Building overdrive from this?..more treble?... I've traced a Levin amplifier

[ericohman]

I took the day off work today and I've completed the "tracing" of a amplifier that I've had since I start playing in mid 90's.. in fact, it's the only amp I've had til now basically... got a JTM45 clone early this year.

I like the  overdrive tone from this Levin retro 15 amp. It is very mid-rich and smooth, I also like the response on the attack of notes. However, the treble knob has always been fully up and there's still way to less treble to be had of the amp alone. I don't want to do any mods to this particular amplifier but it would be interesting to try to mimic the distortion clipping from it and I hope this tracing thing can be a start....

By looking at these pictures, does anyone get an idea of what's going on?
Is it only diode clipping, assymetrical or not, etc..?

I will try to draw a schematic but I guess it's going to be difficult since I'm just a beginner...
Enough talking, here's some pics, and sounds...






Amp with tokai ls80 (1985) with stock humbuckers. Recorded with a digital still camera's video record feature...
Gain set to around 9 and Volume on around 20%
http://djoman.dyndns.org/levin/audio/levin_retro15_demo.mp3

Don't know where to start...

Where does the clipping happen?
I would like to build a stompbox with similiar feeling overdrive... or another of this amp with more treble range, excluding the clean channel and run it off battery.

I will try to draw a schematic this weekend...right now my head feels overloaded and it's 01:55 in the night here in Sweden.

[slacker]

Looks pretty cool, thanks for sharing that. I had a go at doing a schematic, and it looks like it's a similar circuit to the Marshall Guvnor and Shred Master pedals but with some interesting stuff happening in the feedback loops. Some of the diodes might be the wrong way round, but I think the general layout is correct. We just need to figure out what the diodes are.

http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/album170/levinamp.jpg.html?g2_imageViewsIndex=1

The switch selects between the clean or dirty sides and also grounds the input of the dirty side when in clean mode.

[slacker]

Just seen this thread http://www.diystompboxes.com/smfforum/index.php?topic=83014.0 and this is essentially the same thing as the Crate circuit being discussed there.

[ericohman]

Wow, nice job!

I'm pretty sure I can find out what the diodes are... just need to have another close-up look at the parts, will do that today.
I'm sure it isn't much help now that you've already drawn a schematic but the two upper lugs on the switch is used when the overdrive is engaged.
1 1
1 1
0 0
Like that (above) when the overdrive is on, and like this (below) when the clean channel is on:
0 0
1 1
1 1

I will try some ASCII art right now. Some diode symbols looked something like this:
 /
I<-----
/

On the pictures I draw them as /<--
I guess those are all zener diodes determing by the looks and symbol...

That IC2 driver thing. I had a look at datasheets and it seems to be some kind of driver. What does it do in there? Something with the speakers or?

Here's some datasheets for easy access.
IC1 KA3403
http://www.datasheetcatalog.org/datasheet/fairchild/KA3403.pdf

IC2 TDA2030A
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1459.pdf

You may have noticed that there were two D4 on the board.. it was like that and is no mistake by me, there's also duplicates of C3 polarized cap.
There's really no use of the clean channel at all. Is there any parts that could be removed to simplify the circuit, having it overdrive-ON all the time.

[ericohman]

I wonder what voltage is coming into the circuit... doesn't say anywhere so I might measure it...

Both 2200µF caps has leaked some kind of oil that's on the board around them. What's that? I've seen the same thing on the inductor on my colorsound fuzz-wah

[Tonemonger]

It's probably just glue to help keep them secured and act as a bit of a shock absorber - However, over time this can dry out, scorch and become conductive.
The one on the right looks a bit pregnant ,this is a sure indication that it's on the way out.
I'd replace it and pick away the glue while you're at it.

[teemuk]

I believe you have sketched the distortion stages erroneously. The whole thing pretty much looks like a xerox of the distortion circuit that Saint Louis Music (Ampeg/Crate) patented and which was just recently discussed on this forum. I think the two series diodes in the feedback loop are actually Zeners and the other one of them is drawn the incorrect way around. The third diode and the following R-C-R circuit is a DC offset level shifter.

Edit: Slow me, just noticed someone pretty much wrote that already. 

[Paul Marossy]

The whole thing pretty much looks like a xerox of the distortion circuit that Saint Louis Music (Ampeg/Crate) patented and which was just recently discussed on this forum.

So does it sound good? Whenever I think of a Crate amp, I think fizzy cheesy sounding distortion.  

EDIT: I just saw the link to the soundclip. It sounds pretty nice. But you have to remember that the speaker/cabinet interaction is part of the equation here. The circuit in a stompbox might not sound as nice...

[ericohman]

I will post a few more pictures because I took a lot of photos.

I will try to hook up this amp into the normal channel of my jtm45, (from the phones jack on the levin). might give a hint on how it could sound as a distortion box... though I believe it will be boost amount possibilities will be insane!

[Paul Marossy]

Cool. Well, I think you have a good ear. This could potentially be a nice stompbox project. 

[ericohman]

By the way, I hear a lot of people talking about similarities with a Crate amp.
I might add that my father bought this amplifier to me, hmmm, my guess is that it was bought around 1994-1996...
It was sold by a swedish local music store bundled with a fenix stratocaster copy (black/white, clapton style), for a price that was around $350 back then (amp+guitar).

I read that Martin & Co apparently bought Levin in 1973... so I have no idea who really built this amp... apparently Martin & Co? Or someone built it for them, giving the possibility that there may be other other amps around mid 90's being the same amp in a different cabinet/different brand.

Btw, What particular Crate amp model is it people refer to?

[teemuk]

Here's a schematic as according to PC board sketch:

I read that Martin & Co apparently bought Levin in 1973... so I have no idea who really built this amp... apparently Martin & Co?

I suppose it doesn't have any kind of badge in it stating that? I think Philipson, which was likely an Asian OEM factory / amp manufacturer, manufactured these things, most likely commissioned by CF Martin. If I remember right, Philipson also produced some low power, tweed covered SS amps so very likely these are the same, simply rebadged as "Levin". That's quite common industry practice.

Btw, What particular Crate amp model is it people refer to?

Pretty much all of them post 1991. They used almost similar distortion circuit in all of their amplifiers. There were slight differences in component values and some amps replaced the zener diodes with a discrete dual "rubber zener" built out of two transistors and bunch of resistors (the same thing e.g. some Music Man or Fender amps used).

The greatest differences in all those amps come from pre and post EQ'ing and gains driving the stages - not from the used distortion circuit.

[ericohman]

Sweet job!

I suppose it doesn't have any kind of badge in it stating that? I think Philipson, which was likely an Asian OEM factory / amp manufacturer, manufactured these things, most likely commissioned by CF Martin. If I remember right, Philipson also produced some low power, tweed covered SS amps so very likely these are the same, simply rebadged as "Levin". That's quite common industry practice.

Interesting.
No it doesn't say anything anywhere other than Levin on the logo and Levin Guitar Amplifier on the back. Will post more pics later.
The transformer says something with TELECOMM on it and the speaker is a PHILIPSON

[teemuk]

Here's a "Watson" amp made by Philipson.

This one's a bass amp but overall it looks about the same (look at details such as the handle and the corner protectors).

[ericohman]

Even the knobs looks the same.

[slacker]

Nice work Teemuk, that's much better than my quick attempt. I think C4 should be 0.1uF though, I read it as 1uF at first as well, but the component side photo shows it as a 0.1uF film cap.

[Quackzed]

i think its just a general circuit block that crate amps have used in many of their budget amps. crate builds alot of ss amps for guitar for alot of years, and this has been their go to distortion channel topography. do a search of crate amp schematics and you'll likely see
http://www.muzique.com/schem/louis.gif
this arrangement in the lead channel.
this must have been a more than satisfactory clipping style for crate to go through the effort and expense of patentig it...$$$
so i'd guess it  has some type of 'mojo' .
I had a g-60 back in the day, and it was a good sounding distortion for me at the time, though i figure it lends itself to 80's type distortion sounds, as that was what was popular when crate was the de-facto budget amp co.
the opposed series diodes in the feedback path seem unusual to me and are probably at the 'heart' of this patents ..er...patentability?!
i looked for some crate amps that use this, but i came up short??! i'm a bit surprised, maybee theres a really good sounding amp that uses this circuit frag? i hope?

[teemuk]

Just to refresh my memory I went through a bunch of Crate schematics and surprise, surprise, the circuit of this Levin amp is almost the same as Crate's GX-15 amp. They pretty much copied 99% of the circuit.

The main difference is that GX-15 has a mixed-mode feedback scheme in the power amp resulting into a non-linear frequency reponse similar to what many tube amps have (Levin does not use this scheme) and some caps in Crate are paralleled with the same value (mainly in tone stack and in the coupling of the distortion circuit).

The GX-15R is the same but with reverb.

Edit: oh, indeed, the 1uF caps should be 100nF.

[ericohman]

Yes C4 is .1µF
Sorry for the hard to see dot, if you look REALLY close you can see it


EDIT: This is also .1µF, and it is C10 (forgot to retype it to C10 in the first post). Here it is marked in green:



Here's more photos as promised:












And my handwritten stuff whilst trying to determine parts:

[ericohman]

Just to refresh my memory I went through a bunch of Crate schematics and surprise, surprise, the circuit of this Levin amp is almost the same as Crate's GX-15 amp. They pretty much copied 99% of the circuit.

The main difference is that GX-15 has a mixed-mode feedback scheme in the power amp resulting into a non-linear frequency reponse similar to what many tube amps have (Levin does not use this scheme) and some caps in Crate are paralleled with the same value (mainly in tone stack and in the coupling of the distortion circuit).

The GX-15R is the same but with reverb.

Edit: oh, indeed, the 1uF caps should be 100nF.

That "response similar to what many tube amps have.." sounds interesting
There's also levin retro's with an R in the end, the reverb models

I've seen Levin Retro 30R and 50R but not 15R...
Levin 50R (R for reverb):


Makes me think of this... There's no Crate GX-30R and GX-50R are there?



EDIT: I cropped a photo from above post of the pots, might be interested to see the Hz values printed on top of the EQ knobs.