Leak Stereo 20 gain
#1 Leak Stereo 20 gain
Could anyone suggest the best way of reducing the gain of my Leak Stereo 20.
I can't use the turntable because volume is a bit too high on lowest preamp volume.
I can't use the turntable because volume is a bit too high on lowest preamp volume.
- IslandPink
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#2 Re: Leak Stereo 20 gain
What's the input to the Stereo 20 look like ? ( circuit ) . Should be pretty easy to mod some sort of voltage-divider on the input to the first valve's grid , even assuming it doesn't have a volume control on the input.
"Once you find out ... the Circumstances ; then you can go out"
#3 Re: Leak Stereo 20 gain
Here's the schematic showing one channel
- IslandPink
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#4 Re: Leak Stereo 20 gain
I need to do a sketch ; but basically, form a voltage divider, by :
... reduce the 1M grid-leak resistor to eg. 330k, and put a resistor eg. 470k to 1M on the way from the input to the junction where the 1M comes down. Have a look what resistors you have. Carbon composition preferred.
... reduce the 1M grid-leak resistor to eg. 330k, and put a resistor eg. 470k to 1M on the way from the input to the junction where the 1M comes down. Have a look what resistors you have. Carbon composition preferred.
"Once you find out ... the Circumstances ; then you can go out"
#5 Re: Leak Stereo 20 gain
Ok thanks. I didn't think it could be that easy. Will see what I have.IslandPink wrote: ↑Sun Feb 12, 2017 10:21 pm I need to do a sketch ; but basically, form a voltage divider, by :
... reduce the 1M grid-leak resistor to eg. 330k, and put a resistor eg. 470k to 1M on the way from the input to the junction where the 1M comes down. Have a look what resistors you have. Carbon composition preferred.
- Mike H
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#6 Re: Leak Stereo 20 gain
What Mark said, including being carbon composite, as the type of resistor may colour the sound. Depending on your personal taste.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#7 Re: Leak Stereo 20 gain
I changed most of the resistors and all the capacitors. Just a few of the hard to get at resistors still in place.
If I remember correctly all the replacements were carbon film. I had read that metal film didn't sound as good.
Are carbon composite different?
- IslandPink
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#8 Re: Leak Stereo 20 gain
Carbon composition (aka Allen Bradley ) are essentially amorphous and non-inductive. I prefer them for small-signal work, especially in phonos. Carbon films have a spiral cut into the film that form the resistive element ( like metal films ) but the spiral has fewer turns and is less inductive than metal films. Or .. maybe it's the way the end-caps are attached.
"Once you find out ... the Circumstances ; then you can go out"
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#9 Re: Leak Stereo 20 gain
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#10 Re: Leak Stereo 20 gain
I used 470k grid bias resistors and 1M resistors in series with the source. I also swapped out the remaining resistors I hadn't finished doing when I changed the caps. Cleaned up the valve pins with a fibre pen. I have a 4W 100 ohm soldered in such a way as it would hopefully drop out if it overheated though I would prefer fuse protection.
I put some nice new phono sockets in too. It's sounding much better and the volume reduction is just right.
I only had carbon film resistors but I'm happy with the sound.
I'm still unsure about the speakers I'm using with it - World Audio KLS2. With some material they sound a bit bright though generally they are pleasing. Has anyone used/made any of these? I bought them on t'bay.
Update Sunday morning - I realise the amp is still a tad loud on my pre's 1st click. Funny how things seemed different after a couple of beers. Need to experiment some more.
I put some nice new phono sockets in too. It's sounding much better and the volume reduction is just right.
I only had carbon film resistors but I'm happy with the sound.
I'm still unsure about the speakers I'm using with it - World Audio KLS2. With some material they sound a bit bright though generally they are pleasing. Has anyone used/made any of these? I bought them on t'bay.
Update Sunday morning - I realise the amp is still a tad loud on my pre's 1st click. Funny how things seemed different after a couple of beers. Need to experiment some more.
- IslandPink
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#11 Re: Leak Stereo 20 gain
Ok, good work - looks like 330k or 270k to ground then.
"Once you find out ... the Circumstances ; then you can go out"
#12 Re: Leak Stereo 20 gain
Is there any problem with dropping to 270k when the original resistor was 1M?IslandPink wrote: ↑Sun Feb 26, 2017 12:15 pm Ok, good work - looks like 330k or 270k to ground then.
I was going to increase the value of the resistors going to the phono sockets.
- Mike H
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#13 Re: Leak Stereo 20 gain
No I wouldn't want to increase that any more.
Actually 750k -> 220k might preferable, closer to the original 1M input impedance.
Actually 750k -> 220k might preferable, closer to the original 1M input impedance.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#14 Re: Leak Stereo 20 gain
Mike does this mean that I don't have to worry about the value of R1 as long as the input resistance total presented to the source remains around 1M?
- Mike H
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#15 Re: Leak Stereo 20 gain
If you want to keep to its original input impedance.
But to confuse things even further, if you know or can find out what load impedance the source can drive, then I would think about making it that.
So if for example the source can drive 100k (quite a common value for input impedances) then I could think it terms of making the resistor divider 75k and 22k.
As it stands, having such a large value resistor in series with the first valve grid might be a problem with Miller effect, i.e., the input capacitance of the valve.
But to confuse things even further, if you know or can find out what load impedance the source can drive, then I would think about making it that.
So if for example the source can drive 100k (quite a common value for input impedances) then I could think it terms of making the resistor divider 75k and 22k.
As it stands, having such a large value resistor in series with the first valve grid might be a problem with Miller effect, i.e., the input capacitance of the valve.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."