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

"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

"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

"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

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

"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

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