madbeanpedals::forum

General => Open Discussion => Topic started by: Aentons on November 13, 2021, 05:38:49 PM

Title: Low noise resistors for EQ
Post by: Aentons on November 13, 2021, 05:38:49 PM
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?

Title: Re: Low noise resistors for EQ
Post by: mauman on November 13, 2021, 06:33:11 PM
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.
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 13, 2021, 07:15:41 PM
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
Title: Re: Low noise resistors for EQ
Post by: jimilee on November 13, 2021, 07:21:25 PM
You think itís from the power or is it something else?


Sent from my iPhone using Tapatalk
Title: Re: Low noise resistors for EQ
Post by: davent on November 14, 2021, 11:48:48 AM
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.
Title: Re: Low noise resistors for EQ
Post by: Zerro on November 14, 2021, 12:03:03 PM
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.
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 12:18:59 PM
You think itís 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.
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 12:22:39 PM
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?
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 12:35:31 PM
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
Title: Re: Low noise resistors for EQ
Post by: Zerro on November 14, 2021, 12:38:09 PM
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.
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 01:40:55 PM
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
Title: Re: Low noise resistors for EQ
Post by: Zerro on November 14, 2021, 01:54:45 PM
Any schematics for considering? Honestly, don't believe that any resistor in audio path will generate any significant heat...
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 04:14:55 PM
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?
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 14, 2021, 04:19:56 PM
Here are RG's comments on this:

https://www.diystompboxes.com/smfforum/index.php?topic=93431.0
Title: Re: Low noise resistors for EQ
Post by: TGP39 on November 17, 2021, 11:19:02 PM
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.
Title: Re: Low noise resistors for EQ
Post by: jimilee on November 18, 2021, 09:03:30 AM
I wish I would have tried harder in college algebra.


Sent from my iPhone using Tapatalk
Title: Re: Low noise resistors for EQ
Post by: Zerro on November 18, 2021, 11:17:50 AM
Theoretically it can reach comperhensive consumprion for +18V supply and cca 20mA current, 360mW. But not at one resistor. Here is not any power branche in circuit.
Title: Re: Low noise resistors for EQ
Post by: Aentons on November 26, 2021, 04:34:20 PM
After absorbing this for a bit. I think my simple way if understanding it is...

Resistors typically have Thermal and Contact noise. Reduce resistor values to reduce Thermal noise. Reducing the value increases current and therefore Contact noise and self heating. Use higher wattage rated resistors to reduce Contact noise. The closer down you get to 680 ohms the more it matters (potentially)

BTW, I'll be doing a larger analysis of the Rocket.
Title: Re: Low noise resistors for EQ
Post by: Zerro on November 26, 2021, 06:49:39 PM
After all, your ear will show you the best way.