F5 power amplifier

[Nisbeth]

Thanks for the comments guys

NS: Tried swapping inputs already and that makes no difference, the hum stays in the same channel. I have a (dual-channel) scope, so I will do some poking around with that

Andrew: Curious as to why you recommend this, is it because of the load on the PSU (the amp is dual-mono, so presumably no difference) or because of grounding?


/U.

 

[AndrewT]

.............. Curious ............... or because of grounding?

different routes for the return currents between the two channels. That's why I find it much easier to get quiet monoblocks. They cannot have different routes between channels when there is only one channel.

 

[mfrimu]

Would using two transformers be 'monoblock' enough ? I still have not ordered the transformer, would not be that hard to get 2x200VA instead of one 400VA.

 

[tinitus]

---------- would not be that hard to get 2x200VA instead of one 400VA.

or 2x 300VA

or 2x400VA, if you should choose to make it balanced one day

 

[AndrewT]

Would using two transformers be 'monoblock' enough ? I still have not ordered the transformer, would not be that hard to get 2x200VA instead of one 400VA.

No,
Monoblock means one channel. There cannot be shared common routes for any flow nor return currents in a pair of monoblocks.

 

[mfrimu]

Ok, but putting 2 monoblocks into one chasis ? What's the difference?

 

[AndrewT]

They will share some wiring. They are no longer monoblocks.

If we were sufficiently competent to build safe Double Insulated equipment then a dual mono could perform electrically as two separated monoblocks. But we can't, so we are stuck with stereo, dual mono, or a pair of monoblocks. They all perform differently electrically.

 

[6L6]

Nelson Pass, in his article about power supplies, says that separate transformers and capacitor banks gives you most of the benefit of monoblocks.

http://passdiy.com/pdf/powersupply.pdf

Look under 'mono operation'

 

[regiregi22]

They will share some wiring. They are no longer monoblocks.

If we were sufficiently competent to build safe Double Insulated equipment then a dual mono could perform electrically as two separated monoblocks. But we can't, so we are stuck with stereo, dual mono, or a pair of monoblocks. They all perform differently electrically.

What if I put two monoblocks inside one big enclosure? They'll still be monoblocks. What if I start taking out pieces from each monoblock original enclosure, at what point is the two monoblocks situation turned out to be dual mono?

 

[tinitus]

dual mono is 'basicly' two mono blocks in one box
means each channel have each their own complete power supply

but they share the same ground, through chassis
and ground connects to signal ground(neg), one speaker terminal(neg)
and power supply ground
more or less

 

[dionisio]

F5 alive!

First music today....Gee wizz this thing sounds good!!!

As always I gots lots o questions to find answers for but I could use a little help for a couple...
1 Are the thermistors supposed to be touching the fets or just close by,,, say an 1/8 inch or so?

2 My xformer (antek 6218) starts to hum (not loud) every minute or so for about 30 seconds.. during this cycle,, mains V drops 1.5v and supply voltage drops a few tenths... also my supply voltage is lower than i expected at +- 22.5... and I can hear hum on the speaker faintly...
any thoughts?
thanks

 

[triode_al]

This sounds typical of DC in the powerline. Use a bridge in the mainssupply, shorted +/-, and have a dipole capacitor over the unit (6.3 V/1.000 muF or s0).
This should block DC (up to 1,3 volt), toroids are very sensitive to that, get saturated sometimes at even 1 volt DC. They will then start to hum.
That explains the dropping of the output voltage.
imho this will also save on the power bill!

hope such a ting helps.
Power line conditioners of this type have been widely posted.
albert

 

[triode_al]

Hello,

I just noticed another issue - the rectifiers are in a weird configuration with AC to ground. I guess I'll have to use proper recifiers or re-wire.

Thanks

This is just a naming convention on the diagram. No need imho to change the physical layout. The name refers to the 'interface' going to the bridge...
albert

 

[Zen Mod]

......
1 Are the thermistors supposed to be touching the fets or just close by,,, say an 1/8 inch or so? .......

to touch .

...

2 My xformer (antek 6218) starts to hum (not loud) every minute or so for about 30 seconds.. during this cycle,, mains V drops 1.5v and supply voltage drops a few tenths... also my supply voltage is lower than i expected at +- 22.5... and I can hear hum on the speaker faintly...
..

for excessive hum - you either have DC in mains , or xformer is bad - if everything is ok with rest of amp ;
but you say - it's working and making noises , so I resume it's good

PSU voltage is good

 

[Nisbeth]

different routes for the return currents between the two channels. That's why I find it much easier to get quiet monoblocks. They cannot have different routes between channels when there is only one channel.

Just wanted to follow up on this and say thanks to Andrew for the tip about disconnecting one channel (I'll keep that one in mind for another time). Did some poking around in the amp and some resistance measurements and finally found that the cause of the hum was that I'd swapped input and GND cables on one channel

The amp is now very silent in both channels and plays beautifully

/U.

 

[dionisio]

This sounds typical of DC in the powerline. Use a bridge in the mainssupply, shorted +/-, and have a dipole capacitor over the unit (6.3 V/1.000 muF or s0).
This should block DC (up to 1,3 volt), toroids are very sensitive to that, get saturated sometimes at even 1 volt DC. They will then start to hum.
That explains the dropping of the output voltage.
imho this will also save on the power bill!

hope such a ting helps.
Power line conditioners of this type have been widely posted.
albert

Thanks Albert ,,,I have began reading up on it....

to touch .



for excessive hum - you either have DC in mains , or xformer is bad - if everything is ok with rest of amp ;
but you say - it's working and making noises , so I resume it's good

PSU voltage is good

Zen mod,, when you say ,,PSU voltage is good
do you mean my supply at 22.5v is good?
Just clarifying, thanks

 

[Zen Mod]

exactly

2x18Vac , resulting in 2 x 22.5Vdc under load is completely OK

 

[h_a]

Nice amp!

and I can hear hum on the speaker faintly...

Might be a small grounding issue.

Hannes

 

[bear]

First music today....Gee wizz this thing sounds good!!!

As always I gots lots o questions to find answers for but I could use a little help for a couple...
1 Are the thermistors supposed to be touching the fets or just close by,,, say an 1/8 inch or so?

2 My xformer (antek 6218) starts to hum (not loud) every minute or so for about 30 seconds.. during this cycle,, mains V drops 1.5v and supply voltage drops a few tenths... also my supply voltage is lower than i expected at +- 22.5... and I can hear hum on the speaker faintly...
any thoughts?
thanks

kewl heatsink fin idea!

how did you work out the attachment between the "fins" and the back plate?

_-_-bear

 

[dionisio]

kewl heatsink fin idea!

how did you work out the attachment between the "fins" and the back plate?

_-_-bear

Thanks Bear
The heatsink idea was not mine.. I got the idea from the Burning amp chassis that were given away at burning amp a while ago..
Each tube is attached using 2 screws from the inside of the tube into the back plate..