Does somebody have experience with newer 750 F/G Model ?
Is there improvemnet in sound compare to 750 B/C
I know only 750 B/C and the sound was great in club installation
750 F/G very rare and hard to find, never have.....only schematic but never listen
no need output relay, have eectronic turn on/off and triac DC protect
have schematic 750 F/G REV A and B
First Revision 750 F/G have MT220 Sanken output devices
Rev A and B changed to TO3P have 2SA1987 / 2SC5359 or MJL 21193 / 21194
Is it worth to rebuild 750 F/G for FUN ?
Very much semi components compare to N-Channel Mosfet Output stage with same output power
Another quasi-complementary design
500W RMS @ 8 ohm 95 V DC
Is there improvemnet in sound compare to 750 B/C
I know only 750 B/C and the sound was great in club installation
750 F/G very rare and hard to find, never have.....only schematic but never listen
no need output relay, have eectronic turn on/off and triac DC protect
have schematic 750 F/G REV A and B
First Revision 750 F/G have MT220 Sanken output devices
Rev A and B changed to TO3P have 2SA1987 / 2SC5359 or MJL 21193 / 21194
Is it worth to rebuild 750 F/G for FUN ?
Very much semi components compare to N-Channel Mosfet Output stage with same output power
Another quasi-complementary design
500W RMS @ 8 ohm 95 V DC
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Hi NMOS,
I've never seen one either. Something I would like to see.
You will never know the answer to your question without rebuilding one.
-Chris
I've never seen one either. Something I would like to see.
You will never know the answer to your question without rebuilding one.
-Chris
ok I will do
Now its christmas time,....boring cold days ....time to design PCB
will share here with the DIY community
At Frankfurt Fair Germany - Prolight and Sound
BGW attend here self powering Subwoofer and amplifier, I remember had 750F/G heatsink in my hand at the booth ...15 - 18 years ago or more dont know
Ahrrr was hoping for Christmas with BGW working but no.. RHS has stopped!?
So.. will disassemble, check out the relay, and more than likely by pass the stereo/mono switch to remove that from the equation...
Hmmm..
Hey thanks for the comments and pics, next investigation underway soon.
Cheers 🙂
So.. will disassemble, check out the relay, and more than likely by pass the stereo/mono switch to remove that from the equation...
Hmmm..
Hey thanks for the comments and pics, next investigation underway soon.
Cheers 🙂
I owned a 750G in the mid-90s. Had Sankens MT-200.
Was used in my small recording studio.
The 750G sounds like a hi-fi amp.
Can't comment on the 750B/C versions. Never owned them.
I’m intrigued by this later design, and have a spare hafler dh500 transformer that puts out 93v.
And lots of heatsink material too...
And lots of heatsink material too...
Wishing all a very happy new year!!
Okay I have bypassed the stereo/mono switch so I sincerely hope this resolves the RHS channel vanishing.
While apart I checked the relay and it is free to move, connections and internal wiring all look the same as the original, so I am a little stumped as to what is going on here?
I assume the relay is normally open/off, when the amps on switch is switched to on, the relay waits a while and then is switched to closed/on to pass the signals to the outputs. As soon as the amp power switch is flicked off, the relay should go open, but mine does not..
Is there anything in the path that controls the relay that I can check out?
Many Thanks!
Again!
Okay I have bypassed the stereo/mono switch so I sincerely hope this resolves the RHS channel vanishing.
While apart I checked the relay and it is free to move, connections and internal wiring all look the same as the original, so I am a little stumped as to what is going on here?
I assume the relay is normally open/off, when the amps on switch is switched to on, the relay waits a while and then is switched to closed/on to pass the signals to the outputs. As soon as the amp power switch is flicked off, the relay should go open, but mine does not..
Is there anything in the path that controls the relay that I can check out?
Many Thanks!
Again!
The charging of C5 thru R6 is the turn-on delay. When the amp is switched off C5 discharges immediately thru D6 and R2. You should have -77VDC on one side of R2. If no -77VDC there is no path for C5 to discharge and the relay stays energized much longer than normal.
Craig
Craig
Craig - I shall have a look at the drawings I have to see if I can work out what you are referring to. Cheers
Duke - The power light dims to off immediately when the power switch is flicked off.
Two days of running the 750 here and there, still have right channel working 🙂
(I don't particularly look forward to switching the thing off due to the weird noises that come out the speakers, although then there is peace - no fan! ;-) fan will be next after a few more days of soak testing and sorting out the relay) Getting there!!
Many Thank yous!!
Duke - The power light dims to off immediately when the power switch is flicked off.
Two days of running the 750 here and there, still have right channel working 🙂
(I don't particularly look forward to switching the thing off due to the weird noises that come out the speakers, although then there is peace - no fan! ;-) fan will be next after a few more days of soak testing and sorting out the relay) Getting there!!
Many Thank yous!!
I am afraid I don't remember if I mentioned before.. but if, the input music is playing and the 750 is off, as soon as it is powered on the music plays, (ie. no delay) and I know I have stated previously, once the 750 is switched off, the music plays for a good while after, before making weird noises and then fading out.
Confuses me with the resistor and Cap charging and discharging, if it is only related to that...
Cheers
Confuses me with the resistor and Cap charging and discharging, if it is only related to that...
Cheers
It is hard to trouble shoot without full details. Take pictures of front panel, relay assy & PCB of one of the amplifier modules. Several of the posts may not be four your amplifier.
1.Pull the relay out of the socket.
2. Turn on the amplifier
3. If no output on both channel, then the RELAY IS BAD.
4. If you have output on one channel you have a wiring problem or the relay board has a short or solder bridge.
Duke
1.Pull the relay out of the socket.
2. Turn on the amplifier
3. If no output on both channel, then the RELAY IS BAD.
4. If you have output on one channel you have a wiring problem or the relay board has a short or solder bridge.
Duke
Hi Duke
2001 after the nightclub closing forever, (had Richard Long costumized Sound System same NYC Studio 54 / Paradise Garage)
YouTube
I get 1 pcs. 750B from club, and drive now in my Appartment Infinity Studio monitor, my neighbour hate me,... equarthquake
my question is:
Does 750B circuit design have problem with TRIANGLE and SQUARE WAVE ?
Can 750B produce clear perfect TRIANGLE and SQUARE WAVE ?
output same input signal ?
Technican friend check in 2001 my 750B
-SINEWAVE PERFECT - no visible crossover
-TRIANGLE ...look bad, The sharp points were really round
-SQUARE WAVE ... look not good too
750B left and right channel same, no visible difference
same test with Ecler and QSC
TRIANGLE and SQUARE WAVE perfect,
output same input signal.
sorry my english, learning in school
2001 after the nightclub closing forever, (had Richard Long costumized Sound System same NYC Studio 54 / Paradise Garage)
YouTube
I get 1 pcs. 750B from club, and drive now in my Appartment Infinity Studio monitor, my neighbour hate me,... equarthquake
my question is:
Does 750B circuit design have problem with TRIANGLE and SQUARE WAVE ?
Can 750B produce clear perfect TRIANGLE and SQUARE WAVE ?
output same input signal ?
Technican friend check in 2001 my 750B
-SINEWAVE PERFECT - no visible crossover
-TRIANGLE ...look bad, The sharp points were really round
-SQUARE WAVE ... look not good too
750B left and right channel same, no visible difference
same test with Ecler and QSC
TRIANGLE and SQUARE WAVE perfect,
output same input signal.
sorry my english, learning in school
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Hi NMOS
I suspect that a LOW PASS filter was installed to protect the TWEETERS from failing. The 750B/C were not BP limited.
Duke
I suspect that a LOW PASS filter was installed to protect the TWEETERS from failing. The 750B/C were not BP limited.
Duke
Old plastic case with magnets on new relay - problems!?
Boy oh Boy! where did that year go!
Only just called the relay company and asked for a replacement.. to be told sorry its out of its years guarantee!! Ooops!
Long Story -
Ordered another and tried it, it worked :-D
No woooomp through the speakers when switched on and no crackle whistle through the speakers when switched off! :-D Cool!!
Switched the plastic case, so the original old plastic case with the magnets is now on the new working relay, pushed it home so nice and snug.
Relay back in the amp and it's is back to wooomp switching on and crackle whistle when switching off... a!?
Tried the initial, year old, new.. 'non working' relay and it worked.. ??
When the plastic case with the magnets on, is fitted on either of the new relays the relays stay on / connected - magnets causing a problem? hmmm
Looking closely it looks like the internals of the new relay are slightly different, it also looks like the old plastic case is slightly shorter.. slightly. I am wondering if the old slightly shorter case is pushed home on the new relays it actually mechanically holds the relay on/connected! or.... the magnets are having an effect on the new relay..??
Next is to attempt removing the magnets and tape them to the new case and see if that works.
SHORT STORY!
- old plastic case with magnets may mechanically hold new relay in on/connected when case is pushed home on the new relay base...
Boy oh Boy! where did that year go!
Only just called the relay company and asked for a replacement.. to be told sorry its out of its years guarantee!! Ooops!
Long Story -
Ordered another and tried it, it worked :-D
No woooomp through the speakers when switched on and no crackle whistle through the speakers when switched off! :-D Cool!!
Switched the plastic case, so the original old plastic case with the magnets is now on the new working relay, pushed it home so nice and snug.
Relay back in the amp and it's is back to wooomp switching on and crackle whistle when switching off... a!?
Tried the initial, year old, new.. 'non working' relay and it worked.. ??
When the plastic case with the magnets on, is fitted on either of the new relays the relays stay on / connected - magnets causing a problem? hmmm
Looking closely it looks like the internals of the new relay are slightly different, it also looks like the old plastic case is slightly shorter.. slightly. I am wondering if the old slightly shorter case is pushed home on the new relays it actually mechanically holds the relay on/connected! or.... the magnets are having an effect on the new relay..??
Next is to attempt removing the magnets and tape them to the new case and see if that works.
SHORT STORY!
- old plastic case with magnets may mechanically hold new relay in on/connected when case is pushed home on the new relay base...
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Okay just used tape to place the old magnets off the original relay case onto the new plastic case of the new relay, and everything works fine, so if you do use the old case with magnets and push it home on the new relay base your locking the relay in the connected position!! be aware ;-)
Pheww! that's that sorted, so a year later, next step is the fan replacement to something whisper quiet... any pointers?
..think the new mains powered fans are about £50... do they humm or just cause a breeze...?
Cheers 🙂
Pheww! that's that sorted, so a year later, next step is the fan replacement to something whisper quiet... any pointers?
..think the new mains powered fans are about £50... do they humm or just cause a breeze...?
Cheers 🙂
Hi Deaf Cat,
I've never experienced what you have with the old relay cover with magnets causing a problem. The magnets are supposed to cause the length of the arc to be longer where they extinguish more quickly. Interesting.
Fans vary a lot depending on CFM and the amount of noise they generate. The quiet ones are pricey, but worthwhile if you can hear your present fan.
-Chris
I've never experienced what you have with the old relay cover with magnets causing a problem. The magnets are supposed to cause the length of the arc to be longer where they extinguish more quickly. Interesting.
Fans vary a lot depending on CFM and the amount of noise they generate. The quiet ones are pricey, but worthwhile if you can hear your present fan.
-Chris
I once had a Turbosound rig powered by 8 750B`s. One time after cleaning the chassis` and output modules, I reversed the orientation of the fans so that the intake was from the side vents and the exhaust out the back of the amplifiers.
I never experienced any thermal related issues but cleaning the amplifiers became an easier and less frequent task. There was much less dust accumulation in the area of the power supply caps and bridge.
I`m sure BGW had a very valid reason for orienting the fans as they did, perhaps Duke could chime in on that subject. I`ve installed a new fan in the same fashion on a 750B running a JBL B380 at home but found the fan noise to be obtrusive even at low speed. A 250R 25 watt in series with the fan took care of the noise and was still able to keep the amp cool.
That may not be an option in a more demanding situation as the amp heats quicker and may go into high speed fan mode.
Another way to cut down on fan noise is to remove the protective grill, you`d be surprised at how much turbulence it generates but fingers and rodents beware🙂
I never experienced any thermal related issues but cleaning the amplifiers became an easier and less frequent task. There was much less dust accumulation in the area of the power supply caps and bridge.
I`m sure BGW had a very valid reason for orienting the fans as they did, perhaps Duke could chime in on that subject. I`ve installed a new fan in the same fashion on a 750B running a JBL B380 at home but found the fan noise to be obtrusive even at low speed. A 250R 25 watt in series with the fan took care of the noise and was still able to keep the amp cool.
That may not be an option in a more demanding situation as the amp heats quicker and may go into high speed fan mode.
Another way to cut down on fan noise is to remove the protective grill, you`d be surprised at how much turbulence it generates but fingers and rodents beware🙂