Ok, this evening I will fire it up.
Referring to this schematic (http://www.diyaudio.com/forums/imag...ntation/P-BAC-S4V20/P-BAC-S4V20-schematic.pdf) I inserted another 1000uF capacitor between D pad and the node of the 15kOhm, 4.75kOhm and Q113, obviously cutting the trace; source resistors are 0.33Ohm.
P102 is set to 0Ohm and P101 is set to 5kOhm. Will the 0.33Ohm source resistors change the bias range capability of P101?
Another question: will offset influence bias and viceversa during initial settings?
Thanks,
Giulio
Referring to this schematic (http://www.diyaudio.com/forums/imag...ntation/P-BAC-S4V20/P-BAC-S4V20-schematic.pdf) I inserted another 1000uF capacitor between D pad and the node of the 15kOhm, 4.75kOhm and Q113, obviously cutting the trace; source resistors are 0.33Ohm.
P102 is set to 0Ohm and P101 is set to 5kOhm. Will the 0.33Ohm source resistors change the bias range capability of P101?
Another question: will offset influence bias and viceversa during initial settings?
Thanks,
Giulio
Last night I finished assembling my just arrived BA-3 board, drilling the Deluxe U5 rear panel to mount the BA-3 board as 6L6 did in this build thread. Also got stand offs to mount power supply to floor, as well as newly arrive soft start board (now assembled) mounted to floor w/ stand offs. Wiring of power supply to out put boards...bias boards also mounted as in 6L6 build, signal wiring and then fireup soon....too many projects at once!
Russellc
Russellc
6L6, what type of rectifiers are those? I still have a bunch of MUR 3060 from F-5 builds, good enough? Do you have a part number on those heat sinks?
I've got the BA-3amp front end and power supply ready to go except the rectifiers. Once thats fired up and adjusted, I'll add the already assembled bias and output boards for final fire up...hopefully.
6L6, one other question. Does the slow start (I'm using one like you did, already assembled and mounted) bleed off any voltage, or does it let the whole thing through unfettered?
I was wanting to use a 24+24 volt transformer I have for the F-5 Turbo build. It is a large transformer from the group buy 1000VA. I'm afraid such a large VA will create too much voltage for the J-fets. I understand that higher VA transformers have higher voltage in circuit, and with no cascodes, I am assuming my J fets may be facing too much juice.
I also have a 18+18 volt 500 ma transformer laying around if this on is too high for the J fets.
Thanks,
Russellc
I've got the BA-3amp front end and power supply ready to go except the rectifiers. Once thats fired up and adjusted, I'll add the already assembled bias and output boards for final fire up...hopefully.
6L6, one other question. Does the slow start (I'm using one like you did, already assembled and mounted) bleed off any voltage, or does it let the whole thing through unfettered?
I was wanting to use a 24+24 volt transformer I have for the F-5 Turbo build. It is a large transformer from the group buy 1000VA. I'm afraid such a large VA will create too much voltage for the J-fets. I understand that higher VA transformers have higher voltage in circuit, and with no cascodes, I am assuming my J fets may be facing too much juice.
I also have a 18+18 volt 500 ma transformer laying around if this on is too high for the J fets.
Thanks,
Russellc
Russel,
transformers have a specified output voltage, but that depends on input voltage.
It is usually shown a 0-30, 0-30Vac as an example, but should be written as 230:0-30,0-30Vac. The 230 part is the specified Primary voltage to obtain the specified secondary voltage.
The next part is the specifying the power capability.
We use VA. Take a 300VA transformer with the voltage spec as in the first para.
It could be specified as 230:30-0-30Vac 5Aac centre tapped or as 230:30+30Vac 5Aac, for dual secondary.
VA = Vac * Iac
Next is transformer regulation.
EI and similar square cut laminations tend to have a higher regulation. Toroids, Ccore and Rcore tend to have a lower regulation.
A 300VA toroid could be 5% to 6% transformer regulation.
A 300VA EI could be 6% to 8% transformer regulation.
But regulation can be DESIGNED to be different from those typical temperature rated transformers. One can specify YOUR required regulation and the transformer manufacturer can quote you for that target figure. You could ask for 3% regulation 300VA 230:30-0-30Vac transformer. It is likely to be as expensive as two standard 300VA and as big and heavy as a 600VA transformer.
Finally to actual output voltage.
Secondary output voltage on no load (open circuit) is given by:
output voltage = Mains input voltage/specified input voltage*specified output voltage * {1+transformer regulation}
using our 230:30-0-30Vac 300VA 6% regulation transformer fed from a 242Vac supply, the output will be 242/230*30*1.06 = 33.459Vac +-tolerance of the transformer manufacturer.
Note, in the example "Bigness" did not enter into the calculation of output voltage.
transformers have a specified output voltage, but that depends on input voltage.
It is usually shown a 0-30, 0-30Vac as an example, but should be written as 230:0-30,0-30Vac. The 230 part is the specified Primary voltage to obtain the specified secondary voltage.
The next part is the specifying the power capability.
We use VA. Take a 300VA transformer with the voltage spec as in the first para.
It could be specified as 230:30-0-30Vac 5Aac centre tapped or as 230:30+30Vac 5Aac, for dual secondary.
VA = Vac * Iac
Next is transformer regulation.
EI and similar square cut laminations tend to have a higher regulation. Toroids, Ccore and Rcore tend to have a lower regulation.
A 300VA toroid could be 5% to 6% transformer regulation.
A 300VA EI could be 6% to 8% transformer regulation.
But regulation can be DESIGNED to be different from those typical temperature rated transformers. One can specify YOUR required regulation and the transformer manufacturer can quote you for that target figure. You could ask for 3% regulation 300VA 230:30-0-30Vac transformer. It is likely to be as expensive as two standard 300VA and as big and heavy as a 600VA transformer.
Finally to actual output voltage.
Secondary output voltage on no load (open circuit) is given by:
output voltage = Mains input voltage/specified input voltage*specified output voltage * {1+transformer regulation}
using our 230:30-0-30Vac 300VA 6% regulation transformer fed from a 242Vac supply, the output will be 242/230*30*1.06 = 33.459Vac +-tolerance of the transformer manufacturer.
Note, in the example "Bigness" did not enter into the calculation of output voltage.
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Thanks for the info AndrewT, but please try to answer the question or please refrain from comment. I am not ordering a transformer, clearly I stated I am using one or the other that is already in my possession.
Now lets see if I can simplify my question by example: When I built my F-5, I used a transformer with 18 + 18 secondaries and 300 VA. This results in around 24 volts or so DC on the rails. My understanding is, had I used a transformer that had the same secondary voltage, 18 + 18, but had say 1000 VA that my resulting rail voltages would be slightly higher than the previous example of 24 volts.
Is this correct about the higher resulting DC rail voltage when using the transformer with substantially higher VA?
As to the transformers I have on hand 18 + 18 500VA, and I also have a 24 + 24 1000VA. From other builds I see that using 24 + 24 volt transformers usually results in 32 volts DC on the rails. If my transformer with 1000VA results in higher rail voltages, obviously this would be higher than 32 volts?
Zen Mod has recommended that absent cascode, 30 volts or so is ok, I have seen a few (6L6) go slightly higher 32 volt rails. I understand 40 volts is where they cook for certain. Not wanting to tempt melt down ( a fearful amplifier builder I guess) I am inquiring as to which transformer to proceed with. If both will produce the same rails my answer is clear, I will go with the larger of the two! 6L6 build guide shows higher output power with the higher rails, 40 vs 25 watts per channel, and I would prefer 40 or where ever it is. HOWEVER, if it is tempting things I will proceed with the smaller transformer which I have no doubt would be adequate.
Russellc
Now lets see if I can simplify my question by example: When I built my F-5, I used a transformer with 18 + 18 secondaries and 300 VA. This results in around 24 volts or so DC on the rails. My understanding is, had I used a transformer that had the same secondary voltage, 18 + 18, but had say 1000 VA that my resulting rail voltages would be slightly higher than the previous example of 24 volts.
Is this correct about the higher resulting DC rail voltage when using the transformer with substantially higher VA?
As to the transformers I have on hand 18 + 18 500VA, and I also have a 24 + 24 1000VA. From other builds I see that using 24 + 24 volt transformers usually results in 32 volts DC on the rails. If my transformer with 1000VA results in higher rail voltages, obviously this would be higher than 32 volts?
Zen Mod has recommended that absent cascode, 30 volts or so is ok, I have seen a few (6L6) go slightly higher 32 volt rails. I understand 40 volts is where they cook for certain. Not wanting to tempt melt down ( a fearful amplifier builder I guess) I am inquiring as to which transformer to proceed with. If both will produce the same rails my answer is clear, I will go with the larger of the two! 6L6 build guide shows higher output power with the higher rails, 40 vs 25 watts per channel, and I would prefer 40 or where ever it is. HOWEVER, if it is tempting things I will proceed with the smaller transformer which I have no doubt would be adequate.
Russellc
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Really wanted to fireup at least the front end today, but doesnt look that way. I'm going to have to get some sinks for the rectifiers. I really dont want to attach them to the floor like I did with my F-5. Standing up, like 6L6 has his also takes up less floor space.
Russellc
Russellc
Attachments
![IMG_4070[1].jpg](/community/data/attachments/449/449731-62629f40c926004020ab5074498da09b.jpg)
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I did answer the question.
no question marks, but lot's of queries that show a lack of understanding of the way a transformer works.
This confirms that you don't know how to predict the output voltage.
post64 shows you how to predict the transformer output voltage.
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To directly answer your questions --
Yes, the MUR3020 will work perfectly. Finding a 1" mount heatsink in TO-247 might present a challenge. If you find some, I want to know the part number. Attaching them to the floor is not a bad idea. Yes, it uses a lot of real estate.
You could just use some bridge blocks. I much prefer them in power amps.
The better regulation of the bigger transformer is not going to provide you any problems. The best case scenario for rail voltage will be 24 *1.4 = 33.6V minus about 2V for the diode drops, giving approx 31.6V before any losses. That's comfortably within the safe area of the Jfets, and they don't have the full rails across them anyway, so there's a bit more margin there before they get upset.
Yes, the MUR3020 will work perfectly. Finding a 1" mount heatsink in TO-247 might present a challenge. If you find some, I want to know the part number. Attaching them to the floor is not a bad idea. Yes, it uses a lot of real estate.
You could just use some bridge blocks. I much prefer them in power amps.
The better regulation of the bigger transformer is not going to provide you any problems. The best case scenario for rail voltage will be 24 *1.4 = 33.6V minus about 2V for the diode drops, giving approx 31.6V before any losses. That's comfortably within the safe area of the Jfets, and they don't have the full rails across them anyway, so there's a bit more margin there before they get upset.
sure you can, all i am saying is that you can try it both ways and be wiser for it,
ain't no substitute for real practical eperience....
sure you can, all i am saying is that you can try it both ways and be wiser for it,
ain't no substitute for real practical eperience....
Well, it will not be difficult to do. I have the transformer go connections go to a terminal block, then to their destinations. Unhooking and rehooking will be a breeze.
Does the sonic character change with the change? If the smaller transformer leans more towards the "bloom" end of the scale, I much prefer that to the "clinical" end of the scale. Have (I assume you have) you tried such experimentation and have an opinion? I will try both, but was wondering how you felt about such changes...since I am trying both, I will begin with the smaller one. I assume some settings may drift, but I will be powering up with variac anyway to be as safe as possible.
Russellc
Would probably be a miracle if all lined up with the Peter Daniels diode holes on his board...I'll do some measurements when I get home tonight.
In the mean while, what rectifier/heat sink did you use on your BA-3 build as pictured in this build thread? If I have to order heat sinks, I guess I could order diodes as well and save these for something else, they really belong in my box of F-5 Turbo stuff anyway. I guess I could just get some small square/rectangular sinks and drill holes where appropriate.....
Thanks,
Russellc
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I don't member the exact part I used, but these look nice - MBRF20H150CTG ON Semiconductor | Mouser
Are these sufficient? GBPC3502-E4/51 Vishay Semiconductors | Mouser crap, they don't have any....
This? http://www.mouser.com/ProductDetail...=sGAEpiMZZMtQ8nqTKtFS/LDhWhDI65nslKtwYZS2PGo=
or maybe this:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMtQ8nqTKtFS/MRt2/0z7Bct866kwxpWb6Q=
Russellc
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