Smaller Leach Amp V1

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#961
Hi Terry,
I am using 1000VA 4*40Vac secondaries into +-45mF per channel and +-15mF on board. Three sets of nearly monoblocked stereo amps. I'm expecting 300w into 4r but it needs to be a moderate load (phase angle <=47degrees). (300w+300w)*1.5 = 900VA.
I am a believer in many // caps and brute force unregulated PSU. However I also believe that the voltage amp stages need all the help they can get so I will be going regulated upto the predriver. There are many who disagree and they might be right. You have a lot of amps have you started to form an opinion on which audio attributes come from which components/topology within.
 
#962
Hi Terry i am going to use a 1200 VA toroidal with 40,000uF
Per rail in my 2ch and in my 6ch i am using 2 X 2000VA toroidal with 40,000uF per rail per amp module, giving a total of 4000VA and 480,000uF. This should be more than enough for most loads.
The only thing is that its going to be waaaay to heavy. I have a double barrelled Leach (Leach super amp) which runs on +/-95VDC runnig on 1 1500VA toroidal and 50,000uF per rail it puts out 350wrms just before clip at 8 ohms and almost 500wrms at 4 ohms just before clip. It wheighs just over 45kg (almost 100 pounds) I initially ran it on a 1000VA toroidal which was ok at 8 ohms but clipped out too easily when i ran it on my 4 ohm speakers. Sounds alot better too now. Especially on the bottom end, seems more defined, to me anyway. Hope this has helped out a little.

Cheers

Bowdown
 
#963
Terry the difference in sound quality can be noticeable even at lower volumes on a non regulated amplifier. Regulating the front end will minimise the effect. Why don't you build a regulator that outputs the same voltage as the main supply and then compare what you hear when the front end is driven by the regulator and by the main supply.

Like I said in a previous post, just use a 317/337 combination and see if you like what you hear. If you do, sink more resources and then make the regulator better. all you'll need are two ic regulators, small bridge rectifier/ 4 diodes, 2x1000 UF @100v, 4 resistors, 2 diodes, 2x10UF@ 80V caps and 2x100UF @ 80V caps.
 
#964
Mikett said:
Terry the difference in sound quality can be noticeable even at lower volumes on a non regulated amplifier. Regulating the front end will minimise the effect. Why don't you build a regulator that outputs the same voltage as the main supply and then compare what you hear when the front end is driven by the regulator and by the main supply.

Like I said in a previous post, just use a 317/337 combination and see if you like what you hear. If you do, sink more resources and then make the regulator better. all you'll need are two ic regulators, small bridge rectifier/ 4 diodes, 2x1000 UF @100v, 4 resistors, 2 diodes, 2x10UF@ 80V caps and 2x100UF @ 80V caps.
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Hi Mikett,

Thanks for your response. Is there a schematic and/or diagram or foil layout for the regulator you are talking about? I just built the regulator for the A75. I replaced the Zeners for 12V models and used 100V caps. It is putting out 67VDC. I haven't had a chance to hook anything up to the boards yet as I am still working on getting everything mounted in the case. Right now I am planning on just using one regulator for both front ends and using two seperate bridges and filter cap pairs for the outputs. This will give me 54,000uF per side plus the 30,000uF on board. I guess we'll see how this sounds and go from there. I really hadn't thought about building some kind of powerhouse out of this amp. I'm still just trying to learn. Building different types/styles of amps has been working out well for me as I make new and different mistakes with each project and learn much from troubleshooting. It is not my plan to make mistakes, I just do. :xeye:


I initially ran it on a 1000VA toroidal which was ok at 8 ohms but clipped out too easily when i ran it on my 4 ohm speakers. Sounds alot better too now. Especially on the bottom end, seems more defined, to me anyway. Hope this has helped out a little.
Click to expand...

Hi bowdown,

May I ask where you are using that that you were listening to it at clipping? My P101 is only running at 67V rails and by the time I get it to clipping it is way too loud.

Blessings, Terry
 
#965
Think speaker efficiency and dynamic range. Your JBLs are probably pretty efficient so you are less likely to need lots of power. But on dynamic peaks you may still run into clipping.

For example, on Dire Straits "Money for Nothing" on the Brothers in Arms CD, the voltage peaks of drum solo in the beginning are about 30 times higher than the peaks just before them (eyball on the scope, mine doesn't record). This means if you have to use about 1/4 watt peaks on the intro for your desired volume, the amp wants to put out 225W peaks (power is proportional to the square of voltage into a constant impedance load) when the drum solo starts. If your amp cannot do this, it will clip.

This won't be the grungy sound of an overdriven PA with the clip light on almost steady. It will make the attack sound wrong, by adding distortion. If your amp has odd clipping behavior, such as sticking to a rail the sound of clipping may be more pronounced.

In a biamped system, clipping of the bottom end amp MAY be less noticeable becasue the HF distortion products do not reach the tweeter. Yet another reason to biamp, and you with all those amps handy. But I digress...
 
#967
On an unregulated power supply with a small transformer the track will have the drums sound flat and muffled and you won't get the sharp fast sounds it will sound duller and won't have the dynamics as drums should.. It's hard to describe but when I heard that track on a chipamp, the chipamp was instantly a no-go for me. It told me everything about that chip amp's muscle.
 
#968
Hi Bob,

I see what you are saying. That's probably why my P101 sounds so good. It doesn't seem to run out of room when the dynamics get wide.

I have given some thought to bi-amping. I used to do it all the time with PA gear. I'm still trying to learn about amps right now. When I feel a little more competent with them I will start digging into electronic crossovers and the like. My JBL's sound really good to me the way they are right now. I don't really want to tear into them right now. I'm sure the 4425's would benefit from bi-amping but I don't have time to change them right now.

On an unregulated power supply with a small transformer the track will have the drums sound flat and muffled and you won't get the sharp fast sounds it will sound duller and won't have the dynamics as drums should.. It's hard to describe but when I heard that track on a chipamp, the chipamp was instantly a no-go for me. It told me everything about that chip amp's muscle.
Click to expand...


Well I should have this up and playing by the weekend. I guess I'll see how much the regulation changes things. It should be easy to switch back and forth since the voltage is almost the same.

Blessings, Terry
 
#969
Mikett - I know exactly what you experienced with the chip amps. Leach vs LM4780

Of course the amp was clipping, my meter wasn't able to keep up with the peaks.

Terry - When you're ready to learn about active filters, check out Jens' site. His active filter one manual is well written and takes you through the calculations cookbook style. See also his active filter two manual for ideas on an adjustable crossover. There may be another MOX board buy looming.
 
#970
Hi Terry,
depending on where you live there appear to be two different definitions for bi-amping.
I was carefull in my reply to differentiate between active speakers and passive bi-amping.
Active speakers need electronic crossovers before the amps and a lot of skill and time to develop the crossovers and equalisation to get anywhere near the best out of the speaker units.
With passive bi-amping you do not need to tear anything apart and no need to design any extra gear.
Using the bi-wireable terminals on the back of the speaker, connect one amp to the treble terminals and another amp to the mid terminals. If available connect a third amp to the bass terminals.
Then just play the music.
One little word of warning:- if all the amps have the same gain then it is much easier to set the levels between each T/M/B speaker unit than when the amps have different gains.
A passive bi-amping arrangement will not achieve the potential performance of a well designed active system. But it might equal or even exceed the performance of an active system that has just used an electronic crossover without all the design expertise needed to optimise it.
The main advantages of passive bi-amping are less voltage loss in the cables feeding the drive units leading to less interaction between frequencies and reduced loading on each amplifier due to the rise in impedance of each leg of the crossover when out of the pass band. The reduced loading allows the amp to perform better particularly if the PSU is under designed, which is why I suggested that you try bi-amping.
Please try it with your choice of three amps and after you start reaching some conclusions tell us what you have learned (time for pay back).
 
#971
AndrewT said:
Hi Terry,
I am using 1000VA 4*40Vac secondaries into +-45mF per channel and +-15mF on board. Three sets of nearly monoblocked stereo amps. I'm expecting 300w into 4r but it needs to be a moderate load (phase angle <=47degrees). (300w+300w)*1.5 = 900VA.
I am a believer in many // caps and brute force unregulated PSU. However I also believe that the voltage amp stages need all the help they can get so I will be going regulated upto the predriver. There are many who disagree and they might be right. You have a lot of amps have you started to form an opinion on which audio attributes come from which components/topology within.
Click to expand...

Hi Andrew - I was just wondering - The wattages you have quoted. They are continuous?. If so I think the calcs may be a little optimistic. The wattages that I measured into power resistors were more like 128 into 8 and 240 into 4. That was running the rails @ 62 Volts. The traffo was a 750 VA 45-0-45. and there was 20mf in total for each channel

Am I missing something?
 
#972
BobEllis said:
Mikett - I know exactly what you experienced with the chip amps. Leach vs LM4780

Of course the amp was clipping, my meter wasn't able to keep up with the peaks.

Terry - When you're ready to learn about active filters, check out Jens' site. His active filter one manual is well written and takes you through the calculations cookbook style. See also his active filter two manual for ideas on an adjustable crossover. There may be another MOX board buy looming.
Click to expand...

Thanks Bob,

I'll check that out. We used to bi-amp our PA stuff all the time, but that was more for power. Saved on power amps by bi-amping. I'm not sure I prefered the way it sounded though. It was a lot tougher getting things set right because it added more variables. Passives are what they are and you just EQ around them. The PA I have now is bi-amped but it is enclosed in powered speakers and factory set.

Blessings, Terry
 
#974
Hi Terry Yeah i was using it at my house, yeah its pretty damn loud at that level but i dont normally listen to that level only when im mucking about,I did have a problem where my cd player was putting out approx 700/800mV unclipped but was not enough to get my amp output enough, so i am in the process of building a preamp, i think it will be heaps better with the preamp. The speakers i got are pretty insensitive i think about 86db/w or something shocking, Planning on building new ones that are more effecient.

Cheers

Bowdown
 
#975
Hi Byrd,
I am using a spreadsheet designed by Bensen to predict the output power and drive currents and looks at inductive loads relative to the temp derated SOAR.
I have tested a smaller amp running on 50.5Vdc rails unloaded that can output 110w into 8r and 200w into 4r continuous sine wave drive using only one pair of 150w output transistors. these results check out closely with the spreadsheet prediction.
I am surprised that you are showing 128w inro 8r on 62Vdc loaded rails. This peak output voltage is very low indicating to me that a lot of voltage is being lost somewhere. You should be getting at least 150w and maybe nearer 200w on those rails. high Re and long thin wiring and long PCB tracks might be a clue.
 
#978
AndrewT said:
Hi Byrd,
I am using a spreadsheet designed by Bensen to predict the output power and drive currents and looks at inductive loads relative to the temp derated SOAR.
I have tested a smaller amp running on 50.5Vdc rails unloaded that can output 110w into 8r and 200w into 4r continuous sine wave drive using only one pair of 150w output transistors. these results check out closely with the spreadsheet prediction.
I am surprised that you are showing 128w inro 8r on 62Vdc loaded rails. This peak output voltage is very low indicating to me that a lot of voltage is being lost somewhere. You should be getting at least 150w and maybe nearer 200w on those rails. high Re and long thin wiring and long PCB tracks might be a clue.
Click to expand...


The Hafler DH220 has 65VDC rails and is rated at 115W continuous into 8 ohm and 175W continuous into 4 ohm. It is a MOSFET amp if that matters.

Blessings, Terry
 
#980
still4given said:
It is a MOSFET amp if that matters.
Click to expand...

Matters even more that the Mosfets in a Hafler are Hitachi lateral devices.
These have a high resistance between drain and source(collector-emitter)Rds, compared to vertical mosfets.
Combined with emitter resistors, voltage drop at high output currents is higher, unless many are in parallel like Perreaux in Oz did.
With increasing output current the voltage from drain to source(Vds) goes up non-linearly, with constant voltage between gate and source(Vgs).
A Mosfet is self-protective as the resistance between drain and source becomes extremely high once the SOA line is crossed for longer periods, preventing 2d thermal breakdown.
 
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