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Heifetz

preamp hook up wire length - short or long? Differences

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Hi,

Can anyone tell what differences to expect between using long and short wires for the inside of my preamp (back RCA sockets to the attenuator in the front panel).

Thx so much, Bob

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Hi,
Can anyone tell what differences to expect between using long and short wires for the inside of my preamp (back RCA sockets to the attenuator in the front panel).
Thx so much, Bob

How long?
is it passive pre?
what’s the output impedance of the source?
what’s the impedance of the attenuator?

usually should be fine as it’s not like it over a metre.

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9 hours ago, Heifetz said:

Hi,

Can anyone tell what differences to expect between using long and short wires for the inside of my preamp (back RCA sockets to the attenuator in the front panel).

Thx so much, Bob

 

Back RCAs to the front panel attenuator - 'Goldilocks' length, Bob!  😁

 

Too short and it won't make contact - so you'll get no signal.

Too long and you will degrade the signal more than necessary.

So use the length that just connects the two.

 

But twist signal & return tightly, to minimise inductance.

 

Andy

 

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It's more important to avoid noise inducing layout with regard to the wire harness rather than reduce the length by relative low percentages. Most hifi components are relatively noisy places for signal runs.

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It’s helpful to think of it in terms of a piece of string I find

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Thx @andyr ,

i was considering using an extending rod for the attenuator and then the signals wires only need to be 30-40mm. I'm thinking of separating the power and pre to different chassis. see below.

Just to be clear, inside the preamp, the wires that I twist together are

1. both channels?

2. both channels plus ground 

3. not worth twisting if only a few cms?

 

@misternavi

Its a tube pre with power supply inside too. Rectifier tube/transformers and circuitry for caps. The attenuator is 100k.

@guru I am thinking of separating the power supply components to a separate chassis. I will not touch the circuitry or their connecting wires except replace rca wiring and redo the grounding. I'll also replace the 'umbilical' as it will need to be longer. This project is really a separation and rearrangement of the components. May be something like this PDF plan I've drawn up: I have not indicated wiring that connects the components as I will keep them intact. Whilst i've had problems with this preamp (noise/ground and induced hum etc), I believe in it. At the heart of it is a great tone.

Comments and advice is always gratefully received. 

Ravel PSU and Preamp Component Layout.pdf

Ravel AN Preamp.jpg

Edited by Heifetz

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Well seeing as the latest incantation of your pre uses a separate power supply , I would say the designer had the same issues as you with regard to the layout you show in the image. Whilst it's convenient to locate mains switching on the front, it introduces noise right where it should be avoided or shielded. Overall , the layout is asking for problems, hope you have a lot of time and patience.

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@Heifetz

Man that is a small chassis.

Separate the power supply. 

But if you can't be bothered try a shielded coaxial cable for signal?

 

Are you getting a lot of noise? 

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@misternavi

Yes, it is a small chassis. But everyone's comments are very helpful for me to make the right pkan

Luckily, I have another lovely preamp that I can still enjoy music. It has no noise at all. But I think this one has the potential to be better - this has more weight to the sound. I'll persevere and enjoy the journey.

 

 

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I agree with the comments about your layout.  You are probably getting hum due to the close proximity of AC mains to the signal circuitry.  The other thing that will contribute to noise problems is the grounding circuit connections.  Read up about star-grounding if you haven't already.   Adding another chassis connected by an umbilical will add another level of complexity to the grounding arrangement which you need to understand.  You also need to pay close consideration to the safety earthing arrangement which must be passed through your umbilical to the pre-amp chassis.  An alternative to the separate power supply would be to rebuild the whole pre-amp in a bigger, single box......

Edited by RoHo

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2 hours ago, misternavi said:

@Heifetz

Man that is a small chassis.

Separate the power supply. 

But if you can't be bothered try a shielded coaxial cable for signal?

 

Are you getting a lot of noise? 

A small chassis can be made bigger by placing power trannies, chokes, tubes and caps outside and on top.

Lot's of other advantages come with that.

 

Not sure if that is an option for you @Heifetz ?

 

This pre is dead quiet and look at all the room inside.

 

Hope this helps.....

Pre 3.jpg

IMG_1165.JPG

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@Mendes @RoHo ThNK YOU.

Ok, may be the bigger chassis is a better/easier way to go.

How much minimum space should the components be apart to avoid induced noise due to magnetism ect?

How far apart should the transformers be?

Thx

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3 minutes ago, Heifetz said:

@Mendes @RoHo ThNK YOU.

Ok, may be the bigger chassis is a better/easier way to go.

How much minimum space should the components be apart to avoid induced noise due to magnetism ect?

How far apart should the transformers be?

Thx

As far as physically possible.

 

Trace my signal wires around the chassis from input to the pot to tubes and to output and you will see what I mean.

 

Wiser heads than mine can comment further perhaps.

 

Good luck!!

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May be if I use one large chassis then i can also put in some aluminium face panels between components. 

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13 minutes ago, Heifetz said:

@Mendes

Thx. Your pre looks great.

What is the pot that you are using?

 

Thanks....👍.....it's a TKD, quite nice, served me well for many years.

 

Copper face plates would be better.

 

👍

 

 

Edited by Mendes
Thanks

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