the 5pair MJL4281/4301 will give an easy 300W into 8ohm and although the 550W into 4ohm @ 60degree phase angle is outside the 100mS SOAR, many builders claim this is reliable. This is achievable on +-76Vdc.
I recommend a maximum target of 350W into 8ohm from +-82Vdc
or
450W into 4ohm from +-70Vdc.
These are both into 60degree phase angle and within the 55degC 100mS SOAR using +-45mF per channel and 4% regulation 600VA-750VA transformer.
I recommend a maximum target of 350W into 8ohm from +-82Vdc
or
450W into 4ohm from +-70Vdc.
These are both into 60degree phase angle and within the 55degC 100mS SOAR using +-45mF per channel and 4% regulation 600VA-750VA transformer.
Thanks Andrew
On the topic of SOAR, do you still have the calculations for triple slope protection circuit resistor values? I cannot find what I thought I'd saved. It would probably be helpful for others if you could post it. TIA
On the topic of SOAR, do you still have the calculations for triple slope protection circuit resistor values? I cannot find what I thought I'd saved. It would probably be helpful for others if you could post it. TIA
Andrewt, If you implement a good regulated front end at say 85 volts what would be the possible or probable output with 74 volt rails.
The nice thing is how easy it is to wire in the regulated frontend on this board.
Do cascode frontend topologies really sound that much better than what the low-tim offers?
I plan on building another set of these boards with twin 1kva trannies 50-0-50 and separate transformer regulated frontend. Then I will be broke!!
Tad
The nice thing is how easy it is to wire in the regulated frontend on this board.
Do cascode frontend topologies really sound that much better than what the low-tim offers?
I plan on building another set of these boards with twin 1kva trannies 50-0-50 and separate transformer regulated frontend. Then I will be broke!!
Tad
Tad - in the Low TIM the legs of the differentials from which the VAS receives its signal are cascoded.
As I understand it, the benefit of cascoding is to allow the emitter-collector voltage to remain more constant, which reduces voltage dependent capacitance effects and makes the device more linear, and capable of higher speed.
With bipolar outputs, there is no need for the front end rails to exceed the outputs by more than a volt or so (Vbe of the darlingtons). There is a school of thought that says that you want to have the front end clip before the output stage, so matching rails is appropriate. If you are thinking 85V unregulated you're on the right track.
Mosfets require higher front end voltages because their Vgs is typically 4 volts or so. It will take 4 or 5 volts more than the mosfet rails to fully turn them on.
As I understand it, the benefit of cascoding is to allow the emitter-collector voltage to remain more constant, which reduces voltage dependent capacitance effects and makes the device more linear, and capable of higher speed.
With bipolar outputs, there is no need for the front end rails to exceed the outputs by more than a volt or so (Vbe of the darlingtons). There is a school of thought that says that you want to have the front end clip before the output stage, so matching rails is appropriate. If you are thinking 85V unregulated you're on the right track.
Mosfets require higher front end voltages because their Vgs is typically 4 volts or so. It will take 4 or 5 volts more than the mosfet rails to fully turn them on.
Bob, In reading many hundreds of threads on this forum I have found that the Leach topology is consistantly rated amoung the top bjt amplifiers. I know how they sound -- quite good -- but what is in this particular design which makes it a standout? Overall it is not too terrible complex. I was steered toward this particular build by a comment Charles Hansen made to me about a year or so ago. He adamantly proposed I build one to suit my needs since the chipamps were wholly lacking. Thanks Charles.
I only hope the A-75 (almost finished)🙂 🙂 lives up to the same high ratings. It is a true work of art has more aluminum than a 747.
Next project a huge ribbon like Casey built aka. valvetude. It sure would be nice if we had 36 hours in a day and a few more sheckles. More time to play.
Tad
I only hope the A-75 (almost finished)🙂 🙂 lives up to the same high ratings. It is a true work of art has more aluminum than a 747.
Next project a huge ribbon like Casey built aka. valvetude. It sure would be nice if we had 36 hours in a day and a few more sheckles. More time to play.
Tad
Tad -
My guesses on the Leach sound:
Higher than typical emitter degeneration (D Self likes this). This leads to lower open loop gain = less feedback.
Also, the differential is loaded with resistors instead of current mirrors frequently seen in other designs. Ideal current mirrors have infinite impedance that results in higher gain for the stage they load. Higher open loop gain = more feedback
Split feedback path - I don't really follow how this works, but it is different from the typical global feedback from the output to the inverting input.
My A75s seem to be a little smoother on the top end with a hair more low level detail than the Leach. You'll have a nice cozy room with the heat it generates. Down there it is probably a winter only amp. 😀
My guesses on the Leach sound:
Higher than typical emitter degeneration (D Self likes this). This leads to lower open loop gain = less feedback.
Also, the differential is loaded with resistors instead of current mirrors frequently seen in other designs. Ideal current mirrors have infinite impedance that results in higher gain for the stage they load. Higher open loop gain = more feedback
Split feedback path - I don't really follow how this works, but it is different from the typical global feedback from the output to the inverting input.
My A75s seem to be a little smoother on the top end with a hair more low level detail than the Leach. You'll have a nice cozy room with the heat it generates. Down there it is probably a winter only amp. 😀
Bob,
Will the Superamp and universal front end project still be moving forward with prototyping in the near future, or should I be jumping in on the current group buy for the 10 transistor version??
P.S. Thanks for all your time and efforts !!
Will the Superamp and universal front end project still be moving forward with prototyping in the near future, or should I be jumping in on the current group buy for the 10 transistor version??
P.S. Thanks for all your time and efforts !!
Carl is collecting parts for the prototype. No promises on how long it will take him to assemble and test. I would count on 3-4 months (if not longer) before we are ready to go ahead with a buy.
It is 5 pair.
See Brutepuppy's accompanying photo in post 622 and AndrewT's comments in post 641.
See Brutepuppy's accompanying photo in post 622 and AndrewT's comments in post 641.
THE JENS RASMUSSEN LEACH CLONE 10 TRANSISTOR BOARDS ARE ORDERED AND PAID FOR. THEY SHOULD BE ARRIVING AT MY ADDRESS IN 30 DAYS.
I will be sending out invoices to all who have provided me with a Full Name, Street Address, Country of Origin, confirmation E-mail and total number of pcb's required.
Please try and send me payment before the boards arrive so I can send the credit card company full payment.
Enjoy, Tad
I ordered 20 extra boards so let me know if anyone else is interested.
I will be sending out invoices to all who have provided me with a Full Name, Street Address, Country of Origin, confirmation E-mail and total number of pcb's required.
Please try and send me payment before the boards arrive so I can send the credit card company full payment.
Enjoy, Tad
I ordered 20 extra boards so let me know if anyone else is interested.
Tad,
I see that I'm a little late getting in on this GB, but I am interested in 4 boards (2 pair). I will email you my information.
Thanks,
Wilson 😀
I see that I'm a little late getting in on this GB, but I am interested in 4 boards (2 pair). I will email you my information.
Thanks,
Wilson 😀
IMPORTANT CORRECTION TO POST 638
IN POST 638 I MISTAKENLY SAID THAT THE CURRENT GROUP BUY BOARD IS NOT SET UP FOR MPSA42/92 DEVICES
THE SILK SCREEN ON THE CURRENT GROUP BUY BOARD IS LAID OUT FOR MPSA42 AND MPSA92 DEVICES. IF YOU USE THEM FOLLOW THE SILKSCREEN.
IF YOU WANT TO USE BC546 AND BC556 ORIENT THEM OPPOSITE THE PACKAGE OUTLINE.
Sorry for any confusion - I had this board, the 6 transistor version and the upcoming superamp combination board BOMs open at the same time and got it mixed up. The upcoming amp is laid out for BC devices, MPSA will have to be reversed.
IN POST 638 I MISTAKENLY SAID THAT THE CURRENT GROUP BUY BOARD IS NOT SET UP FOR MPSA42/92 DEVICES
THE SILK SCREEN ON THE CURRENT GROUP BUY BOARD IS LAID OUT FOR MPSA42 AND MPSA92 DEVICES. IF YOU USE THEM FOLLOW THE SILKSCREEN.
IF YOU WANT TO USE BC546 AND BC556 ORIENT THEM OPPOSITE THE PACKAGE OUTLINE.
Sorry for any confusion - I had this board, the 6 transistor version and the upcoming superamp combination board BOMs open at the same time and got it mixed up. The upcoming amp is laid out for BC devices, MPSA will have to be reversed.
If I well understand this one is regular Leach with ten output,and not the Superamp (double barrel)