Another Tweddle Dee !

[fred.violleau]

Marcus, I have a log 1M pot. And there are changes throughout the course of the pot, it is not linear, but it works.

Fred.

[norburybrook]

@chopsauce, interesting question! I did remove the 1 Meg resistor on my initial build, but I ended up putting it back. I remember the sound was not very loud without it, but I don't remember if I was connecting the MV button at the right place too... I ended putting it (the 1M resistor) back and connecting the MV as described on the schematics. It may refer more to "SweetSpot" PI grid stopper, but mine puts all the signal to ground when shutdown (I connected the 3 pin to ground).

Fred.

Don't you mean pin 1 to ground?



M

[fred.violleau]

Right, Pin1 to ground, sorry.

Fred.

[norburybrook]

I was playing the tweedle dee today and I noticed that the amp is now noisier with the cascade mod than before. Is this to do with grounding ? is there a way to reduce the background hum now? I have it grounded at the pre amp /filter caps ground. would the input jack be better/any different?


M

[ChopSauce]

Rob Robinette recommends using shielded wire for cascading - if I remember well.

[norburybrook]

Rob Robinette recommends using shielded wire for cascading - if I remember well.

I've used shielded wire from the input to V1 . When you cascade though the switchable jack on V1 that normally grounds when no plug is inserted now is connected to V2 permanently. The cascade switch has a ground and I'm wondering if that needs to be moved etc. The extra noise is when I'm in 'normal' not cascaded mode.



M

[ChopSauce]

Then it is the wires to and from the switch, which collect noise and need to be shielded, isn't it?

If the switch is grounded close to the input jacks then there should be no trouble from this - as far as I understand things.

[norburybrook]

Then it is the wires to and from the switch, which collect noise and need to be shielded, isn't it?

If the switch is grounded close to the input jacks then there should be no trouble from this - as far as I understand things.

I grounded it to the input jacks and it's a lot better


M

[ChopSauce]

Good news!

By looking back at the post of your build, I saw that the input jacks seems to be grounded together. If the jacks are not mounted with isolated washers, this might be a candidate for ground loops, too...

[norburybrook]

Good news!

By looking back at the post of your build, I saw that the input jacks seems to be grounded together. If the jacks are not mounted with isolated washers, this might be a candidate for ground loops, too...

yes, the original has the input jacks grounding through the brass plate on the chassis front along with most everything else other than the cathodes which ground directly to the chassis front. As I have a plastic front faceplate I thought it would act as in insulator so grounded the input jacks to a physical ground point by the input on the base of the chassis like I do with my ODS builds. Same with the rear jacks for the same reason. I was using the amp yesterday in the studio and it's sounding great, even in cascade mode you can get a lovely clean tone with a little hair by using the full NFB on the switch. The excessive bass isn't an issue with a close mic in front of it and a high pass filter when mixing ,as I always do with things will dial out what you don't need, you'd be surprised at how much low end get taken out of guitars in a mix situation


M

[martin manning]

...I saw that the input jacks seems to be grounded together. If the jacks are not mounted with isolated washers, this might be a candidate for ground loops, too... :?

The jack bushing grounds and the input chassis lug ground are close together, and the additional ground wire is short. It's a loop, but a very small loop. I'm not a fan of the multiple preamp ground locations Fender used though, nor of grounds through the pot cases/bushings. Local stars connected to the input ground is a better way to go, IMO.

[fred.violleau]

Funny thing is I was reviewing aiken's recommendations on grounding too
I did use shielded cable as well for the input jack, and basically every connection thats is longer than 3".
But I have never used isolating shoulders, and I realized that my first ODS was a lot quieter than the Tweed Master I built last year.
When diggin on grounding, I noticed my FX loop jacks are using the same ground bus as the speaker's ground..
Which, after reading aiken's post is definitly not a good practice ...

So here I am, ordering a ton of bushing plastic shoulders so I can isolate all the jacks connector (input, FX, speakers) and then choose where and how they ground.

Back to the cascading, I do get more hiss when using the cascading channels, but channel 1 remains very silent when used on its own.

EDIT : I put back the amp with the 470K resistor on the PI entrance, tried the Post PI 2 MV, and don't like it : my MV is a log pot so from 0 to 2 I go from no sound to almost full volume, and then not much happens over the rest of the course...

5e3_Trainwreck_3_PPI_Master_Volume_Mod_small.png

Still struggling with an efficient MV

Fred.

[ChopSauce]

I think I'll go for a pentode/triode (a.k.a. 1/2 power) switch myself. I don't expect it to sound that good, but it should fill my needs for low to moderate volume practice.

About grounding. Actually, what would "best" reproduce the brass plate grounding scheme - I guess - would be having a ground bus going from one only of the input jacks, since the other jacks are already grounded though their connection to the chassis. At least this is what I plan doing using Swichcraft's.

[norburybrook]

Funny thing is I was reviewing aiken's recommendations on grounding too
I did use shielded cable as well for the input jack, and basically every connection thats is longer than 3".
But I have never used isolating shoulders, and I realized that my first ODS was a lot quieter than the Tweed Master I built last year.
When diggin on grounding, I noticed my FX loop jacks are using the same ground bus as the speaker's ground..
Which, after reading aiken's post is definitly not a good practice ...

So here I am, ordering a ton of bushing plastic shoulders so I can isolate all the jacks connector (input, FX, speakers) and then choose where and how they ground.

Back to the cascading, I do get more hiss when using the cascading channels, but channel 1 remains very silent when used on its own.

EDIT : I put back the amp with the 470K resistor on the PI entrance, tried the Post PI 2 MV, and don't like it : my MV is a log pot so from 0 to 2 I go from no sound to almost full volume, and then not much happens over the rest of the course...

5e3_Trainwreck_3_PPI_Master_Volume_Mod_small.png

Still struggling with an efficient MV

Fred.

Fred,

I tried a few master volumes and in the end I removed it preferred the sound without. I wired the ground on my loop back to the input jack ground.

I still like the cascade, I was recording yesterday with it in cascade mode but on a cleanish sound. I still think adding a bass and treble stack would be worth trying. Sometimes on a single coil bridge pickup the extra bass is useful to have , so removing bass with the coupling caps would take away that option.

I'll have to experiment with a tone stack at some point. The extra bass when recording is easy to deal with so no big issue for me at the moment as all gigs are cancelled anyway!!!!


M

[fred.violleau]

ChopSauce,I organized grounding with the same idea as yours : a bus ground running in front of all the pots, connected to a star ground where all my inputs jacks, preamp grounds and FX loop connect. Location : far right of the build, under the input jacks.

I used another ground for the Power Tubes bias, B+1 coupling cap, at one corner of the Power transformer, and speakers inputs are grounded at another end of the power transformer. The Power transformer looks pretty old, was removed from an old Pine electronic tube amp and did not have a center tap, so I added a virtual one with 100r resistors connected on the filament heaters circuit.

Marcus, I also added a line out, in order to drive a second small amp. So far it sounds great, and I think the Dumble setup on channel 1 is a good addition with a lower coupling cap. It tends to make the sound tighter overall and works well with a strat. Agreed a tonestack would help dial the amp with a greater variety of pickups.

Fred.