Traynor Bass Master YBA-1A Tone Stack

[stereomonostereo]

Hey guys,

I picked up a Traynor YBA-1A Bass Master and the tone stack is behaving a bit differently than i remember these being. The Bass pot pretty much has zero affect on the tone, and the Treble pot just kind of makes things 'thin' at the full setting. I know these use a different type of tone stack than a lot of other amps, but it just seems a bit off to me. The coupling caps are all in spec. Thanks

[nevetslab]

Traynor YBA-1A Bass Master Tone Stack response curves, stock

Hey guys,

I picked up a Traynor YBA-1A Bass Master and the tone stack is behaving a bit differently than i remember these being. The Bass pot pretty much has zero affect on the tone, and the Treble pot just kind of makes things 'thin' at the full setting. I know these use a different type of tone stack than a lot of other amps, but it just seems a bit off to me. The coupling caps are all in spec. Thanks

The stock Traynor YBA-1A's four tone controls ARE quite limited in what they do. I haven't finished revising mine, but when I first got it back up and running, I was very disappointed in how little those four controls yielded. I think I have a set of curves I ran on the stock circuit so I could play with values in the simulator.




I made some changes in cap values using these stock circuits, which got a little more out of them, but, still wanting more, I've set out to make more radical changes, and haven't yet made the revisions. Borrowing a little from an Ampeg SVT-CL for the bass control, a LF variable Notch control circuit based on Ampeg's LF Boost circuit, but variable, I forget who's Treble circuit I used, and a Presence control that came from a Sound City SMF Preamp.

The revised curves, so far look like this:

[drewl]

That's pretty normal for these.

Guess that's why people wire them up like a Plexi.

[Leo_Gnardo]

Sure would be handy to have the schemo. I've looked and I'm finding all the other YBA-1 variations except YBA-1A.

In any case I always took these to be pretty close to the Fender 5F6A which Marshall pinched for their amps. Could do worse than copy the Fender circuit... I also put a jumper across mid pot leads to allow a deeper mid cut, a cheap & effective mod.

[nevetslab]

Revised Traynor YBVA-1A Preamp tone circuits

Sure would be handy to have the schemo. I've looked and I'm finding all the other YBA-1 variations except YBA-1A.

In any case I always took these to be pretty close to the Fender 5F6A which Marshall pinched for their amps. Could do worse than copy the Fender circuit... I also put a jumper across mid pot leads to allow a deeper mid cut, a cheap & effective mod.

Now, I haven't yet built this onto a new circuit board. My Traynor still has a modified stock tone circuit installed, with this revised circuit needing the time to build it up and iron out the creases. And, I forget which one of these two circuits I used when I ran the simulations.



The power amp has a pair of KT-88's, along with a 6L6GC Series Regulator to run the screens on them. Still looking into a different driver stage to get as much out of those power tubes as I can. One of those projects that starts and stops......yet to be resumed, but looking forward to the results.

I forgot to add the Yb1A Mk II schematics....attached now.

YBA-1A Bassmaster MK II SvcMan.pdf

[Leo_Gnardo]

The power amp has a pair of KT-88's, along with a 6L6GC Series Regulator to run the screens on them. Still looking into a different driver stage to get as much out of those power tubes as I can. One of those projects that starts and stops......yet to be resumed, but looking forward to the results.

Nice mods nevets! And KT88 are the balls in these old Traynors, though feeding the grids is problematic. Although it's a bit extra work, your 6L6 screen regulator sounds like the bees knees! Looking forward to seeing the power end of your circuit.

[loudthud]

There is a later version of the YBA-1 (and presumably YBA-1A) that deviates from the 5F6A formula. It dispenses with the cathode follower for an extra gain stage and has a 1 Henry inductor in the tone stack. I have never seen the schematic online. I have one of the amps. The schematic on the inside of the amp is almost unreadable. I scanned it, but it was just too bad to even try to touch up. The amp has a sloping front panel like a Fender blackface, but there is still top access like the rubber bumper models. I'll see if I can find that scan.

[Leo_Gnardo]

There is a later version of the YBA-1 (and presumably YBA-1A) that deviates from the 5F6A formula. It dispenses with the cathode follower for an extra gain stage and has a 1 Henry inductor in the tone stack. I have never seen the schematic online. I have one of the amps. The schematic on the inside of the amp is almost unreadable. I scanned it, but it was just too bad to even try to touch up. The amp has a sloping front panel like a Fender blackface, but there is still top access like the rubber bumper models. I'll see if I can find that scan.

That's good to know, thanks loudthud! Traynor must have delivered those a bit later in the 70's, most YBA-1's seem to be concentrated in 1968-73. Can't say I've ever seen one with an inductor in the EQ.

About the EQ setup in the general run of YBA1's of any variation, since they copied the 5F6A / Marshall, some Marshall owners complain to me their EQ's "don't do very much." Without doing much else, putting that jumper on the midrange seems to wake up the EQ a bit, as a deeper mid cut can be dialed in. Wish I knew to do that when a YBA1 was my only amp when I was playing in my college bands. Live & learn! The only improvement I managed back then was when I swapped out the stock cheezy 15" speakers for ElectroVoice. Wow, that sure was a wake up moment!