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F6 Clone amp
F6 Clone amp
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Old Yesterday, 10:10 PM   #1
audioarch is offline audioarch  South Africa
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Default F6 Clone amp

I intend building a First Watt F6 clone amplifier.

With no experience in electronics, this may be ambitious and I have numerous queries. Some are for clarification purposes.

I would appreciate input regarding the following.

Resistors.
Some are 3W, others 1/4W. Is it better to use higher wattage? For instance, a 5w used in place of a 3w and 1/2w in place of a 1/4w?

Are the resistor values specified in the DiyAudio BOM the same as the First Watt F6?
The build guide suggests some changes.
ie: R11/ 12- what is used in the First Watt amp?
R13- I would like the LED (blue) to be on the dim side. What resistor would you recommend?

Considering Takman where possible, the rest Vishay.

Capacitors.
Are these polar or non polar? Considering Audionote Kansai. Any views on these? (1000uf, 25v)

Input Jfets.
The Linear Audio Jfets available are class B... what does this mean? Class A, C?
I note the 170, 174 Jfets are tied together. Why is this?

Mosfets.
Who makes the IRFP 240 Mosfets supplied by Diyaudio? Are they branded?

The First Watt F6 amp was designed around power Jfets... but this version uses mosfets, as the power Jfets are no longer available. Not anywhere?
This site mentions that these power Jfets/ mosfets are interchangable. Is the circuit otherwise identical? ie: Simply a case of substituting mosfets for the power J Fets?
How is the amp altered sonically, and how much does this sound like the original First Watt F6? I am under the impression that transformers were primarily used for phase inversion, as the Jfets were only available in n-type. As mosfets can be both n and p type, what is the purpose of the transformers in this case?

LED.
Could leads be added to the LED’S so they can be fitted to the front panel, as per the original amp?
Seem obsolete if in the chassis.
I note the LEDs are specified as green or red. Would prefer blue... assume this is ok.

Internal wiring- maybe overkill, but is something like the Van Der Hul CS-16, FT-16 appropriate throughout? Any suggestions?

Various.
Do the First Watt amps exclude soft start and speaker protection circuits?
Does the speaker protection circuit negatively affect sound quality? Seems quite complex, does the audio signal go through the relay?
Are soldered joints preferable to spade, mechanical connections. These seem to be used.

What solder will give the best results, ie: professional smooth, shiny finish?

Power Supply.
Antek AS-3218 - 300VA 18V transformer. I understand this can be wired for 230V and is suitable for 50HZ? (My local power supply)
I Intend to use bridge rectifiers, to save space. KBPC04-25. What works better discrete diodes or these?
I note a 400kva transformer is often used. What is the spec on the First Watt F6? Is 300Kva sufficient, or is more preferable?

Chassis.
I like the Mini Dissipante, and assume the 300 x 250mm wide interior is sufficient. although I note that a larger size chassis is normally used,
with much empty space. If various chassis components are bought as separate items from Diyaudio, do the heat sinks come with predrilled fixing holes?

Also looking at other chassis options.

I’me sure more queries will come along once I get started.

Last edited by Pano; Yesterday at 11:39 PM. Reason: formatting
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Old Yesterday, 10:53 PM   #2
Dennis Hui is offline Dennis Hui  Canada
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F6 Clone amp
You'll probably get more feedback by posting to the Pass Labs forum.

You can ask the moderator to more this thread over.
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Old Yesterday, 10:59 PM   #3
PJN is offline PJN  United States
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Join Date: Dec 2004
Location: Pa, USA
It is a great amp, I have a diyaudio clone that I'm listening to right now. Buy the kit at the diyaudio store it comes with all the hard to source parts. Go to the Pass labs section here, there is a great step by step build guide there. It's not a difficult build, and if you run into trouble there's a lot of experienced people there to help you out.
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Old Yesterday, 11:02 PM   #4
PJN is offline PJN  United States
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Looks like Dennis beat me to it
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Old Yesterday, 11:03 PM   #5
zman01 is offline zman01  Bangladesh
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Join Date: Feb 2011
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F6 Clone amp
audioarch,

You have a lot of questions... difficult to answer all at one shot (and not to say that I know all the answers ), and I sure the good folk at diyAudio will chime in.

Let me pick a few questions from the end and provide some brief answers:

Chassis: A chassis with heat-sinks that are 4U (tall) x 300 mm (long) or 3U (tall) x 400 mm (long) will work nicely. If you are looking at cases that do not mention height in "U", then a chassis with heat-sinks that are 150 mm tall (which is slightly less tall than 4U) x 300 mm long, as would one which has heat-sinks that are 120mm (tall) x 400mm (long) chassis. The heat-sinks should have fins in vertical orientation (as in pointing upwards), with a base that is 8-10 mm thick and fines that are around 30-40 mm long. It will be good if you can have 300-330mm of width internally. There are several cases on the diyAudio store that satisfy all these criteria.

Power Transformer: A toroidal power transformer with 2 secondary outputs of 18 volts (AC) is required. The VA rating of 300VA to 400VA will be sufficient. Many builder have built with a 300VA unit and the amplifier works fine. You mentioned that your AC mains voltage is 230V, so the primary should be 230V AC or 2 x 115V AC.

Rectifier Diodes: The one you have mentioned (KBPC04-25) should work fine. However, some folks have preference for fast recovery rectifiers, and perhaps someone with more in-depth knowledge can elaborate on the benefits of using those devices.

Power Supply PCB: the diyAudio store has a power supply PCB, and there are quite a few other options available from the community.

Last edited by zman01; Yesterday at 11:27 PM.
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Old Yesterday, 11:29 PM   #6
Dennis Hui is offline Dennis Hui  Canada
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Location: Toronto, Canada
F6 Clone amp
Some quick answers:

- You can use 5W in place of 3W and 0.5W in place of 0.25W. Just make sure they fit the PCB.
- R11/R12 are gate stopper resistors and their exact value is not important. You can go up to a few hundred ohms.
- R13. Depending on your chosen LED, you might want to increase the resistance. You might need to experiment a bit and see what works for you.
- caps are polar on the schematics. You can of course replace them with bipolar ones.
- LSK170B/LSJ74B: The 'B' refers to the Idss grade (6mA to 12mA). This is the same range as the Toshiba 2sk170BL/2sj74BL. They're tied together in push/pull operation.
- IRFP240 (actually IRFP240PBF - lead free part) very likely by Vishay. Vishay bought a chunk of International Rectifier's portfolio many years ago.
- The F6 project was designed using Semisouth jfets, while the production First Watt F6 uses IRFP240. You can find more details in the F6 owner's manual: http://www.firstwatt.com/pdf/prod_f6_man.pdf
- LED: Choose which ever colour you like. You can wire them off board and place them at the front panel if you like.
- FW amps usually don't have protection circuits and they use NTC thermistors for softstart.
- A good lead based solder should be easy to work with. The store's Fire Metall (Fire Metall Eutectic Solder – diyAudio Store) is very good. Sadly it's out of stock currently.
- monolithic diode bridges are fine.
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Old Yesterday, 11:41 PM   #7
Pano is offline Pano  United States
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Moved to Pass Labs
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Old Yesterday, 11:52 PM   #8
zman01 is offline zman01  Bangladesh
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Join Date: Feb 2011
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F6 Clone amp
Now for your next batch of questions (from the bottom of the list):

Solder: A 63/37 solder, with 0.031" (~0.8mm) diameter will work. I use Kester branded solder and like it. An example is Kester 24-6337-0027.

Solder Joints vs Connectors: Both will work if they are done properly. Lot of people prefer solder joints as it eliminates further metal contacts and also reduces the chance of something coming loose - assuming the solder joint itself is strong. Other people prefer terminals (if the PCB has provision of using them), as the terminals allow for connecting and disconnecting the amplifier board to the other boards/parts (e.g. power supply board) easier. Direct soldering is also easier to do, but as said earlier, can be more work if you need to take any particular parts out.

Internal Wiring: Good quality insulated copper wire of 18-20 AWG should be fine for electrical connections and connecting the speaker terminals. For signal (the input connections) You can go for your preferred option.

I have no experience/idea of the cable make and model you have mentioned.

Soft-start and Speaker Protection circuits : The soft start and speaker protection is not part of the design / PCB layout. You can add them if you feel like it. However a lot of (most) builders do not use speaker protection circuits on the DIY First Watt Clones is because these designs from Mr. Pass are very stable. I cannot recall turn on thump being an issue with the F6. However, a properly designed soft start board will protect your components from the effects of inrush current, even if there is no turn on thump.

A well designed speaker protection circuit, especially one with solid state relay/MOSFET should be sonically transparent and not affect the sound quality.
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Old Yesterday, 11:56 PM   #9
zman01 is offline zman01  Bangladesh
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Join Date: Feb 2011
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F6 Clone amp
Request to the Mods,

The OP has a lot of blanks space in his post after the text - can you please trim it down? Once done, please delete this post.

Thank you.
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