Samuel Jayaraj;
Thanks for the reply on bridging the
AV800 / 1KW Holton amp.
I've spend the past few days
scanning all the solid state forum
for tid bits for my project. I did
find a thread where Holton
confirmed what you said to me
on briding (he hasn't replied to
my email yet - hehe).
Since I want to layout a circuit
board on CAD, I'm still scratching
my head as what extra circuits
to add for protection.
I read on this forum where people
have mixed feeling about using
output relays, between the amplifier
and speaker.
Do I really need protection circuits;
1. DC offset detector ?
2. Output short circuit detector ?
3. Heatsink temperature detector ?
4. Optional op-amp based input stage
with gain control (balanced), just
in case I don't have a pre-amp, I can
enable the extra input stage ??
5. Soft Start ? (not the same as
transformer inrush protector)
6. Fuse the rails, or use resettable
circuit breakers?
All the detector circuits control the
speaker relay.
The idea is to have a soft start
circuit that detects both rails, once
both rails have reached a pre-set
value, the speaker relay is enabled.
Items #1 - #3 above will interrupt
the relay and disable it if a fault is
detected. If item #6 fails, ie a rail
drops below preset, relay disables.
I think I will follow the 1kw design
methodology and use 20 output stage transistors per channel. The
PCB I'm estimating will be 4" x 8",
the transistor will solder on the edge
similar to a car audio amplifier. This would allow to mount 2 modules
side by side on a large slab of heatink
(4 modules per chassis, rack mount,
perhaps 8" height). This will give me
enough area to install PS tranny/caps
in the center of the chassis.
Other esoteric thoughts. What if
have a machine shop build an
interface plate out of copper that
I can mount the output stage
transistors directly to the copper
(via grease) with no insulator.
This interface plate will have all the
machined holes to mount the hardware and provide easy interfacing to any aluminum heatsink
desired. But, the copper interface
plate will have insulator when mounting to the aluminum heatsink
for electrical isolation. Will capacitance
between these two metals be an
problem ?
I hoping I can get some feedback
on these ideas because I'm scratching
my head as to how to implement
the circuit design for the detectors.
I'm collecting data from the archives,
the researching never ends - LOL
Final thought, I want to make
a 4 layer printed circuit board
like so.
Top Layer 1 - signal layer
Inner Layer 2 - Ground Plane
Inner Layer 3 - Pos and Neg Rails
Bottom Layer 4 - signal layer
Most components and routing
will be on the top layer, having
electrostatic protection from the
assosiated ground plane layer.
I want to use "buss bars", that
solder on the top layer, one buss
bar for ground, one for +V and one
for -V so I don't have to rely on the
PCB copper to carry all the current
(overkill design).
Feel free to throw ideas.....
Thanks for the reply on bridging the
AV800 / 1KW Holton amp.
I've spend the past few days
scanning all the solid state forum
for tid bits for my project. I did
find a thread where Holton
confirmed what you said to me
on briding (he hasn't replied to
my email yet - hehe).
Since I want to layout a circuit
board on CAD, I'm still scratching
my head as what extra circuits
to add for protection.
I read on this forum where people
have mixed feeling about using
output relays, between the amplifier
and speaker.
Do I really need protection circuits;
1. DC offset detector ?
2. Output short circuit detector ?
3. Heatsink temperature detector ?
4. Optional op-amp based input stage
with gain control (balanced), just
in case I don't have a pre-amp, I can
enable the extra input stage ??
5. Soft Start ? (not the same as
transformer inrush protector)
6. Fuse the rails, or use resettable
circuit breakers?
All the detector circuits control the
speaker relay.
The idea is to have a soft start
circuit that detects both rails, once
both rails have reached a pre-set
value, the speaker relay is enabled.
Items #1 - #3 above will interrupt
the relay and disable it if a fault is
detected. If item #6 fails, ie a rail
drops below preset, relay disables.
I think I will follow the 1kw design
methodology and use 20 output stage transistors per channel. The
PCB I'm estimating will be 4" x 8",
the transistor will solder on the edge
similar to a car audio amplifier. This would allow to mount 2 modules
side by side on a large slab of heatink
(4 modules per chassis, rack mount,
perhaps 8" height). This will give me
enough area to install PS tranny/caps
in the center of the chassis.
Other esoteric thoughts. What if
have a machine shop build an
interface plate out of copper that
I can mount the output stage
transistors directly to the copper
(via grease) with no insulator.
This interface plate will have all the
machined holes to mount the hardware and provide easy interfacing to any aluminum heatsink
desired. But, the copper interface
plate will have insulator when mounting to the aluminum heatsink
for electrical isolation. Will capacitance
between these two metals be an
problem ?
I hoping I can get some feedback
on these ideas because I'm scratching
my head as to how to implement
the circuit design for the detectors.
I'm collecting data from the archives,
the researching never ends - LOL
Final thought, I want to make
a 4 layer printed circuit board
like so.
Top Layer 1 - signal layer
Inner Layer 2 - Ground Plane
Inner Layer 3 - Pos and Neg Rails
Bottom Layer 4 - signal layer
Most components and routing
will be on the top layer, having
electrostatic protection from the
assosiated ground plane layer.
I want to use "buss bars", that
solder on the top layer, one buss
bar for ground, one for +V and one
for -V so I don't have to rely on the
PCB copper to carry all the current
(overkill design).
Feel free to throw ideas..... 
I'm in the process of building Holton's 400 watt symetrical amp and Im' gonna add a few more output transistors ...2 pair per channel. Holton doesn't have any more of the 800/1kw pcb's. If you are gonna make some...let me know...wink wink. 
I have suggested to Anthony Holton to make seperate driver and output boards. mainly because it'd probably be cheaper. If someone wanted to just buy the driver boards and make the outputs themselves, or has a different # of output they want to use etc. More flexible. Anyway, I'm working on ESP's protection circuitry right now trying to figure out the best way to implement it, and I know its NOT putting relays on the speaker outputs. I just don't like that idea. My idea is going to use fast bleeder resistors to bleed off the caps fast while simultaneously switching the power from the tranny to the bridge rectifier not off....but switch it so it goes through large resistors, so very very little power will be available to destroy the amp if something goes wrong. It'll also be fine for start up.... If I blow up my amp I'll let everyone know, but it seems like a good idea to me. I'll be using 30A DPDT relays...$10+ each. OUCH. Its worth it though. Again, if you are making a small run of 800-1kwatt pcb's...let me know. Make the driver boards seperate Later!
-Matthew K. Olson
I have suggested to Anthony Holton to make seperate driver and output boards. mainly because it'd probably be cheaper. If someone wanted to just buy the driver boards and make the outputs themselves, or has a different # of output they want to use etc. More flexible. Anyway, I'm working on ESP's protection circuitry right now trying to figure out the best way to implement it, and I know its NOT putting relays on the speaker outputs. I just don't like that idea. My idea is going to use fast bleeder resistors to bleed off the caps fast while simultaneously switching the power from the tranny to the bridge rectifier not off....but switch it so it goes through large resistors, so very very little power will be available to destroy the amp if something goes wrong. It'll also be fine for start up.... If I blow up my amp I'll let everyone know, but it seems like a good idea to me. I'll be using 30A DPDT relays...$10+ each. OUCH. Its worth it though. Again, if you are making a small run of 800-1kwatt pcb's...let me know. Make the driver boards seperate Later!-Matthew K. Olson
I've been reading the archives and
it seems that there is a 50/50 mix
on whether to use relays between
the amplifier and speaker.
What people say;
1. Some prefer a non mechanical
solution for reliability.
2. Some people worry about
contact corrosion over time.
3. Some people hear the sonics
of the relay inserted in the circuit.
4. Added cost.
What else ?
Item #1 above -> relay goes bad,
buy another ?
Item #2 above -> will a sealed
relay solve this ? Can we use
a DPDT relay, parralel contacts
for redundency ?
Item #3 above -> If you hear
the contact sonics, perhaps you
have the wrong relay that is
not cable of load ?
Item #4 -> not a factor for me.
it seems that there is a 50/50 mix
on whether to use relays between
the amplifier and speaker.
What people say;
1. Some prefer a non mechanical
solution for reliability.
2. Some people worry about
contact corrosion over time.
3. Some people hear the sonics
of the relay inserted in the circuit.
4. Added cost.
What else ?
Item #1 above -> relay goes bad,
buy another ?
Item #2 above -> will a sealed
relay solve this ? Can we use
a DPDT relay, parralel contacts
for redundency ?
Item #3 above -> If you hear
the contact sonics, perhaps you
have the wrong relay that is
not cable of load ?
Item #4 -> not a factor for me.
I just don't like the idea of sticking something in series w/ the output...regardless of how many amps it handles....sonically...who knows. Cost...well...whatever. Mechanically, should last a long time b/c all it is is an electromagnet and a spring and contacts, since it's sealed, should take YEARS to wear out. Can't wait to try it though.
-Matthew K. Olson
-Matthew K. Olson
The more powerful an amp gets, the more important is to have some sort of protection.thylantyr said:
I have used Schrack relays with silver contacts, worked now perfectly in 10 years!
Here is one secret trick we use at work:
We have a 2 x 8 A. Our load is 1-18 A. We never switch on or off when current flows (motor from batteries).
With help from a microcontroller we rapidly switches the relay on and off 5 times. After that the contact resistance is 1/3 -1/5 of the start value. This has worked very well and we didn't had to change the relay.
My recommendation is to use hardsilver contacts with no gold! Gold is weared down very fast. Normallly gold flashed, or plated contacts are for safety circuits if the relay is a non-signal relay.
A really cool relay type is the "rotating armature" from NAIS. They make small signal relays and bigger ones also. Beware of the price, not cheap....
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.