Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th June 2013, 04:42 PM   #1
brlmat is offline brlmat  Romania
diyAudio Member
 
Join Date: Jan 2013
Default 250w 8ohm amplifier

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!

Last edited by brlmat; 19th June 2013 at 03:42 PM.
  Reply With Quote
Old 20th June 2013, 05:02 PM   #2
brlmat is offline brlmat  Romania
diyAudio Member
 
Join Date: Jan 2013
Guys, really sorry to bump this thread, but can someone please answer my question?
  Reply With Quote
Old 20th June 2013, 05:20 PM   #3
Struth is offline Struth  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: books at londonpower.com
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
__________________
London Power / Power Press Publishing
www.londonpower.com
  Reply With Quote
Old 20th June 2013, 06:34 PM   #4
amptech is offline amptech  Scotland
diyAudio Member
 
Join Date: Jan 2009
Location: Glasgow
Send a message via MSN to amptech
Just to add, I built a 300w per channel amp for the local studio from parts out junk pile cost me less than a 100.. So it pays to look about for such things like large heatsinks from junked power amps as there's plenty of parts to be had.

Regards A.
  Reply With Quote
Old 20th June 2013, 07:31 PM   #5
brlmat is offline brlmat  Romania
diyAudio Member
 
Join Date: Jan 2013
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.
  Reply With Quote
Old 20th June 2013, 08:25 PM   #6
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Quote:
Originally Posted by Struth View Post
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.
Have fun
Kevin O'Connor
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...?
  Reply With Quote
Old 20th June 2013, 08:29 PM   #7
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Quote:
Originally Posted by brlmat View Post
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.
50-0-50vac @1kVA will get you about 200- 230 watts RMS into 8 ohms before clipping...
  Reply With Quote
Old 20th June 2013, 08:30 PM   #8
brlmat is offline brlmat  Romania
diyAudio Member
 
Join Date: Jan 2013
I understand the PT stuff, mine is 2x50 vac 1kw but I can exchange it for one with more voltage, same power, for no more money. So what about the amplifier modules?
  Reply With Quote
Old 21st June 2013, 07:42 AM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
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.
__________________
regards Andrew T.
  Reply With Quote
Old 21st June 2013, 07:58 AM   #10
brlmat is offline brlmat  Romania
diyAudio Member
 
Join Date: Jan 2013
Yeah, I was thinking the same. Soooo, which amp sounds best? I have no idea which one to build.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
300-800W 8Ohm Sub Amplifier KostasTheGreat Solid State 24 29th June 2013 08:27 PM
8ohm resistor in series with 8ohm speakers for a 16ohm OT? Reidy- Tubes / Valves 8 10th January 2010 11:25 PM


New To Site? Need Help?

All times are GMT. The time now is 08:59 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2