Low noise resistors for EQ

[Aentons]

I'm about to do a VFE Rocket parametric EQ build and the official units had the red PRP brand which are supposedly low noise, audio grade resistors.

The unit I have still has some noise even when set flat and there is no boosting. It's not bad but it's there. I figure it's the nature of the beast, especially with high values, but I'd like to explore the options.

https://www.aikenamps.com/index.php/resistor-types-does-it-matter

This article explains about resistor noise and mentions the wirewound type as least noisy because they are only subject to 1 of the 3 types of noise. Does anyone have any experience using wirewound in this regard?

I have also see references to the "bulk metal foil" type resistors as being a newer type with lower noise. Anybody know about these?

[mauman]

IMHO, I don't think you'll be able to hear the difference between different types of resistors in a guitar pedal.  There are so many other and larger noise sources that any differences would be swamped.  It might be measurable and relevant in other applications (instrumentation amplifier for test equipment or other extremely low-noise applications.)  If you're curious, make your circuit with each resistor type and do A/B testing.

[Aentons]

IMHO, I don't think you'll be able to hear the difference between different types of resistors in a guitar pedal.  There are so many other and larger noise sources that any differences would be swamped.  It might be measurable and relevant in other applications (instrumentation amplifier for test equipment or other extremely low-noise applications.)  If you're curious, make your circuit with each resistor type and do A/B testing.

I am curious, but I'm looking to gather knowledge from the experienced before doing.

I'm assuming because Peter from VFE tried to lower noise in this application with special resistors that it is not in vain

[jimilee]

You think it’s from the power or is it something else?


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[davent]

Last year i used Takman 1/4w metal films for the stepped attenuator i put together for my hifi preamp. Completely happy with the results.

Bought here, they also carry the PRP's, as well as bulk metal films, wire wounds, tantalums, the complete gammit of resistor audio insanity.

https://www.partsconnexion.com/takman-metal-film-rey-series-0-25-watt-resistors.html

Comparing prices with vendors in the UK and USA when i was shopping and they would match if lower but in all cases, for everything i was shopping for they were lowest, that and i can pick up the order.

[Zerro]

Don't know your schematics, but try at first power from baterry and compare it with power you use now. Then if you use there 074 try to use JRC4580s.

[Aentons]

You think it’s from the power or is it something else?

I'm not sure but I dont think it's just the power. It's likely cumlative between different sources. I think the OPA2134 chips were used to provide noise reduction in that regard.

What I do know is... the production unit I have is a v4.0, and the board I recently got from the VFE site is also v4.0. Peter's old DIY instructions say "Rocket EQ - built exactly as shown on board". However the assembly sheet is for the v4.1 which, as far as I can tell, have lower resistor values and higher cap values in the RC filters. The v4.1 was the one in the download bundle as well. I assume the changes from 4.0 to 4.1 were mainly to help lower the noise by lowering the resistor vaules. The schematic from the eagle files is a bit tangled so it's hard to make out what exactly is going on circuit wise. The block diagram from the old vfe site helps though.

Im really just using this as a learning opportunity.

[Aentons]

Here is the v4.0 board
and the v4.1 schematic

Are there any certain spots beyond the 4.1 changes to target further noise reduction?

[Aentons]

Don't know your schematics, but try at first power from baterry and compare it with power you use now. Then if you use there 074 try to use JRC4580s.

Last year i used Takman 1/4w metal films for the stepped attenuator i put together for my hifi preamp. Completely happy with the results.

Bought here, they also carry the PRP's, as well as bulk metal films, wire wounds, tantalums, the complete gammit of resistor audio insanity.

https://www.partsconnexion.com/takman-metal-film-rey-series-0-25-watt-resistors.html

Comparing prices with vendors in the UK and USA when i was shopping and they would match if lower but in all cases, for everything i was shopping for they were lowest, that and i can pick up the order.

Thanks. I'll take a look at these

[Zerro]

OPA2134 are better in noise than TL074 but not than JRC4580s. Though 4580s have not j-fet inputs. The question is if it does matter. They all have the same socket. Maybe you should want to try them.

[Aentons]

Since de-rating resistors is said to lower temperatures and thus help noise in any that may be self heating, how do you identify the ones that generate heat?

The VFE production build is using all 1/4 watt resistors so I'm wondering if using 1/2 watt in certain places might help

[Zerro]

Any schematics for considering? Honestly, don't believe that any resistor in audio path will generate any significant heat...

[Aentons]

Any schematics for considering? Honestly, don't believe that any resistor in audio path will generate any significant heat...

The RocketEQ schematic is posted above.

My thinking is that resistors in the signal path with no audio would not generate heat, but when playing, the voltage is boosted by the opamps, in this case, potentially up to 18V. So that (i think) could potentially surpass 1/8 watt. The more they warm up the noisier they get... So there may be room for improvement with 1/2watt resistors... maybe?

[Aentons]

Here are RG's comments on this:

https://www.diystompboxes.com/smfforum/index.php?topic=93431.0

[TGP39]

Since de-rating resistors is said to lower temperatures and thus help noise in any that may be self heating, how do you identify the ones that generate heat?

The VFE production build is using all 1/4 watt resistors so I'm wondering if using 1/2 watt in certain places might help

Heat dissipation within a resistor can be measured by calculating the Power that runs across that resistor.   Since the Formula for Power is P=V2/R, (voltage squared) / Resistance, you can quickly see that resistors with very low values will generate the most power and thus the most heat (assuming voltage is constant across each resistor).

https://brilliant.org/wiki/heat-dissipated-by-resistors/

Hope this helps a bit,

Steve.