Noob question alert! 🙂
Can I calculate headroom, gain and other important info I need to know from these few informations?
Amplifier 60 W / 8 Ohm
Transformer 300VA 240V to (26AC + 26AC) ~6A
If so, how?
Can I calculate headroom, gain and other important info I need to know from these few informations?
Amplifier 60 W / 8 Ohm
Transformer 300VA 240V to (26AC + 26AC) ~6A
If so, how?
Not even the gain? I mean do cd-players, gramophones, tape recorders, DACs and so on not have some sort of "standard" output in i.e. voltage?
Okay thanks, but how do you then usually calculate gain and headroom when you only know that you want a 60W amplifier and have your transfomer?
EDIT: is it possible to calculate these info from a circuit with all values on?
EDIT: is it possible to calculate these info from a circuit with all values on?
Last edited:
Gain: No way.
Headroom:
Search how to calculate voltage rails from a known power supply transformer.
This is basic power supplier calculation.
Search how to calculate output peak voltage from output power and speaker rated impedance.
This is basic electricity calculation.
The voltage difference gives the max headroom one can get. Actual headroom is lower depending of implementation details.
Headroom:
Search how to calculate voltage rails from a known power supply transformer.
This is basic power supplier calculation.
Search how to calculate output peak voltage from output power and speaker rated impedance.
This is basic electricity calculation.
The voltage difference gives the max headroom one can get. Actual headroom is lower depending of implementation details.
Knowing the transformer voltage allows you to calculate a realistic output voltage attainable from a normal amplifier.
26-0-26 volts AC would just about allow a 60 wrms/8 ohm amp to be constructed.
Rough and ready calculation.
1/ 26* root2 gives DC rails voltage (so 36-0-36 volts DC)
2/ Knock off 5 volts to allow for losses. That gives 31 volts peak voltage swing from the amplifier.
3/ Divide that by root 2 to get the rms voltage level available across the load. That gives 21.9 vrms.
4/ Square that and divide by load impedance to get rms power available which gives around 60 wrms.
5/ Gain for a line input needs to deliver the full output for say 500mv rms input voltage. Make it any less sensitive and 'quiet' CD's etc will need the volume turning all the way up. So 21.9/0.5 gives a needed voltage gain of around 40.
The figure of '40' sits comfortably with most amp designs including chip amps, Make the gains to low and most conventional circuits will become unstable.
You can calculate the voltage gain of a given amp design very quickly by working out the feedback factor.
You might be surprised how little voltage (power) is needed:
http://www.diyaudio.com/forums/multi-way/204857-test-voltage-power-speakers.html?highlight=Voltage
26-0-26 volts AC would just about allow a 60 wrms/8 ohm amp to be constructed.
Rough and ready calculation.
1/ 26* root2 gives DC rails voltage (so 36-0-36 volts DC)
2/ Knock off 5 volts to allow for losses. That gives 31 volts peak voltage swing from the amplifier.
3/ Divide that by root 2 to get the rms voltage level available across the load. That gives 21.9 vrms.
4/ Square that and divide by load impedance to get rms power available which gives around 60 wrms.
5/ Gain for a line input needs to deliver the full output for say 500mv rms input voltage. Make it any less sensitive and 'quiet' CD's etc will need the volume turning all the way up. So 21.9/0.5 gives a needed voltage gain of around 40.
The figure of '40' sits comfortably with most amp designs including chip amps, Make the gains to low and most conventional circuits will become unstable.
You can calculate the voltage gain of a given amp design very quickly by working out the feedback factor.
You might be surprised how little voltage (power) is needed:
http://www.diyaudio.com/forums/multi-way/204857-test-voltage-power-speakers.html?highlight=Voltage
How long is a rope? You usually can't buy less than 25' or more than 250', but many different lengths are available.
In very rough terms: audio not from a pickup (microphone, guitar, phono needle, tape head) and not yet intended to make POWER, is "about 1 Volt". This is really "telephone line level" (telephone was the original audio). Telephone was not practical until improved microphones put near 1V on the line to overwhelm other interference (static, hum, buzz). There's no point in putting out huge levels until you get to the speaker.
Modern specifics:
CD players had +/-5V supplies so it was natural for them to put out a 2V audio level. This has become a modern convention.
WalkMans, iPods, cellphones typically have 3V battery and can not make 1V of audio. Also they aim at headphones and 1 Volt in modern headphones is dangerously loud. These devices vary from near 1V down to as low as 0.2V max.
Yes, an all-purpose amplifier needs a wide-range Volume control or other gain adjustment.
Amplifying (ahem…) on Mooly's outstanding derivation, you have 2 givens so far: 8 Ω speakers and a 26–0–26 volt 300 VA transformer. My calculations in 'math' form would be:
Vpeak = VRMS • √(2)…
26 VRMS • √(2) → 36.8 Vpeak
36.8 Vpeak - 5.0 V (losses) → 31.8 Vpeak realistic designing…
31.8 Vpeak / √(2) → 22.5 VRMS
Then, trying to get the maximum out of your 'amp', instead of a classic single-sided split power supply, I'd go with the "class H bridge" configuration. Hey, its me the goat. Its easy enough to do as long as you're making a PCBoard amp anyway. This implies that the maximum Vpeak-to-peak is
VP-P = 2 × Vpeak … in class H
VP-P = 2 × 31.8 Vpeak
VP-P = 63.6 V
And now calculating that into an RMS
VRMS = VP-P / √(2)
VRMS = 63.6 V ÷ 1.414
VRMS = 45 V
OK, remembering Ohm's Law and the Power Law (of resistances, which is informative but not overly accurate for audio-signal work… still "good enough"):
E = IR … volts = amps × Ω (Ohm's Law)
P = IE … watts = volts × amps (Power Law) … then with substitution
P = E²/R = I²R
We just substitute in your proposed 8 Ω speaker and the new VRMS:
P = E²/R
P = 45² ÷ 8
P = 253 W
Probably the limit of what the 300 VA transformer will want to drive. Nice thing is, unlike pure sine wave tones, real music is anything but a full load of the amplifier. 20% is typical. With an extra-large reservoir of power supply capacitors, your proposed amplifier ought to be able to drive VP-P² ÷ 8 Ω = 63.6² ÷ 8 → 500 W peak waveform power to the speakers at clipping, whilst still providing (500 W × 20% → 100 WRMS) continuously. Effortlessly. Right at the limit of clipping.
Moreover, the 300 VA transformer could easily drive a 4 Ω speaker … with various kinds of music source … with large reservoir capacitors … as well. It is surprising how much audio power a Class-H system working off a 63.6 V supply can provide.
GoatGuy
Vpeak = VRMS • √(2)…
26 VRMS • √(2) → 36.8 Vpeak
36.8 Vpeak - 5.0 V (losses) → 31.8 Vpeak realistic designing…
31.8 Vpeak / √(2) → 22.5 VRMS
Then, trying to get the maximum out of your 'amp', instead of a classic single-sided split power supply, I'd go with the "class H bridge" configuration. Hey, its me the goat. Its easy enough to do as long as you're making a PCBoard amp anyway. This implies that the maximum Vpeak-to-peak is
VP-P = 2 × Vpeak … in class H
VP-P = 2 × 31.8 Vpeak
VP-P = 63.6 V
And now calculating that into an RMS
VRMS = VP-P / √(2)
VRMS = 63.6 V ÷ 1.414
VRMS = 45 V
OK, remembering Ohm's Law and the Power Law (of resistances, which is informative but not overly accurate for audio-signal work… still "good enough"):
E = IR … volts = amps × Ω (Ohm's Law)
P = IE … watts = volts × amps (Power Law) … then with substitution
P = E²/R = I²R
We just substitute in your proposed 8 Ω speaker and the new VRMS:
P = E²/R
P = 45² ÷ 8
P = 253 W
Probably the limit of what the 300 VA transformer will want to drive. Nice thing is, unlike pure sine wave tones, real music is anything but a full load of the amplifier. 20% is typical. With an extra-large reservoir of power supply capacitors, your proposed amplifier ought to be able to drive VP-P² ÷ 8 Ω = 63.6² ÷ 8 → 500 W peak waveform power to the speakers at clipping, whilst still providing (500 W × 20% → 100 WRMS) continuously. Effortlessly. Right at the limit of clipping.
Moreover, the 300 VA transformer could easily drive a 4 Ω speaker … with various kinds of music source … with large reservoir capacitors … as well. It is surprising how much audio power a Class-H system working off a 63.6 V supply can provide.
GoatGuy
Sorry Mooly, PRRI GoatGuy I fell asleep and I could not get in here before now! Sorry.
I am wary happy for your great answers!
The schematic I have chosen are from the Densen Beat B-100 I did listen to for many many years ago and find it nearly perfect in musicality, It only lacked in control and base, so I am thinking of, giving it a larger transformer, with higher voltage, ampere and larger caps value.
Would that be a great solution?
I am wary happy for your great answers!
The schematic I have chosen are from the Densen Beat B-100 I did listen to for many many years ago and find it nearly perfect in musicality, It only lacked in control and base, so I am thinking of, giving it a larger transformer, with higher voltage, ampere and larger caps value.
Would that be a great solution?
If you liked the design then yes, but you will need extreme care in building it and using a suitable circuit board layout. Good layout is everything when it comes to amplifier design.
Well, Densen's design isn't complex or particularly unusual. The schematic and PCB pattern are shown in some sketchy detail here: DENSEN B-100 Service Manual download, schematics, eeprom, repair info for electronics experts
If you are are keen to copy the design and since it's a popular European model, I'm sure others have also tried cloning it and would probably have some specific construction advice for you.
However, as a DIY beginner, I would not advise trying to lay out out your own PCB at a first attempt, as it requires quite a lot of study for using the software properly and you need to practice by drafting simpler examples before you arrive at a point where your design will be usable for making a quality board professionally. These days, it's cheaper to have your boards made professionally and maybe sell a few spares to friends. Some interesting drafting guidelines and info. here: PCB Design Guidelines-Engineering Technical-PCBway
My suggestion is not to go this way until you have some DIY construction experience - try assembling a cheap, smaller kit of something else, get it working as best you can - then make your preferred amplifier layout with stripboard, matrix board etc. Make the mistakes, learn how to troubleshoot them and sort the design problems out for yourself before committing to a serious clone of the B100. Anyway, that's what I had to do to get started and the young enthusiasts I know in my area, still have the same problems, with or without PCs, design software and online forums for help and suggestions that we have now 🙂
If you are are keen to copy the design and since it's a popular European model, I'm sure others have also tried cloning it and would probably have some specific construction advice for you.
However, as a DIY beginner, I would not advise trying to lay out out your own PCB at a first attempt, as it requires quite a lot of study for using the software properly and you need to practice by drafting simpler examples before you arrive at a point where your design will be usable for making a quality board professionally. These days, it's cheaper to have your boards made professionally and maybe sell a few spares to friends. Some interesting drafting guidelines and info. here: PCB Design Guidelines-Engineering Technical-PCBway
My suggestion is not to go this way until you have some DIY construction experience - try assembling a cheap, smaller kit of something else, get it working as best you can - then make your preferred amplifier layout with stripboard, matrix board etc. Make the mistakes, learn how to troubleshoot them and sort the design problems out for yourself before committing to a serious clone of the B100. Anyway, that's what I had to do to get started and the young enthusiasts I know in my area, still have the same problems, with or without PCs, design software and online forums for help and suggestions that we have now 🙂
PCB layout is important for stability.
For high performance amps layout is critical.
Old designs are much more forgiving, and worthwhile considering because high perfs are not that important, swamped in unavoidable defects of loudspeakers.
For high performance amps layout is critical.
Old designs are much more forgiving, and worthwhile considering because high perfs are not that important, swamped in unavoidable defects of loudspeakers.
This seems a pretty common design.
However the output stage is of the no feed back kind. It is out of the feed back loop.
This design choice has it's adepts but is not the usual diyaudio choice.
However the output stage is of the no feed back kind. It is out of the feed back loop.
This design choice has it's adepts but is not the usual diyaudio choice.
mchambin yes Densen claims that it is a no feed back design, I do not know if it is bad or not, but it is properly the most musical amplifier for human money I have heard🙂
It did only lack in base and control of the speakers.
so I imagine to add some more voltage for headroom and more ampere for kicking the speaker to do as it get told. 🙂
It did only lack in base and control of the speakers.
so I imagine to add some more voltage for headroom and more ampere for kicking the speaker to do as it get told. 🙂
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