Traynor YVM-1 Conversion to Guitar Amp Suggestions

[Jazz P Bass]

The bypass capacitor on V1 cathode is what makes a Marshal a Marshal.
The low value effectively removes most bass frequencies which do not sound good when distorted.
You are in the ballpark with the two values that you have.
The higher value will pass more bass.
Interestingly, this is the capacitor that gives some Fender amps that 'fart' sound.
They use a 25uf.
Lowering that to 15, 10 or 4.7 uf can remove that noise.

[misterc57]

Very slow progress as I search for parts and try to figure out placement of components and over think... Enjoying the project.

I am bypassing original Traynor V1 and designating Traynor V2 - V4 as JCM800 V1 - V3.

I am progressing from V1 to V3 and still have not completed all of V1.

Some leads are long for now as I will need to order correct value pots and just going with what is there for now.

Hope to test/adjust voltages when done with V3.

[misterc57]

Time for an update... Been fun and a good learn with more to go.

I hope I can be coherent in this post. First power on today with recorded voltages. Tried to get some reference voltages. The Tom Mitchell 2204 and Mark Haus 2204 have very different values. I have some images below of each including a spread sheet of Mark Haus values compared to my recorded values.

My sound is very weak / anemic. I do not have a schematic of my amp as it is preamp 2204, and power amp YVM-1.

I have been using the attached JCM800 wiring image as my preamp wiring guide. My pots are arranged as per this diagram.

I have 1M L volume pots that should be 1M A taper pots and wonder if they are contributing to the anemic issue.

I am not seeing much voltage at pin 2 of V3 where Mitchell states 30V, I see anywhere from 0 to -3.0 based on the master volume pot rotation. I need to review that whole wiring scheme. Also based on rotation of the treble pot (a 250K L) I can cut all output unless the treble is set to 10.

I am missing some of the small bypass caps that should be arriving at the end of the week. Any suggestion on where to order a complete pot replacement kit?

[Chuck H]

It would appear that you don't have a treble capacitor in the tone stack. You have the treble control connected directly to the cathode.

[Chuck H]

You'll need a 470p (or 500p) capacitor as shown in red below.

Still looking at the rest of the work.

[Chuck H]

Also, this wiring looks suspicious. Be sure none of your bare component leads are contacting the pot case here.

[Chuck H]

And... Using lower percentage log taper volume pots won't reduce preamp output. It will only change knob settings for a given gain level. So something like a setting of 4 on a typical Marshall amp might need to be set at 6 or 7 on your amp. Max volume would be the same regardless of taper used and all the same adjustments are available with any taper. Pot taper is just there to make adjustments feel more intuitive.

[misterc57]

You'll need a 470p (or 500p) capacitor as shown in red below.

Still looking at the rest of the work.

How precise does this need to be? I have lots of 220pF I can run parallel...

[Mick Bailey]

Paralleling 2x 220pf caps is fine and makes little difference. You can double-check if you like by using Duncan's TSC (there's an online version).

[Chuck H]

Paralleling 2x 220pf caps is fine and makes little difference. You can double-check if you like by using Duncan's TSC (there's an online version).

Late to the party. Game day... Go Hawks

What Mick said.

EDIT: I will mention that the 500p to 560p value here used on older Marshall 1959 circuits was partly responsible for their signature voicing. A lower value here in that circuit would sound less mid aggressive if you're over driving the amp. With the later stacked channel master models like the 2204 it makes less difference. But there's still some difference. Lower capacitor value would probably be great for tones in the clean to crunchy range. If you want a thicker mid voice you want the 500p value. And THAT said... Since you're using 1uf for your first stage cathode bypass cap you may have already thickened up the tone by enough that you don't need the higher value treble capacitor. It might even turn out to be a voicing you love with the 1uf first stage bypass and the 440p treble capacitor value. Since I've done mostly custom designs I've often made voicing adjustments to correct frequency response before or after where they normally occur because of one consideration or another. I think you'll be good to go with this arrangement of values.

[Mick Bailey]

Whilst I haven't measured actual cap vales in a JCM800, I suspect they're just standard tolerance commercial parts and nothing close-tolerance, maybe +/-10% on film/ceramics and +/-20% for electrolytics.

[Pedro Vecino]

I think that tuning these values between those limits is justified when the amp already sounds perfect. That is: at the end.
But the value of the bypass capacitor is more critical and deserves to be considered from the beginning. Raising the value above 680n (with 2K7) tends to lose definition in the low strings, becoming muddier. At least using high amounts of distortion.

[Helmholtz]

The bypass capacitor on V1 cathode is what makes a Marshal a Marshal.

Depends on what you mean with "The Marshall Sound".
To me the most original and best sounding Marshalls were the JTM45 and the JTM100, followed by later non-MV bass models.
(reportedly Jimmy Page preferred a '69 non-MV 100W bass model 1992)
All these use a large value V1 cathode cap (typically 250µ) and a 250/270p treble control cap as well as 0.1µ power tube coupling caps.

Admittedly, to me a great clean sound is more important than lots of fuzzy amp distortion.

[misterc57]

Should there be V at V3 pins 2 and 7. I would think not and why does the Mitchell chart show V there?

Thank you

Mark Huss schematic attached

[tedmich]

FYI the 2204 grounding scheme has room for improvement, see Lyles 2 pt video on the subject.
He says he's pretty close to what Larry Amps does and that guy is a legend
https://www.youtube.com/watch?v=ZySW1bq_nY0