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1st November 2001, 03:00 PM  #1 
diyAudio Member
Join Date: Oct 2001
Location: UW Stevens Point Campus

Could the Leach superamp be used to drive a 2 ohm load continuously? If so what mods would i need to make if any? I have plenty of power supply, capacitors, and heatsinking for the job. Can the pcb handle to extra current?
thanks Brian 
1st November 2001, 03:49 PM  #2 
diyAudio Member
Join Date: Nov 2001
Location: Ottawa, Ontario

Why not ask Leach himself? He is usually very responsive to emails.

1st November 2001, 06:24 PM  #3 
diyAudio Member
Join Date: Nov 2000
Location: Central PA, USA

There are *very* few amps that are comfortable driving a 2 ohm load. Amps that are capable of doing this (can probably be counted on one hand) are often prone to much higher distortion than they are with 4 or 8 ohm loads. What kind of speaker configuration do you have that you have arrived at such a low impedance?

1st November 2001, 06:58 PM  #4 
diyAudio Member

I haven't looked recently at Leach's page on his
higherpowered amplifier, but given a hefty power supply and heatsinking (I'd recommend a 'wind tunnel' heatsink and forced air cooling), it should tolerate lowimpedance loads. The output stage is seriesparallel. His lowerpower amplifier should work pretty well if you parallel an additional pair of output transistors and use MJ21194/21193 devices and perhaps up to a +/ 75 volt rail. Paralleling will improve distortion at high currents and help with the SOA, but there are limits quickly approached, so don't push it too hard. 
1st November 2001, 08:40 PM  #5 
diyAudio Member
Join Date: Oct 2001
Location: UW Stevens Point Campus

Eric,
I have a 3 ohm subwoofer that I would like to drive on a continuous basis. The reason I want to know if the amp could drive a 2 ohm load is that later I would like to drive two 4 ohm speakers in parallel. Thanks Brian 
19th December 2001, 02:31 PM  #6 
diyAudio Member
Join Date: Dec 2001
Location: Vantaa/Finland

Originally posted by Opie:
> I have a 3 ohm subwoofer that I would like to drive on a > continuous basis. The reason I want to know if the amp > could drive a 2 ohm load is that later I would like to drive > two 4 ohm speakers in parallel. This is what I've found out building Leach Amps, and while planning monstrous SuperAmps, but settling soon for a bit expanded version of the SuperAmp... The original Amp can drive 2 Ohms by default. The devices are either 16A or 20A, and the protection circuit allows a bit over 10A for each. The original Leach Amp would have no problem driving your 3 Ohm subwoofer. But at 2 Ohm (two 4 Ohm speakers in parallel) you'd have a problem if the impedance of the speakers ever goes below 2 Ohms. My friend has a Leach Amp with 6 power transistors instead of 4, and he drives happily two 4 Ohm subwoofers in parallel. The protection circuit limits current at full power if the load drops down to 1.35 Ohm. It would be "only" 2 Ohms with 4 transistors. Cooling is no problem here. He has a 0.4K/W heatsink in it. The Amp would easily handle any techno and bass he ever tortures it with, but he has added two 119mm fans just to be on the safe side. I once tried boiling water in a 3 litre ceramic pot, using sinewaves and ceramic resistors, with the amplifier. I could use full power into 3 Ohms safely for many minutes. The 545VA transformer got once so hot I got scared, but otherwise nothing went wrong. With music the heatsink gets barely warm, used into 2 Ohms, with full power, fans running slow, and for extended time. He gets a little more than 400W RMS into 2 Ohms. The Amp would still be fine  but not as cool  even with fans stopped. But you were into SuperAmp as far as I understood. Basically I'd guess it would put out 20A and then limit. That means a little harder load than 4 Ohms could be used. 93Vcc, theoretically 12V lost in the power devices, we are left with 81V noload output. With 2pcs 10 000uF for one channel, you have 64V peak into 4 Ohms. 510W RMS. The same into 3 Ohms results in 60V peak. 600W RMS, hard to tell if voltage or current limited. 400W into 2 Ohms, current limited. Doing the same with SuperAmp as my friend did with his Amp: 12 transistors for one channel. 30A peak current now possible. You have 700W RMS into 2 Ohm... voltage limited, surprise! With 2pcs 20 000uF in the power supply, ripple halves and you are current limited to 60V output, i.e. 900W RMS. Voltage limit would come at 64V, so it's quite balanced solution. For your 3 Ohm subwoofer (and 2*10 000uF) the figures are the abovementioned 60V and 600W RMS, only this time clearly voltage limited, current limit being quite far away. 68V and 770W RMS@3 Ohms with 2*20 000uF. My formulas are quite demanding, just like the experiment of cooking water with Leach Amp's output power. You can get these voltage and current ratings with 50Hz squarewave (or any frequency sinewave) in the mentioned cases if you want. After the frequency of sinewave rises above a certain limit, the demand for power supply capacitance halves within an octave, and is the same above that. Kimmo S. 
1st March 2002, 04:29 AM  #7 
diyAudio Member

2 Ohms not really an issue
Rather than drive a 2 ohm speaker, I use a bridged Leachamp to drive a 4 ohm load. I have also tested this on a bench supply. On the bench, I was cranking 900+ watts without limiting until I blew the 14 amp fuse... However, I have blown my share of transistors, as follows:
Output: 2 x MJ15003/4 Board: 1 x Q9 (MPS8099) Q9 is part of the protection circuit, and when it blew, so did 2 of the output transistors. This was a freak accident due to some noname transistor I used for the protection (at least I blame it on this). I have since switched to Motorola (On Semi). My current amp that I use to bridge has an interesting problem that developed after abusive bridged use into my monster 8 x 12" subwoofer speaker towers that I built. In nonbridged mode (4 ohms), NO problems occur. In bridged mode, some wierd clipping distortion occurs past 600 watts or so. I haven't taken apart the one (right) channel where this occurs to fix the clipping problem. Keep in mind that this is the leachamp, not the superamp. Summary: with a peak indicator and heatsinks on the transistors on the circuit board, I wouldn't be scared using this amp into a sub1ohm load. =DJSS= 
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