Leak Stereo 20 power up.

[snowman_al]

If I may (butt in)
Yours is the latest iteration of the Stereo 20 with 8778 outputs. The circuit diagram I posted at #4 is the one to use.
If you have changed R5 ensure it is 47K ohms not 100k (and put the step network back).
Always use 470k ohm resistors for R12 R13 regardless of the version.
Use 0.1uF for C5 regardless of the version.
See how R14 R15 fair if you used 2 watt components.
Alan

[Mr Jones]

Ok thanks Al/Andy will get on it

[bikerhifinut]

Originally Posted by snowman_al

If I may (butt in)
Yours is the latest iteration of the Stereo 20 with 8778 outputs. The circuit diagram I posted at #4 is the one to use.
If you have changed R5 ensure it is 47K ohms not 100k (and put the step network back).
Always use 470k ohm resistors for R12 R13 regardless of the version.
Use 0.1uF for C5 regardless of the version.
See how R14 R15 fair if you used 2 watt components.
Alan

Cheers Al, That should clarify it for Howard.
I had thought we'd explained the differences in the versions and the reasons why.
Andy

[Mr Jones]

Yes apologies all, In my ignorance I thought the said `Step Network' was a tweak by a prior owner and hence discarded the components. It was only when I went back to Al's link that I noticed it across R5R/L. I will reinstate it as Al has done when the 47k resistors come It is interesting though that it doesn't appear on the circuit diagram?

I have now ordered the correct resistors to put it all right. Ive only fired it up with speakers, to check both channels which are both working fine. Incidentally does anyone have a diagram to fit a log pot in place of the octal socket for gain control? Rgards

[bikerhifinut]

It'll be ok to use until your bits come Howard.

The reason there's no step network on the circuit diagram is because it wasn't an original design feature. My late ish model with 8778 transformers (1962) and in bronze colour, didn't have the step network and its perfectly stable.
I think it may have been an afterthought on the test bench. Unfortunately the only person I know still around who actually worked in the factory is no longer able to tell us when or if this was a factory modification.

Please don't butcher the amp howard by taking out the octal socket. you'll need to find somewhere to anchor the 1 meg input gridleaks for a start. and you'll reduce its resale value by a large amount. And if you find a nice original Point1 Stereo or varislope stereo preamp then once you've made sure its healthy (usual PIO capacitor-ectomy) it plugs nicely into that octal with an umbilical and if fettled up with decent resistors and caps in tolerance the point1 in particular is quite a nice thing on linelevel sources, a reversible mod on these is to adjust the feedback resistors on all inputs to line level, keep the original bits with it for restoration to original for those who want that. The Disc stage on them is pretty awful and I'd always play LP via a separate RIAA stage.
Why do you want an input potentiometer? If its to use as a free standing "integrated" amp then just get a small project box and bung a pot in that as a passive attenuator "pre", heck a few cheap sockets and a switch and select sources.
What preamp are you using? the amp will work with just about anything out there silicon or valve. Its 125mV sensitivity is a bit of a nuisance for some but theres ways around that with a potential divider across the input sockets if needed. (fit it in the connecting Phono plug at the amp end, works a treat I've done it in the past).
But dont please dont butcher a lovely old amplifier. Love it for what it is.

Andy.

[Mr Jones]

Thanks. Wise words, yes its easy to forget just how easy it is to mess an amp up for convenience. The reason for the pot is a simple but practical volume control as I will be using line level outputs from amp (no pre outs) so amp handling source selection.

[bikerhifinut]

Ah so you are using an amplifier with no preamp output?
I assume you are using a tape out to connect to the leak?
In that case why bother, unless you need the phono stage and knock up a simple "pot in a box" with a selector switch and some sockets. Don't go overboard on these although the nice gold plated ones do look pretty.
As to potentiometers, you pays your money and you makes your choice.
Something around 50k to 100k log is ideal although you can use lower values if your sources are standard modern ones. Prices will vary depending on quality and construction. I wouldnt buy anything more expensive than an Alps RK27 "blue" and the best price I have seen for one of those is at RS online, considerably cheaper than any of the "boutique" DIY shops. The Alps pot is a bit more expensive but is well made, stays quiet in operation, and generally has better channel matching than the budget jobs but as to sound quality then I won't offer an opinion for there lies madness and Audiophilia.
I use Alps RK27 in my diy audio and find them to be as good as it gets.
So just get a wee project box, put in a potentiometer and attach it with Flying leads if its simply to attenuate the signal from a line level fixed volume output, saves the price of 4 RCA phono sockets and a pair of connector leads.
If you havent got a spare set then get a 1.5m or whatever length works best phono to phono lead, cut them in half or whatever ratio works best for distancing and solder the bare ends to the volume potentiometer. Bingo.
Ideally you should run the amp from its own preamplifier but that will get you there, theres more than ample gain and the Stereo20 doesnt need a preamp with extra gain.
I used to use mine with a simple pot in a box and switch set up and it was absolutely fine. Unless you need tone controls............ I find they can be useful although they tend to stay "flat" 99% of the time, its good to have that bit of adjustment.
Hope that helps you.
A.

[Mr Jones]

Good ideas there Andy. Especially the flying leads. the Alps pot I have is the blue variety salvaged from an old project and is a 50k log. So is the way forward.