Hi latala,
Email it directly to a few of us that want it in full resolution. I scan schematics like that at about 320 dpi. Covers and text at 240 dpi. the other alternative would be to host it somewhere and post the link.
You can e-mail it to multiple recipients one time. Then we can go over it.
-Chris
Email it directly to a few of us that want it in full resolution. I scan schematics like that at about 320 dpi. Covers and text at 240 dpi. the other alternative would be to host it somewhere and post the link.
You can e-mail it to multiple recipients one time. Then we can go over it.
-Chris
Hello guys,
I am newebie over here, and just jumped on this thread, the BGW 750B is one of my favorite amps, actually my first "real" amp
I love it's sound (pro sound ) and strong bass...mine is from the early 80's and still performs very well every day...anyway should I consider replacing all caps including the power supply ones? or just wait : "why fix it if it ain't broken"
at that time I also run a SAE X25A (about the same power) the SAE was IMO very close in sound except for better low extended bass anyway here are 2 of my reference amps...
all my friends are buying new jeff rowland's 600w etc...they just laugh at me with my "old bipolars" but I'm not sure that we make much better amps today than 25 years ago...
anyway I am starting to build an ALEPH 30 to experiment newsound and have the pleasure to design an original box for it!
Vince
I am newebie over here, and just jumped on this thread, the BGW 750B is one of my favorite amps, actually my first "real" amp
I love it's sound (pro sound ) and strong bass...mine is from the early 80's and still performs very well every day...anyway should I consider replacing all caps including the power supply ones? or just wait : "why fix it if it ain't broken"
at that time I also run a SAE X25A (about the same power) the SAE was IMO very close in sound except for better low extended bass anyway here are 2 of my reference amps...
all my friends are buying new jeff rowland's 600w etc...they just laugh at me with my "old bipolars" but I'm not sure that we make much better amps today than 25 years ago...
anyway I am starting to build an ALEPH 30 to experiment newsound and have the pleasure to design an original box for it!
Vince
Some misc remarks:
"input signal of the 318 increases and that will finally overload the next stage."
And that is true of 99% of the amps ever made. Leach degenerates the gain in his input stage so the amp is dominated by the second voltage gain stage.
A Carver M1.0 is a pretty good sounding amp. The front end is about the same as the old Crown M600, a design shared by many of the newer Crown amps too.
The output stage on most of these amps are complementary EF type, either two or three stages.
The Carver and Crown front ends are very similar to the BGW, except they add another complementary voltage gain stage stage and delete the capacitor level shift circuit of the BGW. At one time the capacitors were cheaper than the transistors, now the reverse is true. The caps are now replace with a couple of $0.08 transistors (MPSA42/92 types). See Q201, 202 in the PL3 schematic for reference.
http://www.crownaudio.com/pdf/amps/pl_three_schematic.pdf
"I havent changed any electrolytics at all!!
Do you have any recomendations in this direction "
I don't go overboard with the caps, Panasonic electrolytics with small polypropylene bypass tacked in parallel are what I use. There isn't much room for big film&foil types anyway. I do use a pair of 47µF across the main supply filters, this really affects how the bass sounds. In general, the caps I replace and add cost about $4 for the lot.
"Also the fan is a pain and i may fit a autotemp control "
I don't like the variable speed fans, I prefer the thermo-switch controls (like the BGW has). The ones that vary continuously with temperature and/or signal drive me nuts. The noise they make is much more obtrusive as it is constantly changing. Alesis and Carver come to mind. I use some ball-bearing types that are only 28dB SIL, you slow those down by changing the fan speed resistor and they are very quiet. I find a fixed, low , constant speed easier to mentally 'tune out', and if it gets hot it can kick itself up to hurricane (I probably won't hear than when the low end is hitting 130dB+).
"between the metal /plastic can"
They use the same die in all of them. BGW chose to use only the metal cased hermitic sealed semis (and teflon wire) in the earlier units for superior reliability.
"anyone re biased the output stage into AB instead of AB-B"
I converted a 'B' (quasi) into a 'C' (complementary), not something I would recommend to anyone. I have also added a Baker clamp between the voltage gain stage and the output stage. The clamp allows driving 10dB into clipping without the outputs sticking to the rails.
"should I consider replacing all caps including the power supply ones?"
I do them all except the main power supply ones (unless they are bad). Don't forget to add the bypass films in the signal path, and the bypass electrolytics to the power supply. The films in the signal path clean up most of the solid state 'grundge', and the power supply bypass caps make the bass sound much tighter.
"I also run a SAE X25A "
I like SAE, but never owned the newer ones with paralled outputs, just the series connected ones. The series connected ones are a bit fragile for low impedance loads. They all benefit from the cap thing too.
In general, I like a lot of the old dinosaur amps (other than the weight). While I can buy an amp rated at twice the power for about $300, they don't cut it for me. The BGW750 transformer is rated at 50% more VA, even though it puts out half the power. They just sound bigger. They also play louder, especially compared to switching supply amps in limited power availability gigs.
"input signal of the 318 increases and that will finally overload the next stage."
And that is true of 99% of the amps ever made. Leach degenerates the gain in his input stage so the amp is dominated by the second voltage gain stage.
A Carver M1.0 is a pretty good sounding amp. The front end is about the same as the old Crown M600, a design shared by many of the newer Crown amps too.
The output stage on most of these amps are complementary EF type, either two or three stages.
The Carver and Crown front ends are very similar to the BGW, except they add another complementary voltage gain stage stage and delete the capacitor level shift circuit of the BGW. At one time the capacitors were cheaper than the transistors, now the reverse is true. The caps are now replace with a couple of $0.08 transistors (MPSA42/92 types). See Q201, 202 in the PL3 schematic for reference.
http://www.crownaudio.com/pdf/amps/pl_three_schematic.pdf
"I havent changed any electrolytics at all!!
Do you have any recomendations in this direction "
I don't go overboard with the caps, Panasonic electrolytics with small polypropylene bypass tacked in parallel are what I use. There isn't much room for big film&foil types anyway. I do use a pair of 47µF across the main supply filters, this really affects how the bass sounds. In general, the caps I replace and add cost about $4 for the lot.
"Also the fan is a pain and i may fit a autotemp control "
I don't like the variable speed fans, I prefer the thermo-switch controls (like the BGW has). The ones that vary continuously with temperature and/or signal drive me nuts. The noise they make is much more obtrusive as it is constantly changing. Alesis and Carver come to mind. I use some ball-bearing types that are only 28dB SIL, you slow those down by changing the fan speed resistor and they are very quiet. I find a fixed, low , constant speed easier to mentally 'tune out', and if it gets hot it can kick itself up to hurricane (I probably won't hear than when the low end is hitting 130dB+).
"between the metal /plastic can"
They use the same die in all of them. BGW chose to use only the metal cased hermitic sealed semis (and teflon wire) in the earlier units for superior reliability.
"anyone re biased the output stage into AB instead of AB-B"
I converted a 'B' (quasi) into a 'C' (complementary), not something I would recommend to anyone. I have also added a Baker clamp between the voltage gain stage and the output stage. The clamp allows driving 10dB into clipping without the outputs sticking to the rails.
"should I consider replacing all caps including the power supply ones?"
I do them all except the main power supply ones (unless they are bad). Don't forget to add the bypass films in the signal path, and the bypass electrolytics to the power supply. The films in the signal path clean up most of the solid state 'grundge', and the power supply bypass caps make the bass sound much tighter.
"I also run a SAE X25A "
I like SAE, but never owned the newer ones with paralled outputs, just the series connected ones. The series connected ones are a bit fragile for low impedance loads. They all benefit from the cap thing too.
In general, I like a lot of the old dinosaur amps (other than the weight). While I can buy an amp rated at twice the power for about $300, they don't cut it for me. The BGW750 transformer is rated at 50% more VA, even though it puts out half the power. They just sound bigger. They also play louder, especially compared to switching supply amps in limited power availability gigs.
Thanks lads especially DJK
I agree with most of your comments here !
When I say AB-B i meant that the output stage has boosters that have no standing current and wonder if for domestic use there would be an advantage to adjust the bias so that there is a small standing current
Ihave a full range of equipment ie Radford / Sugden distortion measuring equipment to measure any improvement, all though at the end of the day its the sonics that i care about!
I am pleased to say that I have received the manual and will be pleased to post when I can
Sorry re the delay but decoration of my PC room meensd the main PC is not working at present!!!
regards Trev
I agree with most of your comments here !
When I say AB-B i meant that the output stage has boosters that have no standing current and wonder if for domestic use there would be an advantage to adjust the bias so that there is a small standing current
Ihave a full range of equipment ie Radford / Sugden distortion measuring equipment to measure any improvement, all though at the end of the day its the sonics that i care about!
I am pleased to say that I have received the manual and will be pleased to post when I can
Sorry re the delay but decoration of my PC room meensd the main PC is not working at present!!!
regards Trev
Thanks for the capacitor tip DJk!
I will try that for sure, I also agree with the fan tip, it's just a pain to have a near 100db signal to noise ratio an this amp spoiled by this loudy fan all the time , I will make a circuit so that it starts to run only when the amp gets hot...and actually it runs really cool til you ask him more than 10watts...
Vince
I will try that for sure, I also agree with the fan tip, it's just a pain to have a near 100db signal to noise ratio an this amp spoiled by this loudy fan all the time , I will make a circuit so that it starts to run only when the amp gets hot...and actually it runs really cool til you ask him more than 10watts...
Vince
An externally hosted image should be here but it was not working when we last tested it.
D4, 5 form the positive clamp. D6, 7 form the negative clamp. Usually D5, 6 are dual diode drops.
It is possible for the output stage to be driven into saturation with the front end run from a supply isolated by a diode and a cap from the main supply, or a high voltage tier. This can cause the outputs to 'stick' to the rail coming out of clipping.
I had a problem with some 2N3773 in an early BGW750 that were sold to me as epitaxial, but were probably hometaxial. When the amp clipped, one output would still be stuck on when the other was trying to turn on. The resulting current shoot- thru caused the output stage to blow up.
The general idea is that it is better to clip a low current fast device rather than a high current slow one, the fast one will recover better.
D6, D5 are largely cosmetic, as they are completely deprived of current during positive and negative clip respectively....
Much better to get rid of them altogether, and merely connect D4 and D7 directly between the base of Q9 and Q10 respectively and +Vcc1, and -Vcc1.
Additionally, the collectors of Q9, Q10 must be connected respectively to +Vcc2, and -Vcc2, and NOT +Vcc1, and -Vcc1.
Much better to get rid of them altogether, and merely connect D4 and D7 directly between the base of Q9 and Q10 respectively and +Vcc1, and -Vcc1.
Additionally, the collectors of Q9, Q10 must be connected respectively to +Vcc2, and -Vcc2, and NOT +Vcc1, and -Vcc1.
"D6, D5 are largely cosmetic, as they are completely deprived of current during positive and negative clip respectively...."
Uhh.......that's how it works. I suppose with the new high voltage Schottky the forward drop of D4, 7 might be low enough to prevent Q9, 10 from turning on.
Schematic is for reference only, amp in question (BGW) had 1.5KW of safe area (per channel) at rail voltage and has no current limiting other than a magnetic breaker for the mains voltage.
Uhh.......that's how it works. I suppose with the new high voltage Schottky the forward drop of D4, 7 might be low enough to prevent Q9, 10 from turning on.
Schematic is for reference only, amp in question (BGW) had 1.5KW of safe area (per channel) at rail voltage and has no current limiting other than a magnetic breaker for the mains voltage.
djk said:
Nope...the idea is to provide the Baker clams, D4, D7, with headroom to operate.....This doesn't work because D6, D5 are not foward biased during positive and negative clip respectively (contrary to intuition perhaps).
As previously recomended, get rid of D6, D5 altogether, and merely connect D4 and D7 directly between the base of Q9 and Q10 respectively and +Vcc1, and -Vcc1.
Additionally, the collectors of Q9, Q10 must be connected respectively to +Vcc2, and -Vcc2, and NOT +Vcc1, and -Vcc1, to prevent Q9, Q10 from being driven into saturation during clip...
"However i feel that baker clamps can not be fitted as according to the schematic there are only single +/- rails on the BGW."
On amps with a seperate front end rails (APT Model 1, Son of Ampzilla, etc), or diode and cap isolated from the main rails (misc Hafler and others), the full clamp is indicated. On others a dual diode for D5, 6 seems to do the trick. A favorite of mine that is built this way is the Altec 9440, with 2K of SOA per channel and dual fans.
On amps with a seperate front end rails (APT Model 1, Son of Ampzilla, etc), or diode and cap isolated from the main rails (misc Hafler and others), the full clamp is indicated. On others a dual diode for D5, 6 seems to do the trick. A favorite of mine that is built this way is the Altec 9440, with 2K of SOA per channel and dual fans.
