliminate.
Tony, Sir, Unfortunately you will always get people who act dumb, or anonymous brave heroes (at a distance) who just want to create chaos. (Pity them, they are just lonely, sad or angry souls) I, and I guess the majority of your viewers really appreciate the time you spend making these vids, certainly tuition I and many others could not afford to buy. Thank you.
Tony I know you're electronics maintaining in the medical care industry has been rewarding and beneficial, but I can't help thinking that you would've been or could be upon retirement an excellent physics professor.
Very informative Tony, and thanks for taking the time to go through this. I haven't had the need to work on a failed protect circuit yet, but I've also avoided really looking at them because I didn't understand how they worked. After watching this video, I will pay more attention to the protect circuit when I refurb an amplifier. As always, I never watch one of your videos without learning new information.
14:58 Here in Belgium we have 16A breakers for light circuits, and 20A breakers for outlets at 230V in residential use.
Love the schematic analysis
One circuit that I like to use for my DIY " prototype projects is a combined soft-start / speaker protect circuit that uses an external 24 VDC "wall wart" (or external) PS. The power to the 24 VDC can be switched using a pole from the amps main power switch. You can easily modify the turn-on / turn-off delay by changing the size of the "timing" cap. Both circuits use the same type of basic DC RC charge pump. I also like to use 5-8 amp "robust" 24VDC relays. Most relays included in these "pre-fab" kits are only good for low power amps.
if you want an intellectual exercise, take a look at the Marantz 18 power amp. No relay, but a soft start that starts very early in the in the power amp that also detects DC offset. However if an output device is shorted there would be no joy!.
Another funny one was the Marantz 15, it used two car brake lamps as the current limiter and overload indicators.
For total torture look at the Marantz 500. One discrete diff pair feeding to two more diff pairs driving their respective positive and negative drives. You needed four edgewise volt meters side by side to get all three diff pairs balanced.
I worked there as an engineer there after the 15 and 18 was designed so I never got an explanation of why this was done.
Steve
Amplifiers in car audio systems often have an overdrive/limiting circuit. The system in my 2013 Kia Optima does, and there is a setting to enable/disable it.
12:25 ACC 260 (Acoustic Control Corp) has a AGC cirucuit. Picks signal off speaker output cap on one side, uses two 2N2926 in series from E-C with a few caps and a 2N4360 Jfet, and signal from input emitter side of a 2N3391, reduces overall gain by 6db when peaks get high.
Your explanations are So Clear Mr. Thanks. I like you vids so much. From Sri lanka. Thanks Again.
Very good, helps me to understand protection circuits much better.
Thank you Tony. Just helped me solve a problem on a Rotel multi channel. The time base is located on a separate board which acts like the timers for all 5 protection circuits. That’s why I scratched my head when I was looking for something missing on the amp board. I love it when you go into theory. More please sir, can I have some more?
I needed this theory
Thanks
I really love your videos, especially where you explain and share some Details about amplifier or just you talking about anything else.
Love you Sir
Learn a lot when I watch your channel Going back to basic electronics
on the Marantz 140 there are also thermistors - could you explain their role also in a follow-up video. the 140 has a protection circuit that is used in many Marantz amps - like 2325
Do you want to see a FUN protection circuit? Look at the schematic for a McIntosh MC5100 Integrated amp. On the "Output Monitor PC board 043-821, It has, 2 separate protect circuits, 1 for each channel, consisting mainly of a Triac and a "SBS" , or "Silicon Bilateral Switch" ( Which is basically a Diac with a gate lead, and in this case the "G" lead has no connection) (SBS201-202). How it seems to be engineered is, if the channel suffers a failure that passes a high amount of DC to the output, the voltage is shunted through the T1-T2 connection to ground, once it also is high enough to charge a 10uF capacitor in a R-C time constant circuit, and then get past the SBS junction breakdown voltage , it will trigger the Triac, which, should blow whatever 4 Amp fuse, F201~204 that is supplying the fault, to ground, and killing power to the fault, protecting your valuable speakers without inline fuses or relay contacts. It seems to be a logical, low maintenance design that does not add any mechanical contacts ( and the issue of resistance issues due to dirty contacts or higher resistance in general) to the circuit, and since the circuit is sitting idle and unpowered until needed, it should have a longevity factor that surpasses most of the other signal and power circuit components, but it will cause a owner, or tech, to open it up and investigate the issue, as it is not "self resetting" like a relay circuit.
FYI, they call it '' McIntosh's power guard circuit. '' It's a optocoupler attenuator that lowers the input drive signal below a 0.1% distorsion rate ( if memory serves ). Great tutorial and keep up your fine work. Oh BTW, would be nice to see how a crowbar work in detail. Cheers !
Correct, and the Power Guard is intended as a speaker protection circuit and it works well.
33:16
In the video
This is the case I talking about,
You did something like limiting the ac output signal by different values of Bipolar capacitor,
Again my question is, 33uF 50V MUSE BP Nichicon or 220uf 35v BP Panasonic
Which capacitor is more suited for 50W 60W amplifier
Please share Details about it
El amplificador Sansui AU-717 usa ese circuito de sobrecarga. y de verdad es muy efectivo, por mas que quieras hacer distorsionar el amplificador no lo logras porque se auto ajusta solo.
34:02 and until very end of the video
Can you provide the high definition images of those A4 sheets, where you have notes and diagrams for circuits
Great video Tony!!!
Forgive me if I missed it in the video or comments but I didn't hear any discussion about the fact that the protect circuit is putting another component into the signal path at a critical point just before it goes to your speakers. I'm sure the impact is negligible to the sound. However I would think the quality of the relay is an important consideration. I have a Realistic SA-1001 intergrated amp without a protect circuit and I often argue that the simplicity of the design contributes to its wonderful sound. As few components as necessary in the signal path. I guess how important the protect circuit ultimately is depends on how much you love the particular speakers your using and how replaceable and available the drivers are 🤣.
Even the most cheapest sealed relay would have better electrical contact than any banana connector used to connect speakers
Merci! It is an marvellous video. Very interesting the schematic of the protect circuit!!😊
I wonder: why do they use a BJT for Q2 ? Why not a thyristor, e.g. BRX45. Much faster and more definitive switching, and you need that for a relais.
It has a hold current under 5 mA, so if you stay under that, say 2mA through C-A and LED, the LED will still light up OK, but the thyristor will un-latch when the Voltage on the gate goes under .6V in respect to the cathode.
I use UPC 1237 speaker protection IC for all my amplifier builds
Quality content and a pleasure, as always.
Just one quick clarification; for the circuit presentation beginning at 21 minutes. Wouldn't shorting the outputs to ground be unnecessarily destructive ? If the final stage output connects to pin 7 and is coupled to the posts on pin 14, then we get a big badda boom. Perhaps it's the other way around ? Output is on J1/J2 and speaker terminals are represented by J3/J4 and J5/6 ?
Hi Tony.
I'm going to assume that "short circuit protection" (driver failure or sloppy speaker wiring) is covered under the excessive current portion of the protect circuit. Is the protection circuit dependent on the impedance of the speaker (ie: 4 ohm draws more current and causes the circuit to trip before excessive clipping occurs)?
So basically the circuit takes a sample with a high enough impedance to not affect the amp output and uses large enough capacitance to shunt pretty much any freq over around 20 hz to ground then converts whats left to dc as well as directing the dc thats at that point to turn on the transistor to control relay?
Precisely
Just saw your McIntosh videos. Love the board reproduction. I have a couple audio research solid states. Are you interested in taking a look into the mysterious “analog module” they famously put on these old pieces?
Love your video's Tony! A question about the Soft-start Power Circuit, isn't the limiting component placed on the other (mains) side of the transformer?
McIntosh = Power Guard
Can the soft start board be installed between the power on switch on the load side off curse to the wires input of the transformer ? Thanks
-"maybe you have dementia"
-"shut up, i don't recall anyone asking you"
you just explained to me on another video about adding a soft start that the thump i get on my bass guitar amp powering up is from a temp dc offset, thanks again for the reply, so now i'm going to watch this although yt says i've already watched it.. talking about dementia and i'm 40yo :}:}:}
Where are all these nasty comments? I don't remember coming accross many. Thats just life on the internet. You have to ignore or sift through the nonsense.
Great talk! Always enjoy your sessions. Thanks for your time and skills.
what about protection circuit for amplifier in bridged mode? there's no common ground, it's virtually floating.
Thank you for making this video! I have Ad Com GFA 555 hooked up with B&W speakers. Should I add a speaker protection circuit to my amplifier or not? Also, I have heard that protection circuit clamps the power and reduces sound sonic and dynamics
good question
I have also GFA 555 MK2 AND 545 MK2 , I want to upgrade them with this module as well.
Thank you for the nice videos and sharing. Personally hate rellays especially on audio amplifiers.
Hi Tony, the circuit you've shown, would it handle left channel sitting at -5V and right channel at +5V DC? will combining them with 10k resistor equals to 0V or it's a rare condition and it's what it is?:)
Your situation would not be detected.
Xraytonyb your utube videos are awesome
26:32 In your simplified circuit, don't the two 10k resistors at the bridge input become a 5k effective input impedance?
Each individual amplifier will see a 10K input impedance.
But,
the signal at the bridge rectifier input will be halved
since the ”other” amplifiers output impedance is low.
The two 10K resistors will create a voltage divider.
Each channel passes though its own 10k resistor and is also isolated by the 10k resistor on the other channel. It will appear as a 10k input impedance to each channel, however, the two signals will be summed at the tie point. Out of phase signals will cancel/attenuate one another. Equal signals will not affect one another.
@@andersjohansson8588 yes, that divider of two 10k's - from the perspective of the capacitors looking back at the sources - appears as a 5k ohm impedance. Standard circuit analysis will short the sources, and the two 10k become one 5k on the hand-drawn simplified circuit diagram
I like your videos I like the way you explain the Theory the principles of the circuit nicely made. I also have a Pioneer A-70 Non-Switching Integrated amplifier that I bought non-working I did restore it back. Needed pretty much all the electrolytic replacing apart from the main filter caps. Had some resistors that were open-circuit due to that stupid glue that they use from factory. Give me your thoughts on this particular model what do you think is a good design. The only issue that I have I have to retake a look at the safety circuit which is the relay. Either than that the bias was adjusted very well maybe I adjusted it slightly higher than the factory spec. The amplifier sounds amazing has a very clean sinewave and both channels.
How can two polarized caps in series create one bipolar cap?
Assuming both are equal, with identical leakage,
one of them will always be reverse polarized.
using LT Spice - even using extended Capacitor models (with Rp, Rs, Rl) - it clearly requires a protection diode on each part...
One think I did find looking at some datasheets the leakage (Rp) is very non-linear with reverse bias. The current will ramp up very quickly and damage the capacitor.
Of course the 10k on each terminal (5k input impedance) creates an RC with a 0.3Hz corner frequency. That strongly attenuates signals >20Hz, so really it will only cause capacitor failures when there's a very low frequency or DC bias (which ironically is what we are supposed to detect and prevent)
Check out my comment to Bjorn V up above in the comments. I go into a bit more detail how this works.
@@xraytonyb I think you mean the reply comment in the "follow-up" video? You didn't reply to Bjorn V (yet) in the comments from this video
Will this circuit work in an amplifier that does not have a common ground shared between speaker channels?
No. It will not
@@xraytonyb Thanks for the response. Do you know of a protection circuit that will work in this situation? I have two class D amps with power on/off thump noise that I want to eliminate.
@@ecco222também tenho
Can I supply this with 12V DC or I need AC ?
Tony, Sir,
Unfortunately you will always get people who act dumb, or anonymous brave heroes (at a distance) who just want to create chaos. (Pity them, they are just lonely, sad or angry souls)
I, and I guess the majority of your viewers really appreciate the time you spend making these vids, certainly tuition I and many others could not afford to buy.
Thank you.
well done
Got a lot out of this video, I’ll have to view it a few more times to get all U need, though. 😊
Xraytonyb this instresing information on speaker protect circuits