A bit of a belated response here...

lid wrote:
Colin,

SUCCESS! Experience has taught me a good troubleshooting strategy for these amps
and the first 4 transistors are almost always the main culprits when too much DC
offset is present. And, as you found, the solution is relatively simple for those
who have good soldering skills.

Indeed, success at last! My soldering skills were a bit rusty, but have
come back with a vengeance. My next plan is to replace my crappy iron
with a nice new station (Weller WES51, or Hakko 936--any opinions folks?)
and then start putting all of my other projects back together.

As an aside, this amp may be up for sale before too long. Just a heads
up.

Thanks again, everyone who helped.

Colin

"Colin B." wrote:

A bit of a belated response here...

lid wrote:
Colin,

SUCCESS! Experience has taught me a good troubleshooting strategy for these amps
and the first 4 transistors are almost always the main culprits when too much DC
offset is present. And, as you found, the solution is relatively simple for those
who have good soldering skills.

Indeed, success at last! My soldering skills were a bit rusty, but have
come back with a vengeance. My next plan is to replace my crappy iron
with a nice new station (Weller WES51, or Hakko 936--any opinions folks?)
and then start putting all of my other projects back together.

As an aside, this amp may be up for sale before too long. Just a heads
up.

Thanks again, everyone who helped.

Colin

Colin,

What about the temperatures of both the left and right heat sinks? Have they begun to
be similar? FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"

"Colin B." wrote:

A bit of a belated response here...

lid wrote:
Colin,

SUCCESS! Experience has taught me a good troubleshooting strategy for these amps
and the first 4 transistors are almost always the main culprits when too much DC
offset is present. And, as you found, the solution is relatively simple for those
who have good soldering skills.

Indeed, success at last! My soldering skills were a bit rusty, but have
come back with a vengeance. My next plan is to replace my crappy iron
with a nice new station (Weller WES51, or Hakko 936--any opinions folks?)
and then start putting all of my other projects back together.

As an aside, this amp may be up for sale before too long. Just a heads
up.

Thanks again, everyone who helped.

Colin

Colin,

What about the temperatures of both the left and right heat sinks? Have they begun to
be similar? FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"

"Colin B." wrote:

A bit of a belated response here...

lid wrote:
Colin,

SUCCESS! Experience has taught me a good troubleshooting strategy for these amps
and the first 4 transistors are almost always the main culprits when too much DC
offset is present. And, as you found, the solution is relatively simple for those
who have good soldering skills.

Indeed, success at last! My soldering skills were a bit rusty, but have
come back with a vengeance. My next plan is to replace my crappy iron
with a nice new station (Weller WES51, or Hakko 936--any opinions folks?)
and then start putting all of my other projects back together.

As an aside, this amp may be up for sale before too long. Just a heads
up.

Thanks again, everyone who helped.

Colin

Colin,

What about the temperatures of both the left and right heat sinks? Have they begun to
be similar? FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"

"Colin B." wrote:

A bit of a belated response here...

lid wrote:
Colin,

SUCCESS! Experience has taught me a good troubleshooting strategy for these amps
and the first 4 transistors are almost always the main culprits when too much DC
offset is present. And, as you found, the solution is relatively simple for those
who have good soldering skills.

Indeed, success at last! My soldering skills were a bit rusty, but have
come back with a vengeance. My next plan is to replace my crappy iron
with a nice new station (Weller WES51, or Hakko 936--any opinions folks?)
and then start putting all of my other projects back together.

As an aside, this amp may be up for sale before too long. Just a heads
up.

Thanks again, everyone who helped.

Colin

Colin,

What about the temperatures of both the left and right heat sinks? Have they begun to
be similar? FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"

Hi Dick;

lid wrote:
What about the temperatures of both the left and right heat sinks? Have
they begun to be similar? FWIW, I keep my Haflers of this vintage biased
at around 325 mA. The original factory spec was around 250 mA
(conservative) per channel and many guys bias theirs up to 450 mA per
channel -- if the amp is kept properly ventilated. Supposedly a Hitachi
MOSFET reaches optimum operating area with 100 mA of bias so if you add up
this number for each of the 4 MOSFETs per channel and include around
50 mA to drive the circuit card, you can understand how the 450 mA figure
is derived.

I was running mine at 240mA before the repairs, and then set them to
220mA since repairing everything. The heatsinks are close enough that
I can't be sure by touch if they're different or not--the right one
(the repaired channel) might be SLIGHTLY hotter, but it's hard to say.

I think I'll bump the bias up to 300mA and see how hot it is for our
house. If nothing else, the increased bias should get the thing up
to operating temperature faster, when first turned on 'cold.'

Hi Dick;

lid wrote:
What about the temperatures of both the left and right heat sinks? Have
they begun to be similar? FWIW, I keep my Haflers of this vintage biased
at around 325 mA. The original factory spec was around 250 mA
(conservative) per channel and many guys bias theirs up to 450 mA per
channel -- if the amp is kept properly ventilated. Supposedly a Hitachi
MOSFET reaches optimum operating area with 100 mA of bias so if you add up
this number for each of the 4 MOSFETs per channel and include around
50 mA to drive the circuit card, you can understand how the 450 mA figure
is derived.

I was running mine at 240mA before the repairs, and then set them to
220mA since repairing everything. The heatsinks are close enough that
I can't be sure by touch if they're different or not--the right one
(the repaired channel) might be SLIGHTLY hotter, but it's hard to say.

I think I'll bump the bias up to 300mA and see how hot it is for our
house. If nothing else, the increased bias should get the thing up
to operating temperature faster, when first turned on 'cold.'

Hi Dick;

lid wrote:
What about the temperatures of both the left and right heat sinks? Have
they begun to be similar? FWIW, I keep my Haflers of this vintage biased
at around 325 mA. The original factory spec was around 250 mA
(conservative) per channel and many guys bias theirs up to 450 mA per
channel -- if the amp is kept properly ventilated. Supposedly a Hitachi
MOSFET reaches optimum operating area with 100 mA of bias so if you add up
this number for each of the 4 MOSFETs per channel and include around
50 mA to drive the circuit card, you can understand how the 450 mA figure
is derived.

I was running mine at 240mA before the repairs, and then set them to
220mA since repairing everything. The heatsinks are close enough that
I can't be sure by touch if they're different or not--the right one
(the repaired channel) might be SLIGHTLY hotter, but it's hard to say.

I think I'll bump the bias up to 300mA and see how hot it is for our
house. If nothing else, the increased bias should get the thing up
to operating temperature faster, when first turned on 'cold.'

Hi Dick;

lid wrote:
What about the temperatures of both the left and right heat sinks? Have
they begun to be similar? FWIW, I keep my Haflers of this vintage biased
at around 325 mA. The original factory spec was around 250 mA
(conservative) per channel and many guys bias theirs up to 450 mA per
channel -- if the amp is kept properly ventilated. Supposedly a Hitachi
MOSFET reaches optimum operating area with 100 mA of bias so if you add up
this number for each of the 4 MOSFETs per channel and include around
50 mA to drive the circuit card, you can understand how the 450 mA figure
is derived.

I was running mine at 240mA before the repairs, and then set them to
220mA since repairing everything. The heatsinks are close enough that
I can't be sure by touch if they're different or not--the right one
(the repaired channel) might be SLIGHTLY hotter, but it's hard to say.

I think I'll bump the bias up to 300mA and see how hot it is for our
house. If nothing else, the increased bias should get the thing up
to operating temperature faster, when first turned on 'cold.'

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Robert Gault wrote:

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Robert G,

No, I am not saying the design is flawed. The heat sinks could be a little larger, but this
amp was designed to meet several price points, it was never portrayed as a cost-no-object
state-of-the art amplifier. Biasing of Hitachi MOSFETs and the resultant sound seems to exist
on a contiuum and the observed sound difference between a 300mA and 400mA bias per channel is
subtle, at best. Time and again "experts" comment about the subtle improvement in sound as
these devices are biased at a higher current level. Noever, in any of the many articles I
have read over the last 20 years were deleterious effects mentioned, such as the THD or IM
measures you mention.

Personally, I have not run the tests you describe and I really wish you or someone competent
would do so. In the meantime I will ask you if you are familiar with the Audio Amateur
article (4/1981) by Walt Jung and Dick Marsh on the mods for this amp? These authors, very
competent and well known EEs and circuit designers, state the amp should be biased at 400-425
mA per channel. Contact John Hillig at Musical Concepts and he will state that these devices
sound best when biased up to 100 mA each or 400 mA per channel. Mr. Hillig is a competent
circuit designer.

I realize that these "golden ear" type comments are anathema on this technically oriented
newsgroup, but science and art have to coexist, don't you agree? If you can bring to us any
of the type of objective "proof" you mention I believe we all would be grateful.

Dick

Robert Gault wrote:

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Robert G,

No, I am not saying the design is flawed. The heat sinks could be a little larger, but this
amp was designed to meet several price points, it was never portrayed as a cost-no-object
state-of-the art amplifier. Biasing of Hitachi MOSFETs and the resultant sound seems to exist
on a contiuum and the observed sound difference between a 300mA and 400mA bias per channel is
subtle, at best. Time and again "experts" comment about the subtle improvement in sound as
these devices are biased at a higher current level. Noever, in any of the many articles I
have read over the last 20 years were deleterious effects mentioned, such as the THD or IM
measures you mention.

Personally, I have not run the tests you describe and I really wish you or someone competent
would do so. In the meantime I will ask you if you are familiar with the Audio Amateur
article (4/1981) by Walt Jung and Dick Marsh on the mods for this amp? These authors, very
competent and well known EEs and circuit designers, state the amp should be biased at 400-425
mA per channel. Contact John Hillig at Musical Concepts and he will state that these devices
sound best when biased up to 100 mA each or 400 mA per channel. Mr. Hillig is a competent
circuit designer.

I realize that these "golden ear" type comments are anathema on this technically oriented
newsgroup, but science and art have to coexist, don't you agree? If you can bring to us any
of the type of objective "proof" you mention I believe we all would be grateful.

Dick

Robert Gault wrote:

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Robert G,

No, I am not saying the design is flawed. The heat sinks could be a little larger, but this
amp was designed to meet several price points, it was never portrayed as a cost-no-object
state-of-the art amplifier. Biasing of Hitachi MOSFETs and the resultant sound seems to exist
on a contiuum and the observed sound difference between a 300mA and 400mA bias per channel is
subtle, at best. Time and again "experts" comment about the subtle improvement in sound as
these devices are biased at a higher current level. Noever, in any of the many articles I
have read over the last 20 years were deleterious effects mentioned, such as the THD or IM
measures you mention.

Personally, I have not run the tests you describe and I really wish you or someone competent
would do so. In the meantime I will ask you if you are familiar with the Audio Amateur
article (4/1981) by Walt Jung and Dick Marsh on the mods for this amp? These authors, very
competent and well known EEs and circuit designers, state the amp should be biased at 400-425
mA per channel. Contact John Hillig at Musical Concepts and he will state that these devices
sound best when biased up to 100 mA each or 400 mA per channel. Mr. Hillig is a competent
circuit designer.

I realize that these "golden ear" type comments are anathema on this technically oriented
newsgroup, but science and art have to coexist, don't you agree? If you can bring to us any
of the type of objective "proof" you mention I believe we all would be grateful.

Dick

Robert Gault wrote:

lid wrote:
snip FWIW, I keep my Haflers of this vintage biased at around 325 mA. The
original factory spec was around 250 mA (conservative) per channel and many guys bias
theirs up to 450 mA per channel -- if the amp is kept properly ventilated. Supposedly a
Hitachi MOSFET reaches optimum operating area with 100 mA of bias so if you add up this
number for each of the 4 MOSFETs per channel and include around 50 mA to drive the
circuit card, you can understand how the 450 mA figure is derived.

However, the stock heat sinks are just not large enough for much of anything beyond 350
mA -- at least in my experience -- and I don't like the sound of a ventilating fan.

Dick the "HaflerLover"


In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Robert G,

No, I am not saying the design is flawed. The heat sinks could be a little larger, but this
amp was designed to meet several price points, it was never portrayed as a cost-no-object
state-of-the art amplifier. Biasing of Hitachi MOSFETs and the resultant sound seems to exist
on a contiuum and the observed sound difference between a 300mA and 400mA bias per channel is
subtle, at best. Time and again "experts" comment about the subtle improvement in sound as
these devices are biased at a higher current level. Noever, in any of the many articles I
have read over the last 20 years were deleterious effects mentioned, such as the THD or IM
measures you mention.

Personally, I have not run the tests you describe and I really wish you or someone competent
would do so. In the meantime I will ask you if you are familiar with the Audio Amateur
article (4/1981) by Walt Jung and Dick Marsh on the mods for this amp? These authors, very
competent and well known EEs and circuit designers, state the amp should be biased at 400-425
mA per channel. Contact John Hillig at Musical Concepts and he will state that these devices
sound best when biased up to 100 mA each or 400 mA per channel. Mr. Hillig is a competent
circuit designer.

I realize that these "golden ear" type comments are anathema on this technically oriented
newsgroup, but science and art have to coexist, don't you agree? If you can bring to us any
of the type of objective "proof" you mention I believe we all would be grateful.

Dick

Robert Gault wrote:

In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Don't know about Dick, but it seems to me that the bias would help
eliminate crossing distortion, wouldn't it? If so, it should be pretty
easy to measure on a 'scope.

As for measuring THD, I've got a lovely old distortion analyser in the
basement that tops (bottoms?) out at 0.1% THD. Anyone want to buy it?
:-)

Colin

Robert Gault wrote:

In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Don't know about Dick, but it seems to me that the bias would help
eliminate crossing distortion, wouldn't it? If so, it should be pretty
easy to measure on a 'scope.

As for measuring THD, I've got a lovely old distortion analyser in the
basement that tops (bottoms?) out at 0.1% THD. Anyone want to buy it?
:-)

Colin

Robert Gault wrote:

In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Don't know about Dick, but it seems to me that the bias would help
eliminate crossing distortion, wouldn't it? If so, it should be pretty
easy to measure on a 'scope.

As for measuring THD, I've got a lovely old distortion analyser in the
basement that tops (bottoms?) out at 0.1% THD. Anyone want to buy it?
:-)

Colin

Robert Gault wrote:

In effect you are saying that the Hafler design is flawed as 450ma is
grossly different from 200-250ma. You may be correct but what objective
testing have you done to verify that any bias different from the Hafler
spec is better?

Have you performed THD or IM distortion tests at 450ma vs 200-250ma or
any other type of test other than listening? How, if at all, does the
change in bias affect the power rating or other specs as listed in the
Hafler manual?

Don't know about Dick, but it seems to me that the bias would help
eliminate crossing distortion, wouldn't it? If so, it should be pretty
easy to measure on a 'scope.

As for measuring THD, I've got a lovely old distortion analyser in the
basement that tops (bottoms?) out at 0.1% THD. Anyone want to buy it?
:-)

Colin

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

Very nice indeed :-)

Michael

lid wrote in
:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

Very nice indeed :-)

Michael

lid wrote in
:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

Very nice indeed :-)

Michael

lid wrote in
:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

Very nice indeed :-)

Michael

lid wrote in
:

Michael wrote:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Well, since this amp is open on my bench and staying away from my stereo
for quite a while, I plan on playing with it quite a bit. I'm going to
hook up a signal generator and a 'scope, and see how everything gets
created.

Should be fun, at least.

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

So 16 MOSFETs pulling 300mA each at idle? I'm glad I don't have your
power bill! :-)

Colin

Michael wrote:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Well, since this amp is open on my bench and staying away from my stereo
for quite a while, I plan on playing with it quite a bit. I'm going to
hook up a signal generator and a 'scope, and see how everything gets
created.

Should be fun, at least.

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

So 16 MOSFETs pulling 300mA each at idle? I'm glad I don't have your
power bill! :-)

Colin

Michael wrote:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Well, since this amp is open on my bench and staying away from my stereo
for quite a while, I plan on playing with it quite a bit. I'm going to
hook up a signal generator and a 'scope, and see how everything gets
created.

Should be fun, at least.

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

So 16 MOSFETs pulling 300mA each at idle? I'm glad I don't have your
power bill! :-)

Colin

Michael wrote:

The datasheets for the Hitachi Power MOSFETs indicate the zero tempco bias
point is apprx 100mA per device. That's the main reason the 100mA number is
so "popular". It's actually a different for the N and P channel devices but
100mA per device is close enough for rock and roll, as they say :-)

Well, since this amp is open on my bench and staying away from my stereo
for quite a while, I plan on playing with it quite a bit. I'm going to
hook up a signal generator and a 'scope, and see how everything gets
created.

Should be fun, at least.

Currently, I am using somewhat similar lateral MOSFETs manufactured by
Toshiba in my amp (circuit is kinda/sorta similar to a later Hafler
product), biased at over 300mA per device with 4 devices in parallel per
rail per amplifier. I've got bigger heat sinks than the Hafler DH200,
though. And I don't use +/-65V rails. I'm driving 4 ohms loads - Kef 104/2
speakers.

So 16 MOSFETs pulling 300mA each at idle? I'm glad I don't have your
power bill! :-)

Colin