Help with newly built F1 Amplifier

[spades]

Finished building an f1 amplifier today carried out checks to my dismay things appear to have gone to pot.This is my first scratch build amplifier having built valve kits and fiddled with equipment over the years.The numbers are as follows R Q1 11 VDC L Q1 10.53
Q2 12.32 Q2 9.70
Q3 11.06 Q3 11.56
Q4 12.55 Q4 9.63
Q7 Drain 8.02 Q7Drain 7.28

R27 0.565 R27 0.576
R28 0.56 R28 0.565
R29 0.567 R29 0.575
R30 0.559 R30 0.565

Gate Q1 11.04 Gate Q1 11.76
Q2 13.36 Q2 9.50

Dc Offset 2.0vdc Dc offset 2.2vdc
Sorry for the long post would like to get this amplifier working mosfets bought matched irfp240 and irfp9240 ,my aca never gave this amount of trouble to get going.But this is the joy of diy as well as trying to learn from ones mistakes any help guidance would be greatly appreciated .I have read all the posts I can find but none seem to cover my problems.Thanks a lot spades.

 

[Nelson Pass]

Your current sources appear to be working, but the voltages for biasing
and output are off. try adjusting R7 and 8 upward - you want about 7
volts on the Gates of Q1 and Q2 and their Drains want to be around 15V.

Also, check R5, 6,7, 8 to see if the values are way off.

 

[spades]

Thanks for the speedy reply

Thanks for replying Nelson so quickly the figures I gave you were taken after amplifier was on for at least 1.5 hours.Despite my best efforts adjusting p1 the figures were the best I could achieve .I will do as you have suggested but any ideas for a ball park figure for r7& 8 to start with.ps the aca are great these are brilliant and have caused me to investigate your other diy designs depite my aged newbie status Again in my thansks Alrick(spades)

 

[Nelson Pass]

Upward would be maybe 470K.

 

[spades]

Thanks Nelson for the quick reply will order the parts and try those values.Thanks Alrick(spades)

 

[spades]

Tested resistor 8 this is showing 390 ohm as opposed to 390k this take it will affect the figures I have been seeing Nelson.Thanks again Alrick (spades).

 

[spades]

Iam still having problems with this amplifier.Resistors checked none wrong apart from the one mentione in a previouse post.Implemented your change to resistors 7-8 with 470k ,despite adjustment drain on q7 left side on 1.8volts dc right side at 7 volts dc.Ofset on left side is still 1.45volts dc whilst right side is 2.45 volts dc.Afraid to connect any speakers in case it fries them.Anyway nelson any other suggestions.Ps may scrap these boards and try again do you know of any reputable sources for matched mosfets .Thanks Alrick(spades)

 

[Zen Mod]

ask member h_a for matched mosfets

you need , if possible , just one pair per channel , for Q1 and Q2 positions

check all values , parts placement and it must be OK

pictures of your amp would help in troubleshooting

 

[spades]

Thanks ZenMod for the advice my photos could not be sent as a security token was missing.Anyway the chassis i have purchased from an ebay vendor ,later found out that person was banned from the forum.So as not to cause offence if i can sort out security token i will post photos of the boards whilst trying to show as little of the surrounding amplifier chassis.My next build i will source an appropriate chassis. Thanks Spades

 

[spades]

I have rebuilt the f1 amplifier with matched mosfets from a forum member however all voltages very low on q1-4 on both sides drains at 3 volts whilst drains on q7 are 8 to 9vdc on each one plus gates on q1-q2 both sides are 1.5 volts any help appreciated. If no luck may scrap and start f2 at least not balanced.

 

[Zen Mod]

can you post schm with measured values?

 

[spades]

Thanks for your reply zenmod but i have had enough stripped all boards theses never worked properly.Next week will start on f2 as these are not balanced hope they will not be as much trouble to get going .I hope i can count on your help and advice should i need it RegardsAlrick(spades)