The Amp Garage

It recreates the sag of a valve rectifier. Some newer Voxes use it, like the AC15C1, instead of a valve rectifier. So it’ll give a softer response which may be desirable in your case as the original AC30s had valve rectifiers. Not sure about the Champ as Class A doesn’t sag. If you’re worried about ...

Depends on what's possible with the room you have or the layout. AC side - Gives the diodes some protection if there's an inrush of current and you can split the resistance in half. DC side - Only one resistor required but you'll need twice the wattage. Ball park figure from the EL84 datasheet is 22...

That HT is a bit high for an AC30, I think the older ones ran around 320V. Let's hope you have a good amount of screen current to explain why the bias reading is so high, otherwise I'd be looking to install some sag resistors seeing as it's using a bridge rectifier instead of valve. I often find man...

My first ever build was an LM386 chip!

It was the Big Daddy circuit, sounded great.
https://runoffgroove.com/grace.html

There's also this one off the same website:
https://runoffgroove.com/littlegem.html

Very late to this thread but I recently was playing around with the first stage bias in my Vox style amp. Mine is simply the ‘normal’ channel but with no 220k mixer resistors and I was amazed that the bias of the first stage actually affected the tone a lot. 220k/1.5k was very ‘bold’, good for disto...

Thanks for the explanation R.G. I also found a video of Pat Quilter explaining it too https://youtu.be/GAEdc1l-t6g?si=_6Ph1cQxKCP4XTCi So if we take the zero crossing processor example the diodes are biased on at idle by the difference in voltage either side of them. Two diodes, one positive facing ...

Yes that’s one of the pages I’ve been reading, along with this https://www.diyaudio.com/community/thre ... 678/page-2

Is it because of the DC voltage turning the diodes on? 4.5V present at Op Amp output and then a resistor network setting the middle part of the diode strings to 4.3 and 3.8V? Turning the diodes on allowing AC to pass?

The last few days I've been trying to figure out how the soft clipping cell on the end of this circuit works. It's used in the Ethos TWE-1 overdrive pedal and I think many other circuits. How does a sine wave pass through it? Surely diodes back to back in opposite polarities will block this? As even...

Downloaded, thanks Stevem

Sorry, thought I replied. Thank you all for the useful info, it’s making more sense now. I have a lot more reading up to do

Have you looked at how much gain / signal level gets dropped when passing thru a passive tone stack when even just adjusted to normal settings? Yes but not really sure how this links in with how many stages are distorting. In an SLO the tonestack is at the end of the preamp, once all the distortion...

I've started going down the rabbit hole of developing overdrive circuits for pedals, in particular pedals that emulate valve amps. Something I've noticed looking at other designs is they don't always match the same number of distorting stages as the amp but still do a good job emulating them. Why is...

What attenuator are you using? And how much are you attenuating? And is the amp built to the spec in the Express files? What transformers did you use? I run mine through a 2x12 G12M cabinet and have no trouble running everything at 12 o'clock with the bright switch in the 500pf position. Used to use...

All sorted. Made the bias hotter so it’s bang on 100% and used a smaller preamp coupling cap value.