Jason – My Projects

Prep: Converting The Bias Balance to a Bias Adjustment

April 24, 2017 JasonLeave a comment

Last year when I started messing with the Bandmaster, I bought How to Hot Rod Your Fender Amp by Jeffrey Falla. I’ve read the first 6 chapters a few times now, and after practicing my soldering skills on my DS-1, I think I’m ready to jump in.

Falla suggests performing this mod on all silverface amps that haven’t already received it. He also suggests that it is rare to find a silverface amp that has not already had this modification done. Mine certainly falls in this category.

When I first tried to figure out when the amp was built, I had issues placing it and reasoned that it was from 1969 by looking at the information I had available. I may need to try and date the amplifier again (and do a better job of recording what I was looking at to do so), because the electronics (at least for the bias circuit) match the “1968 Silverface Bias Circuit” diagrams in the book.

I had to look at the diagrams and read the procedure a few times with the amp open to understand what I need to do, but now that I get it I think this will be pretty simple to pull off.

I’ve ordered my parts (2, 220K resistors and a 47uF 100V electrolytic capacitor). Once again, I’m nervous/unsure about what brand of components to buy and how much to care about all the specs that the author doesn’t go into. For example, what power/voltage rating should the resistors have? Does it matter? For the record, I bought Xicon resistors with a 3W power rating and a 350V voltage rating… Hopefully that is sufficient.

The parts cost me $6.54 (76.3% of which is shipping) and should get here in a couple weeks. 🙂

Basic Reverb.com DS-1 Mod

February 12, 2017February 12, 2017 JasonLeave a comment

The Boss DS-1 is:

1 – Cheap
2 – “Easy” to modify
3 – Not overly important to my rig.

So, it seemed like a good enough place to start for my first pedal modification. I was initially going to modify my dad’s CE-2, but after discovering that he has a rare version of it, I decided to go with a pedal that I could freely destroy.

I decided to go with a basic modification described at Reverb.com: Simple Boss Pedal Mods: Changing from Stock to Rock

I had some difficulties finding the exact components suggested by the article.

For the first stage, it suggests 2 IRF520 MOSFETs. Every IRF520 MOSFET I could find was listed as out of stock. All I could locate were IRF520PBFs. This is precisely the type of difference that will drive me nuts. Are IRF520PBF the same as IRF520? Are they close enough? Does it matter? What does PBF mean? (Turns out, it means lead free).

For the second stage, the article requests a “Polyester box capacitor, but a regular polyester capacitor would also work”. The only other specific on this I could find was in a caption of one of the photos that showed the author’s replacement capacitor as 0.022uf.

I picked up the MOFSETs and a film capacitor from Mouser for $2.25. I spent more on the shipping than the components.

The mod appeared to be simple and the comments on the page seemed to indicate that a lot of folks have had success with it. I practiced de-soldering by disassembling a few TV remotes that we no longer use. I kept alternating between de-soldering wick and a pump to figure out which I had an easier time with. I’m still not sure which I prefer. What I ended up doing, was using the pump to pull the solder off initially. Once the component was removed, I used the wick to clean the remainder off the board before putting the new components in.

Before I did anything to the pedal, I recorded some samples of the unmodified DS-1 at various settings so that I could compare them later.

DS-1 Before Reverb.com Modification.

I performed the mod out of sequence by starting stage 2 first. Changing the capacitor seemed like an easier introduction to the work and I could see no reason to do them in the suggested order. It took me a few attempts to remove enough solder to pull the original capacitor out. The new capacitor soldered in easily. When it was in place I hooked up the pedal briefly just to make sure that it was still generally functioning. I didn’t want to get to the end and wonder what step I broke it on.

Replacing the capacitor gave me some confidence so I jumped into stage 1. Stage 1 was considerably more difficult and I was convinced at one point that I had destroyed my pedal. There is very little room where the diodes are on the board. They are very small and very close to other components on the board. It took me much longer to remove the solder from these and the pump seemed useless on these so I mostly stuck with the wick. I spent so long trying to get the diodes removed I was convinced that I had delivered too much heat to the board and damaged the pedal.

The article stated that the MOSFETs had to face opposite directions but it didn’t matter which way they were oriented. The picture in the article shows that they author placed them back to back, but I opted to go front to front because it seemed safer to me not to have the metal portions of the MOSFETs facing each other. I don’t know if this actually matters or not.

Soldering the pins of the MOSFETs together was easy. Getting them to fit in the slots left open by the diodes was not. It seemed like I took the smallest components out of the pedal and replaced it with items larger than anything else in the pedal.

The MOSFET pins are flat and were too wide to slide easily onto the board. I took some needle-nose pliers and tried to crimp the pins until they were not as flat and they would fit into the slots. Soldering the pins to the board wasn’t a simple task either. It seemed like the pin that was attached to the center pin took much longer to heat up enough for it to take solder. In an attempt to stop myself from applying heat to the board for too long, I got into the habit of counting out 5 seconds every time the iron touched the board. If I wasn’t done when I hit 5 I would remove the iron for a while before trying again. I wasn’t able to get the solder to take within the 5 seconds on the pins that were soldered together, so I turned up the temperature of the iron a bit. In hindsight, this was probably unnecessary since if the solder wasn’t melting that should mean that the component wasn’t hot enough for it.

Once everything was in place, I hooked up the pedal before putting the case back together just to make sure that it was working and to my astonishment, it made sound. It even sounded like distortion. I put the case back together and when I hooked it up no sound would go through the pedal at all. Luckily, I had read in the comments of the original article that the MOSFETs are big enough that they can touch other items in the pedal when it is closed that could short it out. I took it back apart and put a small piece of electric tape on the top/back of each MOSFET (again, I don’t know if this matters or not) and then tested hooked the pedal up without the case again. To get it to work in the case, I went through a few iterations of pressing the board down as if the case was closed, seeing if the pedal worked, removing it, and bending the MOSFETs and a few other nearby components so that they would lay differently in the closed case. A picture in the article seems to suggest that the author laid the MOSFETs away from each other, but I had difficulty getting it to work in that arrangement. I ended up laying them in the same direction towards the back of the pedal. I was concerned bending the components around that I would break one of them but I didn’t.

Once I had the pedal back together and functioning, I recorded another sample of tones to compare against the original recording.

DS-1 After Reverb.com Modification.

I have to say, this mod did improve the tonal quality of the pedal significantly. I was particularly surprised by how much lower the “level” setting needs to be with the updated components. The new distorion sound still has much more saturation than it probably needs, but tonally it is much fuller. In particular, I noticed that the updated pedal is much more responsive to harmonics than the original. Feel free to compare the videos above for yourself. I apologize for the buzz in them. Something in my house causes my amp to buzz and I haven’t been able to determine what it is.

There are a ton of mods for the DS-1 online. Now that I have a successful one behind me, I may try a few more.

Sound! — New Filter Capacitors

November 27, 2016November 27, 2016 JasonLeave a comment

I’ve been doing some reading the last few months on common maintenance tasks for these amps and have seen multiple places state that the filter capacitors should be changed every 10 years or so. The capacitors in this amp were still the original set, so some new ones were certainly in order.

The amp had paper Mallory capacitors installed. 2 70-uF 350VDC and 3 20-uF 500VDC. I was having difficulty finding replacement capacitors at the exact same ratings and, after some research and what probably amounts to way too much toiling over this detail, I ordered what seemed to be acceptable replacements. 2 F&T 100-uf 350VDC and 3 F&T 22-uf 500VDC capacitors. There appears to be quite a lot of debate around the ideal brand of capacitors that should be used for these amps. Sprague Atom, F&T, Ruby, and Illinois come up quite a bit. Sprague Atom’s seem to be popular because their size more closely matches the size of the original Mallory capacitors. They are also decently more expensive. After I saw a few forum posts indicate that if you cut a Sprague Atom capacitor cut in half you would find that the extra space served no real purpose beyond making the capacitor look larger, my mind was made up and I opted for the less-expensive (and physically smaller) F&T capacitors. The Sprague Atoms may sound a whole lot better. I really wouldn’t know unless I found a way to easily alternate between both and listen to the differences. Perhaps this is something I’ll be able to experiment with later.

The only bump we really hit in replacing the filter capacitors, is that it wasn’t clear by looking at the originals where the solder points should be. We experimented with pulling the entire capacitor out, but realized that underneath the black pad there were wires connecting the capacitors directly to each other. I’m not sure if this is the “right” way to do it, but what we ended up doing was cutting the existing capacitors out and leaving a “post” from the originals in place. We then soldered the new capacitors to our “posts”. I’ve since looked at photos of amps with new filter capacitors installed and am still unable to determine the technique that was used to attach the capacitors. This is something I still need to figure out and I’m certain that a well-placed forum post would yield no less than 3 conflicting responses :).

Once the new capacitors were soldered in, we hooked everything up and… sound! I was expecting noise. I thought once we turned it on we would get crackling, distorted, in-and-out noise but the actual sound was very clear and I had to try and listen for static if the guitar was completely off. The tone was clean and strong with nice present highs and decently full lows. The mids felt a bit under-served to me, but that could have been due to the cabinet or the speakers. We mostly played the amp at a 3, and found that it started to break at about the 5, which is a tad disappointing because I’m not sure how often I’ll have the opportunity to take it up that loud.

The only real issues we discovered were that all the knobs were scratchy, the reverb isn’t functioning, the plug had the ground pulled out of it, and one of the speakers in the original cabinet seems to be out. We put cleaner in the pots for the knobs which seemed to help out quite a bit and I’ll be researching the other issues in the coming months.

I think the next major item I’ll try to work on will be learning how to bias the amp correctly.

The How and the Why

September 11, 2016September 12, 2016 JasonLeave a comment

I have a 1969 (I think) Fender Bandmaster Reverb TFL-5005D (Silverface) head and cabinet in my garage.

When my father was in high school, he didn’t own a gig-worthy amplifier. When his band had a job, he would call up a “friend of a friend” that would let him rent his Fender Bandmaster Reverb for the weekend. After doing this for sometime, he was offered the opportunity to buy the amp for $200 and he jumped on it. This amp was the muscle of his gigging rig through the 1970’s and into the 1980’s. Eventually he picked up a Fender Twin and, after using the twin to drive this cabinet for sometime, the Bandmaster was retired.

It spent a number of years in a shed where his band stored their gear.

It spent a decent amount of time in the garage of my childhood home. I have clear memories of asking my dad if we could hook it up. As I recall, he responded with some variation of “It’s broken.” When I was in high school, I didn’t own a gig-worthy amplifier and I so desperately wanted to use the Bandmaster. This was simply because the amp was much larger than my friends’ amplifiers, and it looked old and “vintage”. I didn’t know anything about the amplifier. I remember we talked back then about fixing it up. When I had a “gig” to play, I would borrow the Fender Twin. He didn’t even charge me rent.

It moved around with him a few times until it ended up in another shed outside his current home and it stayed there until he decided to see what kind of condition it was actually in. He lugged it inside, plugged it in, turned it on, and heard a hum from the tubes warming up. In the amount of time it took him to retrieve his guitar and return, the amp started smoking. He turned it off and did some basic diagnostics. He figured that one or more of the filter capacitors must have failed. Not feeling like investing time and money into the amplifier just to discover additional issues with it, he returned it to the shed.

It was around this time that I was made aware of the amplifier’s status, and offered to give it a home in my garage.

As far as we know, no modifications have ever been done to the amp. It still has all of the original components except for the tubes.

This project is scratching a few itches for me.

First, I have never owned a tube amp and don’t know much about them. My Fender Stage 160 has been a loyal companion over the years. I played out quite a bit in college, but could never afford a nicer amp. The groups I’ve played in after college haven’t really played out enough for me to justify the cost of picking up a nicer amp. Besides, who needs the extra hassle of worrying about a tube going out at a gig? 😉

Second, I have always wanted to understand more about electronics. I know practically nothing about the topic. I recently bought a “learn how to solder” kit and can now poorly reproduce a European siren with a blinking light. I know the basics about capacitors and resistors, and that is about it. I’m hoping to use this project to learn about the tools, diagnostics, and general care and feeding of tube amplifier electronics. That said I’m probably going to make a lot of mistakes on this project. I consider this a good thing.

Third, it has absolutely nothing to do with writing software.

The primary order of business is going to be to get some kind of guitar-like sound out of the amplifier. Dad thinks the problem is the filter capacitors, so we’ll start there.