• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

Juma's LSK Preamp - through hole version

Status
Not open for further replies.
Jump to Latest
#261
The circuit is a capacitance multiplier.
It is used to attenuate hum and it's low harmonics.
That is usually done by setting the resistor ladder to around 90% of the input voltage and feeding that to the gate lead.
The mosFET drops a further few volts, typically 2 to 4V.

if your input is 54Vdc then 90% is ~49V and take off ~ 3V for Vgs and you end up with ~46Vdc.
The average voltage drop across the mosfet is around 8V and thus it stays fairly cool.
 
#266
Folks:

Uhmm, a work in progress. One question: should the attenuator go before or after the LSK boards?

Regards,
Scott
 

Attachments

  • LSK Preamp Mid-Construction.jpg
    LSK Preamp Mid-Construction.jpg
    744.2 KB · Views: 665
#269
Has this project petered out simply because everyone who bought boards is happy, or has it transpired that there is too much difficulty in getting them to work to expected standard?

I ask because I am considering - after all this time to health issues - building the set I bought at the outset of the GB.

[My boards are PS rev.2.7 and pre are rev.3.0]
 
#271
brianco:

Funny, but my build has been, uhmm, sporadic at best. I have high hopes that the LSK preamp will supersede my beloved Aleph P 1.7, but at the rate I'm progressing on the project the LSK won't be finished until long after I've gone completely deaf.

Distractions, distractions...

Regards,
Scott
 
#272
brianco said:
Has this project petered out simply because everyone who bought boards is happy, or has it transpired that there is too much difficulty in getting them to work to expected standard?

I ask because I am considering - after all this time to health issues - building the set I bought at the outset of the GB.

[My boards are PS rev.2.7 and pre are rev.3.0]
Click to expand...

I posted the above quoted almost a year ago; there has been no response as such.

Has anyone built a successful preamp of this circuit on the GB boards?
IF so then what are the comments on the pre in normal usage and what power amp is being used?

Many thanks,

B
 
Last edited:
#275
I'm part of your silent people as I bought the boards some time ago and then bought a used assembled board off one of the members here that had trouble reducing a troublesome dc offset on the output pins - thought I'd have some fun sorting this out but haven't got onto yet - recently, started assembling parts for the F6 amp (to replace the juma version F5) so the preamp (thru hole version) is back on the table

I don't know why it's not had a better support tho - it just didn't seem to 'catch on' and maybe, at the time, there was a lot if other 'stuff' going on

The juma variations to the F5 made a rather large change to the sound (I keep saying HUGE but ...) - I added different components and a better power supply, and the result was a much more relaxed, more musical sounding amp, just like juma originally mentioned

All the best ...
 
#277
Since you guys seem to be having no luck with support for this thread, may I offer Ann alternative?

If anyone is looking for a simple high performance DC coupled preamp, the TimS HPA design that I am developing now with JPS64 could work very well as a Preamp. It also uses BF862 and there are no hard to find or expensive parts.

Simple High Performance DC Coupled Class A HPA with sub PPM THD

We are working on an integrated stereo version with a built in dual rail PSU that doesn’t require wall mains AC.

Another option is the Aksa Lender Preamp, which sounds excellent and can drive an F4 to clipping, but it is AC coupled.

AKSA's Lender Preamp with 40Vpp Ouput GB

Both are/will be well supported throughout the build process.
 
Status
Not open for further replies.
Top Bottom