API 325 to 312...help please.

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:thumb: on getting your pre's going.

Peters pics & the upgrade info he said he got from Dan K. is missing...

Do you have the info &/or pics you could repost?


Also, Did you ever try the BC caps against the FC's... what's your opinion?
O, did you get the BC AML 138's or the "Standard" BC's?

I'm not sure Dave will chime in again but I wounder what he & others are settling on for C3 (value & Brand)... I've been using a 1000uf/35v Nichicon PW & like it a lot but as I'm typing I'm ordering some different brands & values to listen to.

The PW's were the best so far. I did not like Nichicon HE at all, too high end'y, not full or balanced. I also tried Nichicon ES "high quality Bi-Polar"... no good, actually the worst in this position.

I'm ordering the FC's & BC right now - 470uf & 1000uf & just tripped over this thread so I thought I'd ask :green:

Thanks,
Kevin
 
I'll have to check my notes and see if I find that stuff. I know that I basically changed the values of all the caps and the two diodes to higher ones. Which if you look a few pages back (page 3 I think), according to Dave (soundguy) it make a big difference in soundstage. If I find the info I'll let you know. I was pressed for time so I did not try the BC's. Only FC's on mine. Dave is the guy to ask. The killer mixer he made has different caps for more flavors. He does mention something about FC's vs. BC's at the bottom of page two. Anyway, sorry I couldn't be much help but if I find that info I'll get back to you. Best of luck.
 
Im bringing this one back from the dead.....



I've been trying to find a 50K rev log pot for awhile now and I'm having a very hard time. Is there any other suitable values that will work? Can I change the value of R3 to find use a easier to find rev log pot?
 
[quote author="khstudio"][quote author="Sender"]Im bringing this one back from the dead.....



I've been trying to find a 50K rev log pot for awhile now and I'm having a very hard time. Is there any other suitable values that will work? Can I change the value of R3 to find use a easier to find rev log pot?[/quote]

Try here:

http://www.smallbearelec.com/Detail.bok?no=116

Kevin :green:[/quote]

Awesome, thank you!

For testing purposes, I can use a 50K non rev log taper pot and still be okay, correct? It will just not be a smooth increase/decrease correct?
 
[quote author="Sender"][quote author="khstudio"][quote author="Sender"]Im bringing this one back from the dead.....



I've been trying to find a 50K rev log pot for awhile now and I'm having a very hard time. Is there any other suitable values that will work? Can I change the value of R3 to find use a easier to find rev log pot?[/quote]

Try here:

http://www.smallbearelec.com/Detail.bok?no=116

Kevin :green:[/quote]

Awesome, thank you!

For testing purposes, I can use a 50K non rev log taper pot and still be okay, correct? It will just not be a smooth increase/decrease correct?[/quote]

Wire it & use it backwards :wink:

Up is down & down is up (Volume)

Kevin
 
I've converted my 325 to a 312 and so far it's not working. I'm unable to pass any audio and then I turn the pot up all the way the output buzzes. Is it possible that I'm using a bad OP Amp?

I've tryed jumping C4 and R4, jumping C4 and putting a 75ohm resistor in place of R4, and also tryed still having C4 (470u) and R4(75) in.


edit: I got it working, it sounds great!!
 
[quote author="peter purpose"]C1 & C2 changed for more effective power supply bypassing.
The pot wants to be a 'REVERSE LOG TAPER'. 10K to 50K, depending on what you see at R3.
Transformer termination C5 for a 2622 needs to be 220pF & 5K1. Take transformer secondaries (via leads) to HI pin 5, LO pin 4.

peter[/quote]

Hey, bit of a noob, question. Can you explain how R3 and the pot work together, ie. how changing R3 affects the pot value and vice versa.

Thank you.
 
Hey guys

I had these really cool little single 15 pin card cages built by my metal guy for some future projects. each one houses a single 15pin card, edge connector and guides so now it is easy to mount cards in a single space rack. I'll post some pics soon. They will be avalible with the card guides you'll have to provide the card edge connector. they are pretty slick,


Wil
Wilebee
 
Hi Guys,

Bringing this one back from the dead to see if anyone can recommend which BC caps to use on an API 325 --> 312 mod.

I don't see a BC 220uf 50v for instance (C1 and C2 on 325 mod). So can I use a BC 220uf 40v? What would you guys recommend??

For C3 there is a BC 1000uf 16v so that is pretty doable. Has anyone used other values on the BC caps?

thanks!

- Jim
 
2 things...

1. the power supply for these guys is up to max +/- 24 volts so yes, 40 or 35 volt caps would be fine but the smallest voltage possible for the cap in the potentiometer loop...

2. The law of a pot is the rate of resistance change in relation to rotation of the wiper. It doesn't matter which way you wire it . If you wire it backwards you will simply have a pot the works by the same law but in a counter clockwise fashion. Reverse Log is the inverse curve of log and linear is a straight . Any pot will work if it is the right value. The only difference will be how much the gain changes in relation to turing the knob. With linear all the audible change is in the last 1/4 rotation..a little more gradual with log (or audio) and smoothest with reverse log.

Cheers,
Ray
 
[quote author="raysolinski"]With linear all the audible change is in the last 1/4 rotation..a little more gradual with log (or audio) and smoothest with reverse log.
[/quote]

A log (or audio) law will be worse than linear in this circuit. You can use a linear pot, but you loose a lot of control. Get a rev log 10K from JLM or Digikey for $10. It's worth it.

With a 10K pot, you'll need to change the value of R3 to 10K, and R2 to 100R. For 50K, I would change R3 to 50K, and R2 to 500R. These give a max gain of 101x.

pots-f4.gif
 
Hey,

Real quick question about a substitute output transformer. I'm using a Cinemag that only has only one secondary so I have no way to ground the output, via a center tap. So should connect the output ground to the input ground and call it a day?
 
Well, i've finally gotten around to taking some pictures of this project.
6 channels, 2 DI's, jlm go-between's...and possibly output trims.

http://www.flickr.com/photos/23725419@N06/

Thanks to Peter Purpose for all his info here. Really appreciated.
Will post a finished pic. :thumb:

D.
 
Sorry for bringing this back but....
What is the importance of using a 50v rating on the 220uf capacitors for Peters mod? The original ones were 25v. I only ask because I have some FM 220uf 25v sitting here I thought would be nice to put in there. Seems to me with a 15-18v power supply 25v would be fine. Maybe I'm missing something? Again thanks for the tips Peter!
 

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