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Leach Amp pcb group buy interest

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T

tryonziess

Member
Joined 2007
Brian,
Thanks for this bit of information. It must have taken a good bit of your time to compile this plot. I have substituted my rail voltage and Re values plus the 6 pair output and the current level is survivable. I doubt, while using music as the source, anything will begin to approach critical and still have your hearing intact.

In Dr. Leach's original Super Leach layout he pushed the rails to 93 volts and was able to maintain stablity and accuracy. Applying those methods to this layout should garner a degree of success.
I have been wanting any questions regarding the protection circuit to be cleared up before beginning a new group buy. It is hard to change once the copper is cut out of the pcb. Most of this is beyond my area of knowledge and trust to others for insight.


Tad
 
L

Luke

Member
Joined 2001
Hi Tad,

long time no talk. Did you complete you 12 trannie leach amp yet Im just wondering what protection you used and if you have stress tested it?
Im also curious to know how it sounds. I should begin mine soon, just finishishing off my current project and tossing up wether I build the Leach or buffalo32 next.
 
T

tryonziess

Member
Joined 2007
Luke,
I do not have an extremely sophisticatied setup for testing the amp projects. I have completely populated two of the Leach 12 clone boards and connected them to a crude power supply. The first attempt, with way too much bias, smoked the protection circuit. I removed the two resistors which supply feedback to the circuit and everything works O.K. I have quite a bit of 60 Hz. noise which I think is from the exposed crude wiring and such.

Since experimenting with this Bob Ellis and Brian have supplied some enlightening information concerning the protection apparatus. With my current setup 70 volt rails and .33 ohm emitter resistors I will try to calculate what substitutions I will need to get the most from this project.

I have backed off for now and think it is time to assemble the Dantimax remote FM tuner before doing anymore amp projects. I need to get some source hardware completed to my liking including a nice enclosure for the stepped attenuator unit.

I am also going to try and gauge interest in another Group Buy for this Leach 12 project in about another week or so. If we can get some more input on the protection circuit layout for all of the different voltage builds it would help those during assemble phase. I truly wish I had a setup to stress the Leach 12 to the max. I would like to see how much it can withstand.

Tad
 
BobEllis

BobEllis

Member
Joined 2003
Thanks, Brian.

Pingrs said:
In a belated response to Bob Ellis’s plea for a sanity check on his spreadsheets (and since to my knowledge no-one else has taken it on), here’s my two-pen’orth.

Load Line:

(As devised by David Eather and “Excelled” by Ben Janssen)

Cell B9 should read SQRT(2*B7/B5)..

Leach protection file

The lack of the volt drop across the emitter resistor in Bob’s spreadsheet renders the locus somewhat inaccurate. I’ve corrected that in my spreadsheet. Also, I’m not sure that a negative Vce can occur at the positive side of the output stage (or is this merely to allow higher Vcc’s to be displayed?). And the Vce plot should extend all the way to the 2Vcc limit*. I’ve also cleared up some (to me) confusion over designations. Note that only three points are needed to establish the complete protection boundary with such a simple scheme.

I’ve shown Protect_Locus_2 to emphasise the wisdom of including R13 in the protection scheme (the macro for this is not shown here). This enables the horizontal section in Locus_1 to slope below the 250ms SOAR, given suitable resistor values, something that cannot be done with the original Leach scheme. Now, nowhere does the protection locus violate this curve. The load lines may, of course, but that can be avoided by increasing the number of output pairs if the same power is to be achieved.

These schemes have serious limitations at this high(ish) supply voltage since using D1 referenced to 0V makes the break point Vce invariant at around 59V (for a 60V supply). Things get much, much worse when 70-80V rails are mooted. Here a variable break point or better still a triple locus is favoured, but that will require additional component locations on the pcb.

Nothing here is new, but a spreadsheet that instantly shows the effect of varying the supply voltage and resistor values superimposed on the SOAR and load line takes a lot of the headache out of choosing a protection locus.

If you see any errors let me know!


Brian.


*Ref. Michael Kiwanuka: Transparent V-I protection in Audio power Amplifiers (EW Sep-Oct 2002)
Click to expand...
 
a.wayne

a.wayne

Member
Joined 2008
Tad,

What is the lowest PSU Voltage possible to operate the Leach 12 as currently configured ..

regards,

tryonziess said:
Luke,
I do not have an extremely sophisticatied setup for testing the amp projects. I have completely populated two of the Leach 12 clone boards and connected them to a crude power supply. The first attempt, with way too much bias, smoked the protection circuit. I removed the two resistors which supply feedback to the circuit and everything works O.K. I have quite a bit of 60 Hz. noise which I think is from the exposed crude wiring and such.

Since experimenting with this Bob Ellis and Brian have supplied some enlightening information concerning the protection apparatus. With my current setup 70 volt rails and .33 ohm emitter resistors I will try to calculate what substitutions I will need to get the most from this project.

I have backed off for now and think it is time to assemble the Dantimax remote FM tuner before doing anymore amp projects. I need to get some source hardware completed to my liking including a nice enclosure for the stepped attenuator unit.

I am also going to try and gauge interest in another Group Buy for this Leach 12 project in about another week or so. If we can get some more input on the protection circuit layout for all of the different voltage builds it would help those during assemble phase. I truly wish I had a setup to stress the Leach 12 to the max. I would like to see how much it can withstand.

Tad
Click to expand...
 
BobEllis

BobEllis

Member
Joined 2003
Assuming that you have a string of 2x20V zeners in the front end, you should run at least 45-50V. Reduce the values of the zeners so that the cascode reference is lower and you can reduce the rails. I don't think I'd go much lower than 20V total for the zeners and 30V rails, but that is a number pulled from the air. When calculating the resistors feeding the zeners, change the "40" in the equation to the total of your zener string.
 
L

Luke

Member
Joined 2001
hi Tad,

I bought some surplus resistors and built 8ohm and 4ohm loads,I can pretty much test to 100 watts safely, I have no idea what these will resist, but given they are 1 inch diameter by 4 inches long I'm picking 100watts easy.

I like the idea of a spareset of boards, but its going to be awhile yet before I build these up. Im far too slow.
 
S

spookydd

Member
Joined 2012
JCWagener said:
Hi people,

I searched but could not find anything. Are there any Leach designs that make use of SMT and double sided boards?
Click to expand...

The boards layed out by Jens are double sided, but how would you solder your smt parts?

I don't think many diyers are able to handle smt soldering, especially not me, I'm getting too old for this and my hands and eyesight can no longer manage.:eek:
 
P

prairiemystic

Member
Joined 2004
I looked into doing an SMT version of the Leach low-TIM amp, but found it wasn't worth it. Most of the PCB room is used up by output transistors and capacitors. The VAS and many 1/2W-1W power resistors are no smaller in smt, especially after the heat calculations and extra copper for cooling.

You could put the (smt) diff-amps on a daughter-card but it only saves 1-2", which I might do if I make a car amp. Matching SOT-23 transistors is a bit tedious, and nobody likes to change a D2PAK...
 
S

spookydd

Member
Joined 2012
prairiemystic said:
I looked into doing an SMT version of the Leach low-TIM amp, but found it wasn't worth it. Most of the PCB room is used up by output transistors and capacitors. The VAS and many 1/2W-1W power resistors are no smaller in smt, especially after the heat calculations and extra copper for cooling.

You could put the (smt) diff-amps on a daughter-card but it only saves 1-2", which I might do if I make a car amp. Matching SOT-23 transistors is a bit tedious, and nobody likes to change a D2PAK...
Click to expand...

The main thing is that most diyers just wouldn't be able to handle soldering on those tiny smt parts. I certainly couldn't.
 
S

spookydd

Member
Joined 2012
Pingrs said:
In a belated response to Bob Ellis’s plea for a sanity check on his spreadsheets (and since to my knowledge no-one else has taken it on), here’s my two-pen’orth.

Load Line:

(As devised by David Eather and “Excelled” by Ben Janssen)

Cell B9 should read SQRT(2*B7/B5)..

Leach protection file

The lack of the volt drop across the emitter resistor in Bob’s spreadsheet renders the locus somewhat inaccurate. I’ve corrected that in my spreadsheet. Also, I’m not sure that a negative Vce can occur at the positive side of the output stage (or is this merely to allow higher Vcc’s to be displayed?). And the Vce plot should extend all the way to the 2Vcc limit*. I’ve also cleared up some (to me) confusion over designations. Note that only three points are needed to establish the complete protection boundary with such a simple scheme.

I’ve shown Protect_Locus_2 to emphasise the wisdom of including R13 in the protection scheme (the macro for this is not shown here). This enables the horizontal section in Locus_1 to slope below the 250ms SOAR, given suitable resistor values, something that cannot be done with the original Leach scheme. Now, nowhere does the protection locus violate this curve. The load lines may, of course, but that can be avoided by increasing the number of output pairs if the same power is to be achieved.

These schemes have serious limitations at this high(ish) supply voltage since using D1 referenced to 0V makes the break point Vce invariant at around 59V (for a 60V supply). Things get much, much worse when 70-80V rails are mooted. Here a variable break point or better still a triple locus is favoured, but that will require additional component locations on the pcb.

Nothing here is new, but a spreadsheet that instantly shows the effect of varying the supply voltage and resistor values superimposed on the SOAR and load line takes a lot of the headache out of choosing a protection locus.

If you see any errors let me know!


Brian.


*Ref. Michael Kiwanuka: Transparent V-I protection in Audio power Amplifiers (EW Sep-Oct 2002)
Click to expand...

Hi,

I was just looking at that sheet and it has several external links that can't be resolved.

Perhaps it might be better to include the external sheets into this one in a single sheet to avoid dead links.
 
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