Hi all,
Drafance007: Thanks for posting pictures of your project! I just wanted to comment that it looks like the bias generator transistor T18 is mounted by itself on the PCB (?). This must be on the heatsink together with the output stage.
Also, PCB lines made using a marker pen can be a bit thin for the currents involved in a power amp. Perhaps you could reinforce the PSU lines with some copper wire?
An alternative way for making handmade PCBs is to cover the original blank copper surface in a layer of adhesive plastic, drill the holes, and then cut away the plastic with an x-acto knife where the copper is to be removed, leaving broad traces for high currents. This takes some time but gives good results, if the photographic method is not available.
Amp_man_1: Thanks for your comments. It is very interesting to hear if someone finds shortcomings in my design, in order that I can make improvements for future versions or new amp projects. However, I do not fully follow your points. For example, is a complementary output stage really a bad thing? It is not exactly an uncommon topology ?
The constant current source was shared in this design to keep the schematic simple. I have not had problems with this, but I may
very well consider other solutions for future projects.
Best wishes,
Marcus
Drafance007: Thanks for posting pictures of your project! I just wanted to comment that it looks like the bias generator transistor T18 is mounted by itself on the PCB (?). This must be on the heatsink together with the output stage.
Also, PCB lines made using a marker pen can be a bit thin for the currents involved in a power amp. Perhaps you could reinforce the PSU lines with some copper wire?
An alternative way for making handmade PCBs is to cover the original blank copper surface in a layer of adhesive plastic, drill the holes, and then cut away the plastic with an x-acto knife where the copper is to be removed, leaving broad traces for high currents. This takes some time but gives good results, if the photographic method is not available.
Amp_man_1: Thanks for your comments. It is very interesting to hear if someone finds shortcomings in my design, in order that I can make improvements for future versions or new amp projects. However, I do not fully follow your points. For example, is a complementary output stage really a bad thing? It is not exactly an uncommon topology ?
The constant current source was shared in this design to keep the schematic simple. I have not had problems with this, but I may
very well consider other solutions for future projects.
Best wishes,
Marcus
Commentable Thoughts
So Mr.Dimitri u think my thoughts are exaggerated self-appraisal type. OK thanx for these complements.
Friend Marcus I have 6 years of EXperience in Building Power amplifiers From 500W to 2000WRMS.
The thoughts I gave are based on my Expertise in fabricating Amplifiers. So take them in a way which is most suited to u.
I only comment when something is wrong in a circuit and
I am not that kind of a person who does self-appraises.
Regards
Ampman.
dimitri said:
So Mr.Dimitri u think my thoughts are exaggerated self-appraisal type. OK thanx for these complements.
Friend Marcus I have 6 years of EXperience in Building Power amplifiers From 500W to 2000WRMS.
The thoughts I gave are based on my Expertise in fabricating Amplifiers. So take them in a way which is most suited to u.
I only comment when something is wrong in a circuit and
I am not that kind of a person who does self-appraises.
Regards
Ampman.
well Marcus...as i allready wrote this is firs pcb i made and it passed very many test. The Bias transistor originaly was mounted on the heatsink but later i put it back on the pcb...couse i didn't want to lose it. You know how it is ehan working on several sides on several tables several amps 
You also may notes that there is no short-circuit protection...i put it away on prototype but i beleve that it works fine
The copper lines on the board are thick but they did survive averything ...even 2 ohm load.
Some day now i should get 300VA transformer and then i will have to made the original circuit with good semicondutors (mje340/350 instead bd139/140) etc etc.
only one question? I belive i can get the full power with less output devices than original (8 pcs)?
You also may notes that there is no short-circuit protection...i put it away on prototype but i beleve that it works fine The copper lines on the board are thick but they did survive averything ...even 2 ohm load.
Some day now i should get 300VA transformer and then i will have to made the original circuit with good semicondutors (mje340/350 instead bd139/140) etc etc.
only one question? I belive i can get the full power with less output devices than original (8 pcs)?
It's not right to say that something is wrong with a design, in fact there is no such thing as an absolute correct desing, as if this is the case then we wouldn't need to make designs after all and all the amps in the world would be the same (or similar for amps with different power handling).
And as of M250, first it's not single-ended, the shared current source is for simplicity (and maybe economy), and there are actually pros and cons for any output stage, be it complementary or compound. M250 is a reliable amp, is excellent for constructors, and therefore not claiming professional standards.
By the way, i'm not used to posting into forums/thread.
sascica said:
You can order direct from On-Semi - samples,
http://www.onsemi.com/site/products/summary/0,4450,MJE15030,00.html
up to 25 each and pay only US$20 shipping.
hi
vivek , didnt see whats happening in the amps section for some time
ive made the elektor circuit and have modified it to deliver above 300 w rms and have tested it to distruction to 1.65 ohms load
(basically i have added - para push pull tip s and have changed the pcb layout totally)
its a good performer to the cost ratio
though if you do not have pocket limitations go in for the mj 15004 mj 15003 amps
as the square wave responce of the tips in high frequency is of concern
suranjan
transducer design engineer
vivek , didnt see whats happening in the amps section for some time
ive made the elektor circuit and have modified it to deliver above 300 w rms and have tested it to distruction to 1.65 ohms load
(basically i have added - para push pull tip s and have changed the pcb layout totally)
its a good performer to the cost ratio
though if you do not have pocket limitations go in for the mj 15004 mj 15003 amps
as the square wave responce of the tips in high frequency is of concern
suranjan
transducer design engineer
i dont understand how the LTP current is set in this amp
http://www.astro.uu.se/~marcus/private/schm250.jpg
forgive my ignorance, but if the voltage drop across the green LED is 3.5 volts, then the current through the 715R resistor is
2.9/715 = 4.05mA...giving about 2mA per leg of the LTP...is this correct?
also, what is the peak current being provided to the VAS (i mean what sets the VAS current and how do you work it out?)...any help would be much appreciated
http://www.astro.uu.se/~marcus/private/schm250.jpg
forgive my ignorance, but if the voltage drop across the green LED is 3.5 volts, then the current through the 715R resistor is
2.9/715 = 4.05mA...giving about 2mA per leg of the LTP...is this correct?
also, what is the peak current being provided to the VAS (i mean what sets the VAS current and how do you work it out?)...any help would be much appreciated
can i run a quick check?
Erm, can i just ask a few quick q's.
Is the schematic posted on Marcus' website the now new and corrected with all sensible solutions included?
And any ideas to using mje21194/5's for the output stage?
(it just appears i have 25 of each...
also, i'm building some esp P68's for a school project to drive a pair of horn loaded kappa 15's subs for my active pa system. Would these M250's be better? plus i was planning on using the P68's for my tops... again would these be better? and if i used mj94/95's, why can the P68 kick out 500w at 4 ohms with only 8 paralelled output devices and this amp, with the same number of trannies can only manage 250? or is that just into 8 ohm?
Thanks again, and this really does look like a great amp!! Especially for those cheap *** students who cant afford crown and martin audio equip!
Matt
(a cheap *** student!)
Erm, can i just ask a few quick q's.
Is the schematic posted on Marcus' website the now new and corrected with all sensible solutions included?
And any ideas to using mje21194/5's for the output stage?
(it just appears i have 25 of each...
also, i'm building some esp P68's for a school project to drive a pair of horn loaded kappa 15's subs for my active pa system. Would these M250's be better? plus i was planning on using the P68's for my tops... again would these be better? and if i used mj94/95's, why can the P68 kick out 500w at 4 ohms with only 8 paralelled output devices and this amp, with the same number of trannies can only manage 250? or is that just into 8 ohm?
Thanks again, and this really does look like a great amp!! Especially for those cheap *** students who cant afford crown and martin audio equip!
Matt
(a cheap *** student!)
If Anyone is interested, I have done up a PCB Layout for the M250.
I can also make these PCB's.
You can Contact me through my website at: http://www3.telus.net/chemelec
Take care.........Gary
I can also make these PCB's.
You can Contact me through my website at: http://www3.telus.net/chemelec
Take care.........Gary
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