F5 power amplifier

6L6

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Joined 2010
Paid Member
Q7 and Q8 have nothing to do with gain, they are cascode transistors, to keep high voltage rails off the input Jfet.

If your supply is +/- 25vdc then build v2 schematic. If you have 0-25/0-25VAC transformer, you must use cascode transistors (Q7, Q8) on the front end as shown in v3 schematic.

What you describe is exactly what I built in my guide. There are only 4 power transistors, the lower devices are the 'turbo' diodes.
 
Hello Daddy Pass,

hello dear Diy community

F5, B1 and Pearl Two I finished, I'm still excited about the sound and I want to imitate a turbo v3 but only half.

Without Q9, Q10, Q11, Q12 with 24V power supply. So I want to compensate for missing gain in B1 but equal to achieve good playback as F5 original. And for proven stability of the schemes this should also be involved.
Am I right about thinking here?

Has the topic been discussed?
then I need a link for that


Thanks together!

Dezibaby.

The increase in gain with the "turbo" models is because the feedback is different on the turbo models, not because of more mosfets.

Feedback is decreased, gain goes up, amp is more stable because of less feedback.

You probably want to do V2, with 24V rails. V2 feedback scheme will give you 22db gain, but only 25W/8 ohms wattage because rails are only 24V.

You can even raise the gain of an original single pair of mosfets F5 by altering the feedback resistor values. No need for more mosfets like in V2.

In my opinion lower feedback/more gain sounds worse in this amp. But if you want more power (like V2/V3) it may be necessary to keep the amp stable.
 
Hello everybody,
However, everything is correct if I comb with the chain Pearl Two and B1 at 0 dB level, F5 gets in my case but at maximum volume still no 0 dB and this lack of gain (for example, this 11 dB as B1 with Korg Tube) I would like in the power stage again.

So with my current devices, I'm not yet on "promised" 40W to 4 ohms, I mean. that is the goal and not more achievement. And I do not want to miss out on sound quality.

Many many thanks!
Dezibaby
 
Simple question, probably been answered in the near 1600 pages but don’t have the patients to read them all.

Anyway, if I were to build a standard f5 but each channel in a separate enclosure monoblocks) can I mount the Power transistors remotely on a heatsink on either side of the box. I.e. circuit board in centre of box bolted to the base, wires from the q3/4 pcb points to the transistors that will be bolted in the middle of heat sinks which make up the sides of the box?

I would have to fins a way of remotely mounting the thermistors aswell obviously.

Thanks and sorry for the simple question.
 
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Thanks guys, so possible which is good makes the idea of monoblocks with decent size enclosures ok to build.

Did find this F5 Turbo build, looks like he did it. F5 Turbo Builders Thread

xxoeZcp.jpg
 
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Another question, I was looking to pair the F5 with a set of Dallas II back loaded horn speakers using the Fostex FE208e Sigma plus FT96H super tweeter drivers. However, I am not sure if the F5 has a high enough output impedance to make the best of these (can it be changed?).

Anyone care to comment on this combination or suggest an alternative amp (and board supplier). Looking at the specs a F1 or F2 may be more suitable ???
 

6L6

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Joined 2010
Paid Member
TboneAK - As the others have said, it's all about packaging and scaling the PSU appropriately. There's no real challenge aside the increase in scale.
The heat sinking will be massive if not fan-cooled, and if fan cooled will still be big, plus you'll want redundant fans if one fails.
PSU will need a 1000VA transformer and more PSU capacitance than a 2-channel would require.
 
TboneAK - As the others have said, it's all about packaging and scaling the PSU appropriately. There's no real challenge aside the increase in scale.
The heat sinking will be massive if not fan-cooled, and if fan cooled will still be big, plus you'll want redundant fans if one fails.
PSU will need a 1000VA transformer and more PSU capacitance than a 2-channel would require.

6L6 Thanks! After re-reading Papa's F5 article this morning, I realized my error of scale that was in my mind last night(this morning actually).:zombie::sleep: I new that the heat sinking needed to be big. But this AM I realized it's double what I was dreaming. It's totally do-able, but will need a hand truck to move it. It would give new meaning to "floor model":D

Get one with 5 sets of secondaries....each secondary to an independent cap bank..... I have one, and it is massive.

Big E, do you have to use one secondary per channel? It seems most are building 2ch's sharing one two rail PSU, so I see where your coming from. But on a two rail PSU, each of the two channels share the same V+ and V- outputs. It would think you could run more than two channels. So 5ch off one dual secondary 1000va tranny with a two rail PSU with about 100,000uF each rail should work. Or even two AN-5218 trannys with four bridge rectifiers feeding the two CRC rails.

I have thought of a 2ch and 3ch chassis set-up. I have all the parts including the 5U deluxe chassis for a F5Tv2 build. So a 3ch F5 could compliment that. But the F5T isn't intended for HT use. I could just find an Adcom GFA-7500 like the one I sold years ago for the HT set-up. Getting married and moving across the continent, one has to make sacrifices. :(
 
Blowing fuses

Today my F5 decided to blow the 3.15A fuse on startup. I replaced it and it blew that one. Have a 4A in it now and it's working. Last Sunday I had a group over and the amp was run hard all day without a hiccup.



My PS is standard - Antek 400VA 18v, two CL-60s, one on the red wire of one primary and one on the black wire of the other primary, a third from the PS ground to case/earth. I'm using the store PS board. I'm concerned since this is supposed to run on a 2.5A fuse. Any ideas?


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Today my F5 decided to blow the 3.15A fuse on startup. I replaced it and it blew that one. Have a 4A in it now and it's working. Last Sunday I had a group over and the amp was run hard all day without a hiccup.



My PS is standard - Antek 400VA 18v, two CL-60s, one on the red wire of one primary and one on the black wire of the other primary, a third from the PS ground to case/earth. I'm using the store PS board. I'm concerned since this is supposed to run on a 2.5A fuse. Any ideas?


y4m9doVoYr3zLXJ4kv4htKyGaVMZ4y6QdHpaloZJGfklklN2f97CMY8hseNw3kiqg6pD8Dhvqu25HtBP6WqmXEoHfd8kUOcPW43UesIFz6pDT0o42nNDlLcMz0DcyqHZ9TZpAreUfet6K8sPEmf6LAnkfWVqQeQx4cXcJohUXycp4V-CNQzp3CQLNTg-dbrXUJ0_TNJ69kXkl864WsaGVSCkQ


Have you checked the bias and offset?

Let us know what they are.

Rush