# YBA-1 Transient fidelity Mod



## David_Well (Aug 22, 2009)

Transient fidelity

This mod consists of an attempt to extract the most in terms of transient fidelity from the YBA-1 signal path without altering the gain structure or intended dynamics beyond, let's say what one might want to establish as a typically objectionable point in some kingdom somewhere...

[1a] decoupling input bias circuits, i.e., replace the 820 Ohm/250 uF bias circuit of the input gain stages by separate 1k5/125 uF and 1k5/0.68uF cicuits. Cap value varies according to taste, the larger cap will give you deeper bass response - Traynors seem to sound woofy if a too large cap is used here...
Some people like to keep the original functionality of the amp intact but then, in the separated cathode circuit version maybe have a large value on one side and a lean on the other as in Marshall 1986s and 1959s. I prefer
[1b] disabling the second channel altogether and having a non-electrolytic 0.68uF cap as the only cathode bypass cap in the whole signal chain - the amp then becomes a pure single channel, high transient fidelity signal path ...this is especially noticeable during periodes of sharp transient attacks... even at low level it'll knock you out...

[2] change 4Meg volume pot(s) to 1MegA for a less "spongy" attack ...

[3] change tone stack to 5F8/6-A values, i.e., 47k to 56k and 0.1uF to 0.02uF. This network impedance matches well with the spectral nature of many typical guitar pickups... amongst other things it brings in the midrange dip and narrows the treble and bass peaks closer together...

[4] I like the old presence control, i.e. the old "scratchy" style circuit with only the 4.7k Pot and cap on the wiper. Sometimes, as an add-on I like to use a
[5] dual 4.7k pot wired to a DPDT switch (to yield a 2.5k equivalent pot) in the presence circuit in order to alter loop gain of output stage feedback mixing at the flick of a switch... this tends to favorise pentode distortion in the amp and also loosens the output stage a bit - at lower volume settings this gives a normaly stiff class-AB amp a slightly livelier feel... I learnt a simpler version of this this from Dave Vidal in Vancouver who worked for Red Rhoads in LA during the seventies - the version I explain here is my own...

[6] I like reducing the 100k feedback return resistor to 47k, this tightens the output stage and balances things out with mod [5]... set to taste.

[7] The power supply B+ filters caps could use a few more Farads, 80/450 caps can become 100/450 and 40/450 caps become 50/450; as long as these values are not exceeded this won't harm the PT... on the other hand the preamp filter caps I leave as they are value wise.
You can experiment with the triode/pentode ratio when the amp is overdriving by altering the preamp voltage headroom. The values R21=4k7 and R32=10k can be changed to 1k, 2k2 repectively... I use 2Watt resistors for this... you will notice a cleaner and slightly brighter response from the amp... when cranked the pentodes will fire up earlier and give the amp a truely warm and sexy feel once
[8] a careful biasing and funetuning of the output tubes has been done.

I hope this encourages other YBA-1 owners to explore the hidden tone available in this underated beast... especially those who seek enhancements that don't alter the original set of dominant expressive characteristics surrounding the amp... these are my ideas and opinions only, feel free to add or change things to suit your own taste and needs...

Btw, in the single channel version of this mod the discarded gain stage can be used, in conjunction with a relay circuit, to give a 2 channel switching amp that produces a jaw dropping 70's overdrive and compression....


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## parkhead (Aug 14, 2009)

lets hear a clip ?

p


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## parkhead (Aug 14, 2009)

Be aware that if you complete all of the steps of this mod you may not like the result. 

They make the amp cleaner and enhance the upper midrange. This can be great for lifting the tone out of the Mud, but these changes will also make the amp appear louder and decrease your "low volume"utility in some cases.


Here's why quoting from the mod with comments 


Transient fidelity

This mod consists of an attempt to extract the most in terms of transient fidelity from the YBA-1 signal path without altering the gain structure or intended dynamics beyond, let's say what one might want to establish as a typically objectionable point in some kingdom somewhere...

[1a] decoupling input bias circuits, i.e., replace the 820 Ohm/250 uF bias circuit of the input gain stages by separate 1k5/125 uF and 1k5/0.68uF cicuits. Cap value varies according to taste, the larger cap will give you deeper bass response - Traynors seem to sound woofy if a too large cap is used here...
Some people like to keep the original functionality of the amp intact but then, in the separated cathode circuit version maybe have a large value on one side and a lean on the other as in Marshall 1986s and 1959s. I prefer
[1b] disabling the second channel altogether and having a non-electrolytic 0.68uF cap as the only cathode bypass cap in the whole signal chain - the amp then becomes a pure single channel, high transient fidelity signal path ...this is especially noticeable during periodes of sharp transient attacks... even at low level it'll knock you out...

Changing the bypass cap from 220 or 125 to .68 removes a lot of bottom end

An unbypassed cathode resistor has a flat frequency response, a bypassed cathode resistor has a boost above the frequency determined by the cap value 25 mfd is a common full bandwidth "fender value" 220 is ridiculously thumpy but sounds cool, and .68 is a marshall upper midrange boost... value and is beginning to cut off you low end depending on the resistor value 

by itself this change might not be terrible 




[2] change 4Meg volume pot(s) to 1MegA for a less "spongy" attack ...

everyone does this

[3] change tone stack to 5F8/6-A values, i.e., 47k to 56k and 0.1uF to 0.02uF. This network impedance matches well with the spectral nature of many typical guitar pickups... amongst other things it brings in the midrange dip and narrows the treble and bass peaks closer together...

this is critical, part of the magic of the bassman marshall circuit is the 58/ jtm45 tone network .. by using a pair of .02 caps the bass control moves into the midrange territory... leo Fender did this to give apparent low end while protecting the bassman's 10 inch speakers from F4rting out and blowing up ... this is mid boost the part that guitar players fell in love with and marshall has used as their tone network ever since...

this is THE KEY mod for bassmasters 

[4] I like the old presence control, i.e. the old "scratchy" style circuit with only the 4.7k Pot and cap on the wiper. Sometimes, as an add-on I like to use a
[5] dual 4.7k pot wired to a DPDT switch (to yield a 2.5k equivalent pot) in the presence circuit in order to alter loop gain of output stage feedback mixing at the flick of a switch... this tends to favorise pentode distortion in the amp and also loosens the output stage a bit - at lower volume settings this gives a normaly stiff class-AB amp a slightly livelier feel... I learnt a simpler version of this this from Dave Vidal in Vancouver who worked for Red Rhoads in LA during the seventies - the version I explain here is my own...

seems like a lot of work... to decrease negative feedback, then in the next step increase negative feedback however I will note, when in doubt go with the tweed bassman or Jtm45 values as there must be some good sounds happening in those 10k to 15k vintage amps 

[6] I like reducing the 100k feedback return resistor to 47k, this tightens the output stage and balances things out with mod [5]... set to taste.

part 6 is probably the final stage in setting up any amp for personal use 
I've used 27k and even 12k instead of 100k for the feedback resistor in these amps the lower the value the more feedback in the power amp tightening the tone and making the amp richer ...
the higher the value 47k or 100k the more trash in the output and more aggressively loud the amp is for big stage use ... however you lose control of your cleans 
this change is also very deceptive as what sounds good and raunchy sitting around the house ie 100k can sound horribly broken up on the gig with a drummer 
be prepared to adjust the feedback resistor a few times till you get a personal sound 
Marshall played with feedback resistor values constantly till 1980 
generally speaking Plexi marshalls had more feedback and JMPs and jcm800's had less 


[7] The power supply B+ filters caps could use a few more Farads, 80/450 caps can become 100/450 and 40/450 caps become 50/450; as long as these values are not exceeded this won't harm the PT... on the other hand the preamp filter caps I leave as they are value wise.
You can experiment with the triode/pentode ratio when the amp is overdriving by altering the preamp voltage headroom. The values R21=4k7 and R32=10k can be changed to 1k, 2k2 repectively... I use 2Watt resistors for this... you will notice a cleaner and slightly brighter response from the amp... when cranked the pentodes will fire up earlier and give the amp a truely warm and sexy feel once

Danger .... a stiffer power supply makes engineering sense but not musical sense !!! 

Again your typical playing venue will determine your opinion of this change 
if you are playing the Air Canada Center or outdoor concerts this is a good mod ... if you play in a band or around the house you've just stiffened up the powersupply and taken the bounce out of the amp. 

increasing the filtering increases the current reserve so that notes pop faster 
(ever felt the fast attack of an amp was "tiring" to play?) 

Changing those power supply resistors increases the voltage and headroom in the pre amp again great for big stages 

Part 7 is almost the exact opposite of the Blackface mods people do to later fender amps ... in those mods they are reducing filtering back to 60's specs and reducing pre amp voltages as well



[8] a careful biasing and funetuning of the output tubes has been done.

bottom line is you can go too far with some of these headroom mods 
and end up with an amp that needs an attenuator to play around the house 
or with your buddies 

for the most part the earlier bassmaster amps are close knock offs of the Marshall JTM/45 and tweed 5f6a bassman 

your best "mods" are to carefully study all three amps and "unmod" the traynor back to the original bassman specs 

a real bassman or JTM45 is a magical paradox of musically rich cleans and singing and swirly distortion at reasonable volume levels 

people don't overpay for the old ones because they are pretty, rare or loaded with features, they chase these things because they define guitar tone... 

when you play one your brain screams wow how can there be so much going on with the amp just reacting to how I play ? 

the reason Traynor YBA-1's are not in the 10k-15k vintage value club is because Yorkville constantly updated the design for greater fidelity and headroom for bass use 

Marshall tweaked the amp very little, and Fender discontinued the 4-10 bassman after 3 years and offered the improved "super reverb" and piggy back bassman, with more headroom and clarity 

In Marshalls everyone wants a plexi or JTM45, the earliest versions of the amps with the least headroom and transient fidelity 

In bassmasters everyone wants the tube rectifier script logo version, the ones with the least headroom and transient fidelity 

In twins supers and assorted Fender reverb amps everyone wants the earlier ones with "less headroom and transient fidelity" 

as proof that everyone "wants" those versions check out vintage resale pricing ... if people just wanted an old Fender or Marshall the 
Fender Taurus solid state amps from 1969 would be valuable !

go here and fast forward to 3:29 

http://www.youtube.com/watch?v=dU2uNjxvBcs

note the comments at 4:23 

http://www.youtube.com/watch?v=dU2uNjxvBcs

Pete Traynor told me that he was in a Band with Robbie, with Robbie on Bass and Pete playing guitar 
in a short time Robbie was the better Guitar player (man did he practice !) and so they switched 
Pete took a job in a music Store doing repairs ... and Robbie ... who knows what happened to him

Looking at the tone stack in the YBA-1 with the .1 bass cap Pete Traynor was copying the 59- 60 bassman 
vs the 58 with .02 bass cap 

Pete did his feedback loop math correct, adjusting the 27k at 2 ohms of the fender to 100k at 8ohms for the traynor 

Marshall were looking at the 58 bassman with the .02 bass cap 
incidentally intentionally or otherwise they got the feedback loop wrong at first
sticking with 27k but because of the 16 ohm load this is 3x as much feedback at 27k at 2 ohms 
I suspect after they made the "mistake" they realized they had hit upon a great way to make the amp 
grind harder and stuck with 27k till about 67 when they changed a bunch or other stuff 

heres a great example of an original JTM45 
http://www.youtube.com/watch?v=EA0LtElaUIo

in this clip the JTM45 is a PA head so its almost identical to a yba-1 or the tweed Fender 
obviously the celestion 20 watt greenbacks and PAF pickups in the less paul make a contribution to the tone 

but these would be great examples of just how good that circuit can sound... with its low fidelity power supply, 
vintage spec pre amp plate voltages, and muddy 220 mfd/820 shared cathode v1 


oh and I found a clip of the completed transient fidelity mod 

http://www.youtube.com/watch?v=RiWlXgiPa5M

it turned out so well he's selling the amp 



p


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## traynor_garnet (Feb 22, 2006)

parkhead said:


> for the most part the earlier bassmaster amps are close knock offs of the Marshall JTM/45 and tweed 5f6a bassman
> 
> a real bassman or JTM45 is a magical paradox of musically rich cleans and singing and swirly distortion at reasonable volume levels
> 
> ...


Good points Parkhead. People talk about bassmasters as if they never changed and all use the same circuit. The tube rectified, script logo heads like mine are already _very_ close to a JTM 45/Bassman and really don't need any tweaking. The later models still sound great, but are different.

Regardless of which era of amp, too many people get mod happy on these amps and make a bunch of unnecessary changes.

Nonetheless, some cool ideas in the original post. Thanks for sharing.

TG


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## User_X (Feb 1, 2008)

I found, modding a Bassmaster, that it is easier to make it worse than better.
If you have a definite goal and have heard the mod and know that it works, for you, sure. 
If you are experimenting as a hobby, fine. You might hit a home run.
If you want a specific tone and don't know if the BM will deliver just use a pedal and save the time, money and aggravation, imo. Modern pedals can solve many tone searches without amp compromise.


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## parkhead (Aug 14, 2009)

Agreed 100% I usually prefer the "Transient Infidelity mod" 

and set any amp back to its earliest version. 

Before the engineers revised it to resolve "little problems" 

Even with pedals the original pedals usually smoke the later ones. 


p


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