Hi,

My first guitaramp was a Vox Pathfinder that I really liked, but sold it to buy something else (as usual). I'm still thinking of it once and a while, and wonder if I could build the preamp and stick it into my diy combo? I allready found the schematic in this thread (you need to be logged-in to download it).

The thing is, I would only like to build the 'normal' channel of it. So I don't need the boost or the tremolo, nor the poweramp (for I allready have one). I can do an educated guess but I'm not that good at reading schematics to say what parts exactly can be left out and what needs to stay in. Can you help me out please?

Hey,

Old thread I know, but it keeps the forum clean

Still using this little amp a lot. Never got to experimenting with mods though, allthough I recently I replaced the cheap speaker I used for an Emi Legend 1015... wow, now this little fellow has become a little monster, it rocks hard and loud! Really, really nice Not gigged with it though, the poweramp can put out 20W easilly, so I wouldn't be surprised if it could hold its own.

One thing though, and I wonder what it is and if it can be fixed. When the preamp starts to break up the overdrive starts as a funny fizzy crisp. The same thing when the notes fade out: it ends with a funny fizzy crisp. I think this crisp stays when you drive the amp harder, then it sounds more like overdriven highs which can be nice. But it can be annoying when I play with a little OD, blues for instance, than it's quite noticable.
When playing clean it's not there.

I wonder if it is a characteristic of the chip the preamp uses? It has a LM1458 in it. Can this be fixed by using another (type of) chip?

First I thought it was the cheap speaker, but it's the same thing with the Emi, allthough the Emi is not fully broken in yet (played with it a couple of hours).

Okay thanks, thats some good advice. I'll stick to chipamps.

It's funny, this forum is probably the only one on which chipamps are adviced over discrete amps. Why is that?

Thanks guys. I would like to try a discrete design as a learning project, but like everything else it should have a satisfying endresult

I've allready built an amp with a LM1875 gainclone-kit. It's a nice little amp and I would like to compare it to a discrete design. Would the difference in quality be great? I mean, the 80's marshall ss-line shouldn't be that great if it hadn't a good design, doesn't it?

Googling around I find that Marshall made a couple of nice ss-amps with not too complicated mosfet poweramps
Schematics can be found at drtube.com

I could go with one of these, the poweramp of the 5203 for example.
Any tips what would be a great design to start with?

Thanks alot for your help and explanation teemuk!
This schematic seems simple enough to handle. Like you said, it looks familiar. And since I like mosfets it's a nice starting point.

Hi,

I'm looking for simple but effective discrete poweramp designs that can be build easily and perform wel in a guitaramp. I did a view diy-builds but I've never build a poweramp myself, most schematics of poweramps seem way too complicated to start with.

Googling around I find schematics like this:



It comes from an 18W audio amp. But since I haven't much theoretical knowledge, I can't tell wether a design like this perfoms well or is stable enough?
Can you give me some advice?

Well, I've started  a similar topic at musicelectronics. But apparently more people read the some fora as I do

But not at ssguitar, no.

Hi,

I've finished the amp a couple of weeks ago and it works! It's very nice indeed, even the cleans are very acceptable but it really shines when distorted.

Playing with it, you start to wonder how to make the amp a little more versatile. I would like to make it sound just a little more bright when playing clean, to get a little more 'snap' in the highs. Therefore a bright-switch would be usefull. But I wonder, normally this brightcap is placed on the gainpot, but I don't think that's possible in this circuit.
Is it usefull to place a brightcap on the mastervolume pot? And how can I calculate which capvalue I need? Normally I like something like 100pF or lower.

Another mod I would like to try out is a groundlift on the midpot. Looking at the schematic, there's also a little cap (C10) next to the midpot to the ground. What does this cap do, does it roll of some highs? And how do I calculate which frequencies it rolls of?

Wow, didn't expect this topic would go this way. Great

There's another so called 'explanation' about this cutting through the mix. It says that it doesn't have anything to do with loudness or efficient speakers, but with the frequency response. Tubeamps would have the right frequency response and right harmonics that would explain why a tube cuts so well through the mix and ss don't.

Any thoughts on that?

Hi,

You often hear this said/written by many (if not all) guitarists who use or have been using a solid state amplifier in a (live) band situation. They hire a studio/barn with their band and use the PA and gear that's allready in there, or just use their own ss-amp that they bought once for home use. But then they have a really hard time to try to get through the mix and be heard. And when they get through, their gear have never sounded worse than with that amp. And they need at least 3 times more power than with a tubeamp!

Actually this is a wide spread and accepted opinion and has allmost become a definition of ss-amps. But I'm wondering... is it really because of the amp being solid state, or are there other factors involved? I mean, the technology is whidely accepted and preffered in audio equipment and bass-amplifiers, so why is it so bad in combination with electrical guitars?

This topic is meant to bust the myths about solid state guitar amplifiers. So please shoot and share your opinions, experiences, stories and knowledge!

Yesterday I finished the amp and it's alive!!  
It's very quite, no noises, cracks or hisses. There was a little 50Hz hum but I guess that's because I didn't use a grounded wallsocket. The preamp is running on +/- 18V and is doing just fine. Guess that the lifetime of the chip is shortened by running on it's max. voltagerating, but I can change it quite easily if I need to.

Didn't really had the time to test out the amp because my daughter already was asleep (and my wife wanted to watch her favorite tv-show...) But first impressions are good. I build the preamp of a Marshall Lead 12 and it definitely has the Marshall flavour and especially with the high-input it rocks like crazy.
This evening i'll make some time to test it at volume and to hear what it is capable of. Very curious!  

I allready know what went wrong. I measured with the preamp disconnected instead of connected. When I'm at home I'll measure it again, but I don't forsee any problems now.

New problem... I changed the powersupply for the preamp to get from +/-27,5V to +/-15V. In the original schematic there are a 1k Ohm/22 uF, I replaced them by 3k9 Ohm / 47 uF (had those lying around). According to my calculation with the Duncan tool 3k9 would be enough to get the voltage under 16V, but now I measure 27,3V, hardly any lower than the original voltage...

What did I do wrong?
I have a hard time dealing with the powersupply.

Well, according to the datasheet the LM1875 does poor out 20 Watts @ 8 Ohms load.
But I can imagine that you need to get the max out of these gainclones to get it to work properly. So it's not a bad thing that my railvoltage turned out to be much higher than I wanted in the first place, it's now 50-55VDC The max rating for this chip is 60VDC.

Luckilly I don't need that much power anyway, because this amp is meant to be used by my students during guitarclasses. I'm just curious if the powertransformer will hold when I do set this amp at max volume.