Driving a 600R LCR RIAA stage

[IslandPink]

Useful valve - I'm intending to use one as the final valve on my next phono.
Meanwhile, me, Dave and Nick have been having a bit of chit-chat from work today about phono plans, but I'll let Nick post his comments first .

[izzy wizzy]

C3g might be a bit tame to drive lcr direct. Something a bit more mental like d3a or e810f could do it.

Cheers,

Stephen

[IslandPink]

Yes , I wouldn't use C3g for that - Thorsten used E810F and you could try E55L - but lower-impedance is turning out to be better, from what Nick's found - usual suspects like 5687 CF or Aikido with 20ma+ or something like that.

[Nick]

For consistency, I will post what I emailed to Mark and Dave earlier.

TBH, my advice with phono stages is:

1. Get and install a copy of LTSpice, and learn how to use it at least enough to model RIAA networks.

2. Build an inverse RIAA

3. Get a way of measuring, specifically FFT

4. Build a few to get the hang of it.

I would suggest 4 before getting involved with LCR's. One of the key requirements of a phono is low noise, and low hum, and low noise, getting the hang of that with a RC stage is a lot better than throwing yourself in at the deep end with a LCR. A typical transformer driven LCR will have a total of somewhere in the region of 80dB of gain, there are a lot of places in there for hum and noise to appear, and a lot of iron cores to help picking up that hum.

YOU CAN NOT LISTEN THROUGH AND IGNORE HUM.

You cant tell what something sounds like until its quiet. If people tell you hum doesn't matter ignore them and possibly anything else they say.

The WD phono is a good place to start, lots of things that can be done on that to tweek after building. CCS's in anodes, better power supply, different cathode parts. Then maybe a low impedance RIAA network (RC) would be something to try. That adds its own set of problems, and you need to see if you prefer the sound of low impedance. I would suggest if you don't, then you haven't built it right. There are a lot of things to go wrong that you wont be able to pin down if you dont measure, but it just wont sound right.

Then look at power supplies again, VR tubes are good for low current supplies, shunts for higher ones, again, noise matters a lot.

Then play with jfet cascodes compared to step up transformers.

And so on.

There are years of work in something as simple as a phono stage. You would however be surprised just what a difference they can make.

[IslandPink]

and my reply was .. :

"Sound advice in there, Nick, but this would be the ideal if Dave was , say, 35 years old. If we get him to build 4 successive phono stages and go through all of the trials & tribulations we’ve been through ourselves, he’ll be 65 years old and possibly losing his hearing before he gets on to the LCR phono !

How about ( shoot it down in flames if you need to ! ) I suggest a slightly more accelerated programme ?

LT Spice for sure, fun to play with and useful
Inverse RIAA good, I never used it but should have !
Test gear , I need to use more and I never got the hum out of my phonos ( on the list of urgent jobs ! ) so that’s sound advice .

How about doing something like my phono first, if it fits Dave’s gain needs and cable-drive needs ?
It’s about the simplest ‘good’ phono stage I’ve seen and seems to do well at the Owstons vs. most stuff apart from yours.
It’s basically 1:10 step-up, D3a>22kRCnetwork>D3a , with a CCS-VRtube shunt-reg power supply ( ~ 55ma + 20ma shunt ) .
It’s going to be better than what he’s got, and the WD phono ….

If you build that in a sensible way, then you can experiment with the earthing details, filament supplies, wire screening & routings etc to get the noise down . The VR tube shunt can be compared to a valve shunt reg or one of your SS shunts regs ( Nick ) . Probably build it two-box if that’s your advice, Nick ?

If Dave can stand a little less gain than me, then E280F’s are a bit cheaper and easier to find and will still give plenty of gain and drive the 22k .
You can still play around with CCSs in anodes, jFet/triode cascode in front end without much modification if you allow some room to manoeuvre .

So , Dave, what gain do you currently have and/or do you use a step-up in front, and a pre-amp between the phono and the power amp, or what ?
My phono gives enough gain ( with the step-ups ) to go from 103R direct to a power amp with an input sensitivity of eg. 1V ( for normal speakers anyway ) . I think that’s about 70dB when you take away the 20dB or so for the RIAA."

[shane]

Sorry to keep butting in! Chris, do you have any more details of your D3A phono?

[izzy wizzy]

My experience would back up everything Nick and Mark said. It's a good path to success.

Cheers,

Stephen

[Dave the bass]

So , Dave, what gain do you currently have and/or do you use a step-up in front, and a pre-amp between the phono and the power amp, or what ?
My phono gives enough gain ( with the step-ups ) to go from 103R direct to a power amp with an input sensitivity of eg. 1V ( for normal speakers anyway ) . I think that’s about 70dB when you take away the 20dB or so for the RIAA."

Ta for taking an interest and giving me a direction everyone.

OK, currently I run a 103R via Cinemag 1:10 before the MM i/p into my current Phono amp. TBH I have no idea what the gain is (maybe I should measure it....) but it drives (via a passive Vol Control) into my current 5687 -> 2A3 amp well. The last stage is a CF. I use the MM i/p as the MC i/p uses a ground grid stage that introduces too much mush (noise) to the picture, its distracting and makes for a tiring listening experience, yup, just like Hum does. Hum in capitals noticed Nick

I'm going to finish and box up the WD Phono (I can hear our-Thomas fainting!!!) then set to with building an iRIAA when I find the relevant bit in MJ's epic tome.

Onwards.

[IslandPink]

Sorry to keep butting in! Chris, do you have any more details of your D3A phono?

Chris, or me ( Mark ) ?

[shane]

Sorry to keep butting in! Chris, do you have any more details of your D3A phono?

Chris, or me ( Mark ) ?

Sorry Mark, sudden attack of senility. Yes, I meant you!

[IslandPink]

I had a sketch of the circuit on the computer - but checking one copy I had saved at work, it was a bit out of date . I'll run up a diagram this evening if I get chance and scan it at work tomorrow . Need to have something on that for reference .

[thomas]

I'm going to finish and box up the WD Phono (I can hear our-Thomas fainting!!!) then set to with building an iRIAA when I find the relevant bit in MJ's epic tome.

Onwards.

Sounds like a plan!

If people tell you hum doesn't matter ignore them and possibly anything else they say.

Well, I laughed!

[IslandPink]

"If people tell you hum doesn't matter ignore them and possibly anything else they say"

Best ignore any advice I gave you on the DHT filament supplies then !
( Ok , if you want to be pedantic - I didn't say hum didn't matter , but I did listen through a fair bit of hum )

[Paul Barker]

"If people tell you hum doesn't matter ignore them and possibly anything else they say"

Best ignore any advice I gave you on the DHT filament supplies then !
( Ok , if you want to be pedantic - I didn't say hum didn't matter , but I did listen through a fair bit of hum )

Back in the early days I met someone who went with a friend to visit Thorsten. Wen they came out they both looked at each other and said "didn't it hum?"

My stuff used to sound like there was a power station near bye in those days aswell

[IslandPink]

Shane - finished drawing up my circuit last night, so it'll be Monday before I can scan it and post here - sorry for the delay .