Couple of amplifier Qs
 

Hi - I wonder if anyone can shed some light on the operation of a Hitachi
HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser coupling'.
Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when it's
switched in the speakers switch off. 'BLT' is also marked on the LH direct
input on the power amp, and the meters have a range marked BLT, at double
the watt markings of a scale beneath. Any idea what that's all about (apart
from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink - the
RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local and
*very* hot - probably hotter than the casing of a class A valve amp. The LHS
is warmish, more your tepid warm. I've had a nose about inside and I can't
see anything obviously fried or about to fry, and I've tried switching the
inputs and speakers around - same result.

TIA

Rob

Couple of amplifier Qs
 

"Rob" wrote in message
...
Hi - I wonder if anyone can shed some light on the operation of a Hitachi
HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when
it's switched in the speakers switch off. 'BLT' is also marked on the LH
direct input on the power amp, and the meters have a range marked BLT, at
double the watt markings of a scale beneath. Any idea what that's all
about (apart from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink - the
RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local
and *very* hot - probably hotter than the casing of a class A valve amp.
The LHS is warmish, more your tepid warm. I've had a nose about inside and
I can't see anything obviously fried or about to fry, and I've tried
switching the inputs and speakers around - same result.



Drop this mutha in the skip where it belongs and put another record on
instead! ;-)

Couple of amplifier Qs
 

In message , Keith G
writes

"Rob" wrote in message
...
Hi - I wonder if anyone can shed some light on the operation of a Hitachi
HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when
it's switched in the speakers switch off. 'BLT' is also marked on the LH
direct input on the power amp, and the meters have a range marked BLT, at
double the watt markings of a scale beneath. Any idea what that's all
about (apart from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink - the
RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local
and *very* hot - probably hotter than the casing of a class A valve amp.
The LHS is warmish, more your tepid warm. I've had a nose about inside and
I can't see anything obviously fried or about to fry, and I've tried
switching the inputs and speakers around - same result.



Drop this mutha in the skip where it belongs and put another record on
instead! ;-)






Just a hypothesis, but I bet 'BLT' puts the amp into bridged mode,
making a mono amp of twice the power.

--
Chris Morriss

Couple of amplifier Qs
 

Rob wrote:
Hi - I wonder if anyone can shed some light on the operation of a
Hitachi HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' -
when it's switched in the speakers switch off. 'BLT' is also marked
on the LH direct input on the power amp, and the meters have a range
marked BLT, at double the watt markings of a scale beneath. Any idea
what that's all about (apart from sandwiches)?



Not seen a good old "BLT" for ages bad for you, doctors tell me to keep away
from them
Keith should have spotted it :-)


see below ;-)






lower


















Bacon Lettuce Tomato

Couple of amplifier Qs
 

Rob wrote:
Hi - I wonder if anyone can shed some light on the operation of a
Hitachi HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' -
when it's switched in the speakers switch off. 'BLT' is also marked
on the LH direct input on the power amp, and the meters have a range
marked BLT, at double the watt markings of a scale beneath. Any idea
what that's all about (apart from sandwiches)?

Damm missed that need new glasses

Couple of amplifier Qs
 

"Dave xxxxx" wrote in message
. uk...
Rob wrote:
Hi - I wonder if anyone can shed some light on the operation of a
Hitachi HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' -
when it's switched in the speakers switch off. 'BLT' is also marked
on the LH direct input on the power amp, and the meters have a range
marked BLT, at double the watt markings of a scale beneath. Any idea
what that's all about (apart from sandwiches)?

Damm missed that need new glasses


Ya got me any way - I've never heard of them!!

To check it wasn't just my sheltered upbringing I asked Swim 'WTF is 'BLT'?
Quick as a flash she said 'Bacon Lettuce & Tomato'....!!!

Back to me Gluck now (done me Brahms) - you don't get teabreaks playing CDs
do you? :-)

Swim? (pianist, clarinettist, Psychology MA) She's watching a 'talent show'
on tha fekkin' telly......!!!

:-)

Couple of amplifier Qs
 

"Chris Morriss" wrote
Just a hypothesis, but I bet 'BLT' puts the amp into bridged mode, making a mono amp of twice the power.

TWICE?

Should be close(r) to 4 times.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

Couple of amplifier Qs
 

"Keith G" wrote in message
...

"Rob" wrote in message
...
Hi - I wonder if anyone can shed some light on the operation of a Hitachi
HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when
it's switched in the speakers switch off. 'BLT' is also marked on the LH
direct input on the power amp, and the meters have a range marked BLT, at
double the watt markings of a scale beneath. Any idea what that's all
about (apart from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink -
the RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local
and *very* hot - probably hotter than the casing of a class A valve amp.
The LHS is warmish, more your tepid warm. I've had a nose about inside
and I can't see anything obviously fried or about to fry, and I've tried
switching the inputs and speakers around - same result.



Drop this mutha in the skip where it belongs and put another record on
instead! ;-)

:-)

It would actually *make* a good skip, it's flippinnormous. And with its 6
phono settings plenty of fiddlage ahead. Will it survive a tube shootout ...
tbc!

Rob

Couple of amplifier Qs
 

"Chris Morriss" wrote in message
...
In message , Keith G
writes

"Rob" wrote in message
...
Hi - I wonder if anyone can shed some light on the operation of a
Hitachi
HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when
it's switched in the speakers switch off. 'BLT' is also marked on the LH
direct input on the power amp, and the meters have a range marked BLT,
at
double the watt markings of a scale beneath. Any idea what that's all
about (apart from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink -
the
RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local
and *very* hot - probably hotter than the casing of a class A valve amp.
The LHS is warmish, more your tepid warm. I've had a nose about inside
and
I can't see anything obviously fried or about to fry, and I've tried
switching the inputs and speakers around - same result.



Drop this mutha in the skip where it belongs and put another record on
instead! ;-)






Just a hypothesis, but I bet 'BLT' puts the amp into bridged mode, making
a mono amp of twice the power.

--
Chris Morriss

Excellent Chris - that'd make sense and worth a check. Thanks.

Rob

Couple of amplifier Qs
 

"Fleetie" wrote in message
...
"Chris Morriss" wrote
Just a hypothesis, but I bet 'BLT' puts the amp into bridged mode, making
a mono amp of twice the power.

TWICE?

Should be close(r) to 4 times.


Martin
--
M.A.Poyser Tel.: 07967
110890
Manchester, U.K.
http://www.fleetie.demon.co.uk


You could be right here - the meters (OK ...) go up to 400 watts. I can't
find any specs on this amp - the mk.1 was 75 watts stereo and curiously
frequency at 1w - 0Hz - 200kHz?!. So far I've bottled at 2 watts with Dynie
1.1s and put any idea of a subwoofer on hold - and that's before pressing
the 'loudness' button (happy days!).

Rob

Couple of amplifier Qs
 

"Rob" wrote in message
...

"Keith G" wrote in message
...

"Rob" wrote in message
...
Hi - I wonder if anyone can shed some light on the operation of a
Hitachi HMA 7500 mk2 pre/power amp:

1. It can connect through two in/outputs - direct and 'condenser
coupling'. Anyone any idea what this coupling thing is?

2. There's a switch on the front of the power amp labelled 'BLT' - when
it's switched in the speakers switch off. 'BLT' is also marked on the LH
direct input on the power amp, and the meters have a range marked BLT,
at double the watt markings of a scale beneath. Any idea what that's all
about (apart from sandwiches)?

3. 1 side of the power amp gets very hot directly above the heatsink -
the RHS on this photo:
http://tinyurl.com/5eqne

I realise this is close to the transformers, but the heat is very local
and *very* hot - probably hotter than the casing of a class A valve amp.
The LHS is warmish, more your tepid warm. I've had a nose about inside
and I can't see anything obviously fried or about to fry, and I've tried
switching the inputs and speakers around - same result.



Drop this mutha in the skip where it belongs and put another record on
instead! ;-)

:-)

It would actually *make* a good skip, it's flippinnormous. And with its 6
phono settings plenty of fiddlage ahead. Will it survive a tube shootout
... tbc!


Heh heh! I haven't seen a 'tube shootout' since the time I trod on me
Autosol Chrome Cleaner when I was cleaning the motorbike I had at the time!!
:-)

Damn, I've made meself glum now! (No bike for a year or two now..... :-(

Couple of amplifier Qs
 

In message , Rob
writes

Excellent Chris - that'd make sense and worth a check. Thanks.

Rob



Can you just go and check the lettering again?

It might say BTL and not BLT, in which case it would stand for 'Bridge
Tied Load'.
--
Chris Morriss

Couple of amplifier Qs
 

"Chris Morriss" wrote in message
...
In message , Rob
writes

Excellent Chris - that'd make sense and worth a check. Thanks.

Rob



Can you just go and check the lettering again?

It might say BTL and not BLT, in which case it would stand for 'Bridge
Tied Load'.
--
Chris Morriss

Bugger - sorry! BTL it is. Thanks Chris. It's just food food food with me.
I've jut googled it and it seems to mean a form of bridging -correct?!

Rob

Couple of amplifier Qs
 

In message , Rob
writes

"Chris Morriss" wrote in message
...
In message , Rob
writes

Excellent Chris - that'd make sense and worth a check. Thanks.

Rob



Can you just go and check the lettering again?

It might say BTL and not BLT, in which case it would stand for 'Bridge
Tied Load'.
--
Chris Morriss

Bugger - sorry! BTL it is. Thanks Chris. It's just food food food with me.
I've jut googled it and it seems to mean a form of bridging -correct?!

Rob



Yep, it will switch one of the inputs to both power-amps, but phase
invert the signal to one. You take the speaker output between the 'hot'
speaker output sockets.

As someone else said, bridging gives twice the voltage swing, and
therefore theoretically four times the power into the same impedance
load, but it's not usually that simple, as the voltage and current will
need to double, so the amp usually runs out of current well before it
manages to give 4 x the power.
--
Chris Morriss