(AK) classA HA/Preamplifier.

[FritzS]

The recommended KC5418 PSU kits (Jaycar) are only about AU$20 each.

I think they are available in UK too - I live in Austria (not Australia) and wait for the complete part list - so I could order some other parts too, such as caps (electrolyte), power transistors, some mechanical parts ...

Delivers the UK Jaycar to Austria too? How much the postage cost?

Did you use high speed 1N400x diodes too?

[Deleted]

Nov 19, 2010 7:57:44 GMT FritzS said:

The recommended KC5418 PSU kits (Jaycar) are only about AU$20 each.

I think they are available in UK too - I live in Austria (not Australia) and wait for the complete part list - so I could order some other parts too, such as caps (electrolyte), power transistors, some mechanical parts ...

Delivers the UK Jaycar to Austria too? How much the postage cost?

Did you use high speed 1N400x diodes too?

Friedrich
It could be worthwhile organising a small group buy from Jaycar to the U.K. and then posting to wherever in Europe ?
I use the SF12 or SF14 diodes in the bridge rectifier section of the PSU, but UF4002 would also be O.K.
Alex

[Deleted]

Annnnnnd,

Jaycar UK will only supply at UK prices, which on many items is a lot less, if you use an UK delivery address BUT you will probably be hit by customs. If the order is big enough it is still worth it for the saving.
Anywhere else in Europe and you have to use the mail order dept. in Australia.

OT
What's with this new thing of less and less companies accepting Maestro/Solo debit cards on the net? As someone who ditched the credit cards a while ago it makes ordering pretty tough.

[XTRProf]

Nov 19, 2010 7:52:42 GMT @solderdude said:

So yes... 2W is MORE the adequate to drive headphones.
IF you would pump 2W into the HD800, if it would react linear at this levels, which it doesn't AND the voicecoils would able to handle that power it would be putting out 130dB.
I bet your ears won't like these levels !!!

So this is what's needed... only a few Watts BUT with a high voltage.

and yes Alex is right the A HA and Panda will be driving an HD800 in full class A without any problems.

Hope this clarifies some...

Sorry, lost, Fran. I was following you from Class A all the way to Class AB equivalent which says we need at least about 37 to 40 Watts to drive the high ohmage HD800 to full blast until you say 2W is more than enough to do the job. Care to elaborate a bit more to untwist me? Now twisted like a tree trunk.

[XTRProf]

Don't worry, I got an Oscar for the Great Pretender work and I'm now back. Heh, heh, heh ...........

[Deleted]

Nov 19, 2010 9:10:27 GMT @cjarchez said:

Annnnnnd,

Jaycar UK will only supply at UK prices, which on many items is a lot less, if you use an UK delivery address BUT you will probably be hit by customs. If the order is big enough it is still worth it for the saving.
Anywhere else in Europe and you have to use the mail order dept. in Australia.

OT
What's with this new thing of less and less companies accepting Maestro/Solo debit cards on the net? As someone who ditched the credit cards a while ago it makes ordering pretty tough.

Hi

without wishing to get hooked up in an avalanche of requests. I'd be more than happy to order some psu boards from Jcar and post on to those Europeans having problems obtaining them. Austria no problemo

let me know

i will be ordering a few more for myself so can just add on a few more.

take care

[Deleted]

Nov 19, 2010 9:17:28 GMT XTRProf said:

Nov 19, 2010 7:52:42 GMT @solderdude said:

So yes... 2W is MORE the adequate to drive headphones.
IF you would pump 2W into the HD800, if it would react linear at this levels, which it doesn't AND the voicecoils would able to handle that power it would be putting out 130dB.
I bet your ears won't like these levels !!!

So this is what's needed... only a few Watts BUT with a high voltage.

and yes Alex is right the A HA and Panda will be driving an HD800 in full class A without any problems.

Hope this clarifies some...

Sorry, lost, Fran. I was following you from Class A all the way to Class AB equivalent which says we need at least about 37 to 40 Watts to drive the high ohmage HD800 to full blast until you say 2W is more than enough to do the job. Care to elaborate a bit more to untwist me? Now twisted like a tree trunk.

an AB amplifier is called AB because it is in class A for a tiny current (that is for loudspeakers it is) and then goes into B for every current above that value.
An amplifier is in class A as long as the drawn ACrms current is smaller then the idle current x 0.707

So when a class AB amplifier has an idle current between 50 mA and 100mA (which most designs have) the amplifier is in class A as long as the drawn current does not exceed the idle current.
a 40W class AB amplifier with a 'standard' idle current AND a 120 Ohm output resistor therefor can drive an HD800 to its absolute maximum ratings while remaining in class A.

Under normal LS operating conditions the amp is almost always in class B but as high-Ohmic headphones draw very little current even if large voltages are applied to it which this amplifier can it remains in class A and will not go over into class B as the current simply does not reach that level.

So in essence a class-AB amplifier intended for use with loudspeakers can drive a headphone to huge levels while remaining in class A when driving headphones.

a 40W into 8 Ohm amplifier can provide the voltage swing that is needed for the HD800 to reach 0.5W into the 300Ohm HD800.
So the amp may be specified as 40W into 8Ohm but when the headphone is attached and the amp is driven to it's maximum (so an 8 Ohm loudspeaker would draw 40W) the amp only delivers 0.5W into the headphone.

So a headphone amplifier that can reach the same voltage level as a 40W/8Ohm LS amplifier and is able to deliver 2W into headphones is MORE then enough to drive any 'normal' efficiency/impedance headphone.
This does not mean 2W into 8 Ohm as 2W into 8 Ohm as this is only 4V and a 2W/8Ohm amplifier would only be able to deliver 50mW (0.05W) into a HD800 and that's even without an added series resistor.

Not meaning air motion transformers, electrostatic speakers with transformers, certain types of ribbons e.t.c. These do need higher currents and have very low impedances.

[XTRProf]

Nov 19, 2010 12:31:18 GMT @solderdude said:

So a headphone amplifier that can reach the same voltage level as a 40W/8Ohm LS amplifier and is able to deliver 2W into headphones is MORE then enough to drive any 'normal' efficiency/impedance headphone.

This does not mean 2W into 8 Ohm as 2W into 8 Ohm as this is only 4V and a 2W/8Ohm amplifier would only be able to deliver 50mW (0.05W) into a HD800 and that's even without an added series resistor.

Alright, I'm beginning to catch the idea. But how can Alex's Class A 2W HA into 8 ohms provides the voltage swing of the 40 watter into 8 ohms here? So can I say this 2W 8 ohms Class A cannot provide the voltage drive to go full blast the HD800? Only the 40 watter into 8ohms can provide the full voltage swing for the HD800 300 ohms + 120 ohms setting resistor.

Maybe to make it clearer. Is the 40 watter Class AB into 8 ohms equivalent to Alex's 2W Class A into 8 ohms in terms of voltage swing needed for the HD800 to go full blast into 300 ohms + 120 ohms? If that is the case, 40W Class AB into 8 ohms = 2W Class A into 8 ohms. No wonder people are saying Class A always sound louder eventhough it's lower wattage than class AB.

[Deleted]

Only 2Watt was mentioned, not 2W in 8Ohm...

the 2 watt mentioned before was based on 20V supply voltage and 100mA idle current.
But this 2W is not the output power but the dissipated power by the amplifier on the small heatsinks. The output power is MUCH less.
It's not Alex's amplifier but a design from a DIY magazine Alex has done some modifications to or a jaycar kit don't know,(correct me if I'm wrong), never butted in as it is Alex's show (I sorta consider it that way).

the 20V that was mentioned however may not be correct at all (don't know, don't have the schematics).
Is it 20V before regulators ?
Is it +20 and - 20V (so 40V in total)
Is it +10V and -10V (in total 20V)
is the 100mA the actual current ?
can it also be driven into class B ?

So the 2W you can forget.

You only need the output voltage swing.
The current and thus power are of NO importance at these low currents.

An amplifier doesn't 'deliver' power (wattage) it only delivers output voltage, the current which must be delivered by the amplifier, is determined by the impedance (resistance) of the load (be it speaker or headphone).

Since power = voltage X current the power that is needed is determined by the output voltage, the current drawn by the load and the capabilities of the amplifier to deliver the 'asked' current.
The problem with amps lies in the fact that the currents drawn by speakers may be completely out of phase to the applied voltage (caused by crossover filters).
This is where power amps run into problems because they need to be able to deliver currents when the output voltage is 0V or inverse.

class A NEVER has problems with this as they can be considered a current reservoir that only redirects currents.

[toad]

Frans, you should write a book. You're explanations are excellent.

[Will]

Frans, nice clear explanations and very good reading, thanks.

For info, schematic is on page 4, but supply rail is now +/-20V (sounds better than +/-15V).

[Deleted]

O.K. thanks,

I expect it to deliver around 0.28W into an HD800 through the internal 68 Ohm output.
Should you replace this resistor or add values to come to 120 Ohm it will give 0.22W into 300 Ohm.
with 100mA the amp will be dissipating 4W per channel and the HD800 will always be driven in class-A

the maximum output voltage will be around 11Vrms for this amp.
In real life it will always be lower because of the output resistor.

[FritzS]

without wishing to get hooked up in an avalanche of requests. I'd be more than happy to order some psu boards from Jcar and post on to those Europeans having problems obtaining them. Austria no problemo let me know

I am interested for two ... for pcs.

Please send me a PM

Where you live?

[Deleted]

Nov 19, 2010 16:56:13 GMT FritzS said:

without wishing to get hooked up in an avalanche of requests. I'd be more than happy to order some psu boards from Jcar and post on to those Europeans having problems obtaining them. Austria no problemo let me know

I am interested for two ... for pcs.

Please send me a PM

Where you live?

Hi Fritzs

OK thats going to be no problem. I'll put you on the list. you are going to need 8 of 4700 magic suntan caps for the JLH also.

prices in good old UK pounds are

PSU Boards £5.25 each for nice boards and most of the parts required. for +5

4700uf 10v low esr caps £0.47p each for +10

both plus P.P and the possibility of import duty but i paid nothing last time so we will see.

some prices may go down if we have enough interest.

fritzs

I'm happy to stand the cost of your order and when it turns up here we can sort it out then. if the numbers get to big then it's pay up front time. the last order i had from them took just over 7days to arrive then there will be the post on time. don't worry about payment for now till i cry for help it's gonna be just fine.

for now I'm happy

I'll keep the list open for a week so any one who wants to jump in fell free. we have a VAT rise here in the UK so i want to get this one done before that happy day.

weeee're sinking fast.

take care

[Deleted]

JAYCAR GB LIST

er Me 4 PSU kits and 8 caps

Mr Fritzs 2 PSU kits and let me know if you want caps.

anyone else?

take care

[Will]

Nov 19, 2010 7:13:02 GMT XTRProf said:

Oh dear, I wanted that 15 watter as a HA. Anyway, still ok for what you had done so far as it's a class A amp. I will still support after all the work. Anyway, what's the difference between the topology fo the 2W and the 15 Watter?

Hi Chong,

Please don't feel you 'have' to have some pcbs just because you said you would. If you don't want a set then that's fine, and not a problem

The main differences are a difference in supply rail (one for power stage, one for the input stage, extra components for the output zobel (replaces the offset corrector) and also different pads for the output devices. There is also the dc blocking caps. So it's a pretty different board to do it properly.

[Will]

Nov 19, 2010 17:39:09 GMT @shaun said:

JAYCAR GB LIST

er Me 4 PSU kits and 8 caps

Mr Fritzs 2 PSU kits and let me know if you want caps.

anyone else?

take care

Nice one, Shaun!

I'll check my stock, think I need some magic caps...

[Will]

AROOGA!

BOM mistake..

C9 should be a 0.1uF film cap, not a 100uF electrlytic, bit of a difference...

I'll post an updated BOM later this weekend, with a bit more variety in components.

They are a guide though, as I know some of you enjoy part selection as much as I do

[Deleted]

I have just waded through the thread and have a couple of questions.

Firstly, on the JLHs, do the caps have be to uprated from eg 4700uf 10v to a higher voltage of 16v?, when the 20v PSU is used?

Secondly, have the Offset Correctors been incorporated on the latest main board or are they still seperate.

Thirdly, if I have this right, the main "section" count is...

18v-0v-18 30va transformer (or x2 18v 15 or 30va in dual psu)
psu (jaycar) board (x2 in dual)
Dual JLH (x2 in dual)
A Class boards x2
(Offset corrector x2 ?)

Then all your chassis mount hardware, vol pot etc.

Chris

[Deleted]

Nov 19, 2010 19:39:44 GMT Will said:

Nov 19, 2010 17:39:09 GMT @shaun said:

JAYCAR GB LIST

er Me 4 PSU kits and 8 caps

Mr Fritzs 2 PSU kits and let me know if you want caps.

anyone else?

take care

Nice one, Shaun!

I'll check my stock, think I need some magic caps...

Hi Will

let me know what you need and I'll add it to the order.

take care

[Deleted]

SC HA/Preamp - Background.
Just to clarify a possible misapprehension :
The original Class A amplifier that this project is based around,was from Silicon Chip of July 1998 . Douglas Self also published a similar design with striking similarities, that he called the "Load Invariant Amplifier"
An earlier version of the HA/Preamp actually used an emitter follower between the Differential Pair and the VAS stage , as in the Douglas Self design.
Additionally, before a JLH was used with the HA/Preamp, a FET was used as a current source in conjunction with the existing current source (Q3 and Q4) to further reduce ripple.It replaced the 8.2K resistor. With the addition of a JLH, this was no longer felt necessary.

Silicon Chip magazine did not publish either a Preamplifier or Headphone amplifier using the Class A design as a basis.

As the original Class A kits were readily available from both Jaycar and Altronics, I decided to use the same PCB and many of the components that came with the kit, and make modifications to it to suit my own requirements.
The HA/ Preamplifier is also DC coupled, and uses a Servo of my own design to make sure there is no DC offset at the output, as well as further improving performance.It has 2 very different time constants at it's input, to help counter sudden momentary changes in DC offset when an attenuator is used instead of a normal stereo volume control.
A close look at the schematics will show quite a few similarities, as well as some unique changes of my own, and alterations to some types of semiconductors used, as well as quite a few component value changes to better suit the much lower power requirements,
and much lower gain needed. The voltage measurements shown are to illustrate that although a Current Mirror is used, a well balanced differential pair is no longer balanced in a typical circuit.
When adjusted correctly, the voltage drop across the Schottky Diode and trimpot is equal to the difference between the 2 readings shown.The Schottky diode gives a degree of temperature compensation, which may not be strictly necessary with the HA/preamp, but in the case of the actual 15W/Channel amplifier, helps to ensure better tracking between each half of the differential pair, due to the huge variation in temperature of the amplifier from cold to fully stabilised.The heatsinks dissipate close to 100W of heat !

[FritzS]

Mr Fritzs 2 PSU kits and let me know if you want caps.

which caps could you offer?

electrolytics too?

I must make a part list over all ... PSU (2x), JLH (4x) and A class HA (2x) too

Which manufactures are recommend for

resistors
film caps
electrolytic caps
other BJT's (BC...)

for input caps I have some WIMA MKP4 10uF 100V 20% and WIMA MKT 10uF in my stock ... I must look in my »scrabble box« too

My preferred distributors in Austria are Distrelec, RS Components, Farnell (with low delivery costs)

[Deleted]

for input caps I have some WIMA MKP4 10uF 100V 20% and WIMA MKT 10uF in my stock ...

Friedrich
If the sources you will be using have no more than a few mV DC out of them (most do), you will not need Input capacitors.
Normal .6W 1% metal film resistors are suitable, but for those used in the current mirror and differential pair emitters, I would recommend getting a few extra, and matching them to each other.
The actual resistance value is not that important, but the matched values will ensure best results.
The electros and other capacitors are not critical in the amplifier PCBs themselves. Just don't use low ESR types.
Alex

[FritzS]

Nov 20, 2010 7:16:50 GMT @sandyk said:

Friedrich
If the sources you will be using have no more than a few mV DC out of them (most do), you will not need Input capacitors.
Normal .6W 1% metal film resistors are suitable, but for those used in the current mirror and differential pair emitters, I would recommend getting a few extra, and matching them to each other.
The actual resistance value is not that important, but the matched values will ensure best results.
The electros and other capacitors are not critical in the amplifier PCBs themselves. Just don't use low ESR types.
Alex

For input I could make two or a switch - with/without cap
My main sources, CD-SACD players use caps in their output (Marantz use two electrolytics in series - face to face)

Distrelec offers some Vishay MBB/SMA0207 0.4W +- 0.1%
RS Components offers Vishay BCcomponents MRS16, MRS25
docs-europe.origin.electrocomponents.com/webdocs/0d9a/0900766b80d9a016.pdf

Electrolytics - Nichicon and Panasonic available

[Deleted]

Nov 20, 2010 6:46:29 GMT FritzS said:

Mr Fritzs 2 PSU kits and let me know if you want caps.

which caps could you offer?

electrolytics too?

I must make a part list over all ... PSU (2x), JLH (4x) and A class HA (2x) too

Which manufactures are recommend for

resistors
film caps
electrolytic caps
other BJT's (BC...)

for input caps I have some WIMA MKP4 10uF 100V 20% and WIMA MKT 10uF in my stock ... I must look in my »scrabble box« too

My preferred distributors in Austria are Distrelec, RS Components, Farnell (with low delivery costs)

Hi Fritzs

I'm thinking of the 2 x Suntan 4700uf 10v caps which replace the 2200uf 10v on the JLH, 2 per board so you are going to need 8 of those for 4 JLH. if you want me to order you some let me know

i was also thinking that the smoothing caps on the reg will need to have a slightly higher voltage rating due to bumping up to the 18v TX. do we need to worry about the brand, quality and ESR of that cap or will any cap of reasonable quality do

my thoughts are that because that cap is behind the JLH it will be ''hidden'' (so to speak) from the amp circuit by the JLH.

so still learning and open to advice on this.

if we need suntans i can put them on the order list.

what do people think?

take care