Preamp ideas for F5

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juma

juma

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Joined 2005
stein2 said:

....
Edit: So, one question about this one: http://www.diyaudio.com/forums/attachment.php?s=&postid=1613044&stamp=1221762706
Do I have to match the SK170 to pairs for this... ?
Click to expand...


Matching is always nice in LTP, although not mandatory. At least take care that both JFETs belong to same Idss group (BL, V or GR). I used V flavour, but if you choose JFETs with lower Idss, you'll have to adjust CCS' output current, as well as drain and source resistors.
In fact you'll have to recalculate it all over again :rofl:
Ok, tell me what JFETs you have (Idss) and I'll do it for you ;)
 
stein2

stein2

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Joined 2007
juma said:



Matching is always nice in LTP, although not mandatory. At least take care that both JFETs belong to same Idss group (BL, V or GR). I used V flavour, but if you choose JFETs with lower Idss, you'll have to adjust CCS' output current, as well as drain and source resistors.
In fact you'll have to recalculate it all over again :rofl:
Ok, tell me what JFETs you have (Idss) and I'll do it for you ;)
Click to expand...

Thanks for being kind and nice, but you can't help me much around it because I don't have other 2SK170 than the two in the F5 :(

Locally, none of the shops that sell this stuff (Elementa, Lunar etc) don't even have them listed, have to order from Farnell, wait a month or at least two weeks (best case) and somehow I hate to wait for weeks for parts that cost next to nothing. That is why I keep being stupid and have to beg for change... I prefer buying on the spot, have the money, want my stuff...
:devilr:
 
D

dodo

Member
Joined 2004
How about this one
feedback resistors 750R and 2k21 gain 12dB
 

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twitchie

twitchie

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juma said:
Bored by a rainy day I decided to try JFET-CCS-BOSOZ (schematics in attachment) as a preamp for F5. Yes, it has 1k Zout, but that's without significance when driving F5 (100k Zin).

2SK170 are of V type (12mA Idss). CCS gives 20mA. Gain is 6dB (2V/V).
+/- 18V PS is made from F5's PS by means of 7818 and 7918.
Output cap is 1uF MKP + 100nFMKS and it doesn't leave any imprint that I'm aware of.

Preamp is very neutral, nothing is changed in music presentation compared to F5 without preamp, signal is just amplified to level that drives F5 to full power.

I don't know if I like this preamp more than previous one, it's in nuances, so it will take more listening to make a decision. Anyway, circuit is simple, parts are easily obtainable, topology is nice, F5 is light load, it's simple enough to make it p2p, and this preamp sounds better than its' cousin with MOSFETs - what more could a man want to give it a try ? :)
Click to expand...

Will BL grade work here or just become another Choky and Oly Fuse Killer?
 
juma

juma

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Joined 2005
twitchie said:

Will BL grade work here...
Click to expand...

Yes, it will work. But...
Let's say you have JFETs with Idss=8mA. You'd want CCS to supply 12 mA, so R5 should be 56 R. R8 and R3 should be 1k5. R1 and R2 will determine the gain, higher R => lower gain. You can read a lot about it in Mr. Pass' articles (BOSOZ and such) with difference that he used MOSFETs (enhanced mode devices) but you can also find a lot of readings about JFETs on E. Borbely's site.
 
Zen Mod

Zen Mod

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zenmod.in.rs/
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juma said:


Yes, it will work. But...
Let's say you have JFETs with Idss=8mA. You'd want CCS to supply 12 mA, so R5 should be 56 R. R8 and R3 should be 1k5. R1 and R2 will determine the gain, higher R => lower gain. You can read a lot about it in Mr. Pass' articles (BOSOZ and such) with difference that he used MOSFETs (enhanced mode devices) but you can also find a lot of readings about JFETs on E. Borbely's site.
Click to expand...


J310 will work there ...... as a charm

for both Juma & stein - easy and cheap in Su - Elementa

under 10E/100pcs
 
juma

juma

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Joined 2005
After few months of experimenting here is the circuit that sounds best to me - it's the same topology as the first one in this thread but with BJTs in output and higher Id through JFETs (6ma).
It takes the +/- 24V from F5 (they are both in the same case - F5 as integrated amp) and preamp's OUT is connected directly to F5's input.
I used the PCB from the post #3 of this thread but with some diferent components and values.
 

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juma

juma

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Joined 2005
Thanks, estman.
Yes, the MOSFETs could be an option if higher output current is wanted. For driving F5, this preamp sounds better with BJTs. I tried IRF610 and IRF9610 - some smaller MOSFETs, like ZVP3306 and ZVN3306 might sound different but they are unobtainable to me.
 
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estman

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Joined 2005
juma said:
I tried IRF610 and IRF9610 - some smaller MOSFETs, like ZVP3306 and ZVN3306 might sound different but they are unobtainable to me.
Click to expand...

Hi juma,
no...no, I thought to use only AUDIO mosfets - Toshiba 2sj313/2sk3013 for higher output current and for lower current (F5) Hitachi 2sj76/2sk213.
I have too many 2sj313Y - can send to you for Christmas if you PM me with your data. :hohoho:
Unfortunately I have no adverse part - you must have possibility to get it yourself !
 
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