B1 Buffer Preamp

[h_a]

R1 is part of the CRC-filter to reduce ripple of the power supply. Do a search on CRC, a very popular method for ClassA amps.

The B1 has decent PSRR since the jfet is fed by a (jfet) current source, so using a regulator probably brings little benefit. Of course feel free to experiment

Have fun, Hannes

 

[fiscal]

Is R1 the resistor from signal input to signal ground?
If so, then this sets Zin and can be any value from 10k to 100k.

The R1 is that one wich you can see on the full schematic of the B1, just between the alim (+18V) and the C1 (15000uF).

Thanks

 

[Melon Head]

Thanks Jacco
It doesn't hurt to experiment, so I will try your suggestion.

 

[Melon Head]

Hi Jacco
Is this the Shunt Regulator you were referring to?

See attached file.

 

[jacco vermeulen]

Yep, all active parts should be less $ than a single AD825.

 

[Salas]

You can use this one too. Plays good tunes for my NJFET RIAA. Noise floor very low.

 

[Salas]

Compact enough, just warm, won't oscillate easily, readily available Mosfets, leftover unmatched SK170s. Iccs = (Vleds-3.4)/R1 (1W resistor). Start with 10R. Led string of 3 gives different Vdrop total depending on color and maker. Use green ones, more constant. I wanted it ''Kitsch LED Shunt'' so I used tricolore.

 

[jameshillj]

That's interesting, Salas. Could you post the Neg side?

 

[Salas]

Haven't made a negative side. My Riaa is positive only, B1 is positive only with caps, you want to make a capacitor-less one with symmetrical PSUs like I did? I can try to mirror it on the simulator if so.

 

[jameshillj]

Neg reg

That would be nice, if you don't mind Salas.

Instead of the B1, I use a "JC" buffer (k170, j74) like NP's, in the Lightspeed Vol Control for my F3 and headamp (DOA-T) - both have low input Z.

It's nearly totally transparent but is very dependent on the supply - using a "rough" Toole shunt reg at present, and curious to hear the sound of yours, and also in comparison to the "Teddy-reg".

 

[budwiser]

R1 value

I would assume the value is 1 ohm for R1 since the other R values show K or M.

 

[jacco vermeulen]

RC filter only.

1 Ohm times 15000uF times 6.28 ~ 0.0942
1/0.0942~10.5 Hz, an RC filter drops voltage ripple by 20dB/decade.
Means something like 19.5dB ripple suppression in the EC (50Hz mains) and ~1.5dB more in the US(60Hz).

 

[merlin2069er]

I've got a couple of quick questions. I'm got a few more parts to order, but I've got some 'spare' parts I could try.

I've got 100k Stereo pot, and a 100k stepped attenuator from a previous project. I guess I could substitute them in for a while.

What's the best way to scope and test this buffer?

I've got an oscilloscope I haven't used in years, hopefully it still works.

 

[Nelson Pass]

If you get the right DC voltages, the chances are 99% that it's perfect.

 

[merlin2069er]

Great. So substituting pots won't make much difference then?

Thanks,
JG

 

[merlin2069er]

I found this on ebay.

It measures 200mm x 145mm x 70mm (8" x 5.7" x 2.8")

I was hoping I could fit the B1 (sideways) in a case like that and mount the jacks and controls on the front/back.

Aluminum Case

 

[Nelson Pass]

Great. So substituting pots won't make much difference then?

No, they won't.

 

[udailey]

Just put your pot in and try it. It wont hurt anything and if it sounds good to you then you have a winner.
Uriah

 

[Salas]

Re: Neg reg

That would be nice, if you don't mind Salas.

Instead of the B1, I use a "JC" buffer (k170, j74) like NP's, in the Lightspeed Vol Control for my F3 and headamp (DOA-T) - both have low input Z.

It's nearly totally transparent but is very dependent on the supply - using a "rough" Toole shunt reg at present, and curious to hear the sound of yours, and also in comparison to the "Teddy-reg".

OK, I posted negatives. If you ever make any, just let me know about the sound in comparison, since my shunt subjective experience is limited. They are posted in my RIAA thread, and here is the
link.

 

[jameshillj]

Thanks Salas, appreciate your work - will et you know.