F6 Amplifier

[jugi63]

The manufactor states: Vacuum treatment, Magnetic and electrostatic shielding, Epoxy filling.
Audio - TOROIDY.PL Transformatory Toroidalne Producent, Audio, Separacyjne, Trójfazowe, 230/110V, 110/230V, Na zamówienie

 

[Zen Mod]

no problems with that

 

[vdi_nenna]

Run those values through Ohm's Law wheel few times and you'll see that it holds

Thanks juma. I think I see part of my problem now. I was thinking the output was in W, not mW.

 

[jugi63]

Thanks Zen Mod. I'll go on forward with the design / layout.

 

[necplusultra]

need help biasing.

I'm trying to bias my IRF240 F6 and I'm getting 1.2V on Q2 but 0V on Q1.

Looking for possible causes.

thanks

 

[buzzforb]

If using the IRF, you need to use a Zener instead of the LED in order to have enough bias voltage to turn the fets on. Post the schematic you are using and we will walk through it.

 

[necplusultra]

THanks BF

I'm using the schematic from the F6 article using teabag convertible boards. I'm trying out with the IRF before putting the semis in. Are you saying the IRF need more bias voltage and that's why only one IRF is turning on? I would figure none would turn on in this case.

 

[buzzforb]

Are you using LED's? The transformer does a good job of balancing th top and bottom, even to the point that one could steal from the other. At least this is what I have found. You need to make sure you have Zeners in and reset your trim pots to same value and slowly ring both up together.

 

[necplusultra]

I have leds there but I don't think I have zeners on hand.

What is the Vf for that position for irf vs semis?

Other option is to swap out the irf for the semi

 

[buzzforb]

IRF=4-5V, SS=1.1.5V

 

[necplusultra]

thanks BF

just to make sure I get this, those figures are the Vf at the led positions right?

 

[Zen Mod]

put more leds in series

3-4 greens or whatever

use most common ones , not modern super bright ones

 

[buzzforb]

If measuring across the LEd, you should get around 1.8V. If using the Zener, it should be about 9V or whatever value your zener is. The pot uses this voltage as its reference when adjusting Vgs for the gate of the fet.

 

[necplusultra]

I swapped out the leds and put in 2 4.2 zeners and got about 8.5 Vf at the led positions.
I can bias both sides to about a max of 1.5V no higher. I guess if I put in another zener, I can get higher bias.

Problem now is that when I hook it up my system, no sound - dead silent.

Note that I have everything populated on the teabag board so maybe I have to remove some components for IRF to work. Not sure at this point where to go.

 

[buzzforb]

Are you saying you have 1.5v across the source resistors of the fets? Is it possible that you have the transformer mounted the wrong way. Schematic and pics would be helpful for troubleshooting, just to be thorough.

 

[necplusultra]

I.m biasing to 1.2 but tried to go higher and saw that it does not surpass 1.5V bias accross SG on the second IRF close to the offset pot. The IRF on the bias pot goes higher

also, no heat on sinks.

I'll try to get my camera out later for pics.

 

[lhquam]

Thanks Nelson
I did get inspired at Burning Amp


but credit goes to buzzforb !!!!
He did such a great job with the boards

What output FETs are you using?

 

[flocchini]

The SemiSouth R100s

 

[necplusultra]

Update:

I swapped out the zeners and irf and replacev by 1.8 Vf leds and R100's.

1 side bias to 1.200, the other to 1.226

offset set to .5mv

heatsink gets warm.

put into system and get very low sound from speakers even when volume set to max from input.

system works fine when I hooked to F5

any ideas I get no gain from the F6?

 

[buzzforb]

pics? Sure you got transformer in correct? SOmething is stealing your signal. output wiring pics?