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Old 11th November 2013, 06:36 AM   #2301
henryve is offline henryve  South Africa
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@emyeuoi

The process I refer to is Vacuum Impregnation. Basically it prevents the windings from moving excessively with the fluctuating magnetic fields induced, which is the usual cause of mechanical hum. Old style potting of the whole transfomer may also help, but I don't believe as much as Vacuum Impregnation since the latter process fills the cavities between the windings better.
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Old 11th November 2013, 06:51 AM   #2302
emyeuoi is offline emyeuoi  Italy
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Thanks for the clarification
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Old 11th November 2013, 08:13 AM   #2303
emyeuoi is offline emyeuoi  Italy
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Anyway they are from Primerose and I suppose that they well know which kind of technic should be used to avoid the mechanical hum...
Regards,
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Old 22nd December 2013, 04:12 PM   #2304
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Default F5T for headphone?

I am going to build a scale down version of F5T for headphone. For simplicity sake, (1) the current limiters are removed and (2) the thermister are also removed. But, I am not sure whether I have to retain the 2.2k resistors attached to the thermistors in the original schematic suggested by NP. 1/4W resistors will be used except R13 ~ R16, which are 1 ohm non-inductive rated at 2W. I am going to bias output at 100 ~ 150mA. Any comments on the schematic and PCB layout?
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Old 23rd December 2013, 12:32 AM   #2305
Rush is offline Rush  United States
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Quote:
Originally Posted by B&W_arthur View Post
I am going to build a scale down version of F5T for headphone. For simplicity sake, (1) the current limiters are removed and (2) the thermister are also removed. But, I am not sure whether I have to retain the 2.2k resistors attached to the thermistors in the original schematic suggested by NP. 1/4W resistors will be used except R13 ~ R16, which are 1 ohm non-inductive rated at 2W. I am going to bias output at 100 ~ 150mA. Any comments on the schematic and PCB layout?
Why don't you use 2sk2013 / 2sj313 instead of hard to get Fairchild outputs?
Probably sound better too!

Rush
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Old 23rd December 2013, 12:42 AM   #2306
6L6 is online now 6L6  United States
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????

???

By comparison the Fairchild are easy - the K2013/J313 are rapidly becoming genuine unobtanium.

Buzzforb has lots of Fairchild.
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Old 23rd December 2013, 02:51 AM   #2307
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Rush and 6L6

Thank you for the input.

I had done a simple research on the net before I made a post here.

I stick to Fairchild after I checked their availability and price on RS components.

Some of the alternatives are either unavailable or too expensive e.g. Toshiba 2Sk1530/2SJ201 pair.

6L6, I have ordered some Fairchild already and expect to receive them this afternoon.

Since I am not going to parallel the MOSFETs, is matching the N-P pair important?
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Old 23rd December 2013, 03:06 AM   #2308
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you dont need dobble up of source resistors and feedback resistors.
but you might want to get the source resistors close to the output transistors.
you don't need TO-247 transistors. TO-220 is plenty. you can also drop C1-8.
and it is not a scaled down F5 turbo, but a scaled down F5
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Old 23rd December 2013, 03:43 AM   #2309
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and i would not drop the thermistor circut. it's there to keep the bias stable.
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Old 23rd December 2013, 03:54 AM   #2310
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Quote:
Originally Posted by AudioSan View Post
you dont need dobble up of source resistors and feedback resistors.
but you might want to get the source resistors close to the output transistors.
you don't need TO-247 transistors. TO-220 is plenty. you can also drop C1-8.
and it is not a scaled down F5 turbo, but a scaled down F5
AudioSan,

I used TO-220 footpin in the PCB for the MOSFET but did not change the FQA to FQP in schematic. Sorry for the confusion.

You are right. At low current, it may not necessary to double the resistors. I will re-allocate the position of source resistors after the deletion of the doubled resistors.

Regarding the 10u caps., they are founded in the Turbo V1 schematic in the Pass article. The 10u caps are not seen in the original F5.

Agree with you. The 330u may not be necessary. Because 100mA constant current is more than enough to drive most headphones that 300u caps are not needed for high transient load. Is my understanding correct?
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