DC Servo MOSFET Amplifier

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I'm considering to remake this good old amps with some improvements...

If you do that please inform me! I have started to build this amp and in pictures down you can see what i did up til now.

The reason to build this amplifier was as for all APEX amplifiers: strong recomendation in long and reliable work of his amplifiers in hard and not forgiving environment,in places with a lot of cigarette smoke and high humidity like this one on picture:http://www.diyaudio.com/forums/atta...275115810-dc-servo-mosfet-amplifier-apex2.jpg

The other reason is comments like this one,from our friends that listened a lot (and more than that) high class amplifiers for a long long time,from people that know why they said the thing they said-i will try to translate from ex-YU to english:

"....the amplifier it self worked nice on a small voltage regulator (NAIM´s from Nap-140),it has plenty of power and it did not heated much. By the way,the amplifier draws about 30mA (works in class B) and it can be overdone in AB class although i haven´t had any regrats on the sound at that little time i have listened it. The DC offset was 1,7mV on one chanel and 1,1mV on the other-due to contribution of the small IC :)
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For home listening some parts can be omitted:R1 R2 C1 D1 D2,for R22 we put the trimer and BD139 put on a heatsink with output transistors-to convert it to AB class. The amp works at +/-56Vdc but it also can work at +/-35V-all checked!
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On the amps sound i haven´t find any objections,it works just fine!

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After some time i have finished it,the amplifier is in the box with bias set on 70mA per pair of output transistors. DC offset is (really OFF) at one chanel 1,1V and on the other 0V. The PSU is now +/-60V with 2 x 10 000uF. I needed to raise bias because of my loudspeakers(high sensitivity) but on the other loudspeakers everything is all right. It expects some better input capacitors,it has really a lot of power,excellent sound and it is fantastic high frequencies. It is really nice amp to be done!
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This is something i really did not expect from one essentially PA amplifier,it reminds me a bit on Vinton or even Hafler Trans-Nova. Hafler was with me for a long long time,excelent amplifier..."


The reason that i mostly believe in comments from people i know well on forums is that they don´t want to sell me anything,they are not working for anyone and not burdened with money.

This same friend of my said once that this amplifier has given to him a bit more than 200W of power at 4R load...all in all,great amplifier in progres for me,thank you Mile Slavković!
 

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Bias set on 120mA total (60mA / pair) and works with smps. At low power it sounds excellent,hope that this way it will stay at whole range of power. For now it looks great!
 

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theb0b asked me to put files of smps in this thread so here they are.

i used e33 from pc supply with 0,6mm diameter wire in primary and 0,7mm wire diameter at secondary winding.

first wind 20 rounds of primary,than insulation foil/copper foil/insulation foil,than both secondary 17 windings (2 x 17 copper 0,7mm),and than again insulation foil/copper foil/insulation foil,than remaining 20 windings of primary and again isulation foil+copper foil.

copper foils should have soldiered wires on them and when transformer is assembled those wires go to the ground.

transformer should be checked and rechecked many times if it has shorted connections between any of primary-secondary windings or between primary-secondary windings and copper foils,here are high voltages that are extreemly dangerous

transformer secondary should be connected as on picture below: A BC D where A and B are begining (A) and ending(B) of first winding and C and D begining (C) and ending (D) of second winding:so when you connect B and C that will be secondary ground and A and D will be connected to the bridge rectifier.

bridge rectifier is mentioned to be done with four double rectifier diodes,i used MUR1660 http://www.sirectifier.com/datasheet/Ultra Fast Recovery Diodes/MUR1660CT.pdf diodes because they are cheap and can transduce 16A each. on this pcb they are connected in paralell so they are capable to transduce 32A.

in input bridge rectifier there are four 470pF500V ceramic capacitors in paralel with each diode.

storage coil is in my case 47 rounds of 1,3mm diameter copper wire on two gray torus core,you should use at least 1mm diameter wire and about 40 rounds on two torus core and connect it to the smps in that way that current will flow in same direction in paralel wires so they have same direction of magnetising the torus core. than connect the storage coil to smps,turn smps on without any load and monitor do the switching fets tourn heated;if not all is all right,if they do than reduce a few round from strage coil and try again untill ther work without heating on non-loaded smps.

first pluging on to 235V do over 220V40W bulb in series with supply,and use safety glases;that IS MUST BE!

if all is all right you will get these measurings at this smps between + and - outputs:

107V / 0,25A / 26,75W

105,6V / 0,47A / 49,63W

105,6V / 0,62A / 65,47W

104,9V / 0,81A / 84,97W

104V / 1,88A / 195,52W

103V / 2,75A / 283,25W

102,8V / 2,85A / 292,98W

102,5V / 3A / 307,5W

100V / 4,1A 410W

at no load there will be a bit higher voltage but after 250mA and all to the 4A there will be about 7-10 voltage drop,and bear in mind that this is 300W smps so it has been tested with 30% overload in my case. not bad for a such simple device. if you can and have,put bigger capacitor instead 470uF400V ,that will give you much better stability of output voltage due to higher current load. also give to switching fets and secondary rectifier diodes proper heatsinks,best if you have cooling fan.

for the fan you can add three more windings of some thin copper wire (no need for more than 0,3mm diameter) and with separate fast diode rectifier+4,7uF capacitor you will get 12Vdc for the fan-that is how i finally did it.
 

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F100

Dear Sir Mile,

I'm going to try another lovely amp by you.

It is not finished yet.

Before that I need to clarify few things if you don't mind.

What if I use...
6R2/2W instead of 5R6 ?
0R27/5W instead of 0R22 ?

I used BC557 instead of BC556, (a bit low voltage ) hope it's ok

Any equals for
BC327 and BC337 ?
BF421 and BF422 ?

Can I increase the rail voltage up to 65 ? If so, of cause I have to change the rail caps. and what else ?

Thanks and best regards
Lycanlk
 

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Dear Sir Mile,

I'm going to try another lovely amp by you.

It is not finished yet.

Before that I need to clarify few things if you don't mind.

What if I use...
6R2/2W instead of 5R6 ?
0R27/5W instead of 0R22 ?

I used BC557 instead of BC556, (a bit low voltage ) hope it's ok

Any equals for
BC327 and BC337 ?
BF421 and BF422 ?

Can I increase the rail voltage up to 65 ? If so, of cause I have to change the rail caps. and what else ?

Thanks and best regards
Lycanlk

6R2/2W, 0R27/5 and BC557 is ok, for +/-65V use 2N5401 instead BC557 (pins reverted)
BC327/337 can be replace with BC557/547 and BF421/422 with MPSA42/92 but pins for colector-base is reverted.
Regards
 
Thank you!

6R2/2W, 0R27/5 and BC557 is ok, for +/-65V use 2N5401 instead BC557 (pins reverted)
BC327/337 can be replace with BC557/547 and BF421/422 with MPSA42/92 but pins for colector-base is reverted.
Regards

Thanks for the info. I will try it in this weekend and post my results. You have already published it on Facebook, its not finished though :)

Best regards,
Lycanlk
 
My Amp Does not work

Hi,

My amp doesn't work. Don't know whats wrong with it. Checked the voltage according to the schematic.

The schematic is different to the pcb as I marked in blue and red lines. Don't know what is the right one.

Where should I check for this in my amp?

Regards,
Lycanlk
 

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Hi,

My amp doesn't work. Don't know whats wrong with it. Checked the voltage according to the schematic.

The schematic is different to the pcb as I marked in blue and red lines. Don't know what is the right one.

Where should I check for this in my amp?

Regards,
Lycanlk

Amp use BC556 not BC546 and input GND must be connect to PSU GND with separate wire.
Regards
 
Yes, it works!

Thanks for the quick reply!

The mistake was not connecting the signal ground to the power ground.

Anyway I also found out, one of the 1N4007 was gone. I fixed it too.

Amp sounds good though I hear 50Hz hum at very low volume, probably due to not grounding properly.

Compared to others class AB amps which I have made , my F100 heat up quite high but not too high. Quite manageable. My next step is to increase the rail voltage.

What are the power ratings of this amp? Hope it can drive 4 ohms speaker under quite low voltage.

regards,
Lycanlk
 
Thanks for the quick reply!

The mistake was not connecting the signal ground to the power ground.

Anyway I also found out, one of the 1N4007 was gone. I fixed it too.

Amp sounds good though I hear 50Hz hum at very low volume, probably due to not grounding properly.

Compared to others class AB amps which I have made , my F100 heat up quite high but not too high. Quite manageable. My next step is to increase the rail voltage.

What are the power ratings of this amp? Hope it can drive 4 ohms speaker under quite low voltage.

regards,
Lycanlk

F100 can drive 4 ohms speakers with +/-55V rail voltage
Regards
 
From Post122
Old F100 schematic and pcb will be redesign.

Hi Mile,
I got a friend that needs to replace the amps in some powered speakers used in bar.
They are not very high power so 100W amp should be fine.

My question is, which of your amps would you advice for this purpose,
I was thinking about F100 or AX14, would you advice, or maybe you advice other amp?
I like the F100 because the output mosfets are cheap here, and that F100 has 2pairs (four) output devices compared to 1pair (two) outputs on AX14.
Amp will run from a 35Vac-0-35Vac transformer.

Another question is about heatsink.
Ive attached a picture of a heatsink I can get cut to any length at a good price.
It is 200mm wide with 40mm long fins, and cut to any length.
What length of this heatsink would you advice please,
Its going to be inside a powered speaker for bar, no fan

thanks
 

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35+35Vac is perfect for ~100W into 8ohms Power Amplifier.

Is the speaker 8ohms?
How many are there?
How are they wired up?
Do the speakers have transformers on there inputs?

A 50mm length will do one channel, if Ta is normal and you don't overload the amplifier.
80mm for heavier duty use on 1 channel.

For two channels the sink needs to be 4times taller.
It is cheaper to use two 50/80mm side by side or on opposite sides.
 
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