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Old 8th May 2011, 07:16 AM   #1
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Default My F5

I have just built my first Pass Amplifier.

And it is realy all as good as you have been told on those forums.

Yes I know there is loads of treads on this build.

But I rather start my own than barge in on somebody else, besides time to turn a new leaf and get on.
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Old 8th May 2011, 09:33 AM   #2
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You may ask yourself.
(talking heads - once in a lifetime - live 80 rome hq)
Just goggle it.

Why a new tread?

Simple my F5 is making sweet music but a few issues to solve and possibly make it beter.
It is newer going to be good looking as same Flat Pack stuff you buy from IKEA but I have made it.

Recap
26 V rails
Currently biased at 3.5 A
I have a doggy 1000VA transformer
230 V primary
0 20 24 V
0 20 24 V secondary
I am using the 20 V taps at present
150 mU capacitors banks in CRCLC
I have split the last 50 mU between the two channels for total 200 mU
I am using 10mU 63 V capacitors beter quality at 2 times the price on their way

I am building this in the UK and trying to source most of the components from around here supporting the local economy and at the same time get screwed.
Thus the doggy transformer
As it makes a fair bit of mechanical noise (not Much but enough to spoil things)
This is in hand and will be either sorted or manufacturer name and shamed.

I am making my own PCB with a DIY light box 200 + to buy one is rape.
(If you need help on cooking your own just PM)

I have room for 3 mosfets on each branch and I am not using the current limiter.

But I have used the NTE7100 for speaker protection.
Whit Amplimo relays
This worked well in a couple of occasions so I still have
The speakers soon to be replaced are 4 Homs nominal.

At present I have 2 Toshibas on each rail biased at 1.75 A
Next build 1 Toshiba at 2 A and then Fairchild and Cascode and balanced and .

Now just one reason why I think this tread may be a help to others.
R1 and R2 are 10R 2W Holco and the R5 / R8 combinations are also made up with 3-150R Homs 2W Holco
I like the sound of those resistors and for the money I think that is difficult to find beter MF series 2W 15 ppm.
The thing is 2W is plenty they run cool even after 5 6 hours.
If you need same and are in the UK PM
Another thing I am looking at is the value of R3 R4 I am using 1K with the Toshibas and probably can go down even more the advantage is less current trough the pots so more reliability and easier to adjust as more turns
I am using Futabas MCP74 for source resistors the 0.47 R spec values worked quite well but with 720 mV drops across them was a bit to hot so I am using 0.22R instead.


Holco MFR 15ppm 2W for sale
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Old 8th May 2011, 10:46 PM   #3
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Not much progress with the build today
Every time I stop to play a couple of tracks I get carried away and end up pulling out quite a few albums.

The Mule has been playing now for a couple of weeks sound seems to have mellowed down a bit maybe just me getting use to it.

Time to start another round of mosfet testing
While I was doing this the firs time I have noticed that VGS changes quite a bit with the temperature.

I have made myself a little test rig and can get temperature stable with in + - 1 C

A simple 317 a spare mosfet and one of the 4K7 R thermistors + a few bits that may be in anybody bits stash.

May be handy as fan controller for same.

Holco MFR 15ppm 2W for sale
Attached Images
File Type: jpg Testing The dudas 001.jpg (599.3 KB, 1692 views)
File Type: jpg Testing The dudas 002.jpg (606.4 KB, 1421 views)
File Type: jpg Testing The dudas 003.jpg (593.5 KB, 1345 views)
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Old 9th May 2011, 05:25 PM   #4
qusp is offline qusp  Australia
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interesting, i may send you a message tomorrow. this lower vgs/higher gm at low temp is really quite interesting as an angle to gain better performance, interesting because you mainly see reference to devices needing to warm up to reach proper performance levels, where your results and mine indicate that a major factor in performance is actually considerably better at low temp. makes sense i guess what with super conductors performing at low temps, i wonder if its the same mechanism at work?
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Old 9th May 2011, 05:39 PM   #5
qusp is offline qusp  Australia
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i think the fan+controller is very important, as otherwise the heat added by the dut will always impact on the temp of the sink, over and above the temp created by the heating element and without the fan to burn heat off in a controlled manner you will still be relying on environmental conditions, which are not so predictable.
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Old 9th May 2011, 07:49 PM   #6
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Tanks QSP
Ditails of the test rig
A cpu heat sink and a piece of copper big pot in the front to set Gate voltagge


I got the thermistor in a small indent right under the Dut to get rid of a bit of time lag.

While I test one Dut the next ones are warming up on the plate noticed this saves time as well

No much chance for me to do any more work today as I have found
a pair of mint Gales Gold Monitors from the secon hand shop for 35.

They sound realy good so got stuck with listening to more records near field.
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Old 9th May 2011, 07:55 PM   #7
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On cooling so I shall read Papa F5 manual one more time as penitence for being out of topic.
Well I was thinking at one stage that down there you all have Air Con
All you have to do is tee off the cold pipe and run that on a coil of copper pipe wound on the heat sinks.

Not kiding you realy looked in to it even found that Halfrouds sels a botle of proper gass to refill the car air con
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Old 9th May 2011, 09:23 PM   #8
qusp is offline qusp  Australia
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haha aircon, its 15 degrees c here inside at the moment. yes we have aircon, but....

see pm for what i meant
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Old 21st May 2011, 07:35 PM   #9
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Ok long time since I have been here and time for update.


The Mule is no more I have been so impressed by the sound that it is time to invest same time and build something to make Papa proud.
So recap

Holco MFR 15ppm 2W for sale
Attached Images
File Type: jpg Old F5 no more 001.jpg (601.0 KB, 518 views)
File Type: jpg Old F5 no more 003.jpg (611.9 KB, 385 views)
File Type: jpg Old F5 no more 004.jpg (619.6 KB, 296 views)
File Type: jpg Old F5 no more 007.jpg (623.1 KB, 221 views)
File Type: jpg Old F5 no more 011.jpg (614.8 KB, 366 views)
File Type: jpg Old F5 no more 012.jpg (631.1 KB, 258 views)
File Type: jpg Old F5 no more 014.jpg (603.8 KB, 240 views)
File Type: jpg Old F5 no more 015.jpg (604.1 KB, 245 views)
File Type: jpg Old F5 no more 018.jpg (612.4 KB, 415 views)
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Old 21st May 2011, 07:50 PM   #10
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On the previous post a few pictures of the Mule.

I hope that there may be something useful there, as I would like this to be my little way to give something back.

I have seen a few posts complaining about the Hum (mains noise on speakers).

I found this a bit strange, as I did not have any.

The main thing is using star or bus of star for the earth arrangement.

I did not connect the screen of the Input cable at any other place than the RCA Plugs on the Preamplifier and I was using over 15 Ft of cables from the pre.

The green Yellow cables (UK standard) are the ground
The 4 black ones the grounds of the first 2 capacitor banks.

Only one cable back to the mains and as the Pre has this connection as well that is more than enough to keep the input voltage from floating

Holco MFR 15ppm 2W for sale
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