F5 Turbo Builders Thread

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#2,941
If distant memory serves, when fed 120 VAC my 1 KVA rated dual 42VAC rated transformer gave me 61V DC unloaded and 58V with 2 A bias using 90,000 µF per rail, not CRC.

As jdg123 is likely to measure his off load voltage and may have a way to load (light bulbs?) the transformer to help characterize it if he wants to proceed down that path.

But from a design standpoint, he'll be safe if he designs his heat sink setup for 60 VDC since the actual rails will be lower. No need to bicker over a few volts as long as the result is less than 60 😉

Looking forward to hearing your about your journey as I begin to assemble my F5T V2C. Boards are stuffed minus diodes and the output devices that I am about to start matching. I have around 25 each of NOS Fairchild IRFP240/9240. Should be pretty easy to get matched pairs. Much easier than trying to find 6 per set matches for my A75s.

To answer another question, you'd need to buy at least one more board set to add output devices, unless you feel comfortable making your own or going point to point on perfboard.
 
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#2,942
AudioSan said:
those looks fine.
preamp is all about taste. you don't need much gain from it when you have 22db gain in the F5.
J-fet boz, is simple as hell. and People like the sound (have not tried it yet)
aleph P1.7. more complex and expensive. but i love it with the F5.
B1. but this is a buffer whitout gain.
Click to expand...

Thank you AudioSan!

I'm planning to build the BOZ and I've read that it have too much gain for the F5T, isn't so?
 
#2,944
I don't remember, they were surplus custom transformers. I would assume that it was rated at 117/234 since that's what the manufacturer, ToriOd.com: The Leading Electronics Site on the Net, uses for its standard product line. Just to throw another possibility into the mix. 😉

Everywhere I've lived and worked has line voltage of 117 to 120V. That's primarily in the northeast US. Avel Lindberg rates their transformers at 115/230 so I'd expect a bit higher voltage out of them. Plitron rates US spec transformers at 117 and European transformers at 115/230, with a world option of 100/120/200/240. Sheesh - guess you just have to measure what you've got if it is surplus or reclaimed.
 
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#2,945
bob. then it starts to make sense🙂
then you have dual 43.2V sec under heavy load.
58VDC/43.2VAC=1.34.
and 2A load pr sec is a "light" load for that transformer. so sec is likely around 44Vac.
58VDC/44VAC=1.32. add a CRC filter, and we are down to 57.5🙂
57.5/44= 1.306
 
#2,949
The operational resistance of the NTC thermistors depends on the current. Higher current lower resistance. So, when you start cold whichever parallel string has the lowest net resistance/heats up the quickest ends up hogging most if not all of the current. You don't get double the current capacity. A lot like mismatched output devices.

So a string of whatever thermistors are needed to carry the operational current with enough thermistors to get the required cold resistance is the way to go.
 
#2,950
BobEllis said:
The operational resistance of the NTC thermistors depends on the current. Higher current lower resistance. So, when you start cold whichever parallel string has the lowest net resistance/heats up the quickest ends up hogging most if not all of the current. You don't get double the current capacity. A lot like mismatched output devices.

So a string of whatever thermistors are needed to carry the operational current with enough thermistors to get the required cold resistance is the way to go.
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I understand that in this softstart there are 4 equal value thermistors. Are you saying that even the slight differences in resistance between each of them would result in current hogging? Thanks. Just tying to understand this.
 
#2,952
Pre-amplifier with output gain of 212mV, 830mV or 1.25V?

Hello to all,

I bought a pre-amplifier Rega Cursa 3 to F5 V2 Turbo.

The preamp has 3 outputs gain.

Option 1 - 212mV @ 100 Ohms
Option 2 - 830mV @ 100 Ohms
Option 3 - 1.25 V @ 100 Ohms
Maximum output level 8.8 V

What will be the most appropriate for the F5 Turbo V2 output, option 1, 2 or 3.

I'm currently using the one that comes by default which is 2, comes down to the Maia Rega amplifier.

Thanks for the tips.
 
#2,959
Front End Testing Question

It's always a good idea to install FE first, test it with power, before installing output. By doing things in series, you slowly work to the end, checking as you go. That way if something is wrong, you wliminate certain steps. Check gate voltages of the mosfets. Pots could be switched. Basically you have one side contributing most of the output, almost like its in AB mode.
Click to expand...

check that P1 is ok. you can do so by massure resistance over R5 without any power. you will want to see close to 0ohm.
Click to expand...

Finished populating the front end board and getting ready to apply power. Following Buzzforb and AudioSan's recommendation from posts #801/802 above, I measured resistance across the two resistors. For P1 I am able to adjust resistance across R5 to 0. For P2 I am not. I get 845 ohms with no change when turning the pot. I tested the pot before I soldered to board and was able to confirm it's r values thru its range.

AudioSan didn't reference P2 specifically but is the value I'm showing and the fact that it doesn't change when turning the pot OK or a problem?

Thanks in advance.
-Jeff
 
#2,960
Have you turned the pot all the way from one end of it's run to the other? The PCB is set up so one pot (don't remember which) turn 'backwards' to increase resistance.

Can you take a few well-lit, in-focus photos? You might have a missing connection somewhere, or something else than fresh sets of eyes can spot.
 
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