Calrec PQ 1061

[JustinS]

I'm in for a 2/3 position high-pass filter - great when tracking. I don't really use low-pass filters except creatively & then there are other units I'd use over this one... Great work with the gain switching Tom, very cool!

Justin

 

[JustinS]

Also Tom - open up the image in an image editing program ie PaintShop Pro, its so much quicker to navigate around the schematic than in the MS image viewer!

Justin.

 

[BuzAllen]

I completely agree on the 'stock' not being necesary. On that note I know it has been discussed some before but if we reduce the gain positions to 12 in an effort to make the switch easier to get, what range should we go with. I know I probably will never need 70db of gain (the circuit actually has more gain than that, if the 'fader' labled output on the Averill unit is up it is an additional 6db of gain. That brings up another question. Do we include the 'fader', oddly I do see this part of the ciruit in the schematic, but there are pins for it on the unit.

So anyway what do you all think, stick with 5db steps? 5-60db? That sounds practical to me.

Brian

 

[cannikin]

"stick with 5db steps? 5-60db? That sounds practical to me"

Sounds good to me.

 

[soundguy]

I would suggest that if the gain is there, we should use it. I would want a fader regardless of where the steps are, so Id say use the full available gain range with the most practical steps available based upon which ever switch we can decide upon for availability. I would say coarser steps to full available gain with a fader.

dave

 

[TomWaterman]

[quote author="JustinS"]... Great work with the gain switching Tom, very cool![/quote]

Wasn't me dude! Be thanking Brian for that!
:guinness:

[EDIT] oh and thanks for the image tip. When I'm on my machine I use fotoshop but I'm on the net laptop at the mo - so no PSPro or PShop...

-Tom :grin:

Oh and interms of gain. If we could do 6dB steps with +/-6dB fader then we could get up to 70dB of gain on a 12pos switch. Should be enough for ribbons and the like....

 

[BuzAllen]

You know Dave, that is a good point. It begs some more questions. I don't want to get to crazy here, but the 80 db range it has requires the incorporation of the TX tap switch. The second tap provide about 10db reduction from the the first (as well as an input impedance change) If we kept the gain stage switching the same and just broke it with greater steps (it comes to about 7db).

If the TX tap switch is separate it actually allows even greater gain range and maybe it might be interesting to be able to have the TX in the 'line' tap position and use more gain from the active stage or visa versa of that. Simply from a 'more sounds' point of view.

If we look at just the active stage (post TX) it can provide 60db of gain. The extra 10 on the high end comes from the TX and the extra 10 on the low side comes from a post first gain stage pad. Lots of options here. Not to mention that on the working unit I have there is 6db from a post fader amp.

One option might be to have the gain stage give us the 60db of gain in 5 db steps and have a switch for the TX (giving us the extra 10db or not) and also have the pad switchable instead of in the primary switch (this would eliminate extra postions as the pad is incorporated into the primary gain switch).

Make any sense at all?

Brian

 

[soundguy]

thats a lot to digest. I think we need to take this back a few pages and instead of build it into something, we should identify the confines we are working with and work backwards from that.

First off, it should fit in a single space box. Thats what, 17" or less of usable mounting space for switches?

Second, we should be thinking of lorlin switches. they are big and they are shitty but they are cheap and available to pretty much everyone reading here. Thats important.

third, we should be thinking about appropriate available input transformers, might make more sense to use something easy to get and just stick a line pad infront of it for a line input instead of trying to source a multitapped transformer.

I think its real important to think about getting this practical vs. getting it awesome. If that means 60dB of gain only, thats cool. If we can squeeze all the available stable gain out of the circuit with the above in mind, lets see whats involved.

dave

 

[TomWaterman]

Hey Buz does the switch in the TX for extra gain not change the impedance as well? Mic/line thing...

I really should be writing my paper :shock:

-Tom

 

[BuzAllen]

Yes tom, it does change the impedance. If it is 1:3 change in gain I believe it is then a 1:9 change in impedance. I'm not that well versed of transformers though.

Here are my thoughts. I promise they will be less confusing this time.

Agreed 1 space rack, here is a leyout I think will be both about as simple (and therefore cheap as well as provide gain/versatility at all that)

48V switch - SPST toggle
Pre TX pad switch - 10db or so - DPDT toggle
TX tap switch - DPDT toggle

Gain switch - 12 position lorlin (5.45 db steps 0-60db)
Trim pot - 5-6db of trim post gain.

Eliminate the HPF and LPF (simplifies this alot)
Use 6 Position Lorlins for the freq select on HF and LF
Use 12 Position Lorlin for the mid select.

Use three generic pots for the eq gain.
Use a simple 10K pot for the output level.

This gives the same 80db gain range but eliminates the need for a 3-deck switch and eliminate any switch being greater than 12 position.

It still will be a complex circuit, there is a lot of switching going on in the EQ, but doable.

As dave said, we ddo need to figure out the input transformer as well. If it is difficult through sowter, maybe Cinamg can do it. I know Ken Hirsch had them recreate the Quad8 3440 TX and I have a couple of those and they are great.

Brian

 

[soundguy]

If there is a fader for the output of the circuit a fine trim gain pot is redundant IMO. I could see it if maybe there was an interstage transformer before the EQ, but in this circuit it seems redundant to me. Trying to trim the fat, Id say go with either an output fader (which would be best assuming there is gain from the EQ) or go with a trim pot in the preamp gain and use that to counter the EQ gain. Id prefer it post.

dave

 

[BuzAllen]

Possible switch problem. Are the Lorlin switches available in 2 decks? The switches for the calrec need to be. I assumed they would be then I realized I had only seem them single pole.

Brian

 

[JustinS]

Maybe a phase switch as well?? I'd still like a HPF filter if possible...

Oops, yeah thanks Brian for the gain switch calculating.

Justin

 

[TomWaterman]

Good thoughts Brian.

There should be no trouble with Sowter doing the TX. Brian said he could do a run, the prices he gave me are a few pages back. If we do a group buy the price will come down to about 30quid, maybe $40 taking into account no VAT for US customers. I'm planing on an 8 pack for primary recording duties...

I think the original TX is a must - I know 'inspired by' is good but we want to keep it as close to the sound/vibe of the original as poss. If peeps want to build a pre with input iron choices there are loads available - Project2, JLM etc.

Sowter mentioned he can do the inductors no trouble at all, although Cinemag may well be cheaper. He did say it was quite a pricy thing using their custom shop. I'd be guessing about 40 pounds for the inductor.

Either way iron is expensive in this module, maybe close to 100 dollars/pounds per channel....still cheaper than a neve pre/eq.

Maybe its possible to add a more simple HP filter in between the gain stages for the sake of usefulness?

I like the idea of an output fader, if not needed I presume a resistor can be soldered in place.

There is phase and insert switching to be left/implemented plus EQ in/out as well - or do people not want these.

Concerning the TX tap switch - what was the actual point again? How does that and the pad prior to the TX affect the mic/line switching? I'm confused, tired and I've written fu*k all for uni!

I will contact Sowter again at some point and ask about output TXs as well. We have a number from one of peterpurposes fotos. So he should be able to give us some spec details. If anything the one place where iron can be experimented with, is the output. Maybe the new JLM, a Jensen, Lundahl or Sowter.

-Tom

 

[TomWaterman]

Oh yeah I was wondering about the lorlins!

I don't think they do 2 deck switches that are easily available.

The next option for cheapness is the NSF modular range, available at Farnell.
After that its greyhills I think....

-Tom

 

[BuzAllen]

The reason I thought about throwing a pad switch in from is simply so one could leave the TX in the mic position and still have a pad if required. The way the unit works as is, there is no pad really just a combination of tx taps and gain. The unit basically assumes that when you need less than 20db of gain you are hooking up a line input (that is where the switch automatically switches the taps). Since we want to avoid a 3 deck switch, using a simple toggle prior to the tx eliminates the complex rotary.

The additional padding in the unit is actually done post the first gain stage. If you look at the excel chart or html file you'll see the last two positions have a different value than 1 for the 'line pad' column, This is the result of a divider after the first active gain stage. It is also part of the primary gain switch. To eliminate this I thought we could just use a traditional pad in front of everything. Probably not necesary though. Could be an option. For a line input we could just include an insert switch and one could plug into the EQ directly. I remember we talked about this a while back.

If it was just going to be used as a pre and line inputs would be left to the insert point then there might not be a need to switch the tx but it only requires a dtdt switch and then gives our unit the same possible configurations as the original, just throught different means.

Brian

Write your paper Tom!

 

[John Hardy]

I'm not following the discussion, but to clarify someone's earlier comment:

The output transformer that I use in my preamps is the Jensen JT-11-BMQ, essentially the same as the JT-11-BMCF, and it is a bi-filar wound transformer. Thank you.

John Hardy
The John Hardy Co.
www.johnhardyco.com

 

[TomWaterman]

Ahh thanks for the clarification John, there are many Jensens with similar names its easy to forget which is which!

Incidently, any idea what the BMCF/BMQ stands for?

Cheers Tom

 

[John Hardy]

Incidently, any idea what the BMCF/BMQ stands for?

Yes and no. The "CF" stand for "Channel Frame", the steel frame that surrounds the laminations and has the two tabs for bolting the transformer to a chassis or p.c. board.

The "Q" originally stood for "Quadfilar" when Deane Jensen tried a quadfilar version of the standard "JE-11-BM" transformer. But eventually it was changed back to bifilar winding. BUT, the quadfilar version had slightly different DC resistance, so the bifilar version is wound to have the same specs as the quadfilar version. There is more to the story than that, and it was explained in great detail by Steve Hogan, formerly of Jensen Transformers. Here is a link to the thread in another Prodigy discussion where Steve explained it:

http://www.groupdiy.com/index.php?topic=5439&postdays=0&postorder=asc&start=30

Scroll down to Steve's post that starts with "I have enjoyed interacting with you all --Thank you for your kind comments." Thanks.

John Hardy
The John Hardy Co.
www.johnhardyco.com

 

[TomWaterman]

Superb John, thank you very much.

-Tom