L Pad problems with a B1

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Hi all, some of you may remember me from a few years back constructing some concrete and bamboo box's for my Mark Fenlon CHP 70's. Well I'm glad to say they are still giving sterling service and have recently had a make over to improve the finish.
My problem is I've recently added a DAB tuner to the set up, and I cannot seem to get LPad attenuators to make any noticeable difference.
The tuner is a Tibo TI420, and the amp is a MF B1.
So far I have tried
10k with a 4k7 across, which I thought would give about -10 db.
10k with a 1k across, which I thought would be double this or slightly more.
Nether of these seemed to make any noticeable difference. I cant turn the volume pot up more than a fraction, with the obvious channel balance problem, and excessive volume.
Is there something about the B1 that makes LPads not function, or could it be something else.
I am a novice when it comes to diy electronics, but I think I constructed them correctly.
The only value that I am sure about is that the B1 expects 220mv imput signal. I don't know the Tibo output voltage, or either impedance to enable me to use one of the online calculators.
I suffer from dyslexia, and after re-reading the tutorials where I got the values from I have just realized that I used a 10k each time, and not the 1k I originally stated, so I have changed the values I stated earlier in the thread.
Would putting the two 10ks in series work.
I am concerned that higher values may be bad for my amp.
My usual input is from the sound card on my computer, with no problems.
Any help or suggestions would be greatly appreciated.
 
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Hi Dave
You just need a resistor from the input, and a resistor to ground for each channel.
The point where they meet, is your attenuated signal new take off point.

J1 is your input J2 your output. Suggests to me from your post you are somehow
not accessing ground, as one side of the required L Pad.

Try these values 10k in series and 1k2 to ground. They should
give you noticeable attenuation for your DAB Tuner.

You could also make the resistor to ground variable
if you need to experiment with ideal values, in which case make
the grounding resistor a potentiometer of 5k and rotate the pot,
until it gives you required attenuation.

Hope that helps.

Cheers / Chris
 

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.....................
The only value that I am sure about is that the B1 expects 220mv imput signal.
The B1 is a Buffer. As such the output is just a tiny fraction less than the input. Provided you don't put in too big a signal that gets distorted or clipped, there is no 220mVac requirement................
Do you know how to wire up an attenuator?

The two resistors need to be wired into the signal circuit so that they actually attenuate.
I suspect you have got this wrong.

Post a pic and post a schematic of what you think the pic shows us.

Forget Daly's sch. That is not the way to wire up a signal.

You need TWO wires coming for each channel and TWO wires going out for each channel. Both sets of those two wires must be closed coupled. Thus you end up with two pairs of close coupled wires for ONE channel.
For a stereo set up that would require 4 pairs of close coupled wires.
His drawing shows 4wires and they are NOT the close coupled pairs, they are two DIFFERENT channels.
 
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Hi Chris and Andrew. Many thanks for the replies. I decided to try get some values to work with, and went to measure the output voltage from the tuner.
Suddenly realized I must have had an exceptional blond moment.
I had the leads in reversed, so the lpad was at the tuner end.
Now after putting them the correct way round I have too much attenuation even after switching back to the first setup.
Anyway, its back to the shop for some more 4k7s and I will try 4k7 with 4k7 across.
Another thread suggest this will give -6db.
Apologies for wasting your time. My bad.
But thanks again.
Cheers, Dave.
 
The B1 is a Buffer. As such the output is just a tiny fraction less than the input. Provided you don't put in too big a signal that gets distorted or clipped, there is no 220mVac requirement................Do you know how to wire up an attenuator?

The two resistors need to be wired into the signal circuit so that they actually attenuate.
I suspect you have got this wrong.

Post a pic and post a schematic of what you think the pic shows us.

Forget Daly's sch. That is not the way to wire up a signal.

You need TWO wires coming for each channel and TWO wires going out for each channel. Both sets of those two wires must be closed coupled. Thus you end up with two pairs of close coupled wires for ONE channel.
For a stereo set up that would require 4 pairs of close coupled wires.
His drawing shows 4wires and they are NOT the close coupled pairs, they are two DIFFERENT channels.

There was nothing suggesting they should not be closely coupled.
Your strictness with schematic layout is appreciated,, but not available
in many programs." Don;t shoot the messenger" to quote another thread.
 
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