Why Class A Guitar Amplifiers Sound So Good ........

poynton · 2011-03-12 10:51 am

I stumbled across this Ebay listing today.

EPIPHONE VALVE JUNIOR 5W COMBO AMPLIFIER - BRAND NEW!! on eBay (end time 14-Mar-11 12:34:33 GMT)

Now I have all the answers ......... and more

Given that the vendor is from Ireland, where they are noted for the "gift of the gab", I think there is a little more than poetic licence here..

Andy

.

SY · 2011-03-12 12:31 pm

Well, an MI amp is a different sort of beastie. The same coloration, high source impedance, and variable sound with volume that drives people like me away from using SE output stages in music reproducers can be very desirable in a music producer.

To be honest, if I still played in public, I'd be more than tempted to build a 5 watt or so SE amp, then mike it with the PA. For thrashing in the garage, a 5W SE amp is perfect since I could indeed have fun with the tone without going deaf or having a visit from the local gendarmerie. This particular one looks like it's run in pentode, which means effectively current-source drive to the speakers and lots of harmonics and intermod.

Cassiel · 2011-03-12 4:41 pm

I know that amp. Cheap parts, lousy layout, and too expensive. Build quality sucks. I think Fender sells an OK version just a tad more expensive. They're all made in China. It will sound OK but you can do much better with less money. DIY route.

Miniwatt · 2011-03-12 5:51 pm

I made a SE switch on my PP guitar amp. Sounds very hifi-ish, but I rarely use it.

An amp like the one from the link is very easy to make, I'd also say 'go diy!'

Tubelab_com · 2011-03-12 8:37 pm

I don't know what has got into Gibson / Epiphone lately. Gibson owns Epiphone. Both companies use the Les Paul (inventor of the electric guitar) name on their guitars. I have a 10 year old Epiphone Les Paul and it is a decent guitar for the price. Recently thay have been marketing junk and their reputation is suffering because of it.

Any company that stoops to near fraud to make a buck does not get any more of my money. Look at this thread and follow the link in post #5:

http://www.diyaudio.com/forums/tubes-valves/182551-bumblebee-caps.html?highlight=gibson+tone+cap

Want to make a similar but better SE guitar amp. Look here:

AX84.com - The Cooperative Tube Guitar Amp Project

mashaffer · 2011-03-12 9:30 pm

Interesting link George. I would agree with the general thrust of the comments but it is amazing that no one challenged the statements by several that the only thing that matters is the capacitance value. Surely hysteresis and other nonlinearities along with various various parasitics and microphonics must be a factor in the sound however subtle.

The AX84 guys are very helpful folks BTW. They were a tremendous help on the amp that I built for my grandson (even though that was a PP 6V6 design).

Tubelab_com · 2011-03-12 11:00 pm

There is a lot of "guru magic" associated with the "tone cap" in an electric guitar. It is simply a cap in series with a pot wired across the output of the guitar. It is intended to roll off the highs as the tone pot is reduced in value. Some interaction with the inductance of the pickup can create resonant peaks in or above the audio band.

The original Gibson electric guitars used a Sprague "bumblebee" cap which were paper and known for being leaky. They should be replaced in a tube amp for that reason but they are revered in old guitars. Now it seems that Gibson is making knock offs and selling them for $60 each!

Wavebourn · 2011-03-12 11:48 pm

I like this буллшит:

Single ended circuitry, used in the Epiphone Valve Junior amp, means neither side of the output circuit is referenced to ground. The full swing of the output voltage goes across the speaker. An efficient way to get high SPL from a 5 watt amplifier.

Robert F · 2011-03-13 1:16 am

stalker said:
I know that amp. Cheap parts, lousy layout, and too expensive. Build quality sucks. I think Fender sells an OK version just a tad more expensive. They're all made in China. It will sound OK but you can do much better with less money. DIY route.

Well the V3 version is actually a pretty good base for a few modifications. The earlier models hada few problems.I don't agree about the build quality, which I think is pretty good. Cheap parts, agreed..

ChrisA · 2011-03-13 6:45 am

stalker said:
I know that amp. Cheap parts, lousy layout, and too expensive. Build quality sucks. I think Fender sells an OK version just a tad more expensive. They're all made in China. It will sound OK but you can do much better with less money. DIY route.

The Fender version sells for $149. I t would be hard to build that amp for $149 if you had to buy all the parts new. I have one and, well it has that Fender sound. It works well for intended purpose. It uses a PCB put it is a low density design with big sized axial lead parts, easy to work on.

Gilgy · 2011-03-13 7:06 am

The full swing of the output voltage goes across the speaker.

I'm desperately trying to think of anywhere else it might go.

Actually, with that amp anywhere other than the speaker would be an improvement.

poynton · 2011-03-13 8:05 am

As Wavebourn picked up, it was the language of the posting I was commenting on NOT the actual product .... but what the heck, it's turned into an interesting discussion !!

RE: Bumblebee Caps .. If a supposed reputable supplier is "faking" old parts like this, what next ?
"Fake" Blackgate caps, "Fake" Holco resistors, "Fake" transistors ... but all from the original manufacturer?

Andy

.

Wavebourn · 2011-03-13 8:13 am

poynton said:
As Wavebourn picked up, it was the language of the posting I was commenting on NOT the actual product .... but what the heck !!

What the heck??
The buyer have the right to state that "THE ITEM IS NOT AS DESCRIBED!"

Cassiel · 2011-03-13 3:39 pm

The Fender version sells for $149. I t would be hard to build that amp for $149 if you had to buy all the parts new.

Yes, that's true. Not everybody has a big junk box.

BTW, the B+ voltage in that amp is around 350 volts and comes with Chinese tubes. Cross your fingers.

Cassiel · 2011-03-13 3:48 pm

I don't agree about the build quality, which I think is pretty good. Cheap parts, agreed..

We have a different point of view.

DVM's Valve Junior DIY Mods Page

Robert F · 2011-03-13 8:12 pm

stalker said:
We have a different point of view.

DVM's Valve Junior DIY Mods Page

Yes we do, however your point of view would be better supported if you had experience of the version I posted about. The v3 has DC heaters, an extra stage of B + filtering AND the grounding layout sorted. The site you link to is principally concerned with fixing the problems I readily conceded existed with earlier models...

The v3 also has a new output tx with a lower impedence primary.

E.T. · 2011-03-18 7:20 pm

stalker said:
I know that amp. Cheap parts, lousy layout, and too expensive. Build quality sucks. I think Fender sells an OK version just a tad more expensive. They're all made in China. It will sound OK but you can do much better with less money. DIY route.

I agree. If someone wants to build from scratch, just look for the schematic for the 1956 Fender Champ. IIRC it's either model 5F1 or 5F6.

In the 80's I read interviews with Keith Richards and Eric Clapton -- both said that in the studio they never used anything but 50's Champs, because it was the best-sounding amp ever made. Ditto Chuck Berry. I assume this is because it was one of the few SE guitar amps.

In the late 80's I built an amp that used either 4 x 6v6 or 4 x 6L6 wired in parallel SE. Compared to that circuit, regular Class AB Fenders sounded hollow and painfully harsh.

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Why Class A Guitar Amplifiers Sound So Good ........

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