Driving a 600R LCR RIAA stage

[Dave the bass]

I've been thinking, no really, y'know how its been discussed to death how hard it is to drive some of the commercially available 600R LCR modules?,,,, has anyone ever thought about using a transformer to driver the LCR module itself?

Imagine, 1st stage or 2, sweet sweet pure voltage amp/s... feeding a step down TX -> the Lo Z RIAA LCR stage. That way the 1st/2nd stage VA are happy working into Higher Z's, the 'LCR Driver-TX' does the grunt work in trading Voltage swing for driving current not a complex valve network.

Now then, either...

a) I'm some kinda jeanius...
b) someones done it before and its crap.
c) I'm missing a few crucial points.
d) b + c added together.
e) there is no e) (copyright Brighton Beach Babe Ivimey).

I'm preparing for a flaming/public ridicule/humiliation/forum ban!

[thomas]

There's a thought.
Line output transformer. Sowter do them, 10k or 15k to 600r.
Hmmmm…..

[izzy wizzy]

That would be the standard way to do it. Some then use a stepup after the LCR network.

cheers,

Stephen

[IslandPink]

You can do it that way but then you're sending the audio signal through another transformer with its limitations in terms of frequency response ( inductance ) particularly at the low end, and loss of small signal info which needs very special cores and interlayer materials to preserve. It can be done pretty well ( I've probably heard at least one LCR like this in Germany ) but if you can do it avoiding a transformer ( eg. with an active-loaded cathode follower of low Zout ) then all the better. One of the recent improvements to LCRs ( eg. Andrew's and Nick's ) is to get LCR chokes made for higher impedances like 1.5k or more. This is enough to make valve CF or Aikido drivers more attractive .

[Dave the bass]

Ta Mark n Izzy, Meh! No Nobel prize for me then, double meh in fact, thought I was onto a winner there.

I've seen 600R and 10K LCR units on the Silk (Thailand) website here -> http://www.sacthailand.com/Transformer_LCR.html the supporting cct uses easily obtainable (cheap too) Valves too but there's gotta be a catch. DIY HiFi Supply mention there's a slight HFdrop with the 10K unit on their page.

1K5-wise, only the Dave Slagle units seem to come up. There's some familiar names on the Intact forum from a few years ago

I've had enough of my current Phono stage, the RIAA is done in the FB loop and it sounds poop compared to our-Thomas's straight RC types he's built. I've got a WD Phono 3 PCB stuffed that I just need to box and fettle as a standby for now, I'm a-pondering what to play with in the long term.

[IslandPink]

Phono amps are a fertile ground for surprising improvements in system performance . Nick needs to pop in here really - can give you the low down on what's out there at the moment. Dave S can build you to other impedances than 1.5k, but the chokes get tricky if you go too far up. Also Dave doesn't supply screened cans, which is a bit of a PITA - I have gathered a big ali box and some mu-metal sheet for when I do mine ( I have Dave's 1.5k units) .

[Dave the bass]

Ta Mark, yeah I spoke to Nick(G) just before Christmas about phono's and how Thomas's 'wooden box' stage highlighted how poor my current phono stage is amongst other stuff.

I'll keep a-ponderin'.

[thomas]

May as well build up your WD phono for starters, DTB. I don't suppose the pcb makes it very easy to modify should you wish to play around with it, but it would be a handy reference. Inverse riaa build (mine was from 'Jones' 'building' book iirc), Millett box and audiotester beckon!

[Dave the bass]

Acherleee....I've put PCB pins a few areas so I can swap components and tweak values if needs be. Inverse RIAA, good shout, I haven't done one yet. Millet box, yep, check! Audiotester, nope, not yet. I need more Christmas Holidays!

[pre65]

Actually Dave, the first time we met was when you brought a phono stage to Eggborough.

It was both of us's inauguration into the wide world of Fests and DIY fanatics.

[Dave the bass]

You're right, it was G-Popz. 10 years ago this year IIRC?

[pre65]

You're right, it was G-Popz. 10 years ago this year IIRC?

Yes indeed, 10 years.

[Mike H]

'Fraid I have to agree with Mark, best be a low-Z o/p cathode follower but if you also had high Voltage with it gain you might make the output via a potential divider having a final output impedance of 600 Ohms. I'm just surmising tho.

[izzy wizzy]

Sightly higer Z network driven by a pentode is an option. Some have driven a 600R network with a pentode too.

cheers,

Stephen

[shane]

I know nothing worthwhile about phono stages, but mentioning them in conjunction with pentodes makes me think of C3Gs. Is that a sensible comment?