Hello everybody!
I'm looking forward to building a stereo amplifier to drive my 200-250w 8 ohm speakers. What I want is very clear audio, tight bass and very good frequency separation.
I've been looking at the Leach Superamp and Fet400. There's also this GX400 rev.1 ( GX400 rev.1 - 400W Audio Amplifier - Ultimele produse/proiecte Tehnium Azi - Comunitatea Tehnium Azi ) but i thought of waiting for revision 2 as the author promised it's maturity. Tho', it's only gonna be released later, maybe next year and I can't wait that long.
I'm also on a pretty tight budget with these. Something like 50-70 euros for both channels, amplifier only (i already have the preamp and other things such as transformer and so).
I can get IRFP240 (the ones used in fet 400 i think) and their "pair" for like 1,33 euros each (aka one irfp240 is 1,33 euros).
Thank you for your help!
I'm looking forward to building a stereo amplifier to drive my 200-250w 8 ohm speakers. What I want is very clear audio, tight bass and very good frequency separation.
I've been looking at the Leach Superamp and Fet400. There's also this GX400 rev.1 ( GX400 rev.1 - 400W Audio Amplifier - Ultimele produse/proiecte Tehnium Azi - Comunitatea Tehnium Azi ) but i thought of waiting for revision 2 as the author promised it's maturity. Tho', it's only gonna be released later, maybe next year and I can't wait that long.
I'm also on a pretty tight budget with these. Something like 50-70 euros for both channels, amplifier only (i already have the preamp and other things such as transformer and so).
I can get IRFP240 (the ones used in fet 400 i think) and their "pair" for like 1,33 euros each (aka one irfp240 is 1,33 euros).
Thank you for your help!
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Hi Guys
The largest expense will be the PT. For a 200W amp you need 200VA per channel minimum. You will find most transformer makers offer a standard line of dual-secondary PTs that will cover what you need: 40+40Vac at 200W or 50+50Vac for 250W. A bit higher would be better. Higher VA rating per channel would also allow for impedance dips. Look at what is offered and see if a dual-mono apporoach might be cheapest. It would certainly allow for best grounding and lighter amplifier packages if you further split it into true mono chassis.
The DC rails will be about +/-60V to +/-80Vdc. Use 100V caps. Snap mounts are the norm for the voltages and capacitances you will need. Fortunately, modern caps of high quality are both small in size and in price.
The chassis will be a large expense as well. You need significant heat sinking for such a large amp. Look at the SiliconRay chassis advertised on this forum. get the largest one that has heat sinks along the sides, keeping in mind the sizes of PTs you already looked up...
You can build something functional, or take it a step beyond to having good performance and low noise. Silicon prices have come way down, so even complimentary pairs of BJTs are maybe a few dollars per pair. IR mosfets of the usual numbers are similar in price. Note that the output devices and drivers, typical VAS as well, all have to be rated for the full supply range. With +/-80V, that is 160V total, so 200V devices as a minimum. No need to cascode with modern output devices. You expand the standard Leach amp both in voltage and in power output without cascoding. There is a thread about that elsewhere.
The electronics package will be inexpensive, dominated by the output devices which will be numerous. PT and metal work dominate the cost of every electronics project.
Have fun
Kevin O'Connor
The largest expense will be the PT. For a 200W amp you need 200VA per channel minimum. You will find most transformer makers offer a standard line of dual-secondary PTs that will cover what you need: 40+40Vac at 200W or 50+50Vac for 250W. A bit higher would be better. Higher VA rating per channel would also allow for impedance dips. Look at what is offered and see if a dual-mono apporoach might be cheapest. It would certainly allow for best grounding and lighter amplifier packages if you further split it into true mono chassis.
The DC rails will be about +/-60V to +/-80Vdc. Use 100V caps. Snap mounts are the norm for the voltages and capacitances you will need. Fortunately, modern caps of high quality are both small in size and in price.
The chassis will be a large expense as well. You need significant heat sinking for such a large amp. Look at the SiliconRay chassis advertised on this forum. get the largest one that has heat sinks along the sides, keeping in mind the sizes of PTs you already looked up...
You can build something functional, or take it a step beyond to having good performance and low noise. Silicon prices have come way down, so even complimentary pairs of BJTs are maybe a few dollars per pair. IR mosfets of the usual numbers are similar in price. Note that the output devices and drivers, typical VAS as well, all have to be rated for the full supply range. With +/-80V, that is 160V total, so 200V devices as a minimum. No need to cascode with modern output devices. You expand the standard Leach amp both in voltage and in power output without cascoding. There is a thread about that elsewhere.
The electronics package will be inexpensive, dominated by the output devices which will be numerous. PT and metal work dominate the cost of every electronics project.
Have fun
Kevin O'Connor
Thank you for your replies. As I stated earlier, I already have everything but the modules. The transformer is 2x50v 1 kw, the case is actually a modifed suitcase (it housed an amplifier before but I toasted it) and the radiators I have are from the command pcb of a dead cnc. They are incredibly big. So what I need are the amplifiers and the filtering capacitor which I already found, I just have to buy them.
So, which amp sounds best? I was also thinking about the leco amp, just with fewer transistors as I don't require it to work with a 2 ohm load and at so high power.
Looking forward to hearing from you.
So, which amp sounds best? I was also thinking about the leco amp, just with fewer transistors as I don't require it to work with a 2 ohm load and at so high power.
Looking forward to hearing from you.
Correct, PT cost is the highest. On the required voltage... 40+40vac is not going to give him anything close to 200w @ 8ohms... more like 150-160w in real life. I have a 1.2kVA 43-0-43vac and that barely touches 190w at clipping... a 400va unit will probably do 130w 8 ohms.
50-0-50 vac will definitely do 200w... as long as it is a beefy PT. These are real world estimates, not theoretical models.
If he wants 250w, I'd suggest a minimum of 78vdc rails, which calls for a 56-0-56vac PT.
These numbers assume a bit of headroom and not absolute minimum RMS power required...
Other examples:
Adcom GFA 555ii 60-0-60vac +/-84vdc 700va PT = 280 watts 8 ohm at clipping.
GFA-565, same rails, but single 1.2kva PT = 370 watts at clipping
Forte Model 3 56-0-56 78vdc 800va, 245 watts at clipping 8R.
Kenwood Basic M2a 65-0-65vac 92vdc 247 watts At clipping 400va PT.
So rails aside... the regulation offered is what will determine power... perhaps you meant fully loaded rails...?
50-0-50vac @1kVA will get you about 200- 230 watts RMS into 8 ohms before clipping...
Don't go any higher than your existing 50+50Vac.
You will need 80Vdc smoothing caps.
If you go higher you will need 100Vdc smoothing caps.
If you build the PSU and amplifier properly, i.e. you take care not to cripple the current output, you will easily hit your 250W into 8r0 target. Your supply rails are likely to be between +-70Vdc to +-73Vdc.
250W into 8r0 is equivalent to 63.2Vpk. That leaves you a margin of 7 to 10V for PSU sag and losses through the amplifier and wiring.
You will need 80Vdc smoothing caps.
If you go higher you will need 100Vdc smoothing caps.
If you build the PSU and amplifier properly, i.e. you take care not to cripple the current output, you will easily hit your 250W into 8r0 target. Your supply rails are likely to be between +-70Vdc to +-73Vdc.
250W into 8r0 is equivalent to 63.2Vpk. That leaves you a margin of 7 to 10V for PSU sag and losses through the amplifier and wiring.
I wanted to edit my last post, but i couldn't. AndrewT, my caps are 160Vdc (6X10.000uf) with 22k drain resistors across the rails.
Now back to the modules
). Which should i build? Leach Superamp? FET400? GX400 rev1? Any other one? Please, answer this question as i have been stuck with this amplifier open on my desk for a month.
Thank you!
Now back to the modules
). Which should i build? Leach Superamp? FET400? GX400 rev1? Any other one? Please, answer this question as i have been stuck with this amplifier open on my desk for a month.Thank you!
Agree with T Andrew on the psu rails, also some designs push things far to close for caps take the pro sound amps that used 80 volt rails and the poor caps was 6800uf at 80v the top of it was ready to pop with bad hum in the sound... Always use higher Dc rated caps to stop this kind of thing happening.
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Thank yo. Tho' the problem is I can't listen to many good amps round here. What I can relate to is a Technics sa-ex310 home amplifier and in my opinion it sounds good, not excelent, alittle distorted in the mids and a little bit unnatural, but ok. Also, I think that an MC Crypt Pa-5000mkii sounds like ****.
I tend to agree instinctively with your rule. I normally think it in the very simplified way you need a pair of the best SOA BJTs (like the 1st an the 3rd you mentioned) every 100 watts on 8 Ohm.
BUT... Is that rule of the thumb always valid or can it be scaled down with forced ventilation? I am wishing to put some trust on 2 pairs of 15003/4 doing 250W/8 with let´s say a Papst 5" blower in front of the H/S.
And a side note. Unfortunately the rule does not scale well. Going up with the pair numebers (more than 5-6 IMO) the differences in temperature zone on the H/S and/or hfe matching demand even more conservative approaches.
For those that really like to go so up in the OP count in a class AB design.
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