If it is not single dominating pole then it is a oscillator.
Slew rate of a BGW op amp is uninteresting, since the
OP output swing is less than 1V at full output swing.
Therefore virtually any OP has speed enough for this
application. But that doesn't matter these amps sounds
like a POS. Let them be buried together with other unpleasanties
of the 60's and 70's.
OK OK I know there are ways of reaching stability with more poles
with a lot of tricks, in schematics and Spice but this is the real world
where there is spread of component values, stray caps etc.
Andreas Wahlberg
Slew rate of a BGW op amp is uninteresting, since the
OP output swing is less than 1V at full output swing.
Therefore virtually any OP has speed enough for this
application. But that doesn't matter these amps sounds
like a POS. Let them be buried together with other unpleasanties
of the 60's and 70's.
OK OK I know there are ways of reaching stability with more poles
with a lot of tricks, in schematics and Spice but this is the real world
where there is spread of component values, stray caps etc.
Andreas Wahlberg
Completely correct, but how do you maintain that under ALL circumstances. Especially in a construction like BGW where the gain stage, the emitter grounded amplifiers load are a fraction of the amps loading. That load you don't know anything about, that is one dimension. THe other dimension is spread of parameters of components and stray caps in the cirquit. You end up with a two dimensional problem, ie you can't sweep every possibility there is, and in some area you could have a 180degree at one gain, ie oscillations.
I myself have toasted a few speaker components on the altar of bandwith, but not anymore. For me it's 90degree all the way to -10dB gain or more.
Andreas Wahlberg
I myself have toasted a few speaker components on the altar of bandwith, but not anymore. For me it's 90degree all the way to -10dB gain or more.
Andreas Wahlberg
bgw750
Thanks for the tips. By now, I've fixed nearly any problem in my bgw750, but there is still a DC-offset with +13V. Today I've changed all caps, but there is no change. Afterwards I solderd out the second Resistor next to T340, and the dc-offset went to 18Volts. The original resistor has got 10kohm. I think, if I change to 7 or 6 kohm, the Offset will be gone. But...is this usual?
Torsten
Sorry about my bad english...
djk said:
Thanks for the tips. By now, I've fixed nearly any problem in my bgw750, but there is still a DC-offset with +13V. Today I've changed all caps, but there is no change. Afterwards I solderd out the second Resistor next to T340, and the dc-offset went to 18Volts. The original resistor has got 10kohm. I think, if I change to 7 or 6 kohm, the Offset will be gone. But...is this usual?
Torsten
Sorry about my bad english...
thanks amp-guy! at least, now i know the brand. maybe will just look for a near replacement, if not exact...
@djk
am not so of a technical guy, am not very good at reading schematics too. but am interested about putting these capacitors...
so i have some questions:
1) will these mylar polypropylene caps do? http://cgi.ebay.ca/MYLAR-Metallized...ryZ14977QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
2) where exactly is this "signal path" i need to solder it on to? will it be on the amp modules, or somewhere near the octal sockets or input connectors?
and lastly, i couldn't find any 47uF polypropylenes.... or am i getting it wrong? the most i have seen is a 4.7 µF...
i saw a Japanese site that moded a 750C, and in the pictures, there is this mod that the repair guy installed 2.2µF polypropylene across the big electroliytics. i guess this one messed my thoughts all up...
please shed some light
http://images.google.ca/imgres?imgu...ev=/images?q=bgw+750&svnum=10&um=1&hl=en&sa=N
djk said:
@djk
am not so of a technical guy, am not very good at reading schematics too. but am interested about putting these capacitors...
so i have some questions:
1) will these mylar polypropylene caps do? http://cgi.ebay.ca/MYLAR-Metallized...ryZ14977QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
2) where exactly is this "signal path" i need to solder it on to? will it be on the amp modules, or somewhere near the octal sockets or input connectors?
and lastly, i couldn't find any 47uF polypropylenes.... or am i getting it wrong? the most i have seen is a 4.7 µF...
i saw a Japanese site that moded a 750C, and in the pictures, there is this mod that the repair guy installed 2.2µF polypropylene across the big electroliytics. i guess this one messed my thoughts all up...
please shed some light
http://images.google.ca/imgres?imgu...ev=/images?q=bgw+750&svnum=10&um=1&hl=en&sa=N
"and lastly, i couldn't find any 47uF polypropylenes.... or am i getting it wrong? the most i have seen is a 4.7 µF...
i saw a Japanese site that moded a 750C, and in the pictures, there is this mod that the repair guy installed 2.2µF polypropylene across the big electroliytics. i guess this one messed my thoughts all up..."
Solen sells some 200µF polypropylene that I have used before, but they are huge and expensive, that's why I said I use electrolytics across the main filter caps and it's called 'the $4 mod'.
The mylar caps you linked to look way too big to go in the circuit board. You can buy small 50V polypropylene caps for a few pennies anyway, why bother with eBay.
"I am not so of a technical guy, am not very good at reading schematics too. but am interested about putting these capacitors...
2) where exactly is this "signal path" i need to solder it on to? will it be on the amp modules, or somewhere near the octal sockets or input connectors?"
Obtain the schematic and post it. I will mark the parts for you. If you can get the board layout I will locate the parts for you. If you cannot do this you will need a (competent) local technician to do the job for you, and not a general electronics/TV type person.
i saw a Japanese site that moded a 750C, and in the pictures, there is this mod that the repair guy installed 2.2µF polypropylene across the big electroliytics. i guess this one messed my thoughts all up..."
Solen sells some 200µF polypropylene that I have used before, but they are huge and expensive, that's why I said I use electrolytics across the main filter caps and it's called 'the $4 mod'.
The mylar caps you linked to look way too big to go in the circuit board. You can buy small 50V polypropylene caps for a few pennies anyway, why bother with eBay.
"I am not so of a technical guy, am not very good at reading schematics too. but am interested about putting these capacitors...
2) where exactly is this "signal path" i need to solder it on to? will it be on the amp modules, or somewhere near the octal sockets or input connectors?"
Obtain the schematic and post it. I will mark the parts for you. If you can get the board layout I will locate the parts for you. If you cannot do this you will need a (competent) local technician to do the job for you, and not a general electronics/TV type person.
http://i56.photobucket.com/albums/g196/dkleitsch/bgw750c_path.jpg
http://i56.photobucket.com/albums/g196/dkleitsch/DSC02421.jpg
Orange is input signal path, green is feedback path.
C1 and C3 make the biggest difference in clarity, C11 and C12 a smaller one (because they have a DC bias). I tack bypass caps across all of these.
Putting a pair of 47µF across the main filter caps on the chassis makes a big difference in how the bass sounds (observe polarity).
The next step is to replace all the little yellow ceramic discs with silver mica or polypropylene (as size dictates), and the orange
Mylar with polypropylene. I don't generally do this last paragraph, but it is an improvement.
I do the $4 mod (C1, C3, and the 47µF pair) on most amps and then stop. It gives the biggest bang for the smallest amount of money and time invested.
Clean the jacks and sockets with De-Oxit and resolder all the sockets for the outputs if they look grey (old solder must be wicked off first).
http://i56.photobucket.com/albums/g196/dkleitsch/DSC02421.jpg
Orange is input signal path, green is feedback path.
C1 and C3 make the biggest difference in clarity, C11 and C12 a smaller one (because they have a DC bias). I tack bypass caps across all of these.
Putting a pair of 47µF across the main filter caps on the chassis makes a big difference in how the bass sounds (observe polarity).
The next step is to replace all the little yellow ceramic discs with silver mica or polypropylene (as size dictates), and the orange
Mylar with polypropylene. I don't generally do this last paragraph, but it is an improvement.
I do the $4 mod (C1, C3, and the 47µF pair) on most amps and then stop. It gives the biggest bang for the smallest amount of money and time invested.
Clean the jacks and sockets with De-Oxit and resolder all the sockets for the outputs if they look grey (old solder must be wicked off first).
hello Andreas
I have interest at your Amp. Please send me more information.
many thanks
best regards Holger
No no no, it is not constant, thenit wouldn't be a novelty.
The lower cirquit maintains at least ca 1V over the diodes at all time, thereby the upper transistor controls the output at all times, ie class A.
The resistor in parallel to the diodes is 10R ca, giving a Iquiscent of ca100mA, no unneccesary heat. Bingo, no heat and class-A.
I have built about 10 of these, and they sell for $2000. Most customers listen two songs, ask the price and buy, nice people.
Andreas
I have interest at your Amp. Please send me more information.
many thanks
best regards Holger
No no no, it is not constant, thenit wouldn't be a novelty.
The lower cirquit maintains at least ca 1V over the diodes at all time, thereby the upper transistor controls the output at all times, ie class A.
The resistor in parallel to the diodes is 10R ca, giving a Iquiscent of ca100mA, no unneccesary heat. Bingo, no heat and class-A.
I have built about 10 of these, and they sell for $2000. Most customers listen two songs, ask the price and buy, nice people.
Andreas
I have picked up yet another 750
Of course 1 channel was blown However a replacement set of output devices has restored full operation
As to my first BGW I have at last located a LM318 metal can IC that I have fitted so all is well
What an amplifier not the best or worse sounding I have heard but built like a truck and very easy to service
The main reason I have added this is to say that I have been caught out by the fake MJ15024/5
I am not sure where they came from as I am always buying devices having cut open a fake I am stunned at the depths that some people will go to as well as stealing my money thay are also stealing my time
regards Trev
Of course 1 channel was blown However a replacement set of output devices has restored full operation
As to my first BGW I have at last located a LM318 metal can IC that I have fitted so all is well
What an amplifier not the best or worse sounding I have heard but built like a truck and very easy to service
The main reason I have added this is to say that I have been caught out by the fake MJ15024/5
I am not sure where they came from as I am always buying devices having cut open a fake I am stunned at the depths that some people will go to as well as stealing my money thay are also stealing my time
regards Trev
