5F1 sag

[calis]

Hi guys.

This is gonna sound like a newbie question 'cause... well... I'm embarrassed to say that it is. My question is about amplifier sag.

I've played guitar for over 15 years, but a large portion of those years have been on the acoustic guitar. When I was younger, I played the electric guitar the most, but I never had the money to own an amp worth mentioning here. Nowadays, I have more money to spend and Ive been getting back into the electric guitar a lot more over the last 4 years or so (slowly but surely). However, until recently, I've never owned a non-master volume amp that I could realistically crank up and achieve power tube breakup.

So, I built a 5F1 clone and I totally dig it. But one thing I'm not used to is the compression effect that occurs when I crank the amp all the way up. With my Strat, it is less noticeable and the amp just sounds great when it's cranked up and there may be a very mild compression but nothing very noticeable I'd say. However, with my SG with P90s, there is a considerable amount of sudden compression that is very audibly noticeable. Like a newb, I have to ask: is this normal? I mean, I've heard of the sag effect before, but never experienced it. So, I don't know if this is an indication of a bad build or bad parts or if this is totally natural.

Please let me know. As always, I truly appreciate any and all input. Thank you very much.

Justin

[MWJB]

Sounds pretty normal to me.

You could try:

Using the low gain input with P90s

converting to fixed bias

a tighter rectifier (5V4/GZ34/solid state - check plate voltage & current)

a lower gain preamp tube with P90s (5751/12AY7)

a voltage divider before the volume control to attenuate signal.

a bigger, cleaner power tube (5881/6L6 - make sure power tube cathode resistor is 10W rating and bypass cap is rated at 100v if still fixed bias, watch plate current).

Bigger first filter cap - 50uf.

...oh yes, and NOT playing it all the way up - this will just make things worse.

Champs were designed as cheap practice amps, they have small transformers, are underfiltered and are cathode biased - all of which points to a degree of compression, which is why most folks like them, but people don't typically buy them for hard dynamics/a stiff sound.

[calis]

Thanks, MWJB. Your reply was very helpful.

I'm glad to hear that this is normal. To be honest, when I decided to build the Champ, I didn't base my decision on how it would sound or respond or anything like that. I wanted a low watt, simple circuit, non-master volume, inexpensive amplifier that would be easy and cheap for a first build and the Champ was just that. I was surprised to find how much I liked it after it was built though. I didn't expect that and it's led me to think that a lot of the characteristics that I have been looking for in amplifiers can be found in these early Fender designs.

Thank you very much for your advice regarding how I might go about controlling the sag when I use the SG. I was surprised that there were so many ways that I could do this.

Anyway. Thanks again.

[abro163]

I think the main component of sag in a champ is the 10k dropping resistor.

Try place a 1.5k resisitor in parallel with the 10k quickly and see if you like it.

[calis]

Thanks for your input, abro163.