mikefatom
Well-known member
ilfungo said:today I tried the API 312 in my studio ....
They sound so wonderful!!
I want to say thanks to all the forums and the people who helped me
in particular
Thanks Mike for your patience .....
You're welcome!
API 312 Thread!
- Thread starter fallout
- Start date
Help Support GroupDIY Audio Forum:
You're welcome!
bobschwenkler
Well-known member
I have an Excel sheet on my website for calculating amp gain. It allows for input and output transformer gains as well.
Bobschwenkler.com/312
It's the Gain Step Calculator link.
Bobschwenkler.com/312
It's the Gain Step Calculator link.
Piotr
Well-known member
Hi to all !
I'm building two API 312 using Bob's pcbs and EA transformers (EA2622 and EA 2503) and John Hardy's 990Cs.
I had a quick question regarding the Zobel network (C1-220pF and R5-10K according to Jeff).
Should I also solder the load resistor R4 specified on the BOM as being 100K or should I leave it out as it is in parallel with the Zobel ? Sorry if this subjects been tackled before, questions arise as the build goes on... I'll certainly have some more in the upcomming days.
Cheers from France. Piotr.
I'm building two API 312 using Bob's pcbs and EA transformers (EA2622 and EA 2503) and John Hardy's 990Cs.
I had a quick question regarding the Zobel network (C1-220pF and R5-10K according to Jeff).
Should I also solder the load resistor R4 specified on the BOM as being 100K or should I leave it out as it is in parallel with the Zobel ? Sorry if this subjects been tackled before, questions arise as the build goes on... I'll certainly have some more in the upcomming days.
Cheers from France. Piotr.
Piotr
Well-known member
By the way, after Bob's site migration, his site seems down, hopefully not for too long.
mikefatom
Well-known member
Piotr said:
Some people put it in, some people don't.
I install it in all my builds (with and without required Zobel network), and I've never had a problem.
Why not try both and see what you prefer?
Cheers,
Mike
You can go either way with it and see what you prefer. I send a 150K with my kits but have it marked as optional on my VP312 skiz.Piotr said:
You may want to have another DOA around to try. The 990c is a great opamp but does not really shine in a 312 circuit. Just my opinion anyhow.
Have fun!
Jeff
[Edit: Haha.
I see that I posted the same thing as Mike a few seconds later! I suppose I should have read the red note before actually posting! Oh well.]
bobschwenkler
Well-known member
Glad to hear you got it all running. Enjoy!
dalmaproductions
Well-known member
Having a hard time find measurements for the Access 312 boards. I need these for designing a front panel. Like spacing between the 3 front switches/buttons for example.
Does anyone here have these measurements? Or maybe a layout file/front panel express?
Miguel
Does anyone here have these measurements? Or maybe a layout file/front panel express?
Miguel
Piotr
Well-known member
Hi !
Thanks for the infos on the Zobel. Will try both solutions.
About the OpAmp, Jeff you mentionned that the 990C doesn't really shine in the 312 in your opinion.
I chose it as I'm using Bob's hybrid PCB and following his guidelines, thus I was trying to find an OpAmp operating with the +/- 24 V Bob uses in his design. What other OpAmps, using the +/- 24V, would you advise me to try that would fit Bob's board with a 312 circuit and your EA transformers ? I also bought two GAR2520s from you which I could use but I would need to drop the voltage to +/- 16V and that doesn't seem to be a good idea, is it ???...
All infos welcome !!! Thanks !!! Here's Bob's schematic:
Thanks for the infos on the Zobel. Will try both solutions.
About the OpAmp, Jeff you mentionned that the 990C doesn't really shine in the 312 in your opinion.
I chose it as I'm using Bob's hybrid PCB and following his guidelines, thus I was trying to find an OpAmp operating with the +/- 24 V Bob uses in his design. What other OpAmps, using the +/- 24V, would you advise me to try that would fit Bob's board with a 312 circuit and your EA transformers ? I also bought two GAR2520s from you which I could use but I would need to drop the voltage to +/- 16V and that doesn't seem to be a good idea, is it ???...
All infos welcome !!! Thanks !!! Here's Bob's schematic:
For +/- 24V, you could try Forsell, JLM or Pier. Check Pier's White Market Thread.
bobschwenkler
Well-known member
The preamp card itself isn't necessarily voltage specific. You should be able to run +/-16 or 17 volts into the supply rails for the amp stage with no problem.
Piotr
Well-known member
Hi,
thanks for the infos Jeff and Bob.
I get the fact that the board is not voltage specific as it includes only rail filtering caps if I understand the schematic correctly.
My question is more: is it a better idea to try and run the circuit from higher voltage rails (headroom etc...) or not. Since the 990C runs from +/- 12V to +/- 24V it should operate in both situations. Operating the circuit at either +/- 16V or +/- 24V leads to different OpAmps and that's what I'm curious about, as I have to choose.
I'm trying to learn as much as I can from those builds: which design options are available and where do they lead the circuit. Sorry if my questions are redundant or of a basic technical nature... That's the learning process !!!
Again, all inputs welcome. Cheers, Piotr.
thanks for the infos Jeff and Bob.
I get the fact that the board is not voltage specific as it includes only rail filtering caps if I understand the schematic correctly.
My question is more: is it a better idea to try and run the circuit from higher voltage rails (headroom etc...) or not. Since the 990C runs from +/- 12V to +/- 24V it should operate in both situations. Operating the circuit at either +/- 16V or +/- 24V leads to different OpAmps and that's what I'm curious about, as I have to choose.
I'm trying to learn as much as I can from those builds: which design options are available and where do they lead the circuit. Sorry if my questions are redundant or of a basic technical nature... That's the learning process !!!
Again, all inputs welcome. Cheers, Piotr.
bobschwenkler
Well-known member
You need a 2 pole switch to use an LED correctly with my boards. If you panel mount your switches this is an easy change to make. If you're mounting the switches on board it becomes a different thing. You might be able to wire an LED in series with the relay control voltage, and +48 this wouldn't be a good idea. You could also probably install a transistor switch in parallel with all of the supply lines for these functions. Again, +48 might have problems with this depending on how it's done but it should be possible.
scottlangendyk
Active member
- Joined
- Aug 25, 2010
- Messages
- 25
Anyone got any suggestions for adding a simple LED VU meter, or even at the very least, a signal/peak indicator?
I built a -20dB attenuator pad for the output so I can run my 312's nice and hot into the convertors on my interface, but now I'm even less certain as to whether or not I'm close to the clipping point on the 312's.
Thanks,
Scott
I built a -20dB attenuator pad for the output so I can run my 312's nice and hot into the convertors on my interface, but now I'm even less certain as to whether or not I'm close to the clipping point on the 312's.
Thanks,
Scott
Rybow
Well-known member
I remembered reading something a few (dozen?) pages back about load resistor values. I seem to remember reading that when using the EA 2622 that the load value should be 150k. On bob's boards it is listed as 100k, which I will use for the cinemag loaded channel. Do I have it right? I may be out to lunch on this one.
I have spent the last while flip flopping on what transformers to go with as I had planned to do just one channel, but I have decided just to build a 2 channel unit instead. I mean, why not right? One channel will be cinemag 75101/CMOQ 2L with a gar1731, and EA 2622/2503 with a gar2520 on the other. I also decided to get the attenuators from classic api for both channels to play with distortion sounds. Just playing the waiting game now. Come on Mr Postman!
I have spent the last while flip flopping on what transformers to go with as I had planned to do just one channel, but I have decided just to build a 2 channel unit instead. I mean, why not right? One channel will be cinemag 75101/CMOQ 2L with a gar1731, and EA 2622/2503 with a gar2520 on the other. I also decided to get the attenuators from classic api for both channels to play with distortion sounds. Just playing the waiting game now. Come on Mr Postman!
mitsos
Well-known member
- Joined
- May 4, 2007
- Messages
- 2,886
Check around here, there are quite a few possibilities. I think the sound skulptor site has schematics there and IIRC they have clip indicators for all their pres. I never ended up putting one on mine and it was only a "problem" once. I had a pair (I was experimenting with those rotary T-Pad attenuators) on drums that I, without thinking, put the gain way up and turned down the fader so as not to clip the converters... you can imagine what the wave looked like. In the end though, the drums sounded really cool and after that I guess I understand why people use those faders and have not wanted a clip LED again.scottlangendyk said:
to: Insomniac:
The cinemag uses 150K when in 1:10, and IIRC about 17K in 1:5, but double check the latter if you plan on 600 Ohm inputs. It shouldn't need a zobel.
The EA2622 needs a load and zobel, check the last few pages of this thread, someone probably asked recently, but jeff's webstore should probably have that info.
cheers!
bobschwenkler
Well-known member
Insomniaclown said:
The Cinemag CM-75101 does not require a Zobel network. Load resistor value depends on what impedance you want to end up with at the primaries and is affected by the winds ratio you jumper the transformer at. Impedance transfer is the ratio squared (I think, someone correct me if I remember incorrectly). 1:10 winding gives 1:100 impedance transfer. So if you jumper for 1:10, 100k at the secondary will give 1k on the primary. I built my BOM with 1:5 jumpering in mind. Looking at it now I suppose I made that value a bit high for what's normal or recommended, but 4k on the primary is working just fine for me here.
