I recently purchased a 1976 Traynor YBA-1 Bassmaster. This is a later model, but from what I have been able to figure out Pete Traynor was still involved with the company. This particular amp has a factory installed 3-prong cord and does not have a ground switch. I have not seen any photos or schematics for my amp online anywhere so I thought I would document mine as well as changes I will be making.
Schematic
One nice thing about Traynor amps is they are pretty easy to service compared to Fender and Marshalls. Instead of having to remove the chassis from the cabinet, the there are a couple of bolts that go through the top and into the chassis. To service the amp, you simply need to remove the bolts and pop off the top.
Another nice thing Traynor did was include a copy of the schematic on the bottom-side of the top panel. This is especially helpful for me because my amp does not match the schematic for any other YBA-1 I have seen posted online. The following image is actually a photo that was converted to black and white. I might re-draw it some day if I feel motivated.
Another nice thing Traynor did was include a copy of the schematic on the bottom-side of the top panel. This is especially helpful for me because my amp does not match the schematic for any other YBA-1 I have seen posted online. The following image is actually a photo that was converted to black and white. I might re-draw it some day if I feel motivated.
Volume Pots
The first mod people seem to make to these amps is to change the pots to the same value that Fender and Marshall used; 1M audio taper. Earlier models have 4 Meg linear taper pots. The change is supposed to make the response less spongy. I'm not exactly sure what that means because my amp has 500K linear taper pots. Some say that it isn't necessary to swap these pots, but I found the linear taper made the amp get too loud too soon so I swapped them.
Bright Cap
The first thing I noticed about my amp is the bright channel is REALLY REALLY bright. Actually, that was the second thing I noticed, the first thing is the amp is REALLY REALLY loud. But REALLY REALLY loud and REALLY REALLY bright can be painful so I changed the bright cap from the initial value of (original value) to 120pF. This tamed things quite a bit but it is still a little bright for my taste. I may end up removing the cap all together after I make changes to the V1 cathode resistors and capacitors (see below).
The following clip is using a 1992 Starfield with Fender Tex Mex pickups. The Starfield is basically a Strat with only 1 volume and 1 tone control. The amp is set so the Volume is on 2 and all other controls are set to 12:00 o'clock. The cabinet is a 4x12 with two WGS Veteran speakers and two WGS Green Berets. The mics are a Shure SM57 and a Sennheiser e609.
The clip starts with just the bridge pickup into the normal channel low input jack. I use the same riffs and work my way through each position of the guitar and each input on the amp. To hear what I mean by REALLY REALLY bright go to the 10:00 minute mark... it gets worse from there.
The clip starts with just the bridge pickup into the normal channel low input jack. I use the same riffs and work my way through each position of the guitar and each input on the amp. To hear what I mean by REALLY REALLY bright go to the 10:00 minute mark... it gets worse from there.
I don't have a recording of after I changed the bright cap, but trust me... it is much less bright.
Update: I decided that the bright cap was still too bright so I removed it. After I removed the cap, the channels were essentially identical so I decided to make changes to the Cathode Bypass Capacitor documented below.
Update: I decided that the bright cap was still too bright so I removed it. After I removed the cap, the channels were essentially identical so I decided to make changes to the Cathode Bypass Capacitor documented below.
Cathode Bypass Capacitor/Resistor
The next thing I noticed is that the amp is pretty boomy. It has tons of low end even when I turn down the bass control. I guess this makes sense if you want to use it as a bass amp, but I want to use it for guitar. At first I was thinking I should modify the tone stack to be more Bassman/JTM45 like, but then I noticed that the amp does not have any cathode bypass capacitors. None.
Upon further investigation, it appears that the YBA-1 has gone through a number of iterations. The original amp was similar to the Bassman/JTM45 where it shared a cathode resistor and bypass cap on V1A and V1B of 820R and 250uF. The next version went to split cathode resistors and bypass caps of values 1.5K and 125uF. At some point in the 1970's the 125uF bypass capacitor was eliminated from the circuit. I think this may be contributing to the boominess.
I know that later Marshall amps used a bypass cap of 0.68uF so I experimented with values of 100uF, 10uF, 2.2uF, and 1uF that I had in my parts drawer. To be honest the amp doesn't sound a whole lot different regardless which bypass cap I used. The thing I noticed is that things seemed to tighten up a bit when I used either the 2.2uF or 1uF values. Just a little less boom, a little less tubbyness.
My observations can be confirmed using the following Cathode Capacitor Calculator. Enter the following values:
Upon further investigation, it appears that the YBA-1 has gone through a number of iterations. The original amp was similar to the Bassman/JTM45 where it shared a cathode resistor and bypass cap on V1A and V1B of 820R and 250uF. The next version went to split cathode resistors and bypass caps of values 1.5K and 125uF. At some point in the 1970's the 125uF bypass capacitor was eliminated from the circuit. I think this may be contributing to the boominess.
I know that later Marshall amps used a bypass cap of 0.68uF so I experimented with values of 100uF, 10uF, 2.2uF, and 1uF that I had in my parts drawer. To be honest the amp doesn't sound a whole lot different regardless which bypass cap I used. The thing I noticed is that things seemed to tighten up a bit when I used either the 2.2uF or 1uF values. Just a little less boom, a little less tubbyness.
My observations can be confirmed using the following Cathode Capacitor Calculator. Enter the following values:
Tube | = 12AX7 |
Ck | = 100 | 10 | 2.2 | 1.0 |
Rg | = 1000 (this is the 1M pot) |
Rl | = 100 (this is the 100K load resistor) |
Rk | = 1.5 (this is the cathode resistor) |
Initially, I was using a 1uF cap with the stock 1.5K cathode resistor, but I decided to splurge and order the Marshall 1987 values of 0.68uF and 2.7K cathode resistor. This change gave a much more audible difference between the channels.
Mixing Resistors
From what I understand, the lower the values of the mixing resistors, the more interactive the two channels are.The Fender Bassman and Marshall JTM45 use 270K mixing resistors. The later "Plexi" Marshalls use 470K resistors. The Traynor used a comparatively low value of 100K.
As I mentioned above, the bright cap was just too bright. Then I noticed something. The Marshall has a capacitor in parallel with the mixing resistor of the bright channel mixing resistor. I did some searching and found someone recommending moving the bright cap and putting in in parallel with the mix resistor. Actually, "recommending" isn't strong enough word, this poster was very enthusiastic about the mod. I can't find the post at the moment or I would give attribution, but I decided to try it by clipping in the capacitor. I was instantly able to hear a subtle difference. I brought my daughter in (young female ears) to listen and she agreed the that things sounded better with the cap in the circuit so I decided to install permanently. While I was at it, I decided to change the mixing resistors to the Bassman/JTM45 values. No particular reason other than I read of other people recommending this change.
As I mentioned above, the bright cap was just too bright. Then I noticed something. The Marshall has a capacitor in parallel with the mixing resistor of the bright channel mixing resistor. I did some searching and found someone recommending moving the bright cap and putting in in parallel with the mix resistor. Actually, "recommending" isn't strong enough word, this poster was very enthusiastic about the mod. I can't find the post at the moment or I would give attribution, but I decided to try it by clipping in the capacitor. I was instantly able to hear a subtle difference. I brought my daughter in (young female ears) to listen and she agreed the that things sounded better with the cap in the circuit so I decided to install permanently. While I was at it, I decided to change the mixing resistors to the Bassman/JTM45 values. No particular reason other than I read of other people recommending this change.
This is the most significant change I have made! After the substitutions were complete, I fired up the amp. Now the channels sound distinct. The bright channel is bright without being overly harsh. It works great with a humbucker loaded Les Paul, the filtertron loaded Gretsch and the P90 loaded Hamer. Still a little bright with a Strat, but turning down the presence and treble tame that. However, if you want to play a Strat, I suggest using the bass channel.
Phase Inverter
In The Gear Page thread called "Traynor Bassmaster YBA-1 - Read this if you want to tweak yours" the original poster created a list of changes. Changes 8 and 9 in the list suggest modifying the phase inverter values to match the Marshall values. He says, "...replace these with 1meg period, Marshall knew what they were doing."
I replaced the 47K grid leak resistors with 1M and I replaced the 6.8K tail resistors with 10K. After making the change I found the amp breaks up much earlier now. To be honest, I'm not sure if I like it. Let me clarify... it sounds great! But since there is no headroom it makes it difficult to have any sort of clean tone. I can back way off on the guitar volume but I'm not sure I like that solution. I used this Long Tailed Pair Calculator to see what the changes are doing.
According to the calculator, the original Traynor values produced around 24dB of gain while the Marshall values produced around 29dB of gain. I think that explains why the reduction in headroom.
Playing with values in the calculator allows you to see what is going on. Ends up, using the Traynor value of 6.8K in the tail and Marshall values of 1M in the grid makes the phased signals more balanced than either solution. I'm not sure what the solution to reducing the gain is... I can reduce the grid resistors to 100K to get a gain of 26.6dB. This make the most balanced of all the options I have tried in the calculator. Another option to explore is changing the value of the Feedback resistor.
I replaced the 47K grid leak resistors with 1M and I replaced the 6.8K tail resistors with 10K. After making the change I found the amp breaks up much earlier now. To be honest, I'm not sure if I like it. Let me clarify... it sounds great! But since there is no headroom it makes it difficult to have any sort of clean tone. I can back way off on the guitar volume but I'm not sure I like that solution. I used this Long Tailed Pair Calculator to see what the changes are doing.
According to the calculator, the original Traynor values produced around 24dB of gain while the Marshall values produced around 29dB of gain. I think that explains why the reduction in headroom.
Playing with values in the calculator allows you to see what is going on. Ends up, using the Traynor value of 6.8K in the tail and Marshall values of 1M in the grid makes the phased signals more balanced than either solution. I'm not sure what the solution to reducing the gain is... I can reduce the grid resistors to 100K to get a gain of 26.6dB. This make the most balanced of all the options I have tried in the calculator. Another option to explore is changing the value of the Feedback resistor.
Tone Stack
Another area that people recommend changing on the Traynor is the tone stack. I have modeled the tone control using Duncan's Tone Stack calculator. There are two significant differences that stand out between the two tone stacks; bass roll-off frequency and mid-dip frequency.
The frequency range of a guitar is around 82Hz to 12kHz. By examining the curve you can see that the Marshall tone tack starts rolling off the bass frequencies at 100Hz. There isn't much of decrease when reaching the 82Hz, so it probably doesn't really impact the sound much (not including frequencies using effects, tremolo, etc.). On the other hand, the Traynor actually has a slight rise in bass frequencies starting at 100Hz.
The mid-frequency dip of a Marshall is around 700Hz while the dip of the Traynor is around 400Hz.
Most people recommend changing the value of the Bass capacitor (C2) to match the Marshall value of 0.02uF. This will give the Traynor a similar bass response curve dropping off at 100Hz. However, the mid-dip frequency does not change but the dip becomes more shallow. You may or may not want this. Changing the Treble capacitor (C1) to 470pF will move the mid-dip to be more like the Marshall.
The mid-frequency dip of a Marshall is around 700Hz while the dip of the Traynor is around 400Hz.
Most people recommend changing the value of the Bass capacitor (C2) to match the Marshall value of 0.02uF. This will give the Traynor a similar bass response curve dropping off at 100Hz. However, the mid-dip frequency does not change but the dip becomes more shallow. You may or may not want this. Changing the Treble capacitor (C1) to 470pF will move the mid-dip to be more like the Marshall.