Lowering output level using resistors

Hi guys,

I'm looking to further reduce the output voltage from my preamp. It currently has 1 Dale 100k resistor so I've been advised to put another 100k one in series to achieve the desired effect.

Just wondered if I could improve upon this resistor by maybe going carbon or a composite without introducing unwanted noise.

So far on my list I've come across:

Shinkoh
Amtrans AMRG
Arcol carbon composite
Holco
Takman carbon
Takman metal film

I'm assuming I'll only need up to around 0.25w tolerance as it's probably not going near that and the ones in there now are the smallest type so probably 0.25w?

Help and advice much appreciated.

Cheers

Hello !
Do you have a schematics about the Preamp you intend to modify , I don't see anyone in your systems ?
RC

Hi,

it's my Musical Paradise MP-701.

Unfortunately I do not have the schematics but the circuit has been slightly modified (by Mr Firebottle) from the original. It's on his recommendation to add another 100k resistor.

It has a "high" and "low" output. The "high" output is just that and the "low" output has a 100k resistor before the output RCA. I wish there was a better way to lower gain but its quite a temperamental thing as it is.

Sounds glorious though, hence my perseverance with it.

Certainly doesn't help that I've got a big power amp going into very sensitive speakers but its the combination that can sound incredibly good. Just too much gain.

Cheers

Chris

Throughout my career carbon resistors were regarded as noisy, and metal oxide much better.

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Originally Posted by Pharos

Throughout my career carbon resistors were regarded as noisy, and metal oxide much better.

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Seems to be the consensus Dennis.

Think I'm going to go for some Audio Note Tantalum Non-Magnetic Resistors 220k (so I don't have to solder together 2 x 100k's).

'Cheap' enough to try anyway and likely better than whats in there anyway.

I saw in user's manual that you can manage the gain, with dip-switches http://www.musicalparadise.ca/files/MP-701.pdf
How are settled these switches ?
What kind of tubes did you install ?
There is also an option to reduce gain when acting fedback ..how are these pots ?
R.C.

Quote:

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Originally Posted by Ciu

I saw in user's manual that you can manage the gain, with dip-switches http://www.musicalparadise.ca/files/MP-701.pdf
How are settled these switches ?
What kind of tubes did you install ?
There is also an option to reduce gain when acting fedback ..how are these pots ?
R.C.

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Yes indeed, they are quite useful, gain is on low setting and feedback is on. Hence lowest gain. I am using 6sn7 tubes and adapters. When using 12au7 tubes the gain is pretty much the same as the 6sn7's maybe 2-3db difference. I would have thought it would be more but in reality it isn't much different in listening.

Thanks for your help anyway, much appreciated.

Hello!
without any schematics, I can't give more option to help
If I had to do, I would insert a resistor before the preamp pot, value = to pot resistance (10mn,soldering iron , 2 basic resistors to test values)
This option can be modified or reverted to initial .

Sorry to crash in on this debate, but to lower the signal by say 15 dB what value resistor you you pick, and I would recommend the AN tantalums.

This feels a bit like being asked to explain to a man in a different continent, how he should get to a given street when one has no knowledge of the town, or even the country.

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Originally Posted by bumpy

Sorry to crash in on this debate, but to lower the signal by say 15 dB what value resistor you you pick, and I would recommend the AN tantalums.

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I would use a 10 kOhm series resistor in line with the source and a 1.8 kOhm resistor in shunt with the amplifier.

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Originally Posted by Barry

I would use a 10 kOhm series resistor in line with the source and a 1.8 kOhm resistor in shunt with the amplifier.

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Which on a schematic looks like the attached, to the left is your source, and to the right your power amp

Yes. Thanks for the diagram Chris, it explains things a lot more more simply - "a picture is worth a thousand words"! :)

Just to update this I replaced the Dale 100k resistor with 220k AN Tantalum's.

Result, knocked off 7-9 db which dropped the noise floor very nicely. Definite improvement overall, although I concede there are better ways to lower gain but they are currently slightly beyond my abilities.

Appreciate everyone's views.

Quote:

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Originally Posted by Pharos

This feels a bit like being asked to explain to a man in a different continent, how he should get to a given street when one has no knowledge of the town, or even the country.

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Does it?

As I don't have the schematics (as stated) do you have any productive suggestions?

Quote:

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Originally Posted by Barry

I would use a 10 kOhm series resistor in line with the source and a 1.8 kOhm resistor in shunt with the amplifier.

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How do you calculate these values? I have found a T Attenuator calculator here https://www.leleivre.com/rf_tpad.html