Express Parallel Capacitor

[Littlewyan]

I haven't tried changing anything from the original schematic on here as I've heard Glen's amp and think it sounds great. I'm going to keep working at mine to try and get it closer to an original. The only thing that bothers me a bit is I have used a Marshall 6.6K OT so I MAY have to change some of the circuit to compensate for that. Old Marshalls always did have a lot of high mids so this would explain a lot.

Then again I've also read Ken talking about wire choice and how another amp builder used the same wire he used in an Express in another Amp that Ken designed to have Teflon wire used in it. The end result was the amp sounded like mud with the non Irradiated PVC Solid Core Express Wire.

[Mark]

Then again I've also read Ken talking about wire choice and how another amp builder used the same wire he used in an Express in another Amp that Ken designed to have Teflon wire used in it. The end result was the amp sounded like mud with the non Irradiated PVC Solid Core Express Wire.

This is the very least of your issues. I've used both types of wire and I can't honestly say I've heard that sort of dramatic difference. In fact my 18 watter Marshall clone is built with teflon wire and it isn't overly bright sounding. It shares similarities with my Rocket clone which is built with solid core PVC wire, in fact the Rocket is brighter than the 18 watter.

I think your output transformer will make a greater difference than teflon wire. In fact I still believe the transformers make or break these amps.

The problem with teflon wire is it is very stiff and doesn't want to assume the shape I want to put it in, the PVC (multi-core or solid core) is far more obliging. I believe this is the reason Ken used it, along with availability of course.

EDIT: I had a look at a quote on AX-84 where Ken talks of skin effect and silver coated wire on teflon wire. I remember learning about switch mode power supplies where the transformers had to be manufactured to take advantage of skin effect and they are WELL outside the audio spectrum. In fact I can't think of any of the classic valve stereo amps using construction to take advantage of skin effect. They did have complicated interleaving and feedback applied through various transformer tappings but nothing for skin effect.
Then there was talk of silver plating, the specs for the output transformer and the speakers would exclude any benefits for silver plating.

Sorry but I want a bit more proof than Ken said so.

https://www.youtube.com/watch?v=dik_wnOE4dk

[rp]

Lots of debate on silver or tin or whatever plating on copper stranded wire from the hifi guys. Most is negative, hence the Kimber wires being notably unplated (but oddly pure silver wire is the bee's knees). I might loose (a tiny bit) of sleep for hifi, I've learned that worrying too much about guitar amps makes for a worse amp

BTW I use the cheapest ptfe I can find and it's always plated, the non plated stuff is actually rare and more expensive, go figure. I'd happily use PVC but I screw up too much and with PVC by the end it looks like a hamfisted hack was in there.

[Littlewyan]

In that case I might just fiddle with the knobs on the front a bit more and worst case add that .0022uF Ceramic Cap in parallel with the C8 Cap.

I would LOVE to change the Output Transformer, except the question is, what do I do with the old one when I've replaced it? And what if the new transformer doesn't make a difference? Its not a cheap part to just replace on the off chance that it will give me the tone I want :/.

[rp]

except the question is, what do I do with the old one when I've replaced it?

For God's sake man, build a Marshall. I'm usually forced to build an amp because I have one odd part sitting around. I built a 5C8 just because I had a pair of ST 6L6Gs. Skipping a month's utility bills is usually enough money to start an amp beyond the point of no return.

Feed The Beast!

[Littlewyan]

A Marshall is possibly on the cards but not one that requires a 6.6K OT. Maybe I should try to tweak the circuit to work using this OT. Thats probably what Ken would have done. Also there are a lot of amps that I'd love to build but I'm currently saving up for a house. Dont think my girlfriend would be very impressed if I splashed out on a new OT!

[John_P_WI]

A Marshall is possibly on the cards but not one that requires a 6.6K OT. Maybe I should try to tweak the circuit to work using this OT. Thats probably what Ken would have done. Also there are a lot of amps that I'd love to build but I'm currently saving up for a house. Dont think my girlfriend would be very impressed if I splashed out on a new OT!

Just remember, amps are forever, women - not so....

[Mark]

Just remember, amps are forever, women - not so....

You don't want to incur the little woman's wrath, but if it's a problem now you're in for real trouble when your married. How will you explain buying the NOS valves.

https://www.youtube.com/watch?v=zBXwfmUpHOA

The cheap option is to tweak the amp till you get something you like, this isn't bad, and only you will know if that is enough for you.

[Littlewyan]

Haha nah shes cool. I need to take it to my friend's barn so I can crank it and hear it properly. Another thing it could be is the 2x12 speaker cabinet I'm using. They tend to have much less low end than a 4x12 so I think that has something to do with it.

[Littlewyan]

Well I cranked the amp last night and it sounded amazing. The tone was just right, not too bright and not too dark. That was playing with all knobs on 12 and the bright switch on the 500pf position. The only thing I will say the amp doesn't have the snarl that Glen's does when he plays power chords in his Can you hear it ring video at about 3:40. However when I play an Open G Chord through it the mids around great, that snarls beautifully .

I guess it could come down to the Output Transformer used as Mark pointed out earlier. I used a Marshall JTM45 6.6K Transformer in my amp from Danbury Electronics.

[Guus]

Here is a letter Ken sent me back in the day. I had a Liverpool at the time that I liked but thought was a bit too bright, and he sent me some parts for a little tweak. It mentions that he was starting to do this in all his Liverpools from then forward. That said much more recently I also tried it in one of my Express clones and it definitely fattens up the tone of either circuit. I don't know if Ken ever did this in Express amps, but we can take Ken's word for it he did on the later "Pools"... Note that Ken is adding an additional .002 ceramic cap in parallel with the original .002 PCV orange drop, for a net doubling of capacitance. The tonal properties of the two different types of caps is also part of the recipe here obviously. GK

Hi,

I've build several liverpools and an express.
I did try de modifications.
I must say, soldering in a 820 ohm resister is a go. The amp sounds better (smooth) and the amp is still very, very transparant.

Putting in a extra 2 nF cap (parallel) is in my builds (Liverpool and Express) a no go.
The sound changes in the wrong dirextion. May be if you don't use 150kOhm but a lower value resistor to earth, the change of the cap could be a nice tweak to make the sound better.
Fact is: The combination of Cap and resistor (RC) changes the frequency.

grtz
Guss.