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Old 15th December 2006, 12:39 PM   #1
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Default how about this amp

i'm about to build this amp for a school project http://www.redcircuits.com/Page2.htm
what do you think about the design, can it be improved, does it need to be improved? i'm not going for some hi power, i'd rather have better sound quality. i'm building this one, cause i can find all the components for it... i'm planning to run it from a pc, does it need a preamp, or maybe something to reduce the signal from the sound card?
any suggestions would be nice
cheers
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Old 15th December 2006, 12:56 PM   #2
lineup is offline lineup  Sweden
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Exclamation redcircuits Red Free Circuit Designs IRF530 HEXFET

this has been discussed and even warned a bit for
several times, several different years

the hookup, bad thing,
is that only a variable resistor R11 is used
to control the idle current in output stage

for your own safety and your transistor safety
you should, if you know how to:
Replace R11 with a VBE multiplier ( trimpot + transistor put onto heatsink, to sense high temperature )


This is highly important advice
if you use any of the specified IRF530 / IRF9530
or any other HEXFET, IRFxxx output FET transistors
And this warning is not only from me, but from others who had a look at this schematic.


For find more topics regarding this hazardous amplifier,
that is nothing to play with, for those who does not know these things mentioned:

SEARCH this Solid State forum: http://www.diyaudio.com/forums/search.php
Use Search Keyword like:
redcircuits
Red Free Circuit designs
HEXFET
IRF530
IRF9530


Regards
lineup
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Old 15th December 2006, 01:11 PM   #3
lineup is offline lineup  Sweden
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a
GOOD alternative:

Take a look at this well documented amplifier project, in details!
This is totally safe and sound
and besides one of the nicest articles I have ever seen
describing how to build a good amplifier
with reasonable output power
(not too much and not too little power WATT for normal speakers)

It is a fairly simple amplifier, even good for a beginner.
Still it is not so simple it is bad.
I am actually quite sure it is a very good amplifier!

Because reading those texts and see those details described
The Author might as well be a teacher
in A Power Amplifier School.

Click the image to open in full size.

The people of Denmark can make good amplifiers,
as well as loudspeakers ( VIFA and Scan-Speak! )

for sure!

25 W DIY Power Amplifier - Try something simple for a change
These pages are written and maintained by Mads K. Madsen, Denmark




Good Luck, pudge667
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lineup
Lineup Amplifier Laboratory
http://lineup.awardspace.com/
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Old 15th December 2006, 03:10 PM   #4
ilimzn is offline ilimzn  Croatia
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Default Re: how about this amp

Quote:
Originally posted by pudge667
i'm about to build this amp for a school project http://www.redcircuits.com/Page2.htm
what do you think about the design, can it be improved, does it need to be improved? i'm not going for some hi power, i'd rather have better sound quality. i'm building this one, cause i can find all the components for it... i'm planning to run it from a pc, does it need a preamp, or maybe something to reduce the signal from the sound card?
any suggestions would be nice
cheers
Yes it MUST be improved, the bias current generator (single trim pot) is DANGEROUS, if any IRF or IRFP part is used. It would work with something like a 2SJ162/2SK1058 pair but that will be very expensive (~110KN for each pair).
In fact, this schematic has been developed to use the 2SJ162/2SK1058 LATERAL MOSFETs and (pardon my language) some idiot has simply replaced the labeling with IRFxxx, and now it keeps popping up allover he internet. Whoever has done so has no idea anout how what type of MOSFET works. Vertical MOSFETs (like IRFxxx) must be temperature compensated or will spontaneously increase their bias current as they heat up until something goes up in smoke.
To fix this, and use IRF parts, you need tio do the following:
Remove R11 from the schematic.
Buy the following parts:
1) IRF510, 520, 610 or even another IRF530, call it Q10
2) One 2.5k trim pot, instead of R11
3) Two 1.2k resistors, call them R19 and R20
Replace R11 with the above, connected as follows:
1) Drain of Q10 and one end of R19 to collector of Q6 (and other components on schematic)
2) Gate of Q10 to other end of R19 and counter-clockwise side of R11 trimmer
3) Source of Q10 to clockwise side of R11 trimmer and colelctor of Q7 (and other components that conenct to it in the original schematic)
4) R20 between counter-clockwise side of R11 trimmer and wiper (middle pin) of R11 trimmer.
Initially put the trimmer in fully counter-clockwise position. This will put the idle current of the output transistors at zero. Turning clockwise will increase it to the desired current, this will still be between 50-150mA.
5) Q10 MUST be mounted on the same heatsink and in close proximity to the output transistors Q8 and Q9, because it must be at the same temperature.

Also, to prevent gate destruction f the IRF MOSFETs at overcurrent:
Get two zener diodes, 5.6-6.2V (small size is fine)
Connect the diodes in series (A of the first to K of the second)
Connect the free K lead of this series combination to gate of IRF530, the free A lead to the gate of IRF9530, and the middle joint of the two zeners to the output of the amplifier (joined sources of the IRF530 and 9530).
Again, this is needed because the original 2SJ162/2SK1058 for which the schematic was made, have internal zeners, but IRFxxx do not, so they must be added outside.

This should be enough for a good start. Even with these modifications it is far from the ideal amp, but I think it will be more than fine to amplify the output of a PC.
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Old 17th December 2006, 03:56 AM   #5
RSK is offline RSK  Malaysia
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Default Re: how about THIS AMP

Well just a suggestion. At this link,(http://www.pcpaudio.com/pcpfiles/pro...ic/public.html) all information on pcb artwork and adjustment to suit output power is listed.
Maybe one could find it as a good initial project.

Cheers,

RSK
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Old 17th December 2006, 04:09 AM   #6
lineup is offline lineup  Sweden
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Default Re: Re: how about THIS AMP

Quote:
Originally posted by RSK
Well just a suggestion.
At this link,
http://www.pcpaudio.com/pcpfiles/pro...ic/public.html

all information on pcb artwork and adjustment to suit output power is listed.
Maybe one could find it as a good initial project.
Absolutely.
Good link, RSK.
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Old 17th December 2006, 07:16 AM   #7
RSK is offline RSK  Malaysia
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Default Thanks, Lineup.

I made a search and found one of our member(Raka) has done it.(New Amp).Probably a good sounding piece of electronics.
Therefore its a proven design.

Cheers,

RSK.
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Old 17th December 2006, 11:57 AM   #8
Bonsai is offline Bonsai  Taiwan
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For circa 25W I'd try a gainclone. You can probably get the IC's off the Natsemi website as samples. If you go to the chip amp forum on this website, you'll find plenty of circuits and board layouts. These devices are easy to use and give superb performance for the effort. I've built two to replace the power amp section of a Marantz PM68 - great sound (I had to repalce the transformer as well since the PM68 has 57V rails and the Gainclone needed 25V).

If you want to build something with more power, then go discrete.

If you really want to go discrete in any event, try the JLH designs - search the forum - there are lots of memebers who have built this amp (10W only, but very good sound from what I've heard).


By the way, looking at the schematics on this thread, I'd agree with some of the comments - there are better designs out there.

Good luck.
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Old 19th December 2006, 12:37 PM   #9
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thank you for all your help people, guess i'm gonna go for K. Madsen's amp, it seems to be very well documented, and since you recommended it i'm gonna give it a try, and I seem to have the most of the parts for it at my disposal, so i won't spend much on building it!
if i have any questions about this amp, i'll ask here again
cheers
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Old 19th December 2006, 12:37 PM   #10
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ooops, i'm having some problems already...
how to open those *.prn files? the pcb layout is in *.prn and *.ps format for the madsen amp, i guess i don't have the right sofware?
any help plz?
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