Hi Everyone, and Bigman80 thanks for the responses,
Bigman80 you wrote:
"The cable lengths In this discussion are unlikely to be of consequence, as the system has never used any length over 1m".
In his blog Scott Endler said his experiments with resistor based attenuators suggested there was a clear sonic advantage of having the IC cable between the attenuator and the power amp at less than 10cm. He may not be the most reliable word on the matter since at the time he was selling resistor based stepped (shunt type) attenuators that plugged directly into the power amplifier with no cable at all. Nevertheless, in a 2005 review in Positive Feedback Fown-Ming Tien wrote "These $160 volume controls did what no line stage under $2000 I had heard in my system had done—it beat my Aragon line stage in nearly every single sonic category". Based on this review I bought them and enjoyed them for five years until they got very scratchy when I bought the Slagle Autoformers.
Support of the idea that extremely short cables (or none at all) may be preferable when using resister based attenuators also comes from Ralph Karsten AKA "Atmasphere", designer of Atmasphere OTL amplifiers who has nothing to profit from selling any sort of passive "preamp". He also compared resistor to transformer base attenuation. In a 2006 Audiogon thread titled "Transformer based passives vs passive stepladder" he wrote:
"The problem you have is that all passive devices will have an artifact unless they are directly at the input of the amplifier. The reason is that the interconnect cable, even if very short, plays a major role in the results that you get. Resistive passives cannot control the interconnect cable and so loose dynamics and bass impact at lower volume settings.
The problems that transformer units have are bandwidth and hysterisis loss. Hysterisis loss is a phenomena of transformers wherein it takes a little bit of energy to change the polarity of the magnetic field as the signal does the transition from one polarity to the other (this energy comes from the signal itself). The result is low level distortion and low level signal loss."
The question I have from this is if a product such as the Endler (or EVS nude attenuator)that has no IC cable at all could be used would there be any benefit at all in a buffer or active gain stage at all? Leading on from this would a very short, say 7 cm, IC cable benefit from a buffer or active gain stage?
It seems Ralph Carson believes buffers are likely to be of benefit despite extremely short or no IC cable if the amount of resistance needed for volume control goes over 10K. On a 2009 Audiogon thread titled "impedence value.? amp to preamp." He wrote:
"…to really get a passive to work you get into trouble when you get over 10K for a value, even with short cables. That's why you are better off having the control inside the amplifier, or else inside the source (both inconvenient), and buffered from the cable. Even with 10K, the effect can still be heard. There was a lot of talk about buffered PVCs a few years back, but what we are talking about then is an active without gain."
From this it may be inferred that Bigman80's use of 1m cable to trial resistor based attenuators, LDR or otherwise, really didn't allow these types of passives to be heard at their best. It also suggests that buffers may be of benefit even with extremely short or no IC cable if 10K or more resistance is needed.
Bigman80 I had a brief look at BT2 build in the Audioaddicts Forum, but I couldn't work out what the buffer was. Is it listed somewhere else, or still proprietary?
Has anyone tried or heard much about the Universal Buffer sold by Neurochrome? It seems to be affordable and with good distortion values?
Looking forward to everyone’s responses.
Kind Regards,
Ben