Well I just rejoined the forum after having been away.
Here are some pics from my 20+ year old LOW TIM III with fully regulated supplies for front and backend. You can see that the PS regs are over twice the size of each amp board and are located on the sides. Since the PS provides plenty of protection, the VI limiters are totally disabled on the Leach amp. Current is then pretty much limited by thermal buildup on the PS heatsinks so large transients are allowed. The PS also included foldback protection. Thus no output fuses were used as well. I recall feature was used once when one zener on the Double Barrel board failed early on. Only the input to the PS regulators are fused.
The same PS regs are in my Double Barrel Leach which was the predecessor to the Super Leach and runs 85V rails regulated down from 100V and using 2 500VA toroids per channel. Voltages were just lifted by adjusting the zeners within the circuit. The circuit used was the improved version where the output voltage was used to feed the reference voltages for the zeners, essentially the same trick that Walter Jung used in the super regs.
The boards was laid out by my friend whom I lost touch with over the years. It essentially followed the original patterns on Audio Amateur but incorporated the improvements suggested by Walter Jung.
I have two of these boards that I kept over the years that are unstuffed. I just don't think I will be making much anymore at least nothing too elaboarate, Just putting a chip amp into a case is now a task that doesn't interest me any longer and feels to be a chore. I just used a chip amp for a bedroom sub. That tells you. Also I am amazed that I did go to all this trouble over twenty years ago.
Young and Foolish?.... How about no Variac and just the smoke test!
Here are some pics from my 20+ year old LOW TIM III with fully regulated supplies for front and backend. You can see that the PS regs are over twice the size of each amp board and are located on the sides. Since the PS provides plenty of protection, the VI limiters are totally disabled on the Leach amp. Current is then pretty much limited by thermal buildup on the PS heatsinks so large transients are allowed. The PS also included foldback protection. Thus no output fuses were used as well. I recall feature was used once when one zener on the Double Barrel board failed early on. Only the input to the PS regulators are fused.
The same PS regs are in my Double Barrel Leach which was the predecessor to the Super Leach and runs 85V rails regulated down from 100V and using 2 500VA toroids per channel. Voltages were just lifted by adjusting the zeners within the circuit. The circuit used was the improved version where the output voltage was used to feed the reference voltages for the zeners, essentially the same trick that Walter Jung used in the super regs.
The boards was laid out by my friend whom I lost touch with over the years. It essentially followed the original patterns on Audio Amateur but incorporated the improvements suggested by Walter Jung.
I have two of these boards that I kept over the years that are unstuffed. I just don't think I will be making much anymore at least nothing too elaboarate, Just putting a chip amp into a case is now a task that doesn't interest me any longer and feels to be a chore. I just used a chip amp for a bedroom sub. That tells you. Also I am amazed that I did go to all this trouble over twenty years ago.
Young and Foolish?.... How about no Variac and just the smoke test!
Last edited:
Nice work Mikett,
do you have a schematic got the ps? Seems like you got a good run out of this. If this is 20yo low tim III, what is the current version upto? BTW I never use a variac. I normally double and triple check everything before firing it up, and usually take a break before rechecking so its not a mad panic to get it going. I find that I loose interest if I smoke something and it can take me several years to get back to it.
I think I will have to try the Holton reg, maybe have a crack at making my first pcb.
do you have a schematic got the ps? Seems like you got a good run out of this. If this is 20yo low tim III, what is the current version upto? BTW I never use a variac. I normally double and triple check everything before firing it up, and usually take a break before rechecking so its not a mad panic to get it going. I find that I loose interest if I smoke something and it can take me several years to get back to it.
I think I will have to try the Holton reg, maybe have a crack at making my first pcb.
Hi Bowdon,
I tried making a board but gave up due to other home and work related projects. I may dig the holton reg up again but Ive never actually designed a pcb and its not as easy as it may seem.
Ill post here if I ever get teh holton reg up and running, but feel free to join in and design a board yourself if you like.
I tried making a board but gave up due to other home and work related projects. I may dig the holton reg up again but Ive never actually designed a pcb and its not as easy as it may seem.
Ill post here if I ever get teh holton reg up and running, but feel free to join in and design a board yourself if you like.
To complete this thread after so many years. Dug out the monster after so many years.
This is the Predecessor to the super amp. The Leach Double Barrel it was called.
This amp has 4x 500VA transformers it is essentially Dual Mono, has dual 110 Volt rails regulated down to 85V. All transistors were matched including output ones. The current limiters are removed from the Leach circuit and it depends on the current foldback scheme on the regulator board. It can put out up to about 40A of current short term before the reg starts pulling back if it thermally starts to climb too much.
The voltage gain stage is fed via a separate feed from the PS. That way the current output and voltage fluctuations over the wire resistance does not modulate the voltage to the front end.
This remains a daily use equipment after 34 years. Astounding dynamics and punch. Drives a pair of B&W 802F. Also of same vintage.
You would think that the prior LOW TIM III amp with 750VA transformers and also regulated would be a similar sound signature. No. Not at all, the added transparency and muscle over the smaller Leach is easily heard though the fully regulated LOW TIM III is no slouch.
Never thought that I would still be using this 30+ years after it was created.
This is the Predecessor to the super amp. The Leach Double Barrel it was called.
This amp has 4x 500VA transformers it is essentially Dual Mono, has dual 110 Volt rails regulated down to 85V. All transistors were matched including output ones. The current limiters are removed from the Leach circuit and it depends on the current foldback scheme on the regulator board. It can put out up to about 40A of current short term before the reg starts pulling back if it thermally starts to climb too much.
The voltage gain stage is fed via a separate feed from the PS. That way the current output and voltage fluctuations over the wire resistance does not modulate the voltage to the front end.
This remains a daily use equipment after 34 years. Astounding dynamics and punch. Drives a pair of B&W 802F. Also of same vintage.
You would think that the prior LOW TIM III amp with 750VA transformers and also regulated would be a similar sound signature. No. Not at all, the added transparency and muscle over the smaller Leach is easily heard though the fully regulated LOW TIM III is no slouch.
Never thought that I would still be using this 30+ years after it was created.
Attachments
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.