HI guys,
Please help.
I was using a diy xlr/splitter bridging kit on the graaf gm 20,
But the GM 20 design prevents it from outputting an out of phase signal on the other channel.
the DIY bridging kit XlR splitter has the other end wired out of phase,it was connected to both channnels and as standard practice i used the two positive speaker terminals.
I thought this was all it needs, but it is not so, baased on the circuit design.
I am seeking help on how to make my own mono bridging kit, since this amp has an original kit designed for it.
On the Graaf kit ,There is a 4pin connector that has three wires that is connected between channnels.
Can someone help me get a diagram on the 4 pin connector ?
Please help.
I was using a diy xlr/splitter bridging kit on the graaf gm 20,
But the GM 20 design prevents it from outputting an out of phase signal on the other channel.
the DIY bridging kit XlR splitter has the other end wired out of phase,it was connected to both channnels and as standard practice i used the two positive speaker terminals.
I thought this was all it needs, but it is not so, baased on the circuit design.
I am seeking help on how to make my own mono bridging kit, since this amp has an original kit designed for it.
On the Graaf kit ,There is a 4pin connector that has three wires that is connected between channnels.
Can someone help me get a diagram on the 4 pin connector ?
GRAAF model GM20 will not be bridged in an ordinary sense but
wired parallel between channels in order to increase output power.
Remember this is a Circlotron style circuit.
It will be best if somebody provides a good picture of the additional
wiring.
wired parallel between channels in order to increase output power.
Remember this is a Circlotron style circuit.
It will be best if somebody provides a good picture of the additional
wiring.
Here is a short description for the mono conversion :
monooperation - theothor but the pictures are bad.
Output is taken from the red and black posts as before.
monooperation - theothor but the pictures are bad.
Output is taken from the red and black posts as before.
GRAAF GM 20 mono conversion
Details for wiring (two) GRAAF GM 20 stereo OTL in mono
For each amp two heavy cables with solder lugs, black and red,
and a double shielded (balanced) cable with connectors are required.
I am not sure this set is available from distributors any more.
First picture : black and red cable attached to their respective
colour coded connectors
Second picture : shielded double cable inserted between channels
Third picture : details of wiring of the balanced cable - brand of the
connector is unknown to me.
The signal wire has two conductors and a shield, but the connector
has four contacts. Do not worry about this, because both inner
contacts are connected in parallel.
Some points to consider :
This conversion means a paralleling of both amp channels, their inputs
and speaker outputs - the red cable connects red speaker terminals L
and R and the black wire does the same with black terminals. This
is a floating output Circlotron style amp, so both speaker outputs do
not have a direct connection to ground.
The modification allows double output current which is a good feature,
because current of a tube OTL amp is always limited. Max output voltage
is not a point to consider with tubes. This connection is different from so
called bridged or inverted mode.
For repairs and adjustments however remove the connections between
channels. Even a complete breakdown of one channel may be unnoticed
without doing this. I connect for mono operation only after calibration
check and a good test run. Be sure that both channels work properly.
Do not connect GRAAF GM 20 to subwoofers with common ground.
Do not connect speaker outputs to a scope without isolating transformers.
The floating outputs will be shorted by doing otherwise, the amp will not
be damaged, but useful readings are not possible this way.
Additional information is here : Graaf OTL 20 amp
Details for wiring (two) GRAAF GM 20 stereo OTL in mono
For each amp two heavy cables with solder lugs, black and red,
and a double shielded (balanced) cable with connectors are required.
I am not sure this set is available from distributors any more.
First picture : black and red cable attached to their respective
colour coded connectors
Second picture : shielded double cable inserted between channels
Third picture : details of wiring of the balanced cable - brand of the
connector is unknown to me.
The signal wire has two conductors and a shield, but the connector
has four contacts. Do not worry about this, because both inner
contacts are connected in parallel.
Some points to consider :
This conversion means a paralleling of both amp channels, their inputs
and speaker outputs - the red cable connects red speaker terminals L
and R and the black wire does the same with black terminals. This
is a floating output Circlotron style amp, so both speaker outputs do
not have a direct connection to ground.
The modification allows double output current which is a good feature,
because current of a tube OTL amp is always limited. Max output voltage
is not a point to consider with tubes. This connection is different from so
called bridged or inverted mode.
For repairs and adjustments however remove the connections between
channels. Even a complete breakdown of one channel may be unnoticed
without doing this. I connect for mono operation only after calibration
check and a good test run. Be sure that both channels work properly.
Do not connect GRAAF GM 20 to subwoofers with common ground.
Do not connect speaker outputs to a scope without isolating transformers.
The floating outputs will be shorted by doing otherwise, the amp will not
be damaged, but useful readings are not possible this way.
Additional information is here : Graaf OTL 20 amp
