Tweaking My 102 Amp: A Massive Resistor Makeover

[ayan]

A lot of work there Gil, and also in writing it up! If you do similar to your low-plate, please get before and after recordings so we can hear exactly what happened.

Martin, I’m not a clip kind of guy. I’ve been playing in the same band for 19 years and in all of the videos out there in our website, YT and and FB, I’ve used my clones. For the last maybe 13 years, it’s been the low plate, but until 2006 I played high plate classics, and after 2006 I took my Blues Master on a couple of gigs that are on YT. I promise to make before and after clips for anyone who goes through the trouble of watching the existing videos and tells me what amp was used in each. Seriously, the changes I outlined are as useful as the information I posted on 124, the Ry Cooder, etc., back in the day. It’s up I each reader to decide whether it’s worth trying. And if a given amp sounds good enough now, I’d leave it alone.

Cheers,

Gil

[jelle]

Gil, glad it worked out! You were instrumental when I got started in teaching me the beginnings of Dumble amps through your forum posts on Ampage and here. Glad to give back.

Jelle

[jelle]

I have gotten a few messages from people about these resistors. They can be found here: https://www.ebay.com/sch/lampje*2007/m. ... ksid=p3692

When time allows, I will make a list of what I have available and post it here, but for now all is listen on ebay as well, so people can see it there. I apologize for the pricing, these were pulled from the NATO repositories for me and imported.

Also, please do not PM me here, but email through my website. Happy soldering!

Jelle

[Matt J]

This has been a very fascinating thread to read over! Thank you Gil and Jelle for sharing your insights on this!

Can anyone recommend any articles or other reading materials discussing distortion produced by resistors? I'm curious about learning more on this subject.

- Matt J.

[jelle]

I would not know, I got out of the business of writing scientific papers.

jelle

[Matt J]

I would not know, I got out of the business of writing scientific papers.

#1 reason I decided not to go for a Ph.d... My days of wanting to write research papers are long behind me. I lost enough hair just working on my Masters as it is.

- Matt J.

[pompeiisneaks]

This has been a very fascinating thread to read over! Thank you Gil and Jelle for sharing your insights on this!

Can anyone recommend any articles or other reading materials discussing distortion produced by resistors? I'm curious about learning more on this subject.

- Matt J.

Merlin's book has a great write up on all the different components and how they can and do impact tone. I don't recall which book, I'd have to look, but it offered great information like which resistor type had the most or least noise, etc. As well as what types of capacitors modify the sound etc.

~Phil

[ayan]

This has been a very fascinating thread to read over! Thank you Gil and Jelle for sharing your insights on this!

Can anyone recommend any articles or other reading materials discussing distortion produced by resistors? I'm curious about learning more on this subject.

- Matt J.

Merlin's book has a great write up on all the different components and how they can and do impact tone. I don't recall which book, I'd have to look, but it offered great information like which resistor type had the most or least noise, etc. As well as what types of capacitors modify the sound etc.

~Phil

Merlin's a very knowledgeable person and writes in a style that I very much enjoy. I recently got his Designing Tube Preamps for Guitar and Bass, 2nd Edition, which I have enjoyed reading. It has a lot of good information above and beyond what you can find in his website. Interestingly, from an empirical point of view, I resonate with some of his assertions and disagree with others. Specifically about resistors, for example, he submits that the only difference in sound there is between say metal films and carbon comps is that the latter are noisier. That does not agree with my experience. But, for example, he includes a section in which he talks about block distortion, grid stoppers -- straight and bypassed -- and even addresses some amp's ability to have a "phasing or swirling" on the low end. His choice of words brought back memories of reading Tag Skinner's posts at TGP describing his fable 183 Dumble, TR Emerald Pro, etc. And it was cool to read a technical explanation for the effect. I started buying every tube amp book I could get my hands on starting in the early 90s. In my opinion, Merlin's book is definitely the best written.

Gil

[pompeiisneaks]

This has been a very fascinating thread to read over! Thank you Gil and Jelle for sharing your insights on this!

Can anyone recommend any articles or other reading materials discussing distortion produced by resistors? I'm curious about learning more on this subject.

- Matt J.

Merlin's book has a great write up on all the different components and how they can and do impact tone. I don't recall which book, I'd have to look, but it offered great information like which resistor type had the most or least noise, etc. As well as what types of capacitors modify the sound etc.

~Phil

Merlin's a very knowledgeable person and writes in a style that I very much enjoy. I recently got his Designing Tube Preamps for Guitar and Bass, 2nd Edition, which I have enjoyed reading. It has a lot of good information above and beyond what you can find in his website. Interestingly, from an empirical point of view, I resonate with some of his assertions and disagree with others. Specifically about resistors, for example, he submits that the only difference in sound there is between say metal films and carbon comps is that the latter are noisier. That does not agree with my experience. But, for example, he includes a section in which he talks about block distortion, grid stoppers -- straight and bypassed -- and even addresses some amp's ability to have a "phasing or swirling" on the low end. His choice of words brought back memories of reading Tag Skinner's posts at TGP describing his fable 183 Dumble, TR Emerald Pro, etc. And it was cool to read a technical explanation for the effect. I started buying every tube amp book I could get my hands on starting in the early 90s. In my opinion, Merlin's book is definitely the best written.

Gil

Although I do understand your point, a lot of what he means by noise is what is measurable by detection instruments of the different kinds of known noise that can exist in resistors, shot noise, etc. I.e. scientific level tests with highly sensitive machinery designed to capture any changes. That doesn't mean the ear can't hear some other differences. For example I know he's stated that metal film resistors are the most silent, but many (myself included) choose to use carbon film because they do add noise that is 'good' for amps. The metal film amps can feel too 'sterile' as they add nothing to the amp, and that 'nothing' is missed by those used to the sound carbon film adds. Carbon Comp adds a lot more noise, most of which is preferable, but also they, by design drift in value over time meaning they can be way different in tonality 10 years after they were installed. This can be a good or bad thing depending on why/where/how. etc.

~Phil

[martin manning]

Can anyone recommend any articles or other reading materials discussing distortion produced by resistors? I'm curious about learning more on this subject.

R.G.Keen writes about the distortion produced by CC resistors here: http://www.geofex.com/article_folders/c ... oncomp.htm

Here is another article "Selecting resistors for preamp, amplifier and other high-end audio applications". It does not address distortion, though, just noise: https://www.eetimes.com/document.asp?doc_id=1278251

I took the time to measure the NOS Dale MF resistors Tony sent me and some new Dale RN65D's with a B&K 879B LCR meter. They all measure very close to the marked value of resistance, well within tolerance. Parasitics (measured at 1kHz) are essentially the same: 0.1-0.2 pF Cp, and 8-10 mH Ls. These are small enough that the measured impedance is the same as the measured resistance within the display resolution for this magnitude, which is 10 ohms. These measurements are made at low voltage, but there is nothing there to suggest that old ones would sound any different from new ones. In a few days I will make some high voltage measurements using a curve tracer to see if there is any non-linear resistance behavior.

[ayan]

Although I do understand your point, a lot of what he means by noise is what is measurable by detection instruments of the different kinds of known noise that can exist in resistors, shot noise, etc. I.e. scientific level tests with highly sensitive machinery designed to capture any changes.
...
~Phil

I understand. However, maybe what makes a specific type of resistor preferable to some is not -- or not just -- related to noise. If that is the case, trying to explain the tonal differences between resistor types by only addressing their noise characteristics will not get you a complete answer. However, Merlin's view on this topic appears to be unequivocal according to the book.

Gil

[martin manning]

Belencowe’s “Designing High-Fidelity Tube Preamps” book has more discussion on resistors than his guitar and bass preamp book. In it there is a plot of THD+N for CC, CF, and MF resistors that shows 1/8W MF and 1/4W CF resistors (lower wattage is worst) between 0.0005 and 0.001% THD+N from 20 Hz to 20kHz, with the trace of the 1/8W MF being at the noise floor of the analyzer. I just don’t see how it’s possible that resistors are going to “color” the sound in any audible way.

[ayan]

Belencowe’s “Designing High-Fidelity Tube Preamps” book has more discussion on resistors than his guitar and bass preamp book. In it there is a plot of THD+N for CC, CF, and MF resistors that shows 1/8W MF and 1/4W CF resistors (lower wattage is worst) between 0.0005 and 0.001% THD+N from 20 Hz to 20kHz, with the trace of the 1/8W MF being at the noise floor of the analyzer. I just don’t see how it’s possible that resistors are going to “color” the sound in any audible way.

Martin, perhaps the answer to your question may lie in your own words:

I just don’t see how it’s possible that resistors are going to “color” the sound in any audible way.

Rather than visually, maybe approach the topic aurally? I'm curious to know if you have tried different types of resistors and not heard any difference? If so, I can understand focusing on a theoretical explanation for others' claims. If not, it would be really easy to do a little test and find out for yourself. In my experience, the difference between Roederstein MK3s and newer Dales was fairly immediate. I replaced the four V1 and V2 plate loads and the amp's OD character was decidedly different. Now, the difference between the Xicon and Draloric CFs was not as dramatic when taken a few at a time. But I replaced every single resistor in the amp's audio signal path, starting with the 1 Meg at the input jack, all the way to the power tube grid stoppers. That is about 30 resistors total, and there was a distinct cumulative difference. At the end of the journey, as I already said, the amp sounded cleaner, more midrangey and had more sustain. Is that all due to different noise characteristics? It might as well be, for all I know, but there is no question that the end result was a more pleasant sounding amp. I had a gig last Saturday and we played a room that was really bright in comparison to the one the weekend before, so I'm sure this played a role too. When I turned the amp on, at first I thought I had forgotten to plug in the FX loop's cables, the sound was really trebley. During sound check, my guitar was feeding back more than I wanted, to the point that the bass player looked at me and said "Dude, you're going to have to reel that in." I did struggle trying to get things under control. On Sunday, the day after the gig, I plucked the 390 pF SM Mid switch cap and replaced it with a ceramic disc, as both Jelle and Tony had recommended. Next gig is in two weeks, I look forward to seeing if that tames things a bit.

Gil

[erwin_ve]

Gil I notice you have grounded the cathode of v2 to the fx loop?
Have you tried grounding it at the shared v1 cathode ground?
Imo this also make the amp smooth and less jagged in the high frequencies.

I searched my butt off to find the old Dales for the plates, no luck sofar.
Few years ago I found a nice lot of nos CF piher and beyschlag in a army dump store.
Used these in 4 builts and they do affect the tone in a positive way.

The mid cap to a polyprop cap describes exactly what I hear too. Freaked me out so much I put the 6 PS in again, and a week later put the polyprop in again and is still there.
When I came to the ampgarage more than a decade ago I learned a lot from your postings, thanks for sharing and taking time to discuss!

Erwin

[ayan]

Gil I notice you have grounded the cathode of v2 to the fx loop?
Have you tried grounding it at the shared v1 cathode ground?
Imo this also make the amp smooth and less jagged in the high frequencies.

I searched my butt off to find the old Dales for the plates, no luck sofar.
Few years ago I found a nice lot of nos CF piher and beyschlag in a army dump store.
Used these in 4 builts and they do affect the tone in a positive way.

The mid cap to a polyprop cap describes exactly what I hear too. Freaked me out so much I put the 6 PS in again, and a week later put the polyprop in again and is still there.
When I came to the ampgarage more than a decade ago I learned a lot from your postings, thanks for sharing and taking time to discuss!

Erwin

Hey Erwin,

V1 and V2 do share the cathode ground at the ground lug(s) located by the relays, while V3's ground goes to the FX loop jack. Interesting that you had the same experience with the 715 cap.

Cheers,

Gil