peter purpose
Well-known member
Heres how I do mine.
API 325 to 312...help please.
- Thread starter furmound
- Start date
Help Support GroupDIY Audio Forum:
peter-
looking at the schem you posted with your notes, have you noticed a big difference with removing c4 and r4? Looks like that cap is just there to buffer the unbalaced out, kinda stupid to have put it in series with the output transformer...
dave
looking at the schem you posted with your notes, have you noticed a big difference with removing c4 and r4? Looks like that cap is just there to buffer the unbalaced out, kinda stupid to have put it in series with the output transformer...
dave
peter purpose
Well-known member
Hi Dave,
I have always left them out as per Justin's instructions, so have never listened to them with the extras.
What I did do was add a 75ohm resistor in series with the unbalanced output on the edge connector to protect the 2520.
peter
I have always left them out as per Justin's instructions, so have never listened to them with the extras.
What I did do was add a 75ohm resistor in series with the unbalanced output on the edge connector to protect the 2520.
peter
furmound
Active member
Those pcb's sure look good with everything integrated in them. What's the advantage of using relays? Is it for shorter cable runs? If I don't use relays for switching and do stuff off of switches on the front plate is there noticable degradation of sound?
Just wondering, C4 and R4 are the ones that I was supposed to replace with jumpers right? What are you protecting the 2520 from with the 75 ohm resistor? Should I do that too?
Are there any other mods on that red-penned schematic that are specific to the jensen transformer that you used only, and that do not pertain to my setup?
Just wondering, C4 and R4 are the ones that I was supposed to replace with jumpers right? What are you protecting the 2520 from with the 75 ohm resistor? Should I do that too?
Are there any other mods on that red-penned schematic that are specific to the jensen transformer that you used only, and that do not pertain to my setup?
well, curiosity killed the cat tonight.
I have the luxury of a few extra 325 cards, so I stuffed a few following the reccomended changes on the schem peter posted. You definitley want to lose that output coupling cap, makes a huge huge difference. That didnt come as much of a suprise. Going way up in value on C1, C2 and C3 however was a shocker. Soundstage got WAY bigger AND the output level of the amp increased as well with no bad artifacts. These mods were compared against cards that had been recapped with the same cap type just in the stock values (not comparing a recapped card with an old rotted antique). If you've built these circuits, try out those values for those three caps, Im really glad I took the time to do so.
I was prety excited about my mixer, now I cant wait to install these changes.
dave
I have the luxury of a few extra 325 cards, so I stuffed a few following the reccomended changes on the schem peter posted. You definitley want to lose that output coupling cap, makes a huge huge difference. That didnt come as much of a suprise. Going way up in value on C1, C2 and C3 however was a shocker. Soundstage got WAY bigger AND the output level of the amp increased as well with no bad artifacts. These mods were compared against cards that had been recapped with the same cap type just in the stock values (not comparing a recapped card with an old rotted antique). If you've built these circuits, try out those values for those three caps, Im really glad I took the time to do so.
I was prety excited about my mixer, now I cant wait to install these changes.
dave
furmound
Active member
Thanks for testing it out Dave! I built them as specified by Peter so I'm psyched! What mixer do you have(did you make)?
Sammas
Well-known member
[quote author="soundguy"]I made (am making) and 8x2 with 312 and 325 circuits.
dave[/quote]
Oh do share! I've been considering something like this for a while...
Have you modded the 312's for line level input or are you just using it to sum mic level signals?
dave[/quote]
Oh do share! I've been considering something like this for a while...
Have you modded the 312's for line level input or are you just using it to sum mic level signals?
man, every single step of this mixer has been designed with help from people up here, if you search, all the info is there. I'll post some photos when I finally screw the lid on, Im really happy with the way its come out so far. 312's for input channels, 325's for the summing buss.
dave
dave
You can solder right to the board to eliminate any vibration mode failures. (some of these clowns behind the glass really like to crank up those monitors after a few hits off the crack pipe, which is why i stay away from that part of the industry :razz: )
I snagged these cards from somebody, left in the old dried up caps, wired it with some Cinemags innies from Winston, and was good to go. That custom nickel transformer on the right did not make a bit of difference, so don't waste your time or money on anything but the stock M6 2503. heck, look at Peter, running that opamp striaght into the primary, a man of my heart!
:thumb:
I snagged these cards from somebody, left in the old dried up caps, wired it with some Cinemags innies from Winston, and was good to go. That custom nickel transformer on the right did not make a bit of difference, so don't waste your time or money on anything but the stock M6 2503. heck, look at Peter, running that opamp striaght into the primary, a man of my heart!
:thumb:
peter purpose
Well-known member
I aim to please Chris.
fur,
>>What's the advantage of using relays? Is it for shorter cable runs?
Yes. No wiring running all over the box, plus sealed switches.
>>If I don't use relays for switching and do stuff off of switches on the front plate is there noticable degradation of sound?
If you use good shielded cable and route them efficiently, then I can't see a problem.
>>C4 and R4 are the ones that I was supposed to replace with jumpers right?
Right.
>>What are you protecting the 2520 from with the 75 ohm resistor? Should I do that too?
That resistor is only required if you are planning on having an unbalanced output to go with your transformer out. The 2520 has enough grunt to drive them both at the same time. The resistor is there to protect the 2520 from an accidental short.
>>Are there any other mods on that red-penned schematic that are specific to the jensen?
Nope.
fur,
>>What's the advantage of using relays? Is it for shorter cable runs?
Yes. No wiring running all over the box, plus sealed switches.
>>If I don't use relays for switching and do stuff off of switches on the front plate is there noticable degradation of sound?
If you use good shielded cable and route them efficiently, then I can't see a problem.
>>C4 and R4 are the ones that I was supposed to replace with jumpers right?
Right.
>>What are you protecting the 2520 from with the 75 ohm resistor? Should I do that too?
That resistor is only required if you are planning on having an unbalanced output to go with your transformer out. The 2520 has enough grunt to drive them both at the same time. The resistor is there to protect the 2520 from an accidental short.
>>Are there any other mods on that red-penned schematic that are specific to the jensen?
Nope.
peter purpose
Well-known member
Dave,
Glad you like those mods. They were recommended by Dan Kennedy.
peter
Glad you like those mods. They were recommended by Dan Kennedy.
peter
Mike Keith
Well-known member
I would tie the 3 secondary taps in series(2503) for 9db more gain and it sounds better, imho.
If it was me I would leave the 470uf output cap in...
The pre I build I put a .47uf polyprop. in parallel with the 470uf, improves the HF transients.
Just a thought....
If it was me I would leave the 470uf output cap in...
The pre I build I put a .47uf polyprop. in parallel with the 470uf, improves the HF transients.
Just a thought....
furmound
Active member
Thanks for the responses. A lot of useful info. I'm focusing on making a test rig to see if all my eight cards work (fingers crossed). After finding this out I will start figuring in some of these options that you have all suggested.
Padding the output to drive the 2520 sounds interesting yet dangerous. Could this not damage them?
Tying the secondary taps for 9db more gain sounds wonderful but will this change the carachteristics of the sound at all? Mike Keith, specifically what do you mean by "improves the HF transients." (softens harsh ones, recreates them more accurately and faster...)
I'm interested in sound variety, and since I have a few of these cards, I can try some of these modifications on some and not on others. I do want a couple channels to resemble the originals as much as possible though. Which is where the BC series caps that Dave mentioned come in I guess.
Anyway, I'm still trying to figure out the pad/phase/phantom power section of this so I think I may be getting ahead of myself. There's is much useful information on padding and phantom power in the reference section of this forum. I'm just trying to sift through it and figure out how I can incorporate this into my project.
I've ordered C6 (120pf) twice from digikey and both times I got those practically microscopic surface mount things. This one cap has costed me over $20 ($5 packaging fee three times thus far.) This is undoubtedly my fault so I went to my local radio shack and they only had a ceramic disc 100pf. Will this do in the meantime for my test rig? Or will everything explode? I'll order the correct C6 again with a larger order for my SSL comp or something.
Thanks again.
Padding the output to drive the 2520 sounds interesting yet dangerous. Could this not damage them?
Tying the secondary taps for 9db more gain sounds wonderful but will this change the carachteristics of the sound at all? Mike Keith, specifically what do you mean by "improves the HF transients." (softens harsh ones, recreates them more accurately and faster...)
I'm interested in sound variety, and since I have a few of these cards, I can try some of these modifications on some and not on others. I do want a couple channels to resemble the originals as much as possible though. Which is where the BC series caps that Dave mentioned come in I guess.
Anyway, I'm still trying to figure out the pad/phase/phantom power section of this so I think I may be getting ahead of myself. There's is much useful information on padding and phantom power in the reference section of this forum. I'm just trying to sift through it and figure out how I can incorporate this into my project.
I've ordered C6 (120pf) twice from digikey and both times I got those practically microscopic surface mount things. This one cap has costed me over $20 ($5 packaging fee three times thus far.) This is undoubtedly my fault so I went to my local radio shack and they only had a ceramic disc 100pf. Will this do in the meantime for my test rig? Or will everything explode? I'll order the correct C6 again with a larger order for my SSL comp or something.
Thanks again.
peter purpose
Well-known member
Come on fur, I thought you'd have at least a pair up and running by now..!!
>>Padding the output to drive the 2520 sounds interesting yet dangerous. Could this not damage them?
No
>>Tying the secondary taps for 9db more gain sounds wonderful but will this change the carachteristics of the sound at all?
It'll change the output impedance as well as giving you more grunt.
The nicest pair that I've built had a Marinair 1447 1:4 on the front, with 2503 running 1:3 on the out.
peter
>>Padding the output to drive the 2520 sounds interesting yet dangerous. Could this not damage them?
No
>>Tying the secondary taps for 9db more gain sounds wonderful but will this change the carachteristics of the sound at all?
It'll change the output impedance as well as giving you more grunt.
The nicest pair that I've built had a Marinair 1447 1:4 on the front, with 2503 running 1:3 on the out.
peter
Mike Keith
Well-known member
The is the part # for Digikey 120pf Polyprop. P3121
Same cap as what API, JMK Audio and others use (Type not value)
FWIW
Same cap as what API, JMK Audio and others use (Type not value)
FWIW
furmound
Active member
I know, I know Peter...but slow and easy wins the race-I hope! After I find out how many cards work, I gotta figure out the phantom/phase/pad section and then how to build a card cage and so on...so I've got a ways to go.
So I take it that I should not use a 100pf cap for C6 just to check if the cards work. Bummer. Here I go again digikey.
Thanks for the part number Mike. I've certainly had enough of ordering the wrong cap time and time again.
I've read up on pads and phantom power here and it seems like a "U" pad is what I'm going to go for. I think I'm beginning to understand the "U" pad and some phantom power schemes separately but i'm confused about how they interact together. The phantom resistors must come before the pad stuff, right? If not my pad will pad the phantom power, right? I just don't want to burn my precious cards.
So I take it that I should not use a 100pf cap for C6 just to check if the cards work. Bummer. Here I go again digikey.
Thanks for the part number Mike. I've certainly had enough of ordering the wrong cap time and time again.
I've read up on pads and phantom power here and it seems like a "U" pad is what I'm going to go for. I think I'm beginning to understand the "U" pad and some phantom power schemes separately but i'm confused about how they interact together. The phantom resistors must come before the pad stuff, right? If not my pad will pad the phantom power, right? I just don't want to burn my precious cards.
using a 100pf cap for C6 should be totally fine, the 312 used a 120pf, the 325 used 47pf with a different feedback resistor. You are most likley not to damage the opamp and to be honest, you might not even hear a difference if the opamp is stable.
before you do anything, sleep with this schematic under your pillow for a few nights:
http://www.jensentransformers.com/as/as016.pdf
That is thhe basic input circuit that many many many people are using and you can purchase prefab boards from different people to achieve similar results, if not the exact circuit. this is very simple to wire on perf though and you dont need to use powered relays if you dont want to. Yes, it makes sense on paper but if you are mounting the board inside a shielded chasis, the extra wire run in the box is probably not the end of the world and regular switches with audio running through them are good for years before getting noisy, usually. Relays are expensive and they require power, so its a little more complicated. Ive built many boxes both ways and theres not much difference I can tell coming out the speakers when the record is mixed.
that schem should answer all your questions, but the phantom circuit does come before the pad.
I have a card cage I took off an API console with edge connectors, Im never going to use it, PM me if you can use it.
dave
before you do anything, sleep with this schematic under your pillow for a few nights:
http://www.jensentransformers.com/as/as016.pdf
That is thhe basic input circuit that many many many people are using and you can purchase prefab boards from different people to achieve similar results, if not the exact circuit. this is very simple to wire on perf though and you dont need to use powered relays if you dont want to. Yes, it makes sense on paper but if you are mounting the board inside a shielded chasis, the extra wire run in the box is probably not the end of the world and regular switches with audio running through them are good for years before getting noisy, usually. Relays are expensive and they require power, so its a little more complicated. Ive built many boxes both ways and theres not much difference I can tell coming out the speakers when the record is mixed.
that schem should answer all your questions, but the phantom circuit does come before the pad.
I have a card cage I took off an API console with edge connectors, Im never going to use it, PM me if you can use it.
dave
