Pads, what's the difference?

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bluebird

Well-known member
Joined
Jun 11, 2004
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1,070
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Is there anything wrong with using a pad like in the hamptone pre where it's basicly a resitor inline with the signal connected to a resistor to ground after the input transformer?

Or is it better to use the U or T type circuit before the input transformer like in the Jenson schematics?

I'm not really concerned with the input transformer taking a bit more. So it seems easier to build the hamptone type.
 
I was talking to scott about that last week. He does that because he likes to drive the input transformer close to an into saturation for second order harmonics I got a couple of his 1:8 transformers he is using in the jfet pre for some Quad Eight mic pre's I'm building

Wilebee
 
bluebird,

Don't forget that in a circuit such as the Hamptone pre, the transformer is providing voltage stepup/impedance transformation and balanced-to-unbalanced conversion. So the circuit after the transformer is unbalanced- the 0V rail is connected to one side of the winding.

The two-resistor "L" pad can be used after the transformer because it is an unbalanced attenuator. A pad placed before the primary would have to be a balanced "pi" or "h" type pad to keep the impedances equal in either leg of the circuit.

The only place you'd need a balanced-type pad after a transformer is if you were feeding a balanced push-pull type circuit. The two resistor L-Pad can be used in unbalanced circuits, and is basically just the same as a standard "Fader" type volume control.

:thumb:

Mark
 
bluebird-

in regards to something being "wrong" with scotts arrangement, you'd really need to check the spec of whatever input transformer you were planning on using when making a decision on where to put a pad. I can respect scott's idea, but that circuit as is provides sooo much distortion that I dont feel I need more from the input transformer, but thats just me, the circuit does sound good for that kind of thing. But that decision really depends on what kind of headroom your input transformers have and what kind of level your microhpones put out. I for instance cant use a 10468 input without a pad with most of my mics on any kind of drum or guitar cab. If you have high output tube mics, you arent talking about cool harmonics but a square wave in some cases, so having a pad BEFORE the transformer can, in certain scenarios, mean the difference between the pre being usable or not long before it becomes a question of taste on saturation. Some transformers are like the sound sponge that just seem to absorb whatever level you throw at them, while others sound awesome until they poop out and when youve reached the max level, you definitely DEFINITELY know it and having a pad on the secondary isnt gonna help too much if at all in those cases. But again, thats really dependant on the output of the mic and the source you have the mic on. You could always put the pad on the secondary and then use an inline pad built into a barrel connector or something for those circumstances when you need it if you like the idea of trying to get as much color as possible out of the input transformer. On a rock and roll session, until I get to vocals I have to pad almost everything...

dave
 
Thanks,

I'm putting together a discrete opamp micpre. It has a standard input transformer/input circuit. balanced to unbalanced.

so good, I'll just use the fader approach.

:grin:
 
Thanks dave,

I will take all that into consideration. The things that usally push my pres are the kick and snare with dynamic mics. I'm not sure about the input transformers I'm using, as far as what thay can take. I'm using them on the G9 I built and I have never had to use the pad on that pre.

I just dont happen to have the correct switch to do and H type pad with me. I'm just being lazy I guess.

Theres always a point in a project when you just want things to start working, and thats when mistakes are made.

So thanks for all the great info...
 
Fletcher wrote some good things on the Schure pad, transparent and all that.
Don't know where to get one, maybe evilbay.


from http://www.mercenary.com/readguidtovi.html

The Shure variable pad is about as sonically transparent as I have ever encountered. It is an inexpensive and indispensable tool. I highly recommend that everyone in this industry own at least four of them. You will need these when using V-78 modules because their input gain is so high. (No, I'm not a Shure endorser.)

I'll be soldering a few myself since all this stuff is less easy to get here. And thanks to the tip here (well, at the old place) for using 2 XLRs with those 2-screw fastening for a compact casing it'll be easy. I'm thinking about a single setting of 14 dB.

FWIW,

Peter (wannabe)
 
[quote author="clintrubber"]And thanks to the tip here (well, at the old place) for using 2 XLRs with those 2-screw fastening for a compact casing it'll be easy. I'm thinking about a single setting of 14 dB.

FWIW,

Peter (wannabe)[/quote]

please elaborate on this tip! i'm hoping to do this myself.
 
Hi,

A picture would explain it all right away but since I don't have one here right now I'll do my best. You know those XLR-3 connectors that use a small 'bridge' to fasten the rubber end at the cable entry ? That separate bridge is fastened with two small screws. Take two such connectors (one M, one F) and connect them using two of the now four available screws. So you don't use the bridge of each. Should be enough room to put three or four resistors in.

HTH, bye,

Peter (wannabe)
 
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