What is this ic?

[soren_jepsen]

Question from newbie (with a big N) 

I'm looking at the poweramp part of the Dean Markley k-150:
http://deanmarkley.com/Info/LegacyAmps/Schematics/D1509.pdf

- What kind of ic is ic5?
- what does it do, is it a buffer ? 

/Soren

[turbolx5oh]

Opamp and judging by the pin count probably a dual OPamp like a TL072.

http://focus.ti.com/lit/ds/symlink/tl072.pdf

And yes it looks like a buffer to provide a high impedance (1m ohm in this case) input for the input jack.

[joecool85]

It probably is a TL072 since Dean Markley used those in pretty much all of their amps.  It would be super easy to check if someone had one you could open up...  Any reason you wanted to know about the k-150?

[soren_jepsen]

I was kind of browsing thru the schematics, to see what they were made of. People seem to like these amps (?). I've been messing (pretty precise word in my case ;-)) around with building a guitar amp. I've already build a bass amp using this preamp:
http://www.albertkreuzer.com/preamp.htm
and this poweramp:
http://sound.westhost.com/project27.htm

Also I've build an inverted lm1876 amp using scrap pieces and a lm3886 for a guitar amp.

I'm messing around with different preamps for the guitar. The K-150 seems reasonably simple to put together, and i have a pair of the mosfets laying(?) around :-)

...and I'm also aware that I know very little of electrnics and may be out on a limb  xP  ...but I'm having fun  :loco

Anyway (I'll stop soon) I thought about a Tl072 for the ic, but the pinout had me pussled.


/Soren

[joecool85]

Why is the pinout puzzling for you?  It looked pretty straight forward to me.  And yeah, Dean Markley amps are pretty highly regarded around here, but thats mostly due to me lol.  I have one, and I've used others and I really love their sound.  They are also built rock solid.  As far as small practice amps go, I really haven't heard anything that I like better than my K-20X.

[soren_jepsen]

hmm, not even sure I'm using the correct terms. Talk about trashing around in my ignorance 

The ic5 pussled me, because i thought it to be a buffer (not too sure about what this is in detail  ). I looked at the datasheet for a TL072 and it did kind of make sense to me, but then i compared the diagram with the ic's of the preamp, and I got confused.

Guess my knowledge in electronics is very simple theory fusioned with trial by ....smoke. Fortunately Very little smoke has issued so far, but then agin my theory is likewise limited.

By the way, I think a guitarist once showed off his Dean Markley to me. He's a profesional, who played in the danish band "Led Zepelin Jam".

Anyway, and I'll stop babling soon, are there any pitfalls in trying to build the poweramp of the k-150?

/Soren

[turbolx5oh]

As far as small practice amps go, I really haven't heard anything that I like better than my K-20X.

I bought a used Vox DA5 this weekend.  Super nice amp with great effects.

[Bob N]

Guess my knowledge in electronics is very simple theory fusioned with trial by ....smoke.

Don't knock it... That's how I learned too... I was fortunate to have my first 10 projects turn out just fine, probably because I'm a stickler for detail, but as my "trial by smoke" has advanced to tubes and transformers, I'm now finding some of my educational limitations. For some reason, I understand Solid State very well, but tubes and transformers are somewhat baffling to me, then you add the much higher voltages and a healthy fear of being zapped makes you think twice about screwing around with it....

What I've found is that the preamp section of whatever amplifier you want feeding into a well documented DIY Amplifier section (Such as LM3886 or LM1875) makes for a very nice setup most of the time, but that doesn't mean you can't DIY a full blown copy of "name your amp". It just means you might run into custom labeled ICs in the schematics, when they are labeled with the IC part number... The reason I like to stick to the Standard DIY amplifier sections such as listed above is for the support factor, in addition to the fact that the parts are usually very easy to come by and are usually very inexpensive as well.... All of which are huge pluses

[soren_jepsen]

Thanks for the answers  . I have tried the gainclones, and I love the simplicity. Should tweaking more, but a lot of people write about their experience and testing and (imortant) listening. Listening to the ones I've build I belive I can relate to these experiences. I've build mibe them from scrap pieces, so quality is so and so. However I build an amlifier:
http://sound.westhost.com/project27.htm
...witch sounds much more "relaxed" when playing the guitar thru it. This is why I'm seeking elsewhere :-)
In regards to tube amplifiers I've looked at the ax84 project, and find it interresting. However, as you write Bob, it's dangerous voltage if you don't know what you're doing. Besides, finding output transformers in northen Europe seems dificult.

for the tecnical part:
Anyone know how the before mentioned power amp should be bias'd (SVR1)

[teemuk]

The IC5... definitely not an input buffer: This IC is forming the voltage gain stage of the power amp circuitry. It's feedback circuit (taken from the output to the input) is similar to "standard" opamp circuits and the stuff in between (mosfets etc.) is basically just buffering used to provide enough current for the load.

[joecool85]

I knew teemuk would have a good answer, thanks :-)