Traynor YCV40 master volume mods

[Helmholtz]

PI?

[Enzo]

Helmholtz is right, just a typo on my part. U and I are right next to each other on my keyboard, and the letters are worn off the keys.

PI - phase inverter.

[bobloblaws]

PI?

That makes sense. Hit the "U" instead of the "I" I presume. No worries.

[bobloblaws]

So I undid the mod to verify there was no distortion issue (per msg in this thread) to begin with and there was not. To reiterate, with the amp modded for Master Volume in place of the Presence control per the YCV50 I find that the sound is distorting if I hit the strings on the guitar aggressively or if I strum a chord and then turn up the volume control (clean channel) as the chord is sustaining it distorts also. This is with the Master Volume wide open and the channel volume relatively low. I only changed the circuit in terms of R63, R51, C51, and C47. I didn't touch the NFB or the reverb output. Has anyone else still subscribed to this thread tried this same mod? If so, I'd love to hear whether it was done the same way and/or whether similar issues arose. Of course any commentary is welcome.

I'm reattaching the manual that essentially shows the circuit before(YCV40) and after(YCV50).


sm_ycv40_2015.pdf

[g1]

It may be worth trying those parts Helmholtz mentioned in post #13. Oscillation can cause distortion.

[bobloblaws]

It may be worth trying those parts Helmholtz mentioned in post #13. Oscillation can cause distortion.

OK, I can give that a try.

What do you think of the V1:A cathode bypass cap being 22uF in the YCV40 and 1uF in the YCV50. Inconsequential to this issue?

[g1]

Maybe they were trying to eliminate some 'muddiness', but I seem to recall them touting the 50 as more of a British flavour, and smaller bypass there would be more in line with Marshall topology as opposed to Fender.

I'm usually quick to defend Traynor from criticism, but I'm not a fan of these and feel sorry for anyone who has to work on them. There are so many iterations and changes they have gone through that I would not trust any schematic til it was verified for the particular serial number of the unit. So please be sure you have the exact schematic for your amp.

I'm sorry I don't have enough time right now to spend much time looking at it, but I see a pot labelled 'master' on pg.11 of the svc. man. you posted, then another on the power amp page. What is going on?

[bobloblaws]

Maybe they were trying to eliminate some 'muddiness', but I seem to recall them touting the 50 as more of a British flavour, and smaller bypass there would be more in line with Marshall topology as opposed to Fender.

I'm usually quick to defend Traynor from criticism, but I'm not a fan of these and feel sorry for anyone who has to work on them. There are so many iterations and changes they have gone through that I would not trust any schematic til it was verified for the particular serial number of the unit. So please be sure you have the exact schematic for your amp.

I'm sorry I don't have enough time right now to spend much time looking at it, but I see a pot labelled 'master' on pg.11 of the svc. man. you posted, then another on the power amp page. What is going on?

I hear ya about the revisions. Someone in the service department at Yorkville/Traynor told me the hiss was expected on the clean channel because there is no master volume (he made reference to vintage amps that don't have master volumes but any Fender vintage or vintage style amp I've played has had no similar issue, with the possible exception of the Vibrolux Custom) and that they addressed it with the YCV50 design, hence my attempt to mod the YCV40 accordingly. But I know people with YCV40's where the clean channel is dead quiet. So it makes me wonder if it is revision specific somehow. I haven't gone through the revision list and checked it against this amp to ascertain the exact revision but the version of the service manual I uploaded called sm_ycv40_M581-7.10.pdf is darn close to what I have if not identical. At least I haven't seen any discrepancies.

The pot you see labelled "Master" on page 11 is just the Volume pot for the drive channel.

[g1]

Any luck with this? Did you triple verify that you had removed all the 'stuffed' 40 bits shown for the master/presence circuit?

And a bit on the side, you asked about that cathode bypass cap in post #21. That version 15 schem. you are using shows only a few changes (ycv40 vs 50) in that area. Here is all the differences in version 14, only one revision prior. This is what I meant about making sure you have the exact revision schematic.

[bobloblaws]

Any luck with this? Did you triple verify that you had removed all the 'stuffed' 40 bits shown for the master/presence circuit?

And a bit on the side, you asked about that cathode bypass cap in post #21. That version 15 schem. you are using shows only a few changes (ycv40 vs 50) in that area. Here is all the differences in version 14, only one revision prior. This is what I meant about making sure you have the exact revision schematic.

I haven't got to it yet but it's still on the agenda.

I'm confused by the list of apparent discrepancies you sent. I went through the sm_ycv40_2015.pdf drawings that show the differences between the 40 and 50 models and came up with this:

(YCV40 <-> YCV50)

C1 (22uF/50V) <-> C1 (1uF/50V)
C31 (1N8/100V) <-> C31 (1N/50V)
R52 (WJ) <-> R52 (47K)
R105 (10K) <-> R106 (15K)
R62 <-> C58, R76, R77 [Negative feedback]
C17 (10N/250V) <-> C85 (2N2/400V)

I checked the values for the resistors and caps on the chart you provided between rev 15 and rev 7.1 (which is my baseline) and with the exception of C1, C31, and R52 (from the above list) they are all identical. It is unlikely that those values were changed sometime between 7.1 and 14 and then were suddenly restored for rev 15. What is the source of the data you provided?

[g1]

What is the source of the data you provided?

The file with that is 16.7meg so I can't upload. It's titled sm_ycv50b.pdf and appears to be from 2008? (rev.v14.00 schems)

[bobloblaws]

I checked the values for the resistors and caps on the chart you provided between rev 15 and rev 7.1 (which is my baseline) and with the exception of C1, C31, and R52 (from the above list) they are all identical. It is unlikely that those values were changed sometime between 7.1 and 14 and then were suddenly restored for rev 15.

Shoot, I was looking at the wrong column.

Point taken, there are many more differences between the two models than are shown in sm_ycv40_2015.pdf.

Thanks for having my back, G.

[g1]

Not sure if any of them would have anything to do with the distortion you are hearing, but figured that might point to some possible contributors.
If the low value of the pot were an issue, it would be a problem for the 50 as well, so not sure what could be causing your problem.

[bobloblaws]

In case anyone is keeping score at home or interested in doing this mod, here are my conclusions. In the end it kind of worked as advertised but we decided to keep it stock as the clean channel hiss was slightly annoying but not a deal breaker. As for the distortion I was referring to above, I don't know what the issue was at that point in time or what might have been different when I had another go at it.

The majority of differences between the YCV 40 and YCV50 as listed in the chart in post #24 are changes in resistor and cap values in the drive channel and are of little or no consequence to this mod, as near as I can tell anyway.

For the record I left the 220K NFB resistor as is and did not put in the 270K, 470K, and 2N2 components in the NFB loop.

To do the mod you disconnect the one end of R63 from C47 and connect it to the "top" of the presence pot (which now becomes the master volume) in place of C51. That end of C51 goes to a new 1.5K resistor (R51) the other end of which goes to ground. On the stock YCV40 the other two lugs of the pot are joined on the PCB so you need to scrape away some of the conductive material between those lugs. Now take the end of C47 that was connected to R63 and connect it to the middle lug of the pot.

The connection that is originally from the "top" of the reverb pot to R63 needs to be changed so that lug of the pot is connected to a 100N cap and the other end of the cap to pin 2 of the U1 opamp.

With those changes I tried it out and found that the reverb started to feedback almost immediately as the reverb pot was turned up. The "fix" is to disconnect C7 from R63 and instead connect it to pin 1 of the U2 opamp. However, this wasn't a perfect solution as there was still some feedback (and a fair bit of hum) if the reverb pot was turned up to 8+).

With the mod implemented I still found there to be some noise on the clean channel (more hum than hiss) with the MV wide open but that was with it prototyped with jumper wires running all over the place which may have been picking up extraneous noise and it may have been different if I had gone ahead and committed the changes. In any case I found that turning the MV down from dimed to 7 or 8 was a sweet spot, quiet and still lots of headroom for the channel volume.

I think that's all I got!

[g1]

Now take the end of R47 that was connected to R63 and connect it to the middle lug of the pot.

Typo, you mean C47 not R47 here.

I wasn't understanding why the reverb mod until I looked at the M581 schem. from post #8.
It looks like the newer models like in the 2015 schem. from same post already have the reverb revision all taken care of?