Scope trace looks fine, just a bit saturated, focusing the beam might help a little.
The multimeter is reading almost perfectly, as per the first picture we've got ~40 volts peak to peak on the scope, this = 14.2Vrms which is concordant with the multimeter.
The multi reads too high in the images that are clipping simply because the clipped tops/bottoms are artificially increasing the average.
I am still concerned that 60v peak to peak isn't enough to get decent listening levels out of the SR71s. They might only be 84dB sensitive, but 60v is still giving you +17dB for an absolute peak value of 101dB. This isn't earth shattering but it is well above any comfortable listening level. Do you have a particularly large room or like to listen loud?
Then again what Ian says is quite true, C20 should be considerably larger and if neglected this will increase low frequency distortion and this could be having an impact on the sound quality higher up too.
The multimeter is reading almost perfectly, as per the first picture we've got ~40 volts peak to peak on the scope, this = 14.2Vrms which is concordant with the multimeter.
The multi reads too high in the images that are clipping simply because the clipped tops/bottoms are artificially increasing the average.
I am still concerned that 60v peak to peak isn't enough to get decent listening levels out of the SR71s. They might only be 84dB sensitive, but 60v is still giving you +17dB for an absolute peak value of 101dB. This isn't earth shattering but it is well above any comfortable listening level. Do you have a particularly large room or like to listen loud?
Then again what Ian says is quite true, C20 should be considerably larger and if neglected this will increase low frequency distortion and this could be having an impact on the sound quality higher up too.
I do like to listen to music loud and my room is decent size. What amp voltage and amount of output pairs do you recommend for these speakers.
Nope. design limit by BD139/40 is +/-40V, so some new parts and ratings plus the bias arrangements need changing first. Quite a bit of work, actually
Increasing the voltage rails will increase the dissipation of all of the transistors and will also place greater demands on all of the other components, ie are they spec'd for it?
It will also increase the bias through the output stage so will require a change because of that. This is an EF design so will most likely have quite a high standing device bias. 75mA @ 49 volt rails will dissipate 3.6 watts per output transistor for a total of ~15 watts for the stereo pair. This will warm your heat sinks up a bit more.
The SR71s are a benign enough load and a single pair of 5200/1943s will give ~160 watts into 4 ohm resistive under 40 volt rails. 49 volt rails under 8 ohms will give you around 150 watts. Providing you don't drive anything other then 8 ohm loads, then the output stage will probably be okay, but don't take this as a given.
As AndrewT said a while back, increasing the rail voltages is almost like a completely new amplifier because there are many things you need to take into consideration to make sure that it will work properly.
Interestingly though you've currently got a 55 watt/8ohm design. 150 watts/8 ohm will only give you 4.3dB more headroom which really isn't a lot more. In the long run perhaps a more sensitive pair of loudspeakers is really the best idea?
It will also increase the bias through the output stage so will require a change because of that. This is an EF design so will most likely have quite a high standing device bias. 75mA @ 49 volt rails will dissipate 3.6 watts per output transistor for a total of ~15 watts for the stereo pair. This will warm your heat sinks up a bit more.
The SR71s are a benign enough load and a single pair of 5200/1943s will give ~160 watts into 4 ohm resistive under 40 volt rails. 49 volt rails under 8 ohms will give you around 150 watts. Providing you don't drive anything other then 8 ohm loads, then the output stage will probably be okay, but don't take this as a given.
As AndrewT said a while back, increasing the rail voltages is almost like a completely new amplifier because there are many things you need to take into consideration to make sure that it will work properly.
Interestingly though you've currently got a 55 watt/8ohm design. 150 watts/8 ohm will only give you 4.3dB more headroom which really isn't a lot more. In the long run perhaps a more sensitive pair of loudspeakers is really the best idea?
Well there's the problem. Change the loudspeakers, these aren't designed for 'loud'. No properly designed 2 way with a 6.5" mid/bass is. You can throw more power at the situation but the loudspeakers will start to compress/complain before you reach what is probably acceptably loud. Even 150 watts into them wont get you much more.
In my opinion you're after something with a solid 90+dB sensitivity preferably around 92-93dB.
If you want to try the higher supply voltage, at least check the voltage ratings of all the capacitors first.
Also, the idling current is likely to increase, so it would be smart to turn the bias adjustment right down before increasing the supply voltage, then set it properly again.
Also, the idling current is likely to increase, so it would be smart to turn the bias adjustment right down before increasing the supply voltage, then set it properly again.
How can a receiver run off 49v with 1 pair of output transistors and not exceed the soa of the transistors.
It probably does so with output protection built in, meaning it will give full output into 8 ohms, but not into 4 ohms. The protection kicks in to stop you blowing the transistors up.
This is why I said 8 ohms with one pair of 5200/1943s would probably be fine at 49volt rails.
It has to be said though that if the the SR71s are very smooth and refined sounding that this kind of sound does tend to influence you towards turning it up more and more.
I am surprised that the small ~4dB gain of the receiver over your own build gives you the extra volume you require. 4dB isn't all that much.
This is why I said 8 ohms with one pair of 5200/1943s would probably be fine at 49volt rails.
It has to be said though that if the the SR71s are very smooth and refined sounding that this kind of sound does tend to influence you towards turning it up more and more.
I am surprised that the small ~4dB gain of the receiver over your own build gives you the extra volume you require. 4dB isn't all that much.
How many pairs?
Plenty of amplifiers run a single pair of transistors off rails up to 60V even. Some require you to switch over for lower loads and others just leave the low current transformer to sag the rails according to load. Technics, Kenwood, Marantz, Sansui and Luxman even did this. It's standard fare for great, cheap, dynamic capability at normal levels.
The rating of speakers can be hard to accept. Recently, on recommendation, I bought) some Dynaudio DM2 6 speakers. they may be fine quality but even a 100W amp has difficulty getting the apparent volume of those alleged 86dB babies up enough for comfortable listening. Add a subwoofer and somehow it all sounds great - up to point.
Then I get frustrated and drag out ol' faithful - my big 90 dB KEFs which need no help in blowing the windows out at a much lower dial setting. 😱
Ah! real sound! 😎
Plenty of amplifiers run a single pair of transistors off rails up to 60V even. Some require you to switch over for lower loads and others just leave the low current transformer to sag the rails according to load. Technics, Kenwood, Marantz, Sansui and Luxman even did this. It's standard fare for great, cheap, dynamic capability at normal levels.
The rating of speakers can be hard to accept. Recently, on recommendation, I bought) some Dynaudio DM2 6 speakers. they may be fine quality but even a 100W amp has difficulty getting the apparent volume of those alleged 86dB babies up enough for comfortable listening. Add a subwoofer and somehow it all sounds great - up to point.
Then I get frustrated and drag out ol' faithful - my big 90 dB KEFs which need no help in blowing the windows out at a much lower dial setting. 😱
Ah! real sound! 😎
look at and confirm the currents passing R14 and R5.
Your rough measurements of 0.3Vdrop and 0.2Vdrop indicate only 6mA and 4mA.
That is not nearly enough to operate the Front end input amp and to run the Zener and to run the VAS.
Something is not drawing it's design current.
You must confirm that all the design currents are flowing.
It is obvious that you did not do any adequate testing at first build.
Never connect a speaker until after you have convinced yourself that the amplifier is not misbehaving !!!!!!!!
Your rough measurements of 0.3Vdrop and 0.2Vdrop indicate only 6mA and 4mA.
That is not nearly enough to operate the Front end input amp and to run the Zener and to run the VAS.
Something is not drawing it's design current.
You must confirm that all the design currents are flowing.
It is obvious that you did not do any adequate testing at first build.
Never connect a speaker until after you have convinced yourself that the amplifier is not misbehaving !!!!!!!!
Just thinking, you will want to correct your amp problem, but I wonder if you will find it sufficient? You are falling flat at about 35W, with a potential of about 50. That is barely much difference. I found when shopping ( yea, I was busy) for speakers a number of years ago, some just seemed to need bigger power. Canton and the original DM1 for example, were the Paradigm 20's were/are quite happy with a Denon receiver I had back then. You may want to borrow a decent amp or two and see if the SR71's are happier with 125W or so. Maybe find some big cheap amp like a DH220 and modify the DX into a multi-output monster. A mark "iii"
I just found a transformer from a denon receiver that makes 40VDC, should putting that in the amp make any difference in the output of the amp. It also seems that the amp can swing unclipped at 30Hz up to 200Hz at 23V on the meter but after that it clips worse and worse until 20Khz.
Fix the amp first. Or throw it in the bin.
Don't modify an amplifier that is not performing as well as it was designed to do!!!!
Don't modify an amplifier that is not performing as well as it was designed to do!!!!
On my test pcbs I just ran it off 44V+/- and it worked for about 15 minutes of making 32V p-p 120Hz sine into no load and then smoke came out of the VAS and T5 and R5, do u think that I exceeded the 100ma max for the KSC3503D transistor.
The Denon transformer may be fine and get the max. from your present semis but Andrew is right in suspecting input/VAS stages to be shy of bias. It is easy to say "fix" but a lot easier to do if you understand what determines this current shared through the LTP and through the VAS transistor. As a loose guide, you will be looking at near 4 mA shared and 8 mA respectively or 12-14 mA total to the front end as measured at any of the CCS resistors, the VAS emitter resistor and R5 or 14 as previously. Measure these voltages across relevant resistors and calculate the currents as accurately as possible.
Assuming you simulated this circuit when you drafted it, you should be able to determine the currents by a current probe or inserting a meter according to your simulation program's requirements. You should then be able to adjust the virtual LTP current by varying CCS resistors and the VAS by its emitter resistor.
If you don't have simulation such as the free LT Spice, it should not be much more difficult to measure the real quantities anyway. Obviously, you need to take great care not to endanger anything when changing components to more appropriate ones. If there is an error causing the current to be reduced now, it may be all too easy to exceed ratings in a big correction that you may think is needed.
To identify the issues, confirm the rail voltages of the HX design and test the currents with that specified supply voltage. Then, recheck currents when your virtual 35V supply is substituted. They will be less with lower rails. At least with DX's design, you have a known correct starting point, It would be my reference to ensure all was in order without advanced procedures, before assuming what ever I changed should continue to work properly.
At that point you should have also verified HF distortion and AC stability factors like phase shift, open loop bandwidth, Nyquist stabilty etc, and peak output levels at HF and LF with each supply and that completes the picture with approximate correct current levels. This is best properly calculated for the input stage, however. Don't forget an appropriate value feedback cap either.
Good luck and keep carefully at it. 🙂
Assuming you simulated this circuit when you drafted it, you should be able to determine the currents by a current probe or inserting a meter according to your simulation program's requirements. You should then be able to adjust the virtual LTP current by varying CCS resistors and the VAS by its emitter resistor.
If you don't have simulation such as the free LT Spice, it should not be much more difficult to measure the real quantities anyway. Obviously, you need to take great care not to endanger anything when changing components to more appropriate ones. If there is an error causing the current to be reduced now, it may be all too easy to exceed ratings in a big correction that you may think is needed.
To identify the issues, confirm the rail voltages of the HX design and test the currents with that specified supply voltage. Then, recheck currents when your virtual 35V supply is substituted. They will be less with lower rails. At least with DX's design, you have a known correct starting point, It would be my reference to ensure all was in order without advanced procedures, before assuming what ever I changed should continue to work properly.
At that point you should have also verified HF distortion and AC stability factors like phase shift, open loop bandwidth, Nyquist stabilty etc, and peak output levels at HF and LF with each supply and that completes the picture with approximate correct current levels. This is best properly calculated for the input stage, however. Don't forget an appropriate value feedback cap either.
Good luck and keep carefully at it. 🙂
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Ian, This is a popular published design so he will not have a full simulation.
Benproiii,
You now get to find what was smoking. As you need to pull it all apart to find and replace everything you damaged, ( It may be more than the three parts you mentioned) start by triple checking the board and components against the design as you have something fundamentally wrong to start with. You might guess we don't suggest you keep the Denon transformer connected to it.
Your day is going about as well as mine. I dropped a driver and broke the basket and the resin I used on the boxes was too old and will not cure. Total scrap.
I never run an amp with no load at all. If I am questioning what it is doing, I can reconnect my big resistor plate to be 16 Ohms when I don't trust the amp.
Benproiii,
You now get to find what was smoking. As you need to pull it all apart to find and replace everything you damaged, ( It may be more than the three parts you mentioned) start by triple checking the board and components against the design as you have something fundamentally wrong to start with. You might guess we don't suggest you keep the Denon transformer connected to it.
Your day is going about as well as mine. I dropped a driver and broke the basket and the resin I used on the boxes was too old and will not cure. Total scrap.
I never run an amp with no load at all. If I am questioning what it is doing, I can reconnect my big resistor plate to be 16 Ohms when I don't trust the amp.
Smoke, anyone?
BTW, I did say 40V was maximum with BD139/40 drivers etc. Don't try that high a voltage as has been advised a few times already here. The whole design has to be modified with these changes, regardless of what some guys casually tell us. The "regulated" current sources are not really, they change and this simple zener one in particular. Everything changes when you adjust supply voltage to this front end.
You may not yet have a grasp of SOA but you will understand the Vceo of BD139/40 is only 80V. With 40V rails, they are on the thin edge already. Why run over the edge and risk everything? Measure the bias currents.
I think 100mA is maximum current, like at low volts. This max, will be much less with near 88V supply and that output. You know when the temp. rises to hot you have too much bias which should be measured . At lower voltages you have proven it's ok already. Given the time, it could have survived with a larger sink but as it took out its driver, it's still a matter of time and too much bias.
BTW, I did say 40V was maximum with BD139/40 drivers etc. Don't try that high a voltage as has been advised a few times already here. The whole design has to be modified with these changes, regardless of what some guys casually tell us. The "regulated" current sources are not really, they change and this simple zener one in particular. Everything changes when you adjust supply voltage to this front end.
You may not yet have a grasp of SOA but you will understand the Vceo of BD139/40 is only 80V. With 40V rails, they are on the thin edge already. Why run over the edge and risk everything? Measure the bias currents.
I hope you meant to say it was a popular published design,. as godfrey realised, its not Greg's website published design and it's not operating under the same conditions. BTW, what do you understand the supply voltages as?
No prob. without simulation, I've clearly allowed for that. However, when people mod things, even newbs now hop to their simulators to check this stuff out and avoid the smoke.
Did you note regulation to front end to 33V? It makes a difference.
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if you must run higher supply: change BD139/140 to MJE340/350. + heatsink.
with 12v zener- increase R26 to suit. But then at the limit of BC556. maybe increase Zener to 20V and R4 to 8K2.
increase R16 to 2K2 and R15 to 4K7.
enjoy. but maybe you wont enjoy the sound so much anymore. maybe it'll be better 🙂
with 12v zener- increase R26 to suit. But then at the limit of BC556. maybe increase Zener to 20V and R4 to 8K2.
increase R16 to 2K2 and R15 to 4K7.
enjoy. but maybe you wont enjoy the sound so much anymore. maybe it'll be better 🙂
The KSC3503 is more robust then that, but it does depend heavily on what current is going through it. This is determined by tht VAS current source and should be constant at quiescent conditions, or when the amplifier is unloaded.
I have mentioned, as have several others now, that you need to take measurements of the voltage drops across the relevant resistors as a way of checking to see if the correct bias current is passing through them and the stages they are a part of.
I literally laughed out loud when you said you fired it up and smoke came out. You knew this would happen so why do it? You had been told directly that the 139/140s can only tolerate a max Vce of 40 volts.
A lot of good advice and recommendations has already been given in this thread by way of making sure the amplifier you have is performing properly and then some small modifications you can take to improve its performance. These are the first things you should do.
Once you've determined that the amplifier is running as was/is intended and then if it still doesn't do what you want it to do, then you go about redesigning the thing for a higher output power into 8 ohms. Simply connecting higher voltage supplies up to it is a really bad idea. As an example of how bad, the output stage and VAS just exploded, lets say the amplifier hadn't exploded quite so fast and you had then connected it up to the loudspeakers. I can pretty much guarantee that doing so would have loaded the VAS/drivers even more heavily and then it would have chosen to explode. In doing so you would most likely have ended up with +44 or -44v present on the amplifier output, this would fry the SEAS mid/bass in seconds and if you haven't got rail fuses installed you'd really be looking at blown drive units.
I have mentioned, as have several others now, that you need to take measurements of the voltage drops across the relevant resistors as a way of checking to see if the correct bias current is passing through them and the stages they are a part of.
I literally laughed out loud when you said you fired it up and smoke came out. You knew this would happen so why do it? You had been told directly that the 139/140s can only tolerate a max Vce of 40 volts.
A lot of good advice and recommendations has already been given in this thread by way of making sure the amplifier you have is performing properly and then some small modifications you can take to improve its performance. These are the first things you should do.
Once you've determined that the amplifier is running as was/is intended and then if it still doesn't do what you want it to do, then you go about redesigning the thing for a higher output power into 8 ohms. Simply connecting higher voltage supplies up to it is a really bad idea. As an example of how bad, the output stage and VAS just exploded, lets say the amplifier hadn't exploded quite so fast and you had then connected it up to the loudspeakers. I can pretty much guarantee that doing so would have loaded the VAS/drivers even more heavily and then it would have chosen to explode. In doing so you would most likely have ended up with +44 or -44v present on the amplifier output, this would fry the SEAS mid/bass in seconds and if you haven't got rail fuses installed you'd really be looking at blown drive units.
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