API 312 Thread!

[hejsan]

And I also would like to know:
1) Is there a BOM available for the pp2520?
2) Why is D1 drawn as two diodes in series in the schemo?
3) Why is R7 marked with a value of 3k - 5k? is there a trimmer on the opamp?
4) Do Q3 + Q4 also have to be matched, or only Q1 + Q2?
5) Is it enough to match the hfe of Q1 + Q2?
6) Where do I get MZ2361 diodes? Are they the same as 1N4148?
7) The 2N4036 has been discontinued and suggested replacement from fairchild was TN4033A. Will it work the same?
8) The resistors R11 and R12 which are only 5R6, won't they have to be rated for high wattage?

For your ease, here is a link to the schemo:
http://www.thediypill.phx.com.br/forumfiles/schPP2520_R268.gif

Thanks,
hejsan

 

[drpat]

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[BR]

Hey hejsan

just wanted to confirm with you that I talked with Fabio and he confirmed what I said on the previous post about the 48V relay. the only things that change on the preamp board are the LED resistor that should be brought up to about 6.8k. I think..

I'll try it on my next pair. I wonder if they stock those relays..

 

[spica]

Has anyone experienced a very high output level with Bauman's 312s? I have just finished 4 using his melcor opamp boards (with the double diode on d2 mod) and have to use the pad on everything. I'm pretty sure I'm not clipping anything in the preamp, but the levels coming out of it are much higher than anything else I've used, including API 512s, and I'm clipping out my AD converters with ease.

 

[BR]

Which transformers did you use?
i would check your transformer wiring first. It sounds like your input traffo wiring may be incorrect.
if you used the 75101APC you have to short pins 5 and 6, as well as 7 and 8.

 

[spica]

Br, thanks for the response. I'm using cinemag cmmi-8pca for the input, so that may be the issue. they are 150:10k ohms. they sound pretty good, the output is just very high. I may up my gain resistor values instead of buy new transformers.

 

[byoung]

I'm going to be building a few of Fabios 312's, and I've been reading up on all the API threads. Still trying to decide on a few parts to use, wanted to see if I could get some feedback....I'm looking for something close to Vintage API sound.

Are the Cinemag in and out traffos the best for the vintage sound? I've read there are couple cinemags that can be used but which is closest to the vintage sound?

fabios melcor 1731 vs his 25.20 ---what is the difference in sound---and is it a big difference?

 

[louder]

alo byoung
i have one api 3124+,and 4 channels from fabio,with melcor,75101apc in,and sowter clone out.
the api has a little more bass,but very small diference.
also the api has more gain,but very small diference.
...now,there`s one thing that the clones do that the api don`t,and that`s why i love the clones:hit them hard,and they kinda snarl(?).it`s the same effect in guitar amps with tube rectification,and ss rectification.when driven hard,the sound kinda compresses.that`s the best i can tell you in my bad english.
...now you ask:but why does it do it?.
...i answer:i think it`s the melcor.not 100% sure,but close.
you see,i tried it with 2520`s from fabio,and they don`t do it.
the melcors altough sweeter,have more highs.
well,all these opinions were made with little time to get a solid opinion,but some folks here,can enlight you,much better than i.
one more:i think there was one issue with the melcors,but it faded way.
i remember now:2 diodes in series(d2).my melcors only have one,but i like them that way,and that`s why i`m gonna get 10 more boards from fabio,to test the various options.
btw,this is the second time i ask this:don`t you api users,fell the need to an attenuator after the pre,as to avoid using the pad?
sorry for beeing so long.
ps:remember that api went trough lots of changes,so saying "vintage api" leads in several directions.
best regards
pedro

 

[drpat]

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[ruairioflaherty]

[quote author="drpat"]
I've got switchable output pads on all of my API's. It's nice to be able to drive the 2520's into a snarl when you need to, and turn it off when not needed.[/quote]

Patrick,

excuse my ignorance if this is obvious but why does an output pad (after 2520 before tranny?) differ from an input pad sonically?

If I attenuate the input before the tranny I get less tranny distortion and get to drive the 2520 harder for growl. If I attenuate the output I get more transformer distortion but the same (?) growl from the 2520.

cheers,
Ruairi

 

[TomWaterman]

Yeah thats pretty much it, the harmonic saturation in the input transformer can be a good thing. The API type pres are notorioulsy hot, so an output pad makes sense. Or you can do like Joe Malone sugggested and put a pad after the TX but before the amp. Basically make the input TX load resistor a switchable voltage divider. Its even simpler than a typical U-pad on the input.

This is easier than doing an output pad, which would probably need to be a H-pad for balanced. Which would be a prob if you wanted to run the pre into an unbalanced input.

An input U-pad needs to provide the right impedance for mic and transformer. Some say they change the sound by messing with the interaction bewteen mic and tranny. I think thats something to do with inductance and reactance?

Not sure whether the growl Pat mentions is from the amp running at high gains or running at high gains with greater input signals.

The 2520 does sound different running open. I like the pad after the TX before the amp for simplicity and increased headroom without affecting the iron.

Cheers Tom

 

[louder]

hi
the issue with the pad in the input,is that one looses some of the tone of the preamp:just my opinion.
best regards
pedro

 

[drpat]

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[CJ]

Pat have you tried the Melcor Input mod # 400-20?
It came on the AML-27.
Just wonder who made that darn thing and how does it sound.

Does everybody wire the 2622 with the pri's paralleld?
Lots of dc imbalance doing it like that, maybe thats part of the sound.

The imbalance is caused by the single coil struture of pri-1/2 sec-1/2 sec-pri.

You can see that the inner and outer diameters of the pri's will cause major dcr differences, sometimes they mis balance the turns to make up for it, so if you parallel two pris with different dcr and different turns, they might fight each other a bit.

 

[ask]

I didn't get that one.. :roll:
Could someone help?


[quote author="drpat"]
I'm told that the pres on an API console are feeding a gain structure after the pre, which forces you to use more gain. This may explain why pres in the console don't have the same issue...[/quote]

 

[drpat]

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[byoung]

I've got switchable output pads on all of my API's. It's nice to be able to drive the 2520's into a snarl when you need to, and turn it off when not needed.

Patrick can you tell me or link me to the information I would need to put a pad on the 312 as you have done? I would love to implement one as well.

 

[drpat]

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[bobschwenkler]

What size are the op amp holes on Fabio's PCB? Which Mill-max receptacles are people using?

Also, I didn't see any info on the META for that output pad.

 

[byoung]

Also, I didn't see any info on the META for that output pad

Nor did I, I even searched and searched the forum for a couple of hours actually trying to find anything relavent, but with no luck, found a couple post that contained U pad, but nothing to tie it or how to implement it into Fabios circuit. Is there a simple explanation, ie connect this ohm resistor(s) to this point of fabios board to a DPDT which is then connected to this point etc...?