"Compact" VFA

[still4given]

Hi Peter,

I have checked your values - R3, R7 = 1.2K, R4 = 150R are fine (+/-60V rails).
6x5.6K result in VAS current = 15mA. Rather high, but acceptable with a decent heatsink.

Alert to everyone - found a typo mistake!
R7, R17, R18 must be 15K each!!!

Peter, in your case you can use 2x10K for the same value (5K), 2W is acceptable.
R8 = 1.5K, yes, slightly higher voltage gain (29.8db instead of 28.3db) - still OK.

Cheers,
Val

Do you mean R6, R17, R18? Bummer, I just finally received and installed the 8k2 resistors. OK, back to Mouser.

 

[vzaichenko]

Yeah, sorry for that - copy/paste mistake ((

 

[borys]

Thanks Valery, I will get the irf610 mosfets and do some boards to fit my OPS board.

Thanks
Peter

 

[thimios]

Thanks Valery, I will get the irf610 mosfets and do some boards to fit my OPS board.

Thanks
Peter

IRF9610

 

[still4given]

So to be clear. The schematic shows three 8k2,1w resistors for 2k7,3w total. You are saying we need three 15k,1w for 5k,3w total?

I just want to check before I order more parts.

Thanks, Terry

 

[vzaichenko]

So to be clear. The schematic shows three 8k2,1w resistors for 2k7,3w total. You are saying we need three 15k,1w for 5k,3w total?

I just want to check before I order more parts.

Thanks, Terry

That's right - three 15K, 1W for 5K, 3W.

 

[still4given]

Ok thanks

 

[Idefixes]

Hi Valery,

As it's not easy to each precise double layer at home i attemp to do single layer routing job for 6DJ8-All-Fet-IPS. Could take an eyes on it for advices...

 

[vzaichenko]

Hi Valery,

As it's not easy to each precise double layer at home i attemp to do single layer routing job for 6DJ8-All-Fet-IPS. Could take an eyes on it for advices...

Hi Marc, that's great - thank you for doing this 🙂

Looks good, just one thought - it would be useful to keep physical orientation of the MOSFETs (Q2, Q3) in such a way, that it's easy to attach a heatsink to them - in case of rather high VAS current, they will be moderately warm, so some small local heatsink is recommended.

Cheers,
Valery

 

[Idefixes]

Hi Marc, that's great - thank you for doing this 🙂

Looks good, just one thought - it would be useful to keep physical orientation of the MOSFETs (Q2, Q3) in such a way, that it's easy to attach a heatsink to them - in case of rather high VAS current, they will be moderately warm, so some small local heatsink is recommended.

Cheers,
Marc
Valery

i will take a look but think i can attach a local heatsink even in this position

 

[Idefixes]

Hi Marc, that's great - thank you for doing this 🙂

Looks good, just one thought - it would be useful to keep physical orientation of the MOSFETs (Q2, Q3) in such a way, that it's easy to attach a heatsink to them - in case of rather high VAS current, they will be moderately warm, so some small local heatsink is recommended.

Cheers,
Valery

Here the modification according your advice....

 

[Idefixes]

Some little modifications in layout. They allow to suppress two staps

 

[vzaichenko]

i will take a look but think i can attach a local heatsink even in this position

Yeah, it was just an overall recommendation - leave it, I think it's very good as is.

P.S. Ah - did not see the latest version - this one is just perfect!

 

[vzaichenko]

6DJ8 Compact VFA - CORRECTED

Hello All,

Attached are the docs with all the recently discovered mistakes corrected.

Cheers,
Valery

 

[vzaichenko]

Compact Amplifier - Singleton CFA - "as built" refined

Compact CFA Singleton with jFET+BJT Sziklai at the input is refined for ultimate stability and reliable performance.

Attached is "as built" schematic and spectrums, measured at 50W output power @ 8 ohm dummy load.

Power supply is +/-52V DC, quiescent current is 80mA per output pair.
Layout is corrected accordingly. It's mostly TH with some SMD components, including DC servo underneath the board. PCB size: 5.5 x 3 inch.

Have fun!

Cheers,
Valery