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Old 27th August 2012, 09:56 PM   #12571
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hello. a had the same problem the F5 interest came to late
well. i can help you with a BOM.
however. what boards are the best for you, depends on your heatsinks. (so you can spread the heat evenly) but the store's boards are wery good. at least for sinks thats max 300mm. over that, or with 2 sinks conected together. a wider space between the fets will be good.
here is a BOM
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File Type: pdf bom F5 v2.pdf (50.9 KB, 154 views)
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Old 27th August 2012, 10:12 PM   #12572
juma is offline juma  Serbia
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Hi jeffharr, welcome to forum !

F5 is a simple amp and it won't be a difficult build for a DIYer with some experience. Read carefully Nelson's article and you won't be needing any guidance:
http://firstwatt.com/pdf/prod_f5_man.pdf
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Old 27th August 2012, 10:36 PM   #12573
Rush is offline Rush  United States
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Quote:
Originally Posted by jeffharr View Post

Is there someplace where the latest info, BOM and vendors can be found? The idea of culling several thousand posts to try to figure this out is a bit daunting, and I'll bet some of you have nailed this info and made it available easily. I'll order boards (which ones?) from the Store and sure will appreciate getting pointed in the right direction for info for a standard F5 build, BOM, and parts sources.

I sure hope that I'm not asking for too much, and many, MANY thanks for the help!

Jeff
Really you just need to read the F5 manual, then read the F5-Turbo manual (First Watt website).
I built a couple of F5s and decided to leave out the current limiting section. I have the F5c boards and some others. The F5c are great as you can build a F5-Turbo with 2 pairs of outputs per channel (matched) and use a higher volt rail (32 volts) if you want and cascode the input jfets (Nelson said the turbo sounded more relaxed). Or just build a regular F5 with the same boards. Lots of choices from one set of boards. The power supply boards from the store are also good.
Most stuff you can get from Mouser or Digikey. Heat sinks from Heatsinks USA or complete chassis with heatsinks from eBay sellers (soon from the store). There are several DIYAUDIO members selling boards an outputs and various parts. Buzzford, Zhoufang, Jackinnj, Peter Daniel, check the swap meet forum section.
I have some 2SK170BL and 2SJ74BL if you need them. PM me. 2SJ74BL are getting hard to find.
Hope this helps.

Rush
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Old 27th August 2012, 10:58 PM   #12574
Zen Mod is offline Zen Mod  Serbia
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if ordering pcbs from store , then is worth checking Cviller's Blog
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Old 27th August 2012, 11:23 PM   #12575
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Quote:
Originally Posted by Zen Mod View Post
if ordering pcbs from store , then is worth checking Cviller's Blog
agree
http://www.diyaudio.com/forums/blogs...version-2.html
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Old 27th August 2012, 11:50 PM   #12576
6L6 is online now 6L6  United States
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Although a stereo build, here is a log of a complete construction from start to finish -

An illustrated guide to building an F5

Made with Antek transformer, Peter Daniel boards (Audiosector.com) Hifi2000/Modushop chassis

Of course it depends on your chassis, but making a pair of monoblocks would be very easy using these parts.

Last edited by 6L6; 27th August 2012 at 11:55 PM.
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Old 1st September 2012, 12:15 PM   #12577
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Default Problem with paralleling outputs

I have been happily working with an F5 and a single MOSFET output for a year (2SK175/2SJ55) and it worked well.
Well, I decided this week to start to quadruple the output, as I had installed four pairs per side on the heatsink already.

I ran into problems

audio F5 2012 4 65.jpg
Top output bottom input (the HF oscillations are reflected to the input even!); the oscillations can be seen first on the upgoing sine from bottom.

audio F5 2012 2 64.jpg
  1. Instable - there was instability as I increased the bias in the right channel: severe oscillations beyond a point of about 0,8 Amp total in right Ch. Left can get more and I can set the bias there to about 1,5 amp total.
  2. ringing with a capitative load of 100 nF; a bad issue because I have Quad 57 electrostats.

I noted that when I did a sine on 8 ohm with high volume the instability could start to appear (first on the negative rail).
This issue can be heard on the speakers. There is popping sound and distortion as the volume goes up.

The second issue of ringiong I did not have before in my single version F5, but with an input RC (1k2/1 nF=78KHz) the ringing is not triggered and disappears.

What can be the problem? The N/P sets were selected from a large batch; I have 0,47 ohm source resistances.
Probable cause:
I did have an open connection to -Vb (-23V) when I started (ampere meter not connected) and dialed in the positive side this led to a gate voltage of 23 volt on the 2SK175's (they can stand 20 volts Vgs).
The 2SK175's do work though - on the test bench the right channel gives a flat output to >600 kHz without an input filter and it works well up to clipping. At higher volume, the DC shifts. This all at a low bias. In the room, the R channel exhibits clicks and pops (probably as the instability occurs).

Is this the typical behavior of a 'half-dead' MOSFET?

The ringing is of course independent of the half-dead devices, if I am right.

happy with any light that is shed.
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Old 1st September 2012, 01:17 PM   #12578
lhquam is offline lhquam  United States
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Does each FET have its own gate stopper resistor? Perhaps you should show the exact schematic and a photo of the layout.

Quote:
Originally Posted by triode_al View Post
I have been happily working with an F5 and a single MOSFET output for a year (2SK175/2SJ55) and it worked well.
Well, I decided this week to start to quadruple the output, as I had installed four pairs per side on the heatsink already.

I ran into problems

Attachment 299090
Top output bottom input (the HF oscillations are reflected to the input even!); the oscillations can be seen first on the upgoing sine from bottom.

Attachment 299091
  1. Instable - there was instability as I increased the bias in the right channel: severe oscillations beyond a point of about 0,8 Amp total in right Ch. Left can get more and I can set the bias there to about 1,5 amp total.
  2. ringing with a capitative load of 100 nF; a bad issue because I have Quad 57 electrostats.

I noted that when I did a sine on 8 ohm with high volume the instability could start to appear (first on the negative rail).
This issue can be heard on the speakers. There is popping sound and distortion as the volume goes up.

The second issue of ringiong I did not have before in my single version F5, but with an input RC (1k2/1 nF=78KHz) the ringing is not triggered and disappears.

What can be the problem? The N/P sets were selected from a large batch; I have 0,47 ohm source resistances.
Probable cause:
I did have an open connection to -Vb (-23V) when I started (ampere meter not connected) and dialed in the positive side this led to a gate voltage of 23 volt on the 2SK175's (they can stand 20 volts Vgs).
The 2SK175's do work though - on the test bench the right channel gives a flat output to >600 kHz without an input filter and it works well up to clipping. At higher volume, the DC shifts. This all at a low bias. In the room, the R channel exhibits clicks and pops (probably as the instability occurs).

Is this the typical behavior of a 'half-dead' MOSFET?

The ringing is of course independent of the half-dead devices, if I am right.

happy with any light that is shed.
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Old 1st September 2012, 01:24 PM   #12579
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Or possibly reduce the number of power fet pairs receiving the signal - ie, lift the gate stoppers on 2 of the Fet pairs and see if the input jfets are happier with the load - may not be the answer but quite simple to try, and if not, easy to replace.

There was some mention a long time back about a small Gate/souce cap on the power fets to solve oscillation problems of higher capacitive loads, I think ....
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Old 1st September 2012, 02:11 PM   #12580
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Quote:
Originally Posted by lhquam View Post
Does each FET have its own gate stopper resistor? Perhaps you should show the exact schematic and a photo of the layout.
You mean "each JFET" gatestopper -- not absolutely necessary, but it can be done with slight improvement of measurements.

Of course, the gatestopper for the MOSFETs has to be as near the gate as possible.

Using multiple output devices? -- the input stage might be running out of steam due to the paralleled input capacitance of the output devices.
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