API Mic pre (with Yamaha parts) ***COMPLETED***

[khstudio]

[quote author="rafafredd"]I would use at least 1000uF. It´s for flat frequency response on all gain settings. You could go as high as 4700uF.

Also, 12uF is way too low for the opamps bypass. Electrolytics were much more expensive by the time that they drew that API schem.[/quote]

The 1000uf definitly seemed to increace the lows/subs along with the 220uf/.1 mono on the supply rails.

My original test setup had the 250uf = C3 & 22uf/no cap = PS & still sounded great but a hair looser & less SUBs.

I'm concerned with the voltage of C3 - I'm using a 35v cap right now... is this too much & can it affect the "sound" at all :?:

Also, the feedback cap, I've seen mentioned to use a poly in stead of a ceramic... any opinions or preference on this?

Thanks,
Kevin

 

[khstudio]

Here's where I'm at so far:
The Gain pot is backwards because it's not a reverse taper... I'm waiting for the pots to come in. Also, I made a mistake on the PAD switch it has to be "in" for normal "no pad" operation... Damnit!!! Oh well.
Also, the pad resistors are not installed yet but it does work :green:

Kevin

 

[oobedoob]

Oops, I totally forgot about this thread.

Here's mine with parts from a PM700, all handwired and ugly as hell. The gain switch isn't fully populated yet and I have no data on min/max gain and transformer termination. But a quick check shows everything sounding good. Maybe a little rolled off on the high end, but has huge bottom.

 

[khstudio]

Cool :thumb:

I'd be happy to share my PBC Layout file. You can use the "FREE" program to edit it the way you want.

I have a few of those smaller input tranny's too but never tried them... I probably should.

I don't see a ZOBEL on yours... is it there & what did you use? I'd like to raise the rolloff point on mine a little bit.
Also, what is that OT from :?: YAMAHA?

Did you use an output cap & if not, how much DC do you have hitting the OT?

BTW, I started a thread about the "GAIN POT Cap" & it's voltage.
I've tried several different brands & voltages & it's crazy how much the whole pre can change by changing that cap. The freq. curve doesn't really change but the "Feel" of the pre does.

Good Luck,
Kevin

 

[khstudio]

BTW, it looks like your using the stock value (12uf ???) on the supply rails...
You should definitly raise them to at least 220uf, bypassed with a .1 monolythic ceramic. It will clean up the noise a little & tighten up the sound/ low-end.

Kevin

 

[oobedoob]

Answers to questions (more questions too)...

Yes, decoupling is 10u on each rail. I'm going to increase, but 220 seems like overkill. I think the OSA's have 22u as an example of something that works...

No Zobel network yet. I couldn't find an r-c on the output of the trafo in the PM700 channel strip, so I just left it out. I'll re-trace the ckt as I progress and match whatever is in the channel strips.

No output cap yet. Need to measure offset still. How much offset are you seeing on the 80200 output?

Yes, it's the o/p transformer from the PM700. Same one as in the m916 and maybe 1516 as well. again, I need to take some data. And yes, it's zip-tied to the perf board...

You know, I was going to teach myself a new layout program and do some boards for this, but it's really so simple to hand-wire it if I lay it out a little more sensibly than the one in the picture. And I'm only building 4 of them for the time being....

 

[khstudio]

Matt or anyone...

I've had more than a few hangups lately but still have some stuff for you (Matt) :wink:

I've done a lot of testing/listening to these pre's over the past few weeks & think I have them about the best they'll be but I have a few questions:

:idea: I'm using the original 47pf (ceramic caps from the old Yamaha Board) in the feedback loop...
should I get something better & will it make much difference :?:

(I have some Silver micas around.)

I've tried several of Matts sugestions:

:idea: Increased the Zobel resistor from 2.7k to 4.7, 6.8k & 10k -
but the original 2.7k in series with the 47pf sounds best & looks pretty good in RMAA too.

:idea: I Tried an output coupling cap before the OT (Nichicon ES Bi-polar 1000uf/16v) & DEFINITLY thought it was better without it (NO CAP!)

:idea: I tried bypassing the GAIN Cap (Nichicon 1000uf/35v - it was my favorite out of the caps I tried) with a .1 Metal/Poly film...
It added a VERY Little boost in the highs but not enough to turn me on.

:idea: I also tried a 620 ohm loading resistor on the Secondary - OT, I noticed something but not sure good or bad. I did this because I mostly will be running it into MODERN 10k sources but will also be using my LA-2A a lot so I'm not sure what to do here :?:
Even my Distressors & Fatso have a 10k impedence.

I'm up in the air with a few final desisions concerning the GAIN cap & supply filtering:
I built my first pre using ALL the API values except for the ZOBEL.
I built my 2nd using 220uf, bypassed with .01 mono caps for supply filtering & increased the GAIN Cap from 250 to 1000uf.

The first pre sounds very good, not as tight as #2 but a little more natural if you ask me. So I'm wondering about loosening up the supply filtering a bit for my taste

Lastly, after testing many Caps on the GAIN Pot I find they are NOT created equal at ALL
http://www.groupdiy.com/index.php?topic=16426&highlight=api+yamaha

I'm going to order/try (on the GAIN Pot) some:
BC AML 138 series
Panasonic FC
& maybe some lower voltage Nichicon PW's, since I liked those best but only had 35v caps.

HELP & OPINIONS WELCOME :green:

Thanks,
Kevin

 

[rafafredd]

You should also maybe try very high grade and expensive caps like Black gates and ELNA cerafines and stargets, if you are really into cap listening.

I did this because I mostly will be running it into MODERN 10k sources but will also be using my LA-2A a lot so I'm not sure what to do here

Try to add a swithc on the front panel labelled "termination". It opens and closes a 680R resistor on the secondary of the output transformer.

 

[khstudio]

rafafredd,
I actually hate listening to them but once you hear it for yourself your F@#ked... in a circuit with so little parts they all make a difference, some more that others.

Any opinions on the feedback cap? I'm using the "OLD" Yamaha 47pf ceramics I pulled from the M1516 channel strips. :?

Try to add a swithc on the front panel labelled "termination". It opens and closes a 680R resistor on the secondary of the output transformer.
rafafredd

I can do that. It will be a lot more wires running thru the pre which always bothers me... what is the downside of running from the 600ohm tranny to a 10k input anyway? It's very hard to hear a difference. I'll mostly be using this pre for Drum tracking straight into an RME ADI 8 pro converter into Nuendo.

Thanks,
Kevin

 

[mattmoogus]

Just wondering what youre doing your listening tests with, and are you able to do any blind testing when changing cap brands etc...?



M@

 

[khstudio]

[quote author="mattmoogus"]Just wondering what youre doing your listening tests with, and are you able to do any blind testing when changing cap brands etc...?



M@[/quote]

Absolutely. Kick, Snare & vocal tracked into Nuendo thru an Apogee.
& my friend & I take turns working playback while the other listens.

I just tested ALL my pre's with a ribbon mic & it was a real eye opener -
The Presonus MP20/80 (that still beat my new pre on guitars for some reason) FAILED the test. The PM1000 I have kicked ass & the PM2000 & this API/YAM I made sounds almost identical to the PM2000 - but with a little less gain & more open. This really opened my eyes to the components (NE80200-DOA & I/O trannys)

Now I think I realize what Soundguy was saying about the "REAL API" DOA earlier in this thread...

I've been teased by the rich sound of DOA's now I really want to hear some others. I'll be ordering a 99v pre kit to see what all the hype is about :wink:

MATT,
Can you give me any advise on my questions above concerning the feedback cap TYPE & the output 620 or 680 ohm load resistor?

PLEASE :green:

Thanks,
Kevin

 

[khstudio]

The right channel is the raw, sound card looped back in & the white/left channel is the Pre.

Freq Sweep

Noise

IMD

Dynamic Range

THD

IMD Sweep

 

[khstudio]

No output cap yet. Need to measure offset still. How much offset are you seeing on the 80200 output?

oobedoob

Check the 1st page of this thread

 

[mattmoogus]

I was typing this post before and we had a brownout :evil:


You need to disconnect the OT from the output of the opamp and measure the DC offset. If its more than say 10mV you need a cap. Seeing as Yamaha always put large caps after the opamps in their circuit and (like the zobel, you ended up liking their values) Id wager they did it for a good reason. You should idealy use a high value, low voltage cap, say 1000uF 10v. Even if you think it sounds better without, over time a DC offset with magnetise the core of the transformer and youll loose headroom.

The feedback cap, Id use a large value and whatever you think sounds the best as this is more of a tweak than a make or break part of the circuit.


Those graphs look mostly fine, tho it would be nice to be able to see past 20k. Go through all the options in RMAA as you might have to tick something else to get 96k working. Also make sure you pick the actual soundcard driver in the in/out options on the front page and not 'windows sound mapper' or whatever the default is. You might also have to set your soundcards sample rate to auto if its not already.

IMD looks a bit high, which usually means the level going into the transformer is too high. What pad value are you using? This doesnt really matter tho. Usually I only look at the freq and THD graph. What THD did your soundcard measure?

Just keep in mind that RMAA tests are really useful but dont tell you everything, you just have to get used to interpreting the results and getting meaningful info about what youve built. Listening tests are also important but neither on its own gives you the whole picture. Also listening tests are always subjective and usually biased so you have to treat them with caution especially when judging things like cap brands/cable types etc.


On the OT loading - use 680ohms. If you dont want to make a term switch, you could make some dummy loads in an inline XLR tube. I have a few of these so I can plug them inline with the outputs of some of my transformer gear. I dont always use them, just when i think theyll benefit the sound. If the gear always sounds better loaded (like Langevin AM16s for instance) Ill put the load permanantly on the output.

The 99v is definitely worth a listen - as Ive said I recently tried two of them in one of my PM2000 channels and they sounded great, really different from the Yamaha opamps, more Neveish and sweet but not as tight as the NEs...two very useful flavours to have in one console.


M@

 

[rafafredd]

Can you give me any advise on my questions above concerning the feedback cap TYPE & the output 620 or 680 ohm load resistor?

You could try polystyrene or more exoctic silver mica...

 

[khstudio]

[quote author="CJ"]Plug it in, it should work. The core is probably 50 EI instead of 625 EI, which is smaller than the stock API.

But, if the turns are there, you can get away with it. Output will be 1/2 that of stock 2503 due to running 1:1 instead of 1:2, like the stock setup, 75 ohm pri. , 600 ohm sec.

Core area will tell you the difference in Bmax between 50 EI and 625 EI. BTW, the 50 in 50 EI means the tongue is 1/2 inch.
The 625 means 0.625 in, and 75 EI means the tongue is 3/4, get it?

Metric is different, but screw the europeans. Faraday wa a Brit.

area of 625 EI stock API is 5/8 times 5/8 = 0.39

area of Tamura 50 EI is 1/2 times 1/2 = .25.

So you will have 1.56 times as much flux with the Tamura.
This means you need to decrease level by 0.64 of stock to run Tamura at same flux density.




Your offset voltages look ok.

Worst one is 76 mv, so 0.076/20 = about 4 ma dc, which the core should handle, I do not know if the dc will screw up the circuit from which it came from.

I would try a cap feed first, check the sound, then just put a jumper across the cap for a second and look for smoke.[/quote]

Well I finally got around to measuring my Yamaha/Tamura OT
& it measures EXACTLY the same SIZE as the API 2503 ...
So I'm assuming it's a 625 EI :green:
The DC resistance on either side is 20 ohms.

The reason I'm bringing this up again is the pre is COMPLETE & I'm going to be a rebel and NOT use an output coupling cap... I've tested it several ways (& cap sizes & types) & like it better without & it seems to be happy.

I've even gone as far to call Jensen and ask their opinion...
I gave them the dimensions & the DC I measured @ the primarys -
They said "A Nickel core would not like ANY DC very much but with a STEEL Core that size & the low DC (between 15 & 25mv) you don't have to worry... go for it"

Kevin

 

[mattmoogus]

What was the offset you measured?


M@

 

[khstudio]

[quote author="mattmoogus"]What was the offset you measured?


M@[/quote]

-15mv min.
-25mv max.

 

[khstudio]

FINAL PIC's added on Page #1

Thanks MATT & everyone for your help :thumb:

Kevin

 

[khstudio]

There are a few tweek & questions I could use some extra help with to "fine tune" my new pre...

#1
I'm using Ceramic Caps I pulled from the old Yamaha board for the Zobel & Feedback Network...

Should I upgrade these & to what?
Also, what sonic improvement could I expect if any?
I've seen mention of:
COG/NPO
Film ? type ? :?

... & while I'm at it, what are the Ceramics with a BLACK DOT

#2
I'm using .1 Monolythics to bypass the 220uf caps on the power supply rails feeding the Op-amps...

I've seen others use Polyester films for this...

How do the different types effect the sound :?:

#3

I'm using output trannys on every channel & love this thing on drums but I feel I may like the Kick & maybe the snare to have the option of being a little LESS Colored from the OT's...

The problem is I'm not using an output coupling cap so the switch would have to add a coupling cap and at the same time bypass the OT.

Any ideas or tips?

#4
I'm using an AMVECO 22V 1.590A (35 VA) Power Tranny...
& wondered if it gives me enough headroom for a punchy drum pre? :green:

& MOST Important - What size & TYPE Fuse should I have in this thing BTW, the Power Supply regulators DO NOT get hot at all... barly even warm.

Thanks again,
Kevin