The F5X Preamp

PCBs and matched FETs yes. I can even manage myself in the worse case.
Design document has already been written, so only BoM missing.
But no more baby sitting from me, as you are all experienced enough, and can (should) help each other if necessary.

Chassis is probably the most difficult and time consuming. I have not even got mine after 1 year.
So we'll have to see......


Patrick
 
PCBs and matched FETs yes. I can even manage myself Chassis is probably the most difficult and time consuming. I have not even got mine after 1 year.
So we'll have to see......

Patrick

Maybe it would be possible to do something like creating a design for a case and we all order from the manufacturer - Front Panel Express could maybe do it, or someone local to you Patrick, and we put in an order with the manufacturer. That would be easier on all of the Xen team I'm sure.
 
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PCBs and matched FETs yes. I can even manage myself in the worse case.
Design document has already been written, so only BoM missing.
But no more baby sitting from me, as you are all experienced enough, and can (should) help each other if necessary.

Chassis is probably the most difficult and time consuming. I have not even got mine after 1 year.
So we'll have to see......


Patrick

I can certainly sympathize Patrick, my "work in hand" has taken forever with the chassis work...even with my CNC and a lot of redesign and sim work in 3D
...way more time than the electronics.

But it's all been fun ...the fact that i had a similar 2014 to the Xen team did not help...in my case it was my own health.

The Forum team here is what is great to work with so we should have a layered approach to your projects...after you publish the forum should do the support ...we should organize ourselves for that, i think, and so free you and the rest of the Xen team.

Certainly we cannot let the F5X Preamp die....it looks much to good for that, as do all your other projects...Headamp ( s ), IVs...
 
Euvl,
I have etched a set of boards for this preamp and had a questino about biasing procedure. I would guess that the ideal way to do the biasing is to ground the bridge and bias each side individually, reconnecting the two sides after stable and equal bias has been achieved.

Also, is it correct that the two resistors from each output to ground, along with the mosfet source resistors, set the gain of the second stage?
 
If you want to test build, you could have asked me and I shall arrange a pair of boards send to you, at cost.
Better build it according to my layout. You can help to prove that they are bug free.
Contact Gogowatch. I'll ask him to arrange for you.

The building procedure is the same as the F5X.
So check that build thread and just adapt the bias current to those published for the preamp.


Patrick
 
I will proceed with this build and let you know how it goes. My layout is somewhat different and not as efficient, but I hope it gets me most of the way. For the FE, I have chosen to go the BA amp route and put matching source resistors with a trim pot to twiddle with the final outcome. I used 20 ohm source resistors, perhaps more than you had planned. Same is tru of the output, as I am using 10R degeneration to start(possibly moving to 5) and loading the output with 200-400r. Final choice will be based on testing. I have the feedback resistor at 100, as I want overall gain to be around 5. I know this amp can easily do more, but thats all I want. I chose it as i expect that it will be transparent and quiet, and excel at disappearing. I want to retain the character of the power amp that it will be paired with.
 

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You are most welcome to build whatever variants of the circuit to experiment with.
But please call it something else so as not to confuse with what I published.

The offer for original PCBs is still open.
But I guess you want to go your own way, which I encourage whole heartedly.
In that case I suggest you start a new thread to record your adventure.
And I am most interested to know how you end up eventually.


Patrick
 
I would wholeheartedly try your circuit, but do not have teh values you chose. In that regard, I guessed. I think that functionally they are the same, with difference being mostly in values chosen. I believe you decided to go with the Renases laterals, which i cannot get in matched pairs and do not want to invest the money to buy enough to match. I just happen to haev matched Toshibas. If you would be willing to share the values you experimented with in your Toshiba trys, I will happily give it a go. My version is definitely a cheap knockoff, and I was just trying to confirm what I suspected was the general operational nature of the circuit. I dont have the determination or knowledge to go as far as you do in your trials.
 
Kinda what I figured, so I am bastardizing the circuit with values similar to the BA3. I know you match your Jfets with specific Rs values, but in truth, the Zentrimpot accomplishes a similar result. You win in regards to no trimmer in the signal. I used pots for biasing and trimming offset, but these can be replaced with fixed resistors when a value is found. All in all, pretty close, but definitely not at the quality level of yours. Was gonna do SMD, but since I was etching at home, I went with easier through hole. Well thanks for the idea and help. Look forward to your results.
 
Very true. Layout is very important, but i think you are getting into the final 5% of circuit tweaking at that point. operating points are definitely the big one. DId i see tha you varied the gate resistors on your output mosfets? Is this a way to improve their complimentary nature? If i am pleased with the outcome, I may ask to be a test monkey, if that is acceptable.
 
As I mentioned earlier in this thread, the JC-80 from John Curl also uses similar topology.
(I wasn't aware of that when I first published.)
John did his design of course way back, and used different devices and component values.
And there is no doubt that the JC-80 is a fantastic preamp.

But the F5XP is what it is. It is not JC-80, not even a clone or a copy thereof.
Just as the original F5 is not a variant of the ProFET.

http://www.selectronic.fr/media/pdf/4180.pdf


Patrick
 
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