I bought a ready-made amp board with 6 pairs of TTC5200 and TTA1943 giving 6X100W, (5.1 channel) output. The board has 30-0-30 V ac input, with on-board rectifier and filter. This, I presume, will give a 43V dc supply on the rails.
I have a set of 5.1 speakers from a defunct HTS. As of now, I don't remember their impedances but I can get the data in a day or two. However, can you help me calculate whether they can be used safely with the said amp? I need to know whether
a. anything can get fried
b. the complementary power stages are sensitive to impedance match.
Any rule of the thumb will do for now. Maybe a little formula or something to get started.
For a more detailed analysis, I will have to trace out the circuit. I hope to do that soon. I will post that too.
But meanwhile, any little help is appreciated
I have a set of 5.1 speakers from a defunct HTS. As of now, I don't remember their impedances but I can get the data in a day or two. However, can you help me calculate whether they can be used safely with the said amp? I need to know whether
a. anything can get fried
b. the complementary power stages are sensitive to impedance match.
Any rule of the thumb will do for now. Maybe a little formula or something to get started.
For a more detailed analysis, I will have to trace out the circuit. I hope to do that soon. I will post that too.
But meanwhile, any little help is appreciated
A rule of thumb is the total Pd of the devices, divided by the continuous power level.
In your case, it's a pair of 150W devices for 100W, 300/100 makes a factor 3.
Not recommended for 4 ohm use.
2nd rule of thumb is to calculate the max dissipation level of the output stage. For that, you need an estimate of the heatsink C/W rating.
Combined with the rail voltage level, it gives an indication of the lowest impedance level.
@jacco vermeulen. Thanks
Need some clarification. Should the impedance be less than 4 ohms or greater than 4 ohms? How does this work please?
A lower impedance load translates to a higher output current.
Output current times the voltage across the output stage devices, is the heat dissipated in the power transistors.
Lower impedance => higher current => higher dissipation
=> a 2-pair output stage (with 42Vdc rails) is not able to drive loads of 4 ohm or less.
The heatsink is also of importance. If it's relatively small, more likely that the minimum load is in the neighborhood of 6 ohm.
(a car transmission can handle much more torque if it has better cooling, by adding an intercooler. same deal for a power amp)
Output current times the voltage across the output stage devices, is the heat dissipated in the power transistors.
Lower impedance => higher current => higher dissipation
=> a 2-pair output stage (with 42Vdc rails) is not able to drive loads of 4 ohm or less.
The heatsink is also of importance. If it's relatively small, more likely that the minimum load is in the neighborhood of 6 ohm.
(a car transmission can handle much more torque if it has better cooling, by adding an intercooler. same deal for a power amp)
I'd say you should be fine there assuming cooling is OK (and the circuit doesn't have any major flaws like tendency to thermal runaway). Some commercial receivers run 5200s or even 5198s at +/- 56 V! Unsurprisingly, secondary breakdown becomes a real threat if the output is accidentally shorted.
Satellites usually are 6 ohms up anyway. The sub is more likely to be a 4 ohm affair, depending on whether the HTS was supply voltage or current limited.
Satellites usually are 6 ohms up anyway. The sub is more likely to be a 4 ohm affair, depending on whether the HTS was supply voltage or current limited.
Well then, here is the bad news! All the six speakers are rated 3ohms 
But then, is there a possible workaround or a compromise solution? Like, can I get away with limiting the input drive to the power stages? I don't mind losing some audio power as long as the fidelity is OK. (My neighbours would probably approve of this option)
Am I right in assuming that the speakers are dc coupled in these complementary power stages? I don't see any large coupling capacitors on the board.
A little experimentation from my side could save you the bother of a detailed explanation, but right now, a bunch of kids on holiday have locked me out of my hobby room . So I thought i could use this time to catch up on my homework. Thanks for your time.
But then, is there a possible workaround or a compromise solution? Like, can I get away with limiting the input drive to the power stages? I don't mind losing some audio power as long as the fidelity is OK. (My neighbours would probably approve of this option
)Am I right in assuming that the speakers are dc coupled in these complementary power stages? I don't see any large coupling capacitors on the board.
A little experimentation from my side could save you the bother of a detailed explanation, but right now, a bunch of kids on holiday have locked me out of my hobby room
. So I thought i could use this time to catch up on my homework. Thanks for your time.the speakers will almost certainly be DC coupled when the Power Supply is a dual polarity.
The amplifier is very likely to be AC coupled, using DC blocking capacitors in both the Input and the Negative FeedBack leg.
Check for no DC output when powered up with the inputs shorted and with the inputs connected to your sources.
For 3ohms duty you could run the amplifiers at a much lower voltage. Maybe around +-24Vdc.
The amplifier is very likely to be AC coupled, using DC blocking capacitors in both the Input and the Negative FeedBack leg.
Check for no DC output when powered up with the inputs shorted and with the inputs connected to your sources.
For 3ohms duty you could run the amplifiers at a much lower voltage. Maybe around +-24Vdc.
I concede that, but it would be easier and operationally safer if I could limit the drive to a safe upper limit.
I now understand the unique danger of the power supply driving excessive current through the transistors and the directly coupled load.
One little question remains regarding the Jacobi's law in relation to too low a load impedance.
I am tracing out the circuit now. As far as I can see, it looks like a class B circuit. the op-amp (I guess) at the input which receives the feedback (into pin 3) from the emitter resistance (0.22 ohm) has its number erased. Its an 8 pin dip IC. What is the usual candidate?
I now understand the unique danger of the power supply driving excessive current through the transistors and the directly coupled load.
One little question remains regarding the Jacobi's law in relation to too low a load impedance.
I am tracing out the circuit now. As far as I can see, it looks like a class B circuit. the op-amp (I guess) at the input which receives the feedback (into pin 3) from the emitter resistance (0.22 ohm) has its number erased. Its an 8 pin dip IC. What is the usual candidate?
Last edited:
I see many posts here referring to the general type of circuit that I have. I suppose most of you will be familiar with this combination. However, the prolific posts here have left me, well, a little dazed! Can anyone please direct me to a one-stop tutorial or such so that I can read up the basics of structure and working of this kind of amplifier.
It will be a while before I can complete my schematic and post it here, but meanwhile I can give a generic description: this is similar to the complementary-symmetry circuits in the radio receivers of yore, but I think the world has come a long way since then.
Here it is then,
1. power stage 1943/5200 transistor pair, 0.22ohm 5W resistors at the emitters
2. Power supply: bipolar +/- 43 V dc
3. An op-amp receives input from volume control
4. parallel RC feedback loop from speaker output to the op-amp input
5. other npn-pnp transistor pairs between 1 and 3
This will help me come to a position where I can ask for more specific information and save some time for the experts here. Quite generous they are, but I think it is not fair to have them repeat stuff for every new entrant like me!
Thanks
It will be a while before I can complete my schematic and post it here, but meanwhile I can give a generic description: this is similar to the complementary-symmetry circuits in the radio receivers of yore, but I think the world has come a long way since then.
Here it is then,
1. power stage 1943/5200 transistor pair, 0.22ohm 5W resistors at the emitters
2. Power supply: bipolar +/- 43 V dc
3. An op-amp receives input from volume control
4. parallel RC feedback loop from speaker output to the op-amp input
5. other npn-pnp transistor pairs between 1 and 3
This will help me come to a position where I can ask for more specific information and save some time for the experts here. Quite generous they are, but I think it is not fair to have them repeat stuff for every new entrant like me!
Thanks
update
Had to stay off my project for some time. Meanwhile, I got myself a DSO.
To go ahead with my analysis, I have planned the following test procedure. Kindly let me know if you see anything wrong with this.
I am planning to connect my power transformer primary to a Variac and at first drive it with about 50-60% rated voltage.
The NPN-PNP power transistors themselves are directly driven from the supply rails and I guess a lower (symmetrical) voltage on the rails should not bother them.
Can't say the same for the preceding driver stages and their biasing. I will now drive each of the 5.1 channels in turn with a sine-wave and check out the output waveform on my DSO. Biasing problems if any, should cause some clipping or distortion. in the final output.
Although I want to listen to my audio system finally, I am in no hurry to get there because I don't want to miss out on the fun along the way. So if you find my approach a little off-beat, I hope you will understand and stay with me!
regards and thanks
Had to stay off my project for some time. Meanwhile, I got myself a DSO.
To go ahead with my analysis, I have planned the following test procedure. Kindly let me know if you see anything wrong with this.
I am planning to connect my power transformer primary to a Variac and at first drive it with about 50-60% rated voltage.
The NPN-PNP power transistors themselves are directly driven from the supply rails and I guess a lower (symmetrical) voltage on the rails should not bother them.
Can't say the same for the preceding driver stages and their biasing. I will now drive each of the 5.1 channels in turn with a sine-wave and check out the output waveform on my DSO. Biasing problems if any, should cause some clipping or distortion. in the final output.
Although I want to listen to my audio system finally, I am in no hurry to get there because I don't want to miss out on the fun along the way. So if you find my approach a little off-beat, I hope you will understand and stay with me!
regards and thanks
Well then, here is the bad news! All the six speakers are rated 3ohms
.
One solution I see is too use a lower voltage supply with appropriate smoothing caps, and an output stage designed for lower voltage and higher current to match the impedance of a reactive 3R load.
NO.
Don't use a Variac for first power on.
Use a Mains Bulb Tester.
It allows you to start up and check that all the wiring is correct.
It also allows for reversed output and driver devices without any damage.
The input should be shorted at this stage. Measure the output offset and the output noise + hum.
After you have proved the wiring is correct, then you can play about with a variable Mains input voltage.
Don't use a Variac for first power on.
Use a Mains Bulb Tester.
It allows you to start up and check that all the wiring is correct.
It also allows for reversed output and driver devices without any damage.
The input should be shorted at this stage. Measure the output offset and the output noise + hum.
After you have proved the wiring is correct, then you can play about with a variable Mains input voltage.
25-0-25 transformer
Dear members,
The audio power amp board has ac power inputs (from the power transformer secondary) marked 30-0-30 V. After following the precautions mentioned by the members here, I used a 25-0-25 transformer with a Variac and powered up the board with 180V on the primary. The speakers did work, but the output was severely clipped. But since the transistors, heat sink and other power components were relatively cool, I ramped it up to about 200V. The clipping reduced considerably. At the rated 230V, the amp was working satisfactorily, with very little heating. The dc on the rails was +/- 34 V. I could get comfortably loud sound levels with no sign of speaker overload. I have not made any measurements yet, but the whole experience turned out to be deeply satisfying.
I wish to thank the members here for rallying around and lighting my way while I stumbled through the dark labyrinth of ignorance.
Will post more details regarding noise and hum as I go further.
Dear members,
The audio power amp board has ac power inputs (from the power transformer secondary) marked 30-0-30 V. After following the precautions mentioned by the members here, I used a 25-0-25 transformer with a Variac and powered up the board with 180V on the primary. The speakers did work, but the output was severely clipped. But since the transistors, heat sink and other power components were relatively cool, I ramped it up to about 200V. The clipping reduced considerably. At the rated 230V, the amp was working satisfactorily, with very little heating. The dc on the rails was +/- 34 V. I could get comfortably loud sound levels with no sign of speaker overload. I have not made any measurements yet, but the whole experience turned out to be deeply satisfying.
I wish to thank the members here for rallying around and lighting my way while I stumbled through the dark labyrinth of ignorance.
Will post more details regarding noise and hum as I go further.
I should have added "if you also fit the reverse polarity protection diodes."
The output and power input can use a total of 4off 1n4002 diodes to help protect the amplifier from abuse. These cost a few pence (couple of cents).
One each across the local decoupling electrolytics
One each across power rail to Output rail (speaker out).
I recommend that you NEVER use speakers on an untested and/or unproved amplifier.
Instead:
short the input sockets.
leave the speaker outputs open.
Measure the DC output and AC output after you are satisfied all is wried correctly.
Use these to indicate that all is stable for a few days.
Then connect a cheap "throw away" speaker to listen at low levels.
"clipping"? Do you have a scope and signal generator?
If so you should be testing sine, triangle and squarewaves into various resistive loads at various levels to prove adequate performance.
Then add a little capacitance across your resistor dummy loads.
Start with 1nF and step in decades (or half decades, 33xF) to 1uF, again at various frequencies and various levels looking out for excessive ringing, or excessive overshoot.
Overshoot is excess amplification of fast transients. Overshoot sounds crap on music signals, especially female singers after a while.
Instead:
short the input sockets.
leave the speaker outputs open.
Measure the DC output and AC output after you are satisfied all is wried correctly.
Use these to indicate that all is stable for a few days.
Then connect a cheap "throw away" speaker to listen at low levels.
"clipping"? Do you have a scope and signal generator?
If so you should be testing sine, triangle and squarewaves into various resistive loads at various levels to prove adequate performance.
Then add a little capacitance across your resistor dummy loads.
Start with 1nF and step in decades (or half decades, 33xF) to 1uF, again at various frequencies and various levels looking out for excessive ringing, or excessive overshoot.
Overshoot is excess amplification of fast transients. Overshoot sounds crap on music signals, especially female singers after a while.
Thank you AndrewT.
The warnings highlight a host of things that could have gone wrong. Never thought along those lines because I have not worked with these power levels earlier. Pays to be cautious.
(I could hedge my risk a bit because these boards are being sold in the local market in fairly large numbers. I however don't want this to sound like I advocate living dangerously!). Thank you for taking time out to emphasise these issues.
Yes. I do have a scope. I noticed the clipping on my dual trace 'scope using an FM radio signal in the input.
I can arrange for a software based function generator with a D/A output, to begin with.
I need some clarifications please,
1. What is the line-in voltage I should set for the test in order to qualify my amp for use with multiple sources? What are the standard line-out source specs?
2. What are the diagnostics with a triangular wave?
3. "fast Transients" - could this be the rising and falling edge of a square-wave input? Couldn't AC coupled amplifiers take some of the "edge" off these transients?
4. Dummy resistors with capacitors- Don't we need inductors to simulate the phase-lag conditions of real speakers?
Regards
The warnings highlight a host of things that could have gone wrong. Never thought along those lines because I have not worked with these power levels earlier. Pays to be cautious.
(I could hedge my risk a bit because these boards are being sold in the local market in fairly large numbers. I however don't want this to sound like I advocate living dangerously!). Thank you for taking time out to emphasise these issues.
Yes. I do have a scope. I noticed the clipping on my dual trace 'scope using an FM radio signal in the input.
I can arrange for a software based function generator with a D/A output, to begin with.
I need some clarifications please,
1. What is the line-in voltage I should set for the test in order to qualify my amp for use with multiple sources? What are the standard line-out source specs?
2. What are the diagnostics with a triangular wave?
3. "fast Transients" - could this be the rising and falling edge of a square-wave input? Couldn't AC coupled amplifiers take some of the "edge" off these transients?
4. Dummy resistors with capacitors- Don't we need inductors to simulate the phase-lag conditions of real speakers?
Regards
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.