Custom Bent Units

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Robin Hood

Custom Bent Units
« on: 17 Sep 2008, 11:14 pm »
John - your website states that the Autoformer will perform better than the resistor passive and that you offer custom Autoformer Bent Units.  How do the Resistor Passive and Autoformer Bent Units compare sonically and what is the price difference for your standard and custom Autoformer Bent Units?

John Chapman

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Re: Custom Bent Units
« Reply #1 on: 19 Sep 2008, 06:32 pm »
Hello!

Good to finally get a message from Robin Hood. Sorry for the delayed reply.....

There are so many combinations of the TAP parts that I tried to just pick a few of them for the new web page - and still I fear it is confusing for folks - sorry about that guys!

With the resistor passives it is vital for best performance to get the resistor modules as close as you can to your amp inputs. The Bent Unit concept started about 10 years back to solve that issue - placing the unit right at the amp inputs.

The the transformers and autoformers came along and that aspect of the passive changed. The way these devices lower output impedance no longer makes it important to place them like a bent unit - although they work fine that way. I am using a MicroTAP Controller and 2 autoformer Bent Units in my system right now. Nice and clean for a single source system from the important signal path point of view - but then with the fiber optic cables to connect it all up it's not as simple overall as just plunking down a one box single input TAP-X and as described below it's a bit more expensive way to go. 

The above notes I hope help to explain why I did not list the Autoformer Bent Units as a separate item. The only case for using them would be if your system layout was such that separating the display unit (controller) out let you locate the Bent Units to minimize interconnect cable lengths. Also it ONLY makes sense when dealing with a single source (one input) system.  Once you add source switching it's best to go to the single box 6 input TAP-X as it is the cleanest and most optimized way to handle things in a full featured pre-amp. 

Autoformer based Bent Units are a more expensive way to go than the single box single input TAP-X. The Autoformer Bent Units would be about $650 each - sounds like a lot but many folks buy interconnects costing as much and there is WAY more involved here! This would include fiber optic cables to connect back to a MicroTAP ($330) or TRIK ($575) controller and it makes a nice single input system. With the MicroTAP used it's about $200 more than a single box TAP-X and it saves a pair of interconnects in the system from your pre-amp to the amp.

As far as Resistor vs Autoformer sonics both can do a decent job - although I tend to prefer the Autoformers. They actually measure better too. With the Autoformers I hear a bit more meat on the bones - a bit more fleshy and filled out presentation. I'll leave it to others to elaborate on sonics - it's not me specialty I am afraid!

I still think that for a tight budget the single input resistor based MicroTAP system is a great deal. Full featured with 1db steps and balance control via remote and a super clean signal path. It's actually a bit frustrating in a crazy way. I hardly ever get any questions or calls about the resistor units but they are good as any resistor based units out there. I suppose I am known as the Transformer / Autoformer guy so folks don't really look at them as a Bent Audio option. I should talk to another company and spin them out to them to sell - since I think in the resistor passive world they are hard to beat.

Hope I kinda explained it - in a long winded way.......

Thanks!

John




Robin Hood

Re: Custom Bent Units
« Reply #2 on: 19 Sep 2008, 10:11 pm »
Hi John – thanks for the reply.  I’m always happy to hear from you no matter how long it takes especially since most of us want you to be busy building and not writing.  I hope some of your customers can elaborate on the resistor vs autoformer sonics.  I’m not sure if my assumption that the resistor unit will provide better low level details and the autoformer unit will provide better dynamics is valid.

I have a few other questions that you or someone else on this forum may be able to address.

My argument for a single dedicated input has always been twofold.  First is to avoid the colorations of the selector switch contacts.  Second is the sound of the chosen input is always affected negatively if you have another component connected to the preamp.  Are these valid arguments for your single input units over your 6 input unit despite the obvious inconvenience of manually changing interconnects if you have more than one source.

Also your website states for the resistive based units the preamp to amp cable length must be kept VERY short for best performance.  If the distance from my CD player to amp is 2 meters, why is it preferable to have a 1.5 meter cable from my CD player to preamp and a 0.5 meter cable from my preamp to amp instead of a 1 meter cable between the CD player to preamp and 1 meter cable from my preamp to amp?  It also appears that you have a 6 inch cable from the Bent Unit, so an alternate arrangement might be a 2 meter cable from my CD player to the Bent Unit that is connected to my amp by the short 6 inch cable.  If we take any cable differences out of the equation and assume them to be all the same as your short 6 inch cable is the alternate arrangement with a combined cable length of 2 meters plus 6 inches ever sonically superior?

John Chapman

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Re: Custom Bent Units
« Reply #3 on: 19 Sep 2008, 11:50 pm »
Hello!

Quick reply this time!

On the resistor vs autoformer sonics - I don't think that you loose any detail with the autoformer vs the resistor units. After all the signal path of the autoformer is just a length of wire - no junctions and resistive films for the signal to travel through. This also bears out with listening.  One of my first TAP-X customers had the resistive units and then the autoformer units - he's very detail oriented and likes that transparency and he found the autoformer preferable.

The number of inputs question is a personal one. I tend to recommend that if you have more than one input forget about using a single input pre-amp. It is a pain to swap cables and it likely will affect your source choices - ie instead of listening to the record you'd maybe just spin a CD if that is what is plugged into the pre-amp right then. That would be bad.......

The cable length question has 2 separate answers:

1- With a resistor pre-amp you are indeed better to run a longer interconnect from the source and then a short cable from the pre-amp to the amp. The output impedance is essentially how well the pre-amp can drive the downstream load. The lower this figure is the better the unit can drive the downstream impedances. You'd like this to be zero really - then it would drive anything withput flinching - but in real systems we just try and keep it low. As it rises it causes a high frequency rolloff - a well known affect. This affect is easily measurable here in the lab on my test gear and it a well known affect. This impedance will depend on where the level control is set and ALL resistor passives exhibit this behavior.  With a resistor based passive pre-amp this impedance is higher AFTER a resistor passive than the source's own output impedance - quite a bit higher. Therefore the source does a better job of driving the longer cable than the output side of the passive pre-amp. With a resistor pre-amp in your particular system it would definitely be better to run the 2M cable to the Bent Unit and then the short stub cable to your amps. That type of setup is just what was intended  when the bent units were originally created.

2- With the autoformer it is not critical either way - since the mechanism of action through the autoformer causes this output impedance to stay low and get even lower as the level is turned down. At typical listening levels the impedance out of the autoformer passive is lower than that of the source (and comparable to many active pre-amps) and so it does a good job of driving cables.  If using reasonable length cables (like 2M or less) then the source would usually have an easy time driving it well so using Autoformer Bent Units would still be just fine. If you have really long interconnects to your amps then I'd actually suggest not using the Bent Units but instead use a single box TAP-X - so the lower output impedance after the autofomer is driving those longer cables. For most systems the single input TAP-X would be the way to go - that's why I listed that as the 'one input Autoformer' option on the web page.


Hope that rambling explanation is semi-clear.

Thaks!

John