khstudio
Well-known member
Killer :thumb:
API Mic pre (with Yamaha parts) ***COMPLETED***
- Thread starter khstudio
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fallout
Well-known member
Rascal, you sure about that? Reverse log is actually refering to the actual curve of resistance.. RG Keen has a nice page about pots..
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm
-Jay
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm
-Jay
rafafredd
Well-known member
Sorry. I shouldn´t have posted in YOUR thread at all. I thought it was a FORUM and I thought I was part of it. I will keep an eye out for YOUR THREADS, and will surely stay away from now on.
Read back, and you won´t find a trace of unpolite words on my posts. I can´t say the same about yours.
Please, no more about this. Just let it be.
Good luck!
:roll:
rascalseven
Well-known member
The gain pot in a 312 is in the feedback loop of an opamp. Normally, a reverse log taper pot would be used here in order to create a proper 'feel' for the gain pot along with increased gain with CW rotation. Kevin doesn't have a rev-log, so he can use a normal audio taper pot instead -- it just means increased gain will be from CCW rotation instead.
Since the increased gain in this design is a result of decreased resistance, the full CCW position for the audio taper pot must provide the lowest resistance, and therefore, the highest gain. That is why I said to crank the pot full CCW and find the two pins that measure zero resistance. The log taper of the pot's resistance is what will create the proper feel of the gain control, even if it is turning the opposite direction from normal.
You know... the fame and status of the 312 has always struck me as rather funny, since it is really just an extremely basic, simple opamp-based amplifier. You can build the same thing substituting a 5534 or any other opamp instead. The magic of the 312's sound seems to lie in the 2520 as well as the quality of the transformers. Other than that there is really nothing else to screw up the performance. Simple and elegant.
JC
Since the increased gain in this design is a result of decreased resistance, the full CCW position for the audio taper pot must provide the lowest resistance, and therefore, the highest gain. That is why I said to crank the pot full CCW and find the two pins that measure zero resistance. The log taper of the pot's resistance is what will create the proper feel of the gain control, even if it is turning the opposite direction from normal.
You know... the fame and status of the 312 has always struck me as rather funny, since it is really just an extremely basic, simple opamp-based amplifier. You can build the same thing substituting a 5534 or any other opamp instead. The magic of the 312's sound seems to lie in the 2520 as well as the quality of the transformers. Other than that there is really nothing else to screw up the performance. Simple and elegant.
JC
khstudio
Well-known member
rafafredd,
Your a trip dude... I was NOT unpolite.
I'm sorry you feel that way. I was just giving a straight answer.
Your a trip dude... I was NOT unpolite.
I'm sorry you feel that way. I was just giving a straight answer.
rascalseven
Well-known member
Jay,
Thanks for the link. I've actually have that page saved in my DIY stuff already, but it's good to be reminded of it. I've wondered before how it would work to convert linear pots to rev-log for a 312-type circuit, and I'm actually about to resume converting some api 325 cards to 312's right now, so this is a great opportunity to try it out.
Peace,
JC
Thanks for the link. I've actually have that page saved in my DIY stuff already, but it's good to be reminded of it. I've wondered before how it would work to convert linear pots to rev-log for a 312-type circuit, and I'm actually about to resume converting some api 325 cards to 312's right now, so this is a great opportunity to try it out.
Peace,
JC
khstudio
Well-known member
I just fired this thing up & WOW. :shock: Very pure & phat. I think you can really feel the short signal path. I used the Yamaha Zoble - 2.7k/470pf paralleled with a 150k just before...
I went with no output cap. When I test for DC @ the input of the output tranny (+in to GND) I'm getting ZERO. Is this the right spot?
Thanks everybody for your help :green:
I'd like to run a sweep thru & see what it looks like but it does sound great + I'm not sure how to CORRECTLY set it up (The input that is - for the right impedence) :!:
I'll post a ruff schematic & the values I chose later, Got band practice...
kEVIN
I went with no output cap. When I test for DC @ the input of the output tranny (+in to GND) I'm getting ZERO. Is this the right spot?
Thanks everybody for your help :green:
I'd like to run a sweep thru & see what it looks like but it does sound great + I'm not sure how to CORRECTLY set it up (The input that is - for the right impedence) :!:
I'll post a ruff schematic & the values I chose later, Got band practice...
kEVIN
rafafredd
Well-known member
maybe... sometimes. But the fact is that I´m back on your thread. :?
Maybe I got words wrong, who knows. It just didn´t sounded nice when I read it... In a second look, it´s not so bad. It hapens once in a while. Maybe I was just a little tired this afternoon. Now I feel unpolite. Apologies.
But go on with your mic pre discussion, and I´ll keep out of the way with my trips. :thumb:
All and all, it´s good to know you have sonmething that works for you already. You are indeed fast.
khstudio
Well-known member
rafafredd,
It's all good :green: I'm the last person who wants to ruin somthing good.
rascalseven has been helping me with those M1516 channel strips. He's got some good idea's. I should post what he wrote me... I think it's very helpful.
I'm not kidding you guys, I'm very picky with tones & equipment, & as soon as I fired up the Yamaha/API pre, it was killer.
It's all good :green: I'm the last person who wants to ruin somthing good.
rascalseven has been helping me with those M1516 channel strips. He's got some good idea's. I should post what he wrote me... I think it's very helpful.
I'm not kidding you guys, I'm very picky with tones & equipment, & as soon as I fired up the Yamaha/API pre, it was killer.
khstudio
Well-known member
Any tips or good links on how I can test my new pre for accuracy & noise or overall gain?
I do have a scope. It's an old tube one. I'm still not that good at using one... gotta read up more on that one
I do have a scope. It's an old tube one. I'm still not that good at using one... gotta read up more on that one
mattmoogus
Well-known member
[quote author="khstudio"]Any tips or good links on how I can test my new pre for accuracy & noise or overall gain?
I do have a scope. It's an old tube one. I'm still not that good at using one... gotta read up more on that one[/quote]
Have you tested it with RMAA yet?
M
I do have a scope. It's an old tube one. I'm still not that good at using one... gotta read up more on that one
[/quote]Have you tested it with RMAA yet?
M
khstudio
Well-known member
[quote author="soundguy"][quote author="khstudio"]Any tips or good links on how I can test my new pre for accuracy & noise or overall gain?
[/quote]
listen to it?
dave[/quote]
Well it sounds great... just want to look at it just to see. I think I used an 18k in the feedback, if I up that to 22k the gain should increase right?
Also, With the same input tranny(as used on the PM2000) they show a 150k across the secondary, just before the Zobel... what does this do? I tried to remove it but it had a slight hiss & didn't sound as good.
MATT, I don't have an RMAA
Any second best choices?
[/quote]
listen to it?
dave[/quote]
Well it sounds great... just want to look at it just to see. I think I used an 18k in the feedback, if I up that to 22k the gain should increase right?
Also, With the same input tranny(as used on the PM2000) they show a 150k across the secondary, just before the Zobel... what does this do? I tried to remove it but it had a slight hiss & didn't sound as good.
MATT, I don't have an RMAA
Any second best choices?
khstudio
Well-known member
soundguy,
Your CAT stopped running on my screen... did it yesterday too :?
We gotta fix that :green:
kevin
Your CAT stopped running on my screen... did it yesterday too :?
We gotta fix that :green:
kevin
khstudio
Well-known member
Anybody :roll:
I'm ready to rack up 8 channels of these... I just want to make sure everythings cool. For such a simple pre this thing is blowing me away
BIG QUESTIONs :?:
How much current will I need for 8 channels of these +/- 24v rails & 48v Phantom? (No relays or extras, just 8x NE80200 discrete op-amps)
When checking for DC on the output tranny - Can I just take a reading across the primary of the OT?
How much DC is TOO much?
20k in the feedback - How high can you go... How can I determin the limit or sweet spot?
Also, With the same input tranny(as used on the PM2000) they show a 150k across the secondary, just before the Zobel... what does this do? I tried to remove it but it had a slight hiss & didn't sound as good.
BTW,
Thank you Joel
:guinness: :thumb:
I'm ready to rack up 8 channels of these... I just want to make sure everythings cool. For such a simple pre this thing is blowing me away
BIG QUESTIONs :?:
How much current will I need for 8 channels of these +/- 24v rails & 48v Phantom? (No relays or extras, just 8x NE80200 discrete op-amps)
When checking for DC on the output tranny - Can I just take a reading across the primary of the OT?
How much DC is TOO much?
20k in the feedback - How high can you go... How can I determin the limit or sweet spot?
Also, With the same input tranny(as used on the PM2000) they show a 150k across the secondary, just before the Zobel... what does this do? I tried to remove it but it had a slight hiss & didn't sound as good.
BTW,
Thank you Joel
:guinness: :thumb:
khstudio
Well-known member
Here it is :green:
The schematic shows the values I used (so far)
The schematic shows the values I used (so far)
[quote author="khstudio"]
How much current will I need for 8 channels of these +/- 24v rails & 48v Phantom? (No relays or extras, just 8x NE80200 discrete op-amps)[/quote]
if your multimeter measures current, put it in series between the amp and the power supply, make a reading, multiply by 8 and then build the power supply to provide maybe %25 more than you need.
use your ears. Put a pot in place of the resistor in the feedback loop. When you have so much gain that the amp oscillates then you know you've definitely gone too far. Most opamps Ive played with have a decreased bass response as you go to the outer limits of where they want to be. Each opamp is different so you have to listen. bummer.
it makes it sound good.
put it back?
dave
How much current will I need for 8 channels of these +/- 24v rails & 48v Phantom? (No relays or extras, just 8x NE80200 discrete op-amps)[/quote]
if your multimeter measures current, put it in series between the amp and the power supply, make a reading, multiply by 8 and then build the power supply to provide maybe %25 more than you need.
use your ears. Put a pot in place of the resistor in the feedback loop. When you have so much gain that the amp oscillates then you know you've definitely gone too far. Most opamps Ive played with have a decreased bass response as you go to the outer limits of where they want to be. Each opamp is different so you have to listen. bummer.
it makes it sound good.
put it back?
dave
3nity
Well-known member
looks interesting. Instead of racking those pm1000 or 2000 you used the parts for an API??
tell me how does they sound?? better to those yamaha channel strips??
did you ever heard one APi 312?? how do they sound against API??
Good work.....
tell me how does they sound?? better to those yamaha channel strips??
did you ever heard one APi 312?? how do they sound against API??
Good work.....
mattmoogus
Well-known member
If you have the net, you have RMAA - its a free download. Just google Rightmark Audio Analyzer. Its a great program, we use it every day.
You can use it to see whats going on when you do things like remove that 150k load resistor. Itll show you changes in the freq response and noise floor, and THD/IMD if there is any.
Before you test, be sure to tightly twist the wires from the input XLR and gain pot, in fact you probably want to use shielded cable for the gain pot. Also keep your input and output wires away from eachother if possible This help you get more gain out of the opamp before it starts oscillating.
This is what you use your CRO for - checking for HF ocillation when youre trying to find the max gain it can do in that layout. You probably should wait until you have a final layout and a case before you experiment with cranking the gain. Be careful with this as leaving the opamp osciallating for too long (sometimes even a short time) can kill it.
PSU - youll definitely need to put those regs on a decent heatsink (the side of the case) if youre going to run 8ch from it. Id also put some 100nF mono caps between each rail and ground right at the opamp.
AFAIK any DC in the output transformer is too much. If youre unsure use a 1000uF 10v cap.
3nity - I think its safe to say that once you take out the API opamp and transformers, its no longer an API pre. This is basically a first principals opamp circuit, so it takes the sound of whatever opamp you put in it.
Simple always sounds best!
M
You can use it to see whats going on when you do things like remove that 150k load resistor. Itll show you changes in the freq response and noise floor, and THD/IMD if there is any.
Before you test, be sure to tightly twist the wires from the input XLR and gain pot, in fact you probably want to use shielded cable for the gain pot. Also keep your input and output wires away from eachother if possible This help you get more gain out of the opamp before it starts oscillating.
This is what you use your CRO for - checking for HF ocillation when youre trying to find the max gain it can do in that layout. You probably should wait until you have a final layout and a case before you experiment with cranking the gain. Be careful with this as leaving the opamp osciallating for too long (sometimes even a short time) can kill it.
PSU - youll definitely need to put those regs on a decent heatsink (the side of the case) if youre going to run 8ch from it. Id also put some 100nF mono caps between each rail and ground right at the opamp.
AFAIK any DC in the output transformer is too much. If youre unsure use a 1000uF 10v cap.
3nity - I think its safe to say that once you take out the API opamp and transformers, its no longer an API pre. This is basically a first principals opamp circuit, so it takes the sound of whatever opamp you put in it.
Simple always sounds best!
M
[quote author="mattmoogus"]This is basically a first principals opamp circuit, so it takes the sound of whatever opamp you put in it.[/quote]
more people gotta realize that the entire api sound is that 2520 opamp. The transformers and supporting circuit are a very small part of the overall equation which is pretty much almost my exact opposite impression of most neve stuff.
dave
more people gotta realize that the entire api sound is that 2520 opamp. The transformers and supporting circuit are a very small part of the overall equation which is pretty much almost my exact opposite impression of most neve stuff.
dave
