bepone wrote: ↑Sun Oct 09, 2022 7:34 pm
will start like "exotic" version (i didnt see any build with PRP resistors! couldnt wait for the review
) and probably after some time "eric johnson" parts will find their place..
That's not far from the truth! The idea, is really to use none or at least the very minimum of exotics - the listening tests are going to be very important.
Here's a breakdown of the exotics I'm going to be trying out...
Amtrans AMRG Carbon Film Resistors
100k and 180k in series with the coupling caps (OD V2a out and V2b out). For those positions, I have Xicon CF, 1W - about 100th the cost
amtrans_350.jpg
Amtrans, from Japan, used to be the distributor for Riken resistors. In 2005 they bought a resistor factory, whether this was the original Riken premises they wouldn`t confirm. Soon came the AMRG carbon film resistor, which they claim is better than the Riken as they have employed cutting edge technologies for production. Indeed they aren`t far from the truth, these are truly amazing.
They are available in 0.75 watts and 2 watts, from 10R to 1.5M. The full E24 range is available for the 0.75W and the E12 range for the 2Ws. They have a 1% tolerance, non-magnetic, they are encapsulated in a black anodized aluminium case, potted in a highly thermally conductive resin, brass end caps, and gold-plated oxygen-free copper leadouts. A lot to boast we believe and at an incredible price.
PRP PR9372 Series Metal Film
100k for the FX (Dumbleator) recovery side plate - I've used Dales with success but I am trying to integrate the Dumbleator in this build with similar components to the rest of the amp. Otherwise, I have an H4P MF 1W for this position.
150k and 220k for the plates of V1 and V2. Similarly, I have H4P 150k 1W and Xicon MF 0.5W for those positions.
prp_pr9372_350.jpg
The PR9372 Audio Resistor is manufactured in Mediapolis, Iowa, USA, by Precision Resistive Products Inc. and has been designed into many high-end audio products worldwide. Designed specifically for audio use after exhaustive listening tests were performed by a well-known high-end audio manufacturer who auditioned ten different prototypes – all of which had a unique blend of materials and manufacturing techniques. The winning design became the PR9372.
These resistors are metal film, a Ni-Chrome thin film construction, completely non-magnetic, offering a high-resolution sound. They have a flat frequency response with incredibly low distortion and thermal EMF. We have selected to stock the 1%, 100ppm tolerance range.
They are reasonably priced, coming in somewhat lower than the Takman metal films.
Ohmite Audio Gold Resistors
1k5 5W for the screen grids on the power tubes. I like the look of these over the Xicon cement types which will be trying as well.
ohmite-audio-gold-350.jpg
Ohmite now offers the Audio Gold Resistor Family, specifically designed for high-end loudspeaker and amplifier applications. These resistors utilize high quality resistance wire wound on a ceramic core, terminated, and finished with their flameproof Centohm® coating.
Ohmite’s Audio Gold resistors have been carefully engineered with non-magnetic materials to eliminate the effects of these stray magnetic fields on circuit performance, thereby resulting in simplified shielding requirements and improved sound quality. Audio Gold resistors are designed for use in cross-over networks and as source, emitter, or cathode resistors in balancing applications for output transducers.
Ohmite Little Demon Carbon Composite Resistors
22k for the bias trimpot/tail. For this position, I also have a TE Connectivity CFR series CF 1W. If the bias circuit really has an impact on tone it should be present with either of these.
ohmite-little-demon-carbon-resistors-350.jpg
Ohmite’s Little Demons are small, reliable carbon composition 0.5 Watt resistor with exceptional strength. They are made tough by a moulding process that combines the terminals, insulation and resistive element into an integrated unit.
Along with their small size, Little Demons perform with low noise, dissipate heat rapidly and offer high-temperature stability.
Colour codes are readable even after prolonged use thanks to a very durable coating that resists abrasions and chipping normally associated with automatic insertion equipment.
Holco Metals Films (Originals)
150k for the slope. Alternatively an H4P or I have some other exotics (Kiwame, PRP)
holco_resistors_350_0.jpg
The Holco H2 1W and Holco H4 0.5W series of resistors that we stock are the original Meggitt Holsworthy, UK made resistors. They give a crisp, full sound, superb. We have limited stocks as the originals are no longer made.
The manufacturing facility utilises closely controlled production processes including the sputter coating of metal alloy films to ceramic substrates, and laser spiralling to achieve close tolerance and high stability resistors. An epoxy coating is applied for environmental and mechanical protection.
Kiwame
270k 2W as balance resistors on the reservoir caps. There's also an option to use Allen Bradley's here for that mixture of CC and CF which I also want to try in the power supply. The PS is being commissioned with Xicon MO but dropping string values are only estimated at the moment and once I have it dialled in I can think about tinkering with the sets of resistors in this section. It would be nice to get some Q-line-esque resistors here I think.
kiwame_350.jpg
These are an excellent match for Hi-End Audio. Kiwame resistors are from Japan and are characterized by lower noise than metal film resistors and a more natural sound. There is a growing enthusiasm for these carbon film resistors because they recapture the vintage tube sound without the drift of carbon comps. They are also very compact given their wattage rating. The resistance material is a carbon film with coated silicon and finished in green.
Since their first introduction to the audio industry, they have managed to gain the reputation and the respect of both manufacturers and worldwide DIY-ers. In fact, several manufacturers openly suggest Kiwame resistors along with the 'usual suspects' (quality capacitors etc.) for the upgrade of their products. Lately, Kiwame resistors found another audio application, that of the step ladder attenuators used as volume potentiometers.
Browsing internet audio forums and DIY discussion groups proves that Kiwame resistors really make a difference! Kiwame resistors are made of carbon film and their case is actually the first one for use in audio applications with superior specifications! Considerably lower thermal noise levels, lower than metal film resistors!
On the other hand, they offer true 0.5% tolerance despite their nominal E24-series 5% label! If you don't believe it a multimeter will certainly convince you. Their sonic character can be briefly described as follows: Effortless reproduction ('non-fatigued) is subjectively perceived as an increase of headroom. Extensive neutrality.
Allen Bradley
270k 2W 5% Alongside the Kiwame an option for the balance resistors in the PS.
22M 0.25W 10% for the PAB relay circuit. No readily available CCs in these values though there are CF and MF from KOA, Vishay, etc
allen_bradley_box_600.jpg
The write-up is rather long on these so here are the main points...
For many many years, these carbon composite resistors from the States have been held in high regard for hi-fi and for guitar amp use. Their natural organic tone is truly sublime. Unfortunately, production stopped in the 1990s and ever since then the stocks have been diminishing fast.
These "hot-moulded carbon" resistors offer the simplest of concepts for a resistor design. They effectively consist of a solid cylindrical carbon resistive element with leads embedded at each end. Making them incredibly rugged and highly reliable, together with their non-magnetic and non-inductive characteristics these little gems are remarkable in performance and sound...
The Hi Fi Collective has many values of these but even their inventory is starting to dwindle. Of note, they offer instructions on reconditioning the CCs
Allen Bradley RESISTORS special treatment method
As stated Allen Bradley resistors are carbon composite, being made of organic material they do have the tendency to absorb water from the atmosphere. This absorption can increase the actual resistance of the component, hence the slightly higher than normal tolerance published on this page. To fix this simply remove the water from the component and seal it. The best method is to place the resistor/s on a baking tray, set your oven to 80 degrees centigrade and leave in the oven for 8 hours. The secret is to remove the moisture slowly if you rush it it will become noisy in the circuit. Once cooked seal the body of the component in Shellack (preferably the flakes) to stop any further water absorption. At the end of this procedure, you will have much lower noise, more closely tolerance resistors. Special thanks to Colin Cornish for this excellent tip.
Which is fine I suppose if you have ten-thousand of them to revive. Otherwise, leaving the oven on for 8 hours - fuggedaboudit
The Holcos and the Allen Bradleys are pretty much non-starters in this race for utility. Being out-of-production, their only place here is to provide some kind of benchmark from which to judge other worthy (in-production) contenders. The PRPs look interesting though, and the Ohmite, both of which if it wasn't for all the Brexit bullshit and misery, would make the Hi Fi Collective a more frequently visited shop. The Amtrans, also in-production, are just a too expensive for anything other than singular, critical components, but we will see how they sound.
That's it then! Unless you guys come up with some other alternatives that I know I will find it hard to resist, my wallet is shut.
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