TAP System FAQ
I've read the overview and am still confused
Having so many parts and module options is great but it also can lead to confusion. If you are building a pre-amp and would like to add remote control give me an e-mail or call. Together we can quickly see if either the TAP system or a more tranditional attenuator like an ALPS pot or a Stepped attenuator might suit your project plans.
Even though they are 100% passive devices Autofomers 'look' in many respects like an active pre-amp. They present a nice easy load for your sources to drive while at the same having a nice low output impedance to drive cables and amps downstream. It's all due to the way they 'translate' the impedances. As you lower the level on a traditional resistor attenuator (any potentiometer, stepped attenuator, LDR, etc) you are simply throwing away the signal you don't want and passing what you do want out of the device at that lower level. With an Autofomer as you turn the volume down the excess voltage is turned into potential current (the ability to drive) at the output. This is much like the way the power company sends high voltage power along big power lines then 'kicks it down' to the lower voltage we use in our houses. Imagine if they simply tossed out that excess power... The Autoformer Volume Control makes use of that extra potential current to drive the cables and amp inputs (or even headphones - see below). This impedance 'kick' along with the VERY simple and clean signal path (it is simply a coil of wire) account for it's extraordinary sonic abilities.
Autoformers vs. Transformers?
An Autoformer (AVC) is a single coil of wire wound on a core material. A Transformer (TVC) is made up of two coils of wire wound on a core material - with the signal 'jumping' from the primary coil to the secondary coil. Both Autofomers and TVC's make use of the impedance translation mechanism mentioned above. Just like all tubes or all planar speakers don't sound alike all autoformers and all tvc's don't sound alike either. I've heard fine sounding examples of both Autoformers and TVC's and two different AVC's (or two different TVC's) are likely to sound different. Many other design aspects such as coil winding geometry and core materials come into play.
Why this particular Autoformer
I was on the lookout for a new device some years back when I heard and fell in love with the sound of the Autoformer made by Dave Slagle of www.intactaudio.com. It's this unit that together we packaged up to create the Slagleformer used in the TAP System and in the AVC-1 Pre-amp Parts Package.
Can I drive headphones direct from Autoformers?
This works surprisingly well. The idea here is to run straight from your source to the AVC pre-amp and then out to the headphones with no additional circuits (buffers or gain stages) in the signal path. I had a customer (with fairly hard to drive Grado headphones) who tried it as a test and was very excited by the results so I gave it a go here. I am using 2 different headphones - nominal 300 ohm Sennheiser HD800 headphones and rather difficult to drive 25 Ohm Fostex headphones. Testing on the bench indicated that it would work well but I was shocked to find just how good it was. This is really making use of that impedance translation talked about above - the way the autoformers turn that unused voltage into current drive is what saves the day. In the case of the Fostex almost no sources would drive them if connected directly but with the help of the autoformers in-line they work wonderfully.
There is one gotcha that can get in the way of this working. If your source is very low in output voltage or high in impedance then it might not give good results - especially if at the same time the headphones are both inefficient and low impedance. Some planar headphones fall into this category - an extreme example of this is the AKG 1000 headphones that were designed for amp connection but I am guessing that some of the new planars like the (very good from what I understand) Audeze would be tough to optimize. At some point it is just to much to ask - kinda like connecting your speakers up directly to the pre-amp would be. In the case of the HD800 it is not the most efficient headphone but thankfully it is also not a low (hard to drive) impedance. In my system I typically have the levels set between 40 and 50 when listening. The much harder to drive 25 ohm fostex are more efficient and as a result I turn the level down a bit more (getting more and more ability to drive from the autofofmer impedance lowering action) and in this case tend to be between 30 and 40 or so level wise. If you are thinking of giving it a go please do e-mail or call and I would be happy to review your system to see if it is likely to work out.
Why even offer the Hybrid Resistor Modules?
As Mentioned in our Tap Overview page there are times when the Hybrid Resistor Modules might be the best choice. Specifically this is when the either the budget or the enclosure can not fit the Slaglefomrmers. In thhose cases the Hybrid Modules are a fine way to go. If you have space and can afford them the Slagleformers are the preferred attenuation choice - especially so in an all passive pre-amp design.
How do the Parts in the TAP system connect up?
Audio signal path connections should be made with good quality wire carefully soldered to the connection points at each module. The control system connections are made along an included ribbon cable - the 'Bent Buss'. This included cable can be made up once your parts are mounted in place by sliding the crimp on connectors onto the ribbon cable (all facing the same way) then crimping them onto the cable (with channel lock pliers or a similar tool). This method makes for cleanest routing since the lengths can be set exactly to fit the parts layout in the cabinet. Alternately I am happy to make these cables up here if you send a list of the distances needed between connection points. The AVC-1 Pre-amp Parts Pack ships with this cable pre-installed. Note that there is no 'order' to these connections - the cable can connect up from module to module in any way that suits the chassis layout.
Can the TAP System Run Fully Balanced?
I use a fully balanced Slagleformer based pre-amp here myself and it works wonderfully. The modular nature of the TAP system makes it easy to setup a fully balanced system. Simply include 2 additional Slagleformer (or Hybrid Resistor) modules and you now have a fully balanced attenuator. This is much like going from 2 decks to 4 decks on a stepped attenuator. Also the input selector pcb's are easy to setup for balanced operation. If you are building an AVC-1 Slagleformer based pre-amp I do have some back plates here that can include 2 balanced inputs and 2 balanced outputs - please send an e-mail or call to discuss options that fit your exact requirements.
Can The TAP System Mix RCA and XLR Connections?
Yes - but I like to be sure that the system is optimized and that you are not wasting $ on the extra parts needed if the system does not really benefit from it. There are several ways that OEM and DIY pre-amp builders include balanced connections in their products. All these options are ok as long as the end user understands just what is implemented. So much of the time I fear that when this is not well understood the result could be wasteful - spending $$$ to make use of balanced connections when the system as a whole does not benefit. Note that I have nothing against balanced connections - as mentioned above I run my system that way here myself.
Here are two of the more common ways to MIX RCA and XLR connections along with a few notes on each:
Install XLR and RCA connectors but run only single ended (RCA) circuits inside
If the internal circuits of the pre-amp are by design single ended but users want to connect up gear that might only have XLR connections this is a handy way to do it - BUT it does not make any use at all of the XLR source(s) or amp. In a pre-amp wired like this just the PIN2 (hot) and PIN1 (gnd) side of the XLR connection is used and the PIN3 side is not used (no pin3 connection at the XLR input / grounding pin3 at the XLR output). The plus to this is that it is really cheap to implement. Also it does save the user from inserting RCA/XLR converters into the signal path. The troubling downside with this is that if the user does not understand what is actually being connected internally they might spend extra $$$ specifically for an XLR source, XLR pre-amp, or XLR amp not knowing that one component in the chain is simply throwing away 1/2 of the balanced signal. It likely will sound great but the extra $ spent to go balanced connections when the source OR pre-amp OR amp run this way are completely wasted..... All 3 need to be implemented internally with fully balanced circuits to get the benefits.
Install both XLR and RCA connectors and use fully balanced circuits inside
This works well and is what I do here in my listening room. When using 4 Slagleformer modules the XLR inputs and XLR output signal path is fully balanced in every way. An example of this kind of build can be found by clicking HERE . When an RCA input is selected the input switching routes the hot(+) from the RCA jack to the pin2 side of the internal circuits and then usually grounds the pin3 side of the internal circuits. This is not specific to the TAP system - many balanced pre-amps run just this way. This setup is perfect when your amp likes to run balanced AND you have a source or two that are best run balanced as well but also need to mix in some RCA sources. Note that if you use the RCA output in this setup you make no use at all of the extra modules. Note also that not all amps and sources with XLR jacks installed are best used in that mode. This is especially true when it comes to amps. Some amps might include a balanced connector but really only use the pin2 side of that connection (the internal circuits are single ended) thus making no use of the balanced circuits in the pre-amp or the source(s). Worse yet (because you actually loose out sonically) some amps not using balanced circuits throughout include extra 'stuff' in the signal path to make the conversion from balanced to single ended - meaning a direct connection to the RCA jack would almost certainly be a better way to go. Here are some guidelines to use when checking if this configuration fits for your system:
Please e-mail or call with any TAP system configuration questions. I'm happy to work with customers to be certain they end up with the very best solution to fit each project.