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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 21st Aug 2017, 10:00 am   #1
Tedbear3
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Default Leak Stereo 20

Hello.

I have a Leak Stereo 20 fitted with a volume control knob, but when connected to my Croft Super Micro A preamplifier there is too much volume control conflict. Help.
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Old 21st Aug 2017, 10:51 am   #2
Edward Huggins
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Default Re: Leak Stereo 20

Is the volume control ganged to control both input levels on the Leak? Not quite sure what you mean by "conflict". Can you elucidate more please?
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Old 21st Aug 2017, 2:19 pm   #3
Tedbear3
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Default Re: Leak Stereo 20

Edward. Thanks for the reply and please excuse my non existent technical knowledge. I am not aware of any input levels on the Leak but when I connect my CD player to the Croft Super Micro A and then connect the Leak to the Croft, the two volume controls on the Croft have barely any influence on the sound emanating from the speakers-even when I turn the Croft volume pots to zero the Leak operates the volume perfectly up and down-my impression of the way the set up should be is for one item or the other to control volume but not both.
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Old 21st Aug 2017, 2:29 pm   #4
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Default Re: Leak Stereo 20

I've probably got it completely wrong, but I didn't think the Leak Stereo 20 was fitted with a volume or volume controls.

If it has been modified by fitting a volume control then I expect a Leak expert can advise whether it's best removed.
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Old 21st Aug 2017, 2:45 pm   #5
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Default Re: Leak Stereo 20

What input are you using on the Croft? Is it designed to work with the high level output to be expected from a CD Player?

I remember some years ago working on a vintage amp with a separate preamp. One input to the preamp had been fitted with an attenuator to enable it to be used with a CD Player.
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Old 21st Aug 2017, 2:47 pm   #6
Lucien Nunes
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Default Re: Leak Stereo 20

A Stereo 20 does not have a volume control so some kind of modification has been carried out. We would need clear pics of this area of the circuit to identify exactly what. The normal input sensitivity is 125mV RMS for full output - this is much more sensitive than modern power amps and it is easily overloaded by modern +4dBu sources and even -10dBV. If the source is attenuated then the noise floor is raised, so modifications are quite common to overcome this. The volume control might be part of that, or might simply have been tacked on in series with the existing input.

You are definitely connected to the Main Out on the preamp? The Rec Out naturally is not connected via the volume control. I wonder if the Croft has been modified or has an open-circuit internal ground connection? Its volume control works in a perfectly conventional way and should reduce the level to zero. Have you used this with another amp and does the volume control work then?

In truth I don't think it adds anything here when used with a line-level source. It is simply buffering a source that is already at too high a level, with plenty low source impedance, ready for it to be attenuated again to suit the power amp, adding a little noise and distortion in the process.
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Old 22nd Aug 2017, 2:55 pm   #7
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Default

You mentioned a Leak expert in your reply and if such person/people subscribe to the forum please get in touch with me.

Not at all clued up on output levels or attenuators but I do know that the end product music through the speakers sounds superb. My aim is to try to control the sound from the Croft only but this does not work at the moment-any help/pointers gratefully appreciated.

Lucien -thank you for your technical response in your first paragraph but I'm afraid to say that I understood none of it. The Leak is connected to the Main out on the Croft preamp but I do not know if the pre has been modified and I do not possess another amp to experiment with. Paragraph 3 of your reply leaves me lost in the techno wood again and I feel that my general lack of knowledge in this field will require the equipment to be looked at by a Leak/vintage equipment guru- does such a person/people exist near me?
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Old 22nd Aug 2017, 4:11 pm   #8
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Default Re: Leak Stereo 20

The simple fact is that you are not going to achieve what you want without modifying, demodifying or repairing the amplifier or the preamplifier.

As, by your own admission, you lack technical expertise, I suggest posting in the Repair and Restoration Services Wanted section seeking someone to do the work for you.
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Old 22nd Aug 2017, 4:38 pm   #9
Ted Kendall
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Default Re: Leak Stereo 20

Could do worse than talk to Mike Solomons at London Sound. Not cheap, but good.
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Old 22nd Aug 2017, 5:03 pm   #10
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Default Re: Leak Stereo 20

Let's try paraphrasing things to see if they are any clearer.

An unmodified Stereo 20 only needs an input of an eighth of a volt to drive it to full power. They are unusually sensitive in this way.

Most CD players put out about two volts of signal.... around sixteen times more than your Leak is designed for.

So you do not want to amplify the output of your CD player any further, in fact you want to scale down the signal from the CD player. So you don't actually need a preamplifier at all. This is the point Lucien was making.

The Leak Stereo 20 did not have a volume control on it when it was new, so someone along the way has added it. None of us has seen your amplifier, so we don't know how it's been added and whether any other changes got made at the same time. So we can only guess.

The simplest thing that could have been done is for someone to have just drilled a hole in the chassis, mounted a volume control, and wired it into the connection from the input connector to the amplifier circuitry.

If this is what's been done, the signal from A CD player is still so strong that the Leak amplifier will be driven to full power and then overloaded before the volume control is moved up much. You'll feel that moving the volume control just a bit above minimum will blow your head off.

If this is so, then you need something to reduce the strength of the signal between the CD player and the Stereo 20. These things are called Attenuators. They are simple, cheap, and one of the most basic circuits possible. They don't need mains power, either.

Your simplest route is to get one of the people near you to have a look at it. If you want to learn electronics, you may want to start with something a lot less valuable. A leak Stereo 20 in good condition can be worth a fair bit of money.

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Old 22nd Aug 2017, 7:59 pm   #11
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Default Re: Leak Stereo 20

https://www.vintage-radio.net/forum/...973#post969973
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