tnx, nice advice!
p.s.
It looks like super Leach is set at a lower bias current than optimal ( from Leach site) ... if I understood correctly ..
but super amp approx. 30mA is enough it seems. If you take into account that many factory-made amplifiers have a very low quiescent current (not hi-end) .. 10mA or less ..
p.s.
It looks like super Leach is set at a lower bias current than optimal ( from Leach site) ... if I understood correctly ..
but super amp approx. 30mA is enough it seems. If you take into account that many factory-made amplifiers have a very low quiescent current (not hi-end) .. 10mA or less ..
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at such a voltage there will be quite a lot of heat at 75mA
yes humming transformers are annoying - i had one toroidal who was humming at high mains voltage. If the voltage was normal - it didn't buzz ... probably the core saturate . It all depends on the core material. i don't even know if there is a solution for that ..
yes humming transformers are annoying - i had one toroidal who was humming at high mains voltage. If the voltage was normal - it didn't buzz ... probably the core saturate . It all depends on the core material. i don't even know if there is a solution for that ..
Power conditioner. Not the stupid-expensive snake oil kind, but a pro unit designed for road use. Just get one with basic voltage regulation and severe over-voltage shutdown. The kind you use if you’re running a live sound rig off a generator or temporary wiring. Doesn’t need to be super precise, do anything special with the waveform or have a nanosecond response time. The mid-priced ones just have an autotransformer with multiple taps that change as needed and will do the job. Especially a good idea if you’re going to be cranking the bias way up in your amp, as it will have less tolerance to high line conditions.
If you mean the leach amp, the one I build is version 4.5
https://www.google.com/url?sa=t&sou...QIFRAC&sqi=2&usg=AOvVaw2Pi38P9BdHlwbDfF_Xo5RN
https://www.google.com/url?sa=t&sou...QIFRAC&sqi=2&usg=AOvVaw2Pi38P9BdHlwbDfF_Xo5RN
Cant believe I found this forum after 40 years
I built the original Leach LNF1A back in 1976 when I was a student.
Back then it was close to state of the art and being a bit of a perfectionist I matched Every part, every transistor, replaced all the poor capacitors with Silvered Mica and Polypropylene's. Removed the output protection, wound a custom power transformer with almost perfect regulation.
It was good them and it is still great now. Problem is I am not all that interested anymore but cant bring myself to bin it.......
What can I do with it now? got no idea....
I would like to pass it on to someone who will use and appreciate it.
If I lived in the USA no issues doing that... But in Australia not sure where to look....
I built the original Leach LNF1A back in 1976 when I was a student.
Back then it was close to state of the art and being a bit of a perfectionist I matched Every part, every transistor, replaced all the poor capacitors with Silvered Mica and Polypropylene's. Removed the output protection, wound a custom power transformer with almost perfect regulation.
It was good them and it is still great now. Problem is I am not all that interested anymore but cant bring myself to bin it.......
What can I do with it now? got no idea....
I would like to pass it on to someone who will use and appreciate it.
If I lived in the USA no issues doing that... But in Australia not sure where to look....
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I have always designed my own amplifiers, but I will credit the Leach Amp for being an early influence.
The fully-complementary "Low TIM" approach was state-of-the-art at the time that I became interested in audio. Prof Leach certainly changed amplifier design for the better.
Ed
The fully-complementary "Low TIM" approach was state-of-the-art at the time that I became interested in audio. Prof Leach certainly changed amplifier design for the better.
Ed
My first built-from-scratch amp including making PCB's was the Leach "Low TIM" amp. This was at least 40 years ago. I didn't think the Leach sound was anything special so I pulled out all the protection components. Best sound I had ever heard! - until I accidently shorted the speaker leads. The amp never sounded right after that.
My current amp is a built-from-scratch MOSKIDO including professionally made PCB's of my own design.
Thanks for the memories Ed.
My current amp is a built-from-scratch MOSKIDO including professionally made PCB's of my own design.
Thanks for the memories Ed.
Built many amps over the years that were generally limited to around 100WRMS per channel output but they all had a hard time controlling my speakers, as did 2 x Hafler DH-220 amps in a bi-amp configuration. Decided to build the Leach Super Amp to provide more speaker control and It's been doing just that and running flawlessly for about 12 years.
All parts are the original values including the output transistors, except for the transformers, the R13/R14 bias resistors were changed to 7.5k ohm (if I remember correctly) as the supply rails are +/-102VDC, and the C13,C14,C21,C22 capacitors connected from the DC supply rails to ground that were upped to 250VDC from 100VDC. These caps were a tight fit on the PCB.
Everything is enclosed in a 7U tall Hammond instrument cabinet to keep the power supply and transistors away from "little fingers" as the TO-3 cases are at rail voltages. The amp was load tested by running each channel into its own 60W incandescent light bulb at 60hz, 120VAC for 24 hours. The outputs got warm during testing but never hot.
I'm very happy with how it sounds but I am concerned that any bad behaviour from a marginal component at 102VDC supply rails will immediately toast the speakers, so I've recently started building a DC speaker protection circuit to try and mitigate that risk.
All parts are the original values including the output transistors, except for the transformers, the R13/R14 bias resistors were changed to 7.5k ohm (if I remember correctly) as the supply rails are +/-102VDC, and the C13,C14,C21,C22 capacitors connected from the DC supply rails to ground that were upped to 250VDC from 100VDC. These caps were a tight fit on the PCB.
Everything is enclosed in a 7U tall Hammond instrument cabinet to keep the power supply and transistors away from "little fingers" as the TO-3 cases are at rail voltages. The amp was load tested by running each channel into its own 60W incandescent light bulb at 60hz, 120VAC for 24 hours. The outputs got warm during testing but never hot.
I'm very happy with how it sounds but I am concerned that any bad behaviour from a marginal component at 102VDC supply rails will immediately toast the speakers, so I've recently started building a DC speaker protection circuit to try and mitigate that risk.
Since this thread has gotten bumped up, I am curious if people think there is still merit to keeping poles out of the audio band (a "Low TIM" amplifier avoids slew-rate distortion by not placing poles below 20KHz).
This is in contrast to the modern design practice of having a very low-frequency pole but insuring sufficient slew rate to cover non-linearities.
I feel that the "Low TIM" approach is more restrictive than necessary but does not get in the way of designing a good amplifier.
Ed
This is in contrast to the modern design practice of having a very low-frequency pole but insuring sufficient slew rate to cover non-linearities.
I feel that the "Low TIM" approach is more restrictive than necessary but does not get in the way of designing a good amplifier.
Ed