Metal film resistors in a marshall ptp board?

[kt2345]

Hi anyone tried metal film instead of carbon comp resistors in a marshall? im about to ad a ptp board to my 100 watt and was curiuos what the tonal difference would be if i did the whole turret board with metal film?

[neikeel]

The really honest answer (even as someone who uses some CCs in builds) is that there is probably very little difference between types.

Metal films are robust, accurate and do not drift (carbon comps are usually +/-10% and will often drift higher).

If I had time I would love to build 4 metro clones (probably JTM45 or 50watt) one all NOS AB CC, another all carbon film, another all metal film and another with my preferred option of carbonfilms for most positions (cheap, fit, look ok) with metal oxide or other flame proofs in the B+ line and AB carbon comps on plates, tone stack and NFB (also V1a and V2a for lead length!).

I could then split the signal 4 ways with x4 identical mics into x4 identical speakers etc to play the same riffs, lines and be able to scientifically say if there is a difference.

Most of these things are so subtle just the act of installing and uninstalling stuff affects the tone

[myker]

i second that. i also would like to add that i have experienced no noise level increase in not using metal films in high gain circuits. if you can tell the difference you might be a dolphin or a bat, neither which play the guitar, so no loss there. metal films are great in production amplifiers or where consistency from one amplifier to another is desirable.
mike

[RAM]

Have to agree with the answers too. Maybe try all metal film and then swap to CC's in certain parts of the signal chain. As neikeel said: they are so many factors that go into determining the sound of an amp. Even two amps of the same model and the same components will sound slightly different due to % differences in resisitance and capacitance values, the metal in the transformers, tubes, pots etc.

Rob

[kt2345]

Thanks everyone! well my ptp board had mainly carbon film ,and i changed some locations to carbon comp and i have to say the tonal difference is quite alot! BUT i dont know if i prefer it or not,for a start with carbon comp the noise flaw is noticably higher..the amp hisses even when the volume is completly off,where as before with CC it was silent....hmmm..i do think the amp sounds more "vintage" with carbon comp,but less headroom

I changed the 100k plate,the tone stack,the 2 820ohms and the neg feedback to carbon comp and i suspect that the plate resistors being carbon comp are where the extra noise is coming from??
im going in the amp room now to change the plates back to CC ill report back!

Tony

[kt2345]

Update: for those who are interested, so i spent all day changing things,including changing back to carbon film,but in the end much prefered the carbon comp!The sound is warmer and nicer IMO with carbon comp,so much so that im going to do the WHOLE amp with carbon comp!

One big suprise was the massive difference the silver mica caps make! in fact more so than the resisor change ! the tonal change just swapping those around was massive,i now really like the thicker sound of 470pf on the mixer resistor and treble wiper,way more so than the 250pfs i had in there

[charles]

I just A-B'd a 1968 and 1969 100 watt SL. The 1968 has a mix of carbon comps and carbon films, the 1969 has 1 watt non-magnetic audio metal film resistors. The 1968 is fairly noisy which I guess is normal for a plexi of this era. The 1969 however is absolutely quiet, like did I blow a fuse I don't hear anything quiet. I had a guy come over to buy the 1968 the other night who owns a bunch of vintage Marshalls. He played the 1968 and liked it, said it sounds as good as any Marshall he owns. Then I let him play the new 1969 plexi, he said whoa!! The richness and harmonics were clearly superior to the 1968. It would have been a no brainer if you were trying to chose which amp to buy.

This was not an apples to apples comparison. The amps have different filtering, transformers, etc. but the boards are close, the major difference being the resistors. The resistors lowered the noise for sure but were they also a factor in improving the tone? Never mind the type of resistors, maybe it was the accuracy. The metal film resistors are less than 1% tollerance and I measured every component that went into the 1969 and all were less than 1% out of spec which means the math behind the circuit design is pretty much right on the money. The 1968 well those components are +- 5% to 10%.

1968 100 Watt SL


1969 100 Watt SL

[Joe Popp]

I used Carbon Films and Metal Films in 4 different JCM800 builds and they all sounded great! I wasn't able to do a direct AB comparison but I honestly say I could not tell between these 2 types. The JTM45 I am building now is going to be all carbon comp which I am curious to hear what it sounds like. Here's a pic of a 2204 circuit with Dale Metal films through out. I sold it to a guy in California that love's it!

[Riscchip]

That's a beautiful build, Joe. Nice work.

Yours too, Charles. Spectacular.

Sorry...off topic...hehe.

[joshwilson3]

...

[JamesHealey]

They provide a certain ammount of resistance between two electrical points, surely they cannot have a tone of their own? I dont believe it myself, I think they can add noise and this can make the amps high end warmer due to distortion of the signal.

but I don't think the noise difference between Carbon Film and Metal Film should be much, Carbon Comp might be different though because they drift wildly and are very noisy.

[Froumy]

Kt2345,

Good to see you tested them all out, to see what you prefer. Seems like many guys who prefer carbon Comps in the signal path, prefer carbon films for plate resistors. Not just for noise concerns, but a little added dimension that the comps just didn't have in that location. Something to try out, if nothing else. Sometimes a blend can be the best option.

[rip]

What brand MF are those? And what is the "non-magnetic" for?

I believe charles uses PRP resistors from sonic craft

[joey]

What brand MF are those? And what is the "non-magnetic" for?

Those are Vishay RN65's 1/2 super low noise Military grade metal film, you can find them at mouser. I have used them in super high gain builds everywhere, and between those, and a good layout and ground scheme, I have been able to make super high gain amps whisper quiet. They have a non magnetic body and leads, (which you want to be mindful of if you use any resistor in series with your signal, one of the reason CC actually excel in grid stopping locations, well that and the non-inductive nature of CC)

The 3W GS-3 are supposed to be very good too

[rip]

Okay well Charles is using PRP's and Joe Popp is using the Vishay Dales.

Rip