uberschall question... the mystery dial! Phase Symetry Adjust

[Dmoney]

Possibly a variable resistor in series with one of the Phase Inverter anode resistors. It would allow adjustment of the PI outputs to allow you to balance them, or not if you prefer an imbalance.

Same idea as having 82k/100k anode resistors on Marshall's etc, but a bit more precise. It's not a new idea, and better suited to hifi/PA anyway. The Sai PA amp the sgmypod owns has this feature.

There's debate over whether a perfectly balanced PI is a good thing in a guitar amp. Most would say not, or at least thatbi doesn't make much difference.

I would concur.

I expect that it is a method of balancing the AC signal in a long-tail pair phase splitter.

This is hardly a new. The earliest schematic I've seen this feature on is the Harman Kardan Citation II from 1960! Not many guitar/ bass amps have this feature, although Ampeg used it in the SVT.

The jury is still out as to whether perfectly balanced AC drive to the power amp is of any benefit in a guitar bass amp, although my personal view is that it isn't, and that balance in most guitar amps is "good enough for rock and roll".

On a more practical note, pots/ variable resistors are relatively unreliable compared to fixed resistors, so unless there is a very good reason for using a pot here then you will ultimately be compromising the reliability of the amp.

I've heard the 82K 100K anode resistor setup is a legacy thing that goes back to the early marshall's and isn't reeeeeeeeeeeeeally needed. meaning you could get away with 100k/100k

i was just tapping on the V1 tube and i could hear some nice 'TINGS' out of the speakers. so im guessing this is microphonic and probably where my noise is coming from.

[jpfamps]

The 82k/100k resistor values originated in the tweed Bassman which of course Marshall copied. Later Blackface Fender circuits used 82k/100k values as well, although 91k/100k would have given better balance with the circuit values they chose. Maybe they didn't bother recalculating the values, or perhaps 91k resistors were harder to get, I don't know. Anyhow, all the resostors used in the Fender amps of this era were 10% tolerance band anyway.

In the later Silverface amps Fender went to 47k/47k to reduce gain in the PI, probably to give more clean headroom

Incidentally, the current Hot Rod Fenders use 91k/100k.

From my experience it really doesn't make much difference and I tend to use 100k/100k in new builds, but in older amps will replace with the original value.

Regarding tapping V1, in a high gain amp virtually any 12AX7 will make a noise if you tap it.

[Dmoney]

only V1 did.
i just swapped it for another gold pin, when i put that in i tried the tapping test again and it made no sound. initially it made a very dull and very quiet 'thud' sound if i tapped it pretty hard. now it doesnt make a noise.

there is still high gain hiss from the amp, but there is an improvement.

[AndyR]

Can't tell you naff all about the amp stuff.

But back to the important part of this thread: she is mighty fine ain't she? :D

She tried to sell me all sorts of stuff...

In fact, I was so scared I might be tempted to get my wallet out, I took the missus in on the next few visits :lol:

And then I went in on my own again one day...

And I bought a resonator :roll:

(If you find out her name, let me know - I'll name the reso after her!)

There you go, that's an in for you! "There's a guy I know on the BKP forum wants to know your name so's he can name his resonator after to you..." ... never know, might work!

:lol:

[hunter]

Just wondering, I watch you investigating a lot into how to improve the amp and all. My feeling is that in fact you seem to really want to like it but maybe it's just not the right amp?

Please take no offense, it's just I had similar experiences in the past trying to make things work for me that were just not right in the first place, but I might be completely wrong here.

[Dmoney]

no offence taken
i had the same feeling.
i think its an amp that sounds much better loud.

i had a lot of fun yesterday using the chorus and boosting the cleans with an OD-808
the gain side is dark at low volume but it gets better when its louder. there is definetly a point where it kicks in and its like some of the brightness comes back. i think its also taken me a real long time to get the hang of the presence and mid controls, and how all the tone controls interact.

i will say, i am happier with it, but my favourite amp is still my avenger.
but a two channel avenger with EL34's and a fx loop is a rare thing. (or is it a Hot Rod + with a depth mod and EL34's?)