simplicity itself - a line stage

andrew Ivimey · Post by **andrew Ivimey** » Fri Jan 04, 2008 8:08 pm

PSU is brightened up from being choke loaded LcLc, with a couple of OD3s to give 300volts. Just using these VRs sharpened things up nicely, so no probs there.

I decided to do a simple single stage pre/line stage so 76 or 6J5 for comparison. Off the anode to cap comes a 1mfd cap with a 1meg to ground. Anode resitor and cathode cap/resistor is standard stuff.

It works, it sounds good and the VRs look good. 76 sounds musical. 6J5 sounds rather dull but does the job.

The question:-
Now, is the output high or low impedance and why would an output transformer improve things???

This is the world of SE so nothing fancy. I have some WAD pre2 trafos doing nothing and I have some cheap Honkers 10K to 600ohms begging for a job. So things are there to be played with.

enlightenment please?

Post by **Nick** » Fri Jan 04, 2008 10:15 pm

Just for a alternativle, how about swap one of the VRs for a 0c3, and adjust he dropper to give you 250v, the use the 76 with a bipassed 2k7 on its cathode, and the TX as a choke load, cap couple to output. And then see what comes out of the secondary instead of using the cap?

andrew Ivimey · Post by **andrew Ivimey** » Fri Jan 04, 2008 10:55 pm

Thanks for replying.

Some of what you say is missing Nick (the odd letter, the odd comma) but I know what you are saying.

That is the alternative I had in mind to what I have so far. I will try it.

But,

Why is what you suggest so much better?

Post by **Nick** » Sat Jan 05, 2008 10:22 am

Well, the choke gives a flatter AC load line, but mainly having tried it in the past I much prefer the sound of a choke loaded 76. You may not.

Paul Barker · Post by **Paul Barker** » Sat Jan 05, 2008 10:40 am

Nick is it possible to do a simulation on pspice to demonstrate a solid state ccs load then passed through a correctly sized choke? I like the sound.

The beauty of it is that you don't need a dropper resistor in an integrated amp, just set the current pass it through the choke load and let the B+ sort itself out.

Post by **Nick** » Sat Jan 05, 2008 10:56 am

Yep, I can do that. Nice thought using the two, the CCS sets the DC conditions, and the choke hides the anode from anything questinable in the CCS.

qwertyuiopasdfghjklzxcvbnm,,,'''''

There you go andrew, some spare characters to apply to my posts

.

Feeling picked on now, I don't remember you having a go at Paul when half his keyboard stopped working

.

Darren · Post by **Darren** » Sat Jan 05, 2008 11:05 am

Yeah, but he's a techno clutz....

andrew Ivimey · Post by **andrew Ivimey** » Sat Jan 05, 2008 11:12 am

Sorry Nick - Your advice is always valuable and interesting.

Paul's missing keys was funny as it was a bit of a puzzle which, when I looked at the keyboard I could make out what he was saying.

From that post of yours, I had to understand what you meant first and then work back to the missing comma and letters, which then confirmed what I understood.

So, if I had less understanding than I do now of treating valves as they deserve, (no obvious sarcasm, please

, I wouldn't have been able to understand your advice.

Post by **Nick** » Sat Jan 05, 2008 11:31 am

So, if I had less understanding than I do now of treating valves as they deserve, (no obvious sarcasm, please Wink, I wouldn't have been able to understand your advice.

And if I thought you had less understanding than that, I might have written it in another way, or not at all.

By the way, where does the closing bracket happen in your above text?

Paul Barker · Post by **Paul Barker** » Sat Jan 05, 2008 11:39 am

Nick wrote:Yep, I can do that. Nice thought using the two, the CCS sets the DC conditions, and the choke hides the anode from anything questinable in the CCS. .

One would hope so, but perhaps the choke is eneffective at the frequency of anything nasty in the ccs, and a spiral of wire linking the ccs to the valve would have the same effect.

I got some nickel anode chokes off ebay and was using those, to good effect then I changed my power supply to step up the output stage to 300b and had extra HT to shed before the first two stages, and I thought simplest thing was a ccs before the chokes, which led to the thought of puting one on each choke to kill two birds with one stone, sort out the HT supply and supplement the load.

I am still using the grid chokes.

But in the back of my mind I suspect a much smaller lighter neater amp with no chokes might sound pretty good.
It sounds good, but we are in that territory where you and I were when we were trying to discern a difference between using grid choke or not, at the time of an instant ab it was hard to call.

My advice to anyone would be if you have the space for the chokes and they are good ones and you already own them and the inductance is sufficient for the valve throw them in. If not keep it smart and light just use the ccs.

andrew Ivimey · Post by **andrew Ivimey** » Sat Jan 05, 2008 11:40 am

its the smiley!

I know, I know. I do it too. <sick grin>

Paul Barker · Post by **Paul Barker** » Sat Jan 05, 2008 11:47 am

sorry i wasnt quite clear neough, need to borrow lynn olsons script writer.

progressing to choke load to ccs load interceded by choke is a clear good sound, you get the same romance as the choke gave you alone but extra welly.

what I can't be sure about is whether the choke is adding value.

That's still not clear is it?

And another thing my duff keyboard laptop is for scrap.

So now when I miss type it's me.

and another thing that lovely mesh plate 300b and it's mate are dead now. Damn regulated power supply went open circuit and lit them up with 30v for about 30 seconds which is how long it took me to work out which plug it was on, to get to the main plug would have involved dangerous amp traversing barefoot. I elected to alow the valves to suffer rather than risk HT up me soles.ho knows the anode isn't meant to be turqoise when it's on? And that thes bottles weren't made with smoked glass?

Post by **Nick** » Sat Jan 05, 2008 11:52 am

Andrew: You would never make a programer Andrew (good says he), its

( hello world

)

You get to be obsessive about brackets (thank god its not lisp).

Paul: what CCS were you using, should I use a c4s for the model? And should I use some sensible R and C values for the choke?

Paul Barker · Post by **Paul Barker** » Sat Jan 05, 2008 11:55 am

valve is 112a
choke is 80h 1k
ccs is ixys ixcp10m45s-nd set at 7mA
bias is fixed at 9 volts

same amp I had at yours that day when we were trying out the grid chokes.

Only changes made are I swapped the hammond 156c's for these nickel chokes, which was a progression.

I think at yours I had 211's in output stage

with my efficient speakers I went right down to 45, then realised 2a3 was sufficently good sounding but was required for the bass. Then discovered that 300b was likewise to the 2a3 as 2a3 was to 45, so after many years of dissing the 2bass is now satisfactory 300b I am back with it, well just long enough to kill them.

In this particular amp I don't think I could get sufficient bass from the 211.

andrew Ivimey · Post by **andrew Ivimey** » Sat Jan 05, 2008 12:00 pm

It'll do!

I am experimenting with a single stage at the mo' because it really looks like Amity (as a 2 stage) really needs some guts to sing properly - (I'm still waiting on the O-Netics to arrive). An additional front end makes it an 'Aurora', (which Lynn Olson concluded was not to his taste) but I really don't want a preamp infront of the 'Amity' I am building.

So, I'm looking to slip in a front end but the output from whatever valve I use here has to be at least less than 600ohms impedance to match Amity's front end. Or I change the input/splitter transformer - (I'm running on threadbare here, I need a pay rise.)

So more experiments .... WAD pre2 drove the Amity well as I had got it all up&running, but as I said, I don't want a proper preamp.

audio-talk

simplicity itself - a line stage

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