F5 meets Buzquito

In which position you use them as paralleled triplets without source resistors (Q2, Q3, Q4) ?
How tight are they matched (Vgs diff. 0.01V, 0.001V or less) ?

They are used in Q2, Q3 positions, matched to 0,05V, but I am sure 0,1V or even higher will cause no risk of thermal runaway (although that will be negative for a sound). Only violation of SOA can be a problem for laterals.
 
...Is this in general, or because you have tried to get higher gain ?...
I didn't try to get more gain from laterals when building F5 with them. The point is that gm of laterals is low - you don't get enough Amperes for Volts invested (in this type of amp - F5)

...
I mean, Profet with same input Jfet and the laterals is supposed to be ok, or ?
If you by "OK" mean that it works, you are right, it is OK. But how it works, i.e. how it sounds? is where it's not OK (IMHO)...
 
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Ah, OK :D

Those drivers k2013 / j313 seems not so easy to find, or am I looking in the wrong places ?

You have chosen not to cascode the input jfets
Maybe you like to say something about that ?

Btw, slightly OT, but I suppose you know Elliot(ESP) did a design(AB) with these Hitachi laterals, project 101
But at some point he put it on hold because he found Hitachi devices hard to get, and most were fakes
Tho this may have changed with the Renesas

But yours is more interesting to me as I have not only Renesas but also the Jfets, and its outsprung from F5 :)
 
...Those drivers k2013 / j313 seems not so easy to find, or am I looking in the wrong places ?
I don't know - j313s were a gift from a friend (thanks estman) and k2013s were bought for me by a friend on a bussines trip to Tokyo.

You have chosen not to cascode the input jfets
Maybe you like to say something about that ?
No need for cascoding here, although I understand that it's a popular fetish these days ;)
 
Hello Juma

Do you still using these amplifier?
I want to know because probably I will give try. I have some orig Japanese Hitachi laterals .
I like these amp , has better feedback than Zenquito .
I have one question , what type of capacitors U use parallel with the feedback resistors and what is the value ?
Please let me know .
Thank you :)
Cheers
 
Hello Juma

Please be so kind answer my question .I'm serious about your amp , I wanted to give a try to the Zenquito but I like these one better .
I think the current feedback much better than what Zenquito amp uses . And the fet driver also I think better than hat old BJT what the Zenquito use for driver .
I already made the PC boards and I ordered the Dale resisters .
I promise I do not bother you just please let me know the missing capacitor values .
I think foil capacitors U use but can be polyprop ,PIO etc .Also the value is important to .
Thanks :)
Greetings gabor
 

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Hello thanh
On the silk screen there is two capacitors next to the feedback resistors, I did mark them .
I have 4 stuffed PC board for the Zenquito , I think these amp would perform better .
Usually Juma has great idea to put together great amps , preamps etc .
Did you finished your F5?
Greetings
 

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Hello

Thank you , unfortunately I don't have scope . But I will give a try. I hope Juma will answer my question .
Also my F5 X not finished yet .
I used Takman metal film resistors , also I used those resisters in a very simple Class A amp and sound to soft compared with the Caddock resisters .
I need to do more test to be sure those Takmans are at least OK or have to replace them .

Thank you
 
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I made room for caps parallel to feedback resistors (150R 2W) in case of oscillations (p2p model didn't show any signs of instability but...)

It looks like Juma didn't have problems with his point to point version.
I would leave out the capacitors to start with, or build one channel with capacitors and the other channel without capacitors bias them both at 100mA and see if the amp without capacitor gets hotter (ie oscillates) than the one with capacitors.
 
Hi Gabor,
I was on vacation (far from computers :) ) so that's why I didn't answer your questions.
This amp is no longer in my possesion (I built it and sold it few months ago to finance other projects).
Caps in parallel with feedback resistors can be from 100pf to 1nF - if you experience oscillations (I didn't - even with PCBs, although I expected it). The cap type is MKP Wima or similar.

This amp sounds very nice, bit more precise and a bit more mellow than F5. The trick is to adjust it nicely. R5 and R6 set the current through k2013/j313 drivers (try different values, about 100mA worked for me) and voltage drop across R9 and R10 sets the current through output laterals. R25 loads the Q3 and Q4, you might want to lower it somewhat (I liked 4k7 in the end). R23 and R24 degenerate voltage gain MOSFETs and if you change their value, you'll have to readjust R5 and R6.

As you see, this is not an industrial type of amp (build-it-by-manual approach is no good here) and you'll have to find the balance of values that suits your sound preferences.
Just take it easy, don't rush it (don't burn anything ;) ) take time to listen, and you'll be fine...
 
Hello Juma

Thank you very much!:)
The main reason I interested on these amp I wanted to build the Zenquito , I have the stuffed PC boards for that to.
When I saw your amp somehow I like these better , mostly because it uses current feedback ,Toshiba mosfet drivers (instead those old TO5 case bi polars), simple nice circuit.
Of course I will give a try for both when I already have them only interested to bias both amp in Class A.
Since I already I ordered the resisters (Dale) and the Toshiba mosfet (drivers) , the rest I have at hand.
I have some 12 pair orig Japanese Hitachi laterals also some EXICON I want to put them in a good use .
I tried the Hitachi laterals in the Profet but I do not like them at all. I got way to soft sound , I have the feeling the pair JFet does not drive them well. It is interesting because with the Exicon laterals in the Profet sound wonderful!
3Watt 0.22R 1% metal film resisters is enough or better to go with 5W cement type?:confused:
Thank you one more time

Greetings Gabor
 

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