F5 Turbo Builders Thread

To start it all off, I'll outline my plan:

I have some nice, single output winding 35V, 750VA transformers that have been sitting around collecting dust. Two of these transformers will be used per channel. I'm planning on monoblock F5 Turbos running at ~+/-48V rails. This will be based on the F5 Turbo V3 schematic, without any modification initially.

A few questions:

What are the current, reliable sources for matched 2SK170/2SJ74 devices?

For the output devices, is matching even more critical in the F5 Turbo than the standard F5, given the diode action across the source resistors?

For those that built an F5, how many output devices did you purchase to make sure you got enough matched sets?

More to follow...
 
My question is what Jfets can be used for the input stage and can they be source from the more common parts house's like Digikey or Mouser or even Newark?

If so which ones are they?

I don't like having to chase down obsolete parts that are not being made anymore as well as the very high prices when they are actually found.

A few of the semiconductor company's do make some complimentary N and P jfet's and some that are matched in one package.

Can any of these be used?

Please excuse my ignorance on this as I don't no may way around small signal jfet's too good.

I really would like to start building some F5 amps and this is my only stumbling block.



Thanks !!

jer :)
 
1) Spencer and while ago Blues

2) Yes diode action take source resistor out and source resistor are there as a cushion for poor matching

3) I got 100 each FQA12P20 and FQP19N20 (could not get the FQA type FQP is TO220)

Got them from Farnell and batch is all over the place avoid if you can as looks like loads of different production runs mixed up.

Do you have Papa Pass mosfet matching paper?

48 V rails sound realy good and most probably what I will go for on nex build

you will need loads of 63 V capacitors and with current involved I would scale up on Papa design.
 
My question is what Jfets can be used for the input stage and can they be source from the more common parts house's like Digikey or Mouser or even Newark?

If so which ones are they?

I don't like having to chase down obsolete parts that are not being made anymore as well as the very high prices when they are actually found.

A few of the semiconductor company's do make some complimentary N and P jfet's and some that are matched in one package.

Can any of these be used?

Please excuse my ignorance on this as I don't no may way around small signal jfet's too good.

I really would like to start building some F5 amps and this is my only stumbling block.



Thanks !!

jer :)

Same for all Liner make LSK170 and promised the 2SJ74 equivalent but nothink so far

Papa Pass is the best person to keep naghin to give us same alternatives.

F6 with devices currently in production is my bighest dream
 
One thing be realy nice and abowe my capability

Spec sheet with plans for current demands number of devices in parrallel

Power dissipation and sinks.

Capacitance of those is about 2 times the ones on the specs.
so help (explanating delucidification for the mentaly mechanicaly minded) regarding this is certanly a big fawor to ask.

264,000 sound jut about right

Planning for CRCRC wuld also be big improvment especialy with couple of cokes
 
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One thing be realy nice and abowe my capability

Spec sheet with plans for current demands number of devices in parrallel

Power dissipation and sinks.

Capacitance of those is about 2 times the ones on the specs.
so help (explanating delucidification for the mentaly mechanicaly minded) regarding this is certanly a big fawor to ask.

264,000 sound jut about right

Planning for CRCRC wuld also be big improvment especialy with couple of cokes

I'm going to start off with 8 output devices per channel, as per Papa's V3 schematic.

Bias will be determined once I see how hot the sinks get. Heatsinks are 11" x 11" x 2" from R-Theta from the long-ago Aleph-X group buy. Each bank of N or P channel devices will get their own heatsink.

I'm also thinking about starting with CRC and maybe going CRCRC later. Instead of the paralleled 3W, 0R47 resistors Papa has in his schematic, I'm going to use a single 0R07/25W Dale per rail mounted to the main heatsinks. Or at least that's what I'm currently considering!
 
with 4 mosfets on each you may need to paralel the imput J fets
What bias current you planning on ?
Papa said mentioned the hiher the beter they sound
the traffo and I am most probably wrong shuld give you about 11A (750 VA / 70 V )
1 A bias wuld dissipate 48W device well in the TO3P specs and the 4 amps is again prety close to Papa recomendation for the trafos

You be looking at about 380W dissipation on the sinks
I got same 300 X 400 X 83 (12 x 16 x 8 ) and I recon they are good enoug for 250 W

With the rails split between the 2 sinks that sems to be prety much a good fit.

Sems like you done a fair bit of thinking about it already
 
with 4 mosfets on each you may need to paralel the imput J fets
What bias current you planning on ?
Papa said mentioned the hiher the beter they sound
the traffo and I am most probably wrong shuld give you about 11A (750 VA / 70 V )
1 A bias wuld dissipate 48W device well in the TO3P specs and the 4 amps is again prety close to Papa recomendation for the trafos

You be looking at about 380W dissipation on the sinks
I got same 300 X 400 X 83 (12 x 16 x 8 ) and I recon they are good enoug for 250 W

With the rails split between the 2 sinks that sems to be prety much a good fit.

Sems like you done a fair bit of thinking about it already

From Papa:

"The V3 schematic shows 4 pairs of output devices. Realistically you can
expect to get more than 100 watts rms Class A into 8 ohms and 200 watts
Class AB into 4 ohms. You are going to need some serious heat sinking, and
I suggest that the power supply of V2 would be appropriate for a single
channel. Peak output currents of 70 amps are expected but not guaranteed."

The cascoding of the input Jfets solves the challenge of higher rail voltages and is suitable for 4 pairs of output devices. As for the efficacy of the heatsinks I have, this will be determined once I get a board layout completed, have PCBs fabricated, and actually build one!
 
I also have 2 pairs of the 11" R-theta heatsinks and am hoping to do something along the lines of 50W per channel balanced monoblocks per the V3 layout.

For you guys who are fans of big PS capacitance, have you done blind tests to see if you can tell the difference? Say between the 100K uF on the pass circuit vs something like 200K uF? Or lower ESR caps vs higher ESR? I've often wondered how much of it is simply for the bad-a** factor, and although better in theory, isn't audible.

Austin
 
I cold not hear much difference with 100 150 and 200 K rails apart from riple reduction that cames with CRCRC instead of CRC

It wuld be much different if the capacitance was low for the load

say going from 20mU to 40mU as 20 will be definetly to low and 40 border line.

about esr I got a mix of eswa 63 V (cheap) and Rifa 40 V (Rifa) so cant realy say

If I build the 48 V the Rifa are going in the bin (sinfull waste)

I shuld have got 63 V Rifa to start with

With the caps is beter if you get a few hi voltagge ones and add when possible
insted of loads of low voltagge and have no use for them later.

If you need just a 50 w even standard balanced F5 will do

Not many have eard the turbo so far so you may compromise sound quality for power

How did you decide on the 50 W figure?
 
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I always struggle with finding the right enclosure/sink. It would be great to have some guidance on where to get affordable sinks/enclosures that are sized for the job. Someone brought up that they got good sinks from Antek on their ebay store. I like Antek toroids, so that might be a good option.
 
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I cold not hear much difference with 100 150 and 200 K rails apart from riple reduction that cames with CRCRC instead of CRC

It wuld be much different if the capacitance was low for the load

say going from 20mU to 40mU as 20 will be definetly to low and 40 border line.

about esr I got a mix of eswa 63 V (cheap) and Rifa 40 V (Rifa) so cant realy say

If I build the 48 V the Rifa are going in the bin (sinfull waste)

I shuld have got 63 V Rifa to start with

With the caps is beter if you get a few hi voltagge ones and add when possible
insted of loads of low voltagge and have no use for them later.

If you need just a 50 w even standard balanced F5 will do

Not many have eard the turbo so far so you may compromise sound quality for power

How did you decide on the 50 W figure?

Oh not for any rational scientific reason - partly because I already have enough heatsinking for 50wpc, and 25wpc monoblocks with that much heatsinking feels a bit underwhelming. Also, I'll be using them on my zaph sr71 speakers, which aren't the most efficient. My cheap 15W T-amp is fine for now in a small room but I'd feel better with the head room. I have been watching the F5X threads, but I'm guessing the F5T will start gaining more popularity and support over time, as I won't get around to starting assembly for another half a year or so.
 
Scientific reasons and math escape me (or me try to escape)

Yeah I wan't more power to.

There is an easy way to find out how much you need

Set the volume to party time (Uny dorm party time maybe not)

and then play low frequency sine at -12 dB mesure up with DM and multiply by 4
that is the max voltagge you will ask out of the amp F5 clip at 2 V from rails so a bit spare on top of that bit of mat give you the minimum rails voltagge from that the rest is post 12 but I am shure you have read Papa paper and don't need patronising old git to go over it a different way. :D

Pano started a tread about it on multy way and first few post are worth reading.

If you are planning to wait for 6 months by then F6 shuld be out and then it all change
If you got spare bits start with F5 well worth it.

F5turbo sound good on paper for now but does it sound better than F5 ?

Head room is big thing especialy if you listen to Classical
Not so big an issue with modern CD
 
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I always struggle with finding the right enclosure/sink. It would be great to have some guidance on where to get affordable sinks/enclosures that are sized for the job. Someone brought up that they got good sinks from Antek on their ebay store. I like Antek toroids, so that might be a good option.

If you are after same monster sinks gogle up Gorini SRL
They do up to 400 mm wide and can weld 2 or more togheter and cut to any leght

Price put to shame the rest but P&P is the killer