PeeCeeBee Preamplifier GB

[Oracle1]

May i ask again...
Increasing R55~R58 give more gain. (#362). Let say 2,7k or 3K is enough for F4 ?

 

[shaan]

Hi Oracle1.

2K7 should be enough. You will notice output bias to increase after the mod. Turn the trimmers to get it to ~15mA.

 

[shaan]

isn't this preamp similar to weyn line stage 2018?

Is it?

 

[Kokanee]

Hi shann,
I am wondering if this Tx is OK for this preamp. I measured the blue-black-blue unloaded and got 16.2V for each blue-black and 32.5V total. Specs say 2A/250V as in the pic attached.

Also have an Rcore type, but the yellow V's are 28V, the orange V's are 20V, and the grey V's are 35V. So the 20V are a bit high for this. I will probably be able to use in another preamp or power amp. See pic attached.

 

[shaan]

Hi Myles.

16.2V may get the rectified voltage too close to the filter caps' max 25V rating.

 

[Kokanee]

Thanks shaan, May have to go toroid transformer shopping or could I possibly use a good quality laptop brick brick/wallwart and a Dc-DC boost to get the correct voltage. Sounds like +/- 15V is maximum, Correct?

 

[shaan]

You can connect the boosted DC to the AC inputs, 0V to the center terminal, + and - to any of the other two. If you want good filtering from the regulator and 15V rails to the gain sections then at least 19V input per rail is a good idea.

 

[Kokanee]

Thanks shaan,

So choices are a 15V-0-15V/30VA center tapped transformer or the wallwart/laptop brick (with added filter to clean up noise) and the DC-DC boost to 19V per rail.

If going for the CT trans., is a toroidal type good enough (probably Antek)?. My hearing is compromised and I am not sure I would receive any benefit from an R-core type. It may measure better, but I may not be able to hear any benefit.

 

[shaan]

Yes, go for a 15V center tapped toroidal. R core not required.

 

[Kokanee]

Thanks shaan. Nice to see you back. Waiting on some parts for pre and psu, then shall continue. Working on V4H in the meantime.

 

[poseidonsvoice]

May i ask again...
Increasing R55~R58 give more gain. (#362). Let say 2,7k or 3K is enough for F4 ?

See this post. And this post.

Best,
Anand.

 

[inyashd]

Can use 1k for VR5 & VR6 as per schematic.
In BOM 5k.

 

[sunilmani]

Hey inyash, I see that like me, you are from Pune as well. I am interested in the pre-amplifier and wanted to know if you could find all parts from the local shops here

 

[sunilmani]

@shaan - do we have anymore PCB's left? Appreciate if you can message me the details directly

 

[r mani]

I got a Pre module from Shaan with resisters in VR1 to VR4 instead of trimmers without any note....

 

[hd3291]

Anyone using this as HPA ?

 

[shaan]

@shaan - do we have anymore PCB's left? Appreciate if you can message me the details directly

One PCB left from last batch. New batch will be printed next month.

I got a Pre module from Shaan with resisters in VR1 to VR4 instead of trimmers without any note....

The trimmers I got were all fakes and caused crackling/static noise within a month of usage. So I measured which value give the required bias and install fixed resistors of nearesr value. Sorry for not telling you.

 

[VIPINSAINI20]

hey Shaan ,
can you post pics of those fakes 3296 pots

 

[VIPINSAINI20]

this one is available here, do you think are they fakes too

 

[asuslover]

Take a look at some authentic ones.