Melcor Deconstructed

[dissonantstring]

man, now that's what i call a response!
thanks Doug, Fabio and Peter! you guys rock!:thumb:

AP: i checked out anchor this past weekend and they have some pretty cheap stuff like 10 dual leaf DIP-8 sockets for a dollar!! cool!
thanks for the the tip! :thumb:

-grant

 

[clintrubber]

[quote author="dissonantstring"]you guys rock!:thumb: [/quote]
Uhh, how did you know ? :shock:

http://www.shirtlifter.nl/:wink:
Too bad our mp3's are down now :evil:

 

[dissonantstring]

peter! get your damn mp3s back up!
i wanna hear them...and barkmarket influences! i remember they were one of the first bands i saw in s.f. when i first moved here. d.sardy's pretty cool. have you heard of the refused from sweden(?) sorry...OT (will not post such things again.)
-grant

 

[Greg]

I didn't know about the double diodes... must've missed that one... thanks guys. :thumb:

 

[clintrubber]

[quote author="dissonantstring"]peter! get your damn mp3s back up!
i wanna hear them...and barkmarket influences! i remember they were one of the first bands i saw in s.f. when i first moved here. d.sardy's pretty cool. have you heard of the refused from sweden(?) sorry...OT (will not post such things again.)
-grant[/quote]

Hi Grant, thanks ! I'll need to relocate those mp3s, the place where they were hosted from has disappeared we saw...

Barkmarket impressive band indeed :thumb: That rhythm section, yummy ! :sam: :guinness: :guinness: :sam: :guinness: :sam:
Stay tuned !

Will check out Refused, never heard of them.
And IMNSHO it's about time The Jesus Lizard make a comeback, that'd be yummy to the max (and we'd forgive them those last few albums :twisted: )


Bye,

Peter

 

[Jonkan]

Clintrubber, check out refused: the shape of punk to come.

Good record!

Back to melcor:

Has anyone got a clue which values are better for r3,r4: 2x 39k2, or 39k2 and 43k9?

/Jonas

 

[Greg]

43K9

 

[Jonkan]

thanks Greg!

since there are not any 43k9 easily available over here.. Will 43k2 do?

Should be ok, right?

I love these little buggers already btw, so Im thinking of building two more channels on veroboard maybe, with servo outputs and beyer transformers on input.

/J

 

[Greg]

Do what you can to get as close to 43K9 as possible. A 43K2 in series with a 600R will get you to 43K8.

 

[mick]

Damn when did that one happen, I thought it was 39.2K, I'm in the middle of stuffing these boards now and thought that I had read through all the threads.

 

[Jonkan]

I had some 39k2 and 4k7 lying around=Bingo!

/J

 

[mick]

Thanks Jonas, so just to double check, Fabio's boards R3= 43K9 and R4+5=43K9 ?

 

[Jonkan]

i think its supposed to be r3=39k2, and r4 = 43k9
(r5 isnt really same on the pcb as on schematic as there is no trim pin)

/J

 

[mick]

:? I'm a bit confused about this, if you look back at page 8 of this thread
rafafredd has a diagram (yes I know it's not Fabio's) showing them both to be 39k2.
Fabio's diagram show the trim pin but it's not on the actual boards like on his BC boards, I thought the idea of these two resistors (R3 R4/5 )was to be the same or is it different on the melcors?.

 

[Jonkan]

i just realised i had posted the same question before... I have such bad memory!! :green: (At the time I thought that the 39k2 resistors needed to be matched.)

This is what prr replied:

> Im wondering about the 39k2 0.1% resistors (r3,r4)

They are not 0.1%. In practice they may have to be 10% different to get best-possible input offset voltage. This interacts with input pair balance, R1 value and negative rail voltage, all the balances in the oddball second stage, and input common-mode voltage.

39k2+10%= 43.12= almost 43k9.

/J

 

[mick]

Thanks Jonas, I'll go with R3=39k2 and R4=43k9 and see how it goes.

 

[Mendelt]

I've been playing around with the melcor in LTSpice and found some interesting stuff. I havn't tried anything out in the real world yet so please correct me if i made mistakes.

Connecting C2 to the -input or to the base of Q4 will both introduce negative feedback on high frequencies. The problem with the -leg solution is that the -3dB point for C2 depends on the impedance to ground on the -leg so this won't work in every situation.

Things seem to get more stable when you leave out C3. I don't really know why this is but when i get around to building one I'll try out how this sounds.

Whatever i did with this opamp I kept getting a bump of 3 to sometimes 8 Db at about 1.5MHz when i set it at unity gain. But it seems to be stable.

I tried to find more information on the real 1731 because there still seem to be some questions on it's construction. I found some websites by forum members with links to pictures of a disecteds melcor but these were dead links. Is there anyone who still has these?

 

[Mendelt]

In my search for more information on the 1731 I found this old page

http://www.recording.org/users/kev/discrete_op-amps.htm

There are a lot of pictures missing. I'm especially interested in the pictures of TommyTones disection of the melcor. Has anyone still got these?

 

[deveng]

Mendelt,

I've been playing with the simulations on the 1731 and the 2*5*2*0 and they both have this bump. There's an explanation of this in the thread.

It's inherent in the design of these opamps but can be reduced with some manipulation. Just changing the local feedback cap values won't do it but I was able to reduce it by adding a series resistor (39k) feeding the lower half of the 3rd stage in my design. I've built and tested it and it stands up to an original 2*5*2*0.

Regards,
Jeff

 

[mick]

Hi all I've just tested one of Fabio's 312 with his melcor boards, and all seems to be well and sounds fine (just a little hum in the background, but for testing it's all out of the box so I'm not to worried). For the melcors I went with Fabio's (Boards) Part's list and schematic with:

Q1=BC550C
D2=2x 1N4148 in series
And I did the mod with C2, I just lifted one leg of the C2 and put it on the V- IN pin

So my question is, this problem that keeps getting mentioned is it something that I should be able to hear and notice straight away or what ? because going through the gain min to max I don't notice anything strange happening. I don't have any test equipment just ears so if it's not audible I'm not able to tell if I do or don't have this problem ?