OD & carbon film resistors

[tubenit]

Just thought I'd share another successful experiment that I tried.   Some of the guys over on the Amp Garage commented about using 1w carbon film resistors in portions the signal path of just their Dumblish OD channel for added smoothness.

I got some 1w Xicon carbon film (not carbon comp) resistors and tried this in the D'Mars ODS.  There is a noticeable significant difference in smoothness.

Note that I used metal film for plate and cathode resistors in the OD & every where else. I only used the 1w carbon film where indicated on the schematic.

So for those of you who are trying to coax out every bit of smoothness that you can find without compromising transparency and touch sensitivity, you might want to give this a try?  I think I am getting more harmonics in the OD then before also for some reason?

BTW, the OD channel is actually quieter with the 1watt carbon film then with the 1/2 metal films in the same spots.

With respect, Tubenit

[EL34]

Hmm, that's interesting


I trust your ears

[jed]

I bought an assortment of 1W carbon film resistors from Futurlec very cheaply. When I built the last amp which is loosely based on a TW Rocket, the amp was a bit noisy with mostly hiss. I had used the carbon films throughout so I went through and changed out select resistors to metal film as a way to lower the noise. The amp then sounded less lively to my ears so I changed them back to all carbon films. Maybe it was only my imagination...

[Willabe]

What's interesting to me is it's the series R's that Tubenit changed.

Not the plate or K R's that would have hi voltage on them. (Some guys use carbon film for those as a compromise between CC's and MF R's. Warmth verses noise.)

[HotBluePlates]

What's interesting to me is it's the series R's that Tubenit changed.

Not the plate or K R's that would have hi voltage on them.

Maybe look at it as the resistors which "don't have d.c." on them? Note that tube cathode resistors won't have high voltage, but will have d.c. across the resistor.


Off the top of my head I don't know why that would make a difference, but I don't discount it either.

[tubenit]

I have NO idea why it worked either?  But I am happy with the results.

From the Amp Garage:

One person uses just a few carbon comp in the OD entrance

The only thing I can add is since the older gen amps with the funky 3 resistor OD entrance network can sometimes benefit by using all CC's there to smooth out the tone since those amps can be a bit gritty at times..On mine I used AB CC's there and on the grids and that amp sounds pretty smooth and still has some clarity..For what it's worth.. Wink

And then another person talks about using carbon film

,

I have obtained best results in non HRM amps using MFs for all plates and cathodes, and the two PI 1 Megs, carbons everywhere else

Hi Tony! I haven't bought resistors in probably 9 years. But I had good results with the Xicons CF in the past. Just recently I replaced 3 old NTE MF (they are very nice) in one of my amps in the OD chain (220k, 100k and 150k) with 1W Xicons CF and the OD was noticeably smoother after that.

And a 3rd person's comments:

1W carbon films are my favorite. Either XICON, TE, KOA or a few others. I went through my Metal Film stage. No sonic nirvana there.

With respect, 10thtx

[John]

Since they're 1 watt instead of 1/2, maybe the physical size plays into it too?    Along with the carbon instead of metal film.

[Fresh_Start]

Since they're 1 watt instead of 1/2, maybe the physical size plays into it too?    Along with the carbon instead of metal film.

I was thinking the same thing.

Thanks for sharing the results of your experiments.

Cheers,
Chip

[jojokeo]

Tubenit - are the 1watt CF's just the basic type or Vishay or??? I've done this on a lot of builds but used CC's in the signal path, I use CF's for "basic duty". Here's an early DumbleWatt with CC's in the signal path. I wonder if you tried 1/2watters if you'd be just as "smooth"? (also another build using a potpourri of resistors for amusement)

[tubenit]

are the 1watt CF's just the basic type or Vishay or???

I got some 1w Xicon carbon film

My reading has suggested 1w are quieter.  I don't know if they're smoother?

All I can say for certain is that I'm happy with the results on this particular amp.

With respect, Tubenit

[DCbluez]

Hello Tubenit,

First time replying to you. I have bought the Tweed Overdrive Special from Doug and putting it together last night and about complete on the board build. Question: Is the schematic and layout on Dougs site the latest version?

I have built up successfully 4 2204s and 4 Tweed Deluxe and a Hoffman Stout. Also an 80 watt tube bass amp head using 2 KT88s. All sound great and sold half of them to good guitar players.

I found your Tweed Overdrive a very interesting design and decided to build one up. I was looking for a tube overdrive,(controllable) like the one on your design and not a simple diode clipping circuit.

I build all my amps for club use and play clubs frequently and test them on site with the band. I build my own PTs and OTs and chassis and cabs and use some 2X12 and 4X12 Marshall cabs also.

Also on the carbon comp deal I have found places to use them and not. Plate resistors can be fine using 1/2 watt carbon comps and then some may hiss but not all. I have used 1 watt and 2 watt carbon film and also metal film. The Overdrive special preamp most all 1/2 watt Allen Bradley carbon comps and power section 2 watt metal film. This has worked for me well on the 2204s and the Tweed Deluxes.

The voltages on your preamp on the Special fall right inline with my builds which I have modded for tone and the ability to handle pedals well. I have found that too high of preamp voltages, V1 mostly cause some harsh tones, especially using pedals. In a club scene using pedals is something you gotta do or just too loud or not enough flexability for different tones for different tunes etc so handling pedals is a must.

Looking for the 5879 tube.Where did you find them?

[tubenit]

DCBluez,  I appreciate your sharing your experience and success with different resistor types.  Thank you!

Regarding 5879's.  I got them all off ebay. I have not a particular brand that seems "better" to me then others. All of them have sounded really nice, IMO.  I maybe have gotten only 1 microphonic one out of a dozen.

With respect, Tubenit

[DCbluez]

DCBluez,  I appreciate your sharing your experience and success with different resistor types.  Thank you!

Regarding 5879's.  I got them all off ebay. I have not a particular brand that seems "better" to me then others. All of them have sounded really nice, IMO.  I maybe have gotten only 1 microphonic one out of a dozen.

With respect, Tubenit

[PRR]

> Plate resistors can be fine using 1/2 watt carbon comps

In My Experience.....

At guitar-amp voltages, 1/2W plate Rs are "fine" for 30-day warranties. They have a low chance of "failing" in 30 days. They may even last for many years before drift and hiss-crackle happen. OTOH a tube-short will kill a 1/2W in an hour (300V@100K is 0.9 Watts). In carbon-comp, drift and hiss and crackle are roughly related to hours times temperature, so a small hot-running resistor will go sour sooner.

If you care past next month, IMHO it is better to use 1W or 2W parts for g-amp plate resistors. The extra dime of cost is more than paid-back if you *ever* have to replace the part (you, or your customer or tech). Not to mention down-time (and disappointed brides) and a hit on your reputation.