Tube Power Amp Reviews

Doshi Audio Evolution Monoblock power amplifier Associated Equipment

Sidebar 2: Associated Equipment

Digital sources: dCS Rossini SACD/CD transport, D/A converter, Clock, and Network Bridge; EMM Labs DV2 Integrated DAC; Synology 5-bay NAS 1019+; Roon Nucleus+ server; Uptone Audio etherRegen; Small Green Computer Sonore opticalModule; TP-Link gigabit Ethernet media converters (2) with multimode duplex fiberoptic cables; Linksys routers (2); Arris modem, all powered by HDPlex 200W (1) and 300W (2) four-component linear power supplies; external hard drives, SSD USB sticks, iPad Pro; Apple 2017 MacBook Pro computer.
Preamplifier: Dan D'Agostino Momentum HD.
Power amplifiers: Dan D'Agostino Progression monoblocks.
Loudspeakers: Wilson Audio Specialties Alexia 2.
Headphones: Audeze LCD-X with Nordost Heimdall 2 headphone cable.
Cables: Digital: Nordost Odin 1 & Odin 2 & Valhalla 2 (USB) & Frey 2 (USB adapter), Wireworld Platinum Starlight Cat8 (Ethernet). Interconnect: Nordost Odin 2. Speaker: Nordost Odin 2. AC: Nordost Odin 2 & Valhalla, AudioQuest Dragon HC, Kimber Palladian.
Accessories: Grand Prix Monza 8-shelf double rack & amp stands, 1.5" Formula platform, Apex footers; Nordost QB8, QX4 (2), QK1 & QV2 AC power accessories, QKore 1, 3, & 6 with QKore Wires, Titanium and Bronze Sort Kones, Sort Lifts; AudioQuest Niagara 5000 power conditioner & NRG Edison outlets & JitterBugs; Tweek Geek Dark Matter Stealth power conditioner with High Fidelity and Furutech options; GreenWave AC filter; Ansuz Darkz T2S resonance support feet; Wilson Audio Pedestals; IsoAcoustics Orea footers, Vibex PDR footers; Stillpoints Aperture panels; Resolution Acoustics room treatment; Stein Music Super Naturals, Blue Suns/Diamonds, Quantum Organizer; Bybee Room Neutralizers; Absolare Stabilians; Symposium Ultra Platform; Marigo Aida CD mat.
Room: 20' L × 16' W × 9' H.—Jason Victor Serinus

COMPANY INFO
Doshi Audio LLC
Charlottesville, VA
USA 22901
(917) 952-2758
doshiaudio.com
ARTICLE CONTENTS

COMMENTS
JRT's picture
Submitted by JRT on April 16, 2021 - 7:40pm

JA1, I always enjoy reading your measurements page(s), and I have one suggestion for measurements of any amplifier using an output transformer. You are probably well aware that at some combination of lower frequency and higher current the transformer core will begin to saturate and 3rd order harmonic distortion will significantly rise. My suggestion would be to include measurement(s) that better explore the high pass corner of the full power bandwith. That is intended as suggestion, and not any negative criticism of the measurements, explanations and other commentary you are already providing, all worthwhile. Thanks for what you do.

Jack L's picture
Submitted by Jack L on April 19, 2021 - 2:24pm

Hi

Besides nonlinear hysteresis transfer of the transformer core, high frequency distortion of any output transformer is also caused by its leakage inductance & winding capacitances, which in turn, change the loudspeaker loading impedance & phase angle.

More complicated will be: such leakage inductances of each half of the primary winding of a push-pull output transformer, like this $21,000 monoblock reviewed above, should be as little as possible. Otherwise, this will cause incomplete cancellation of 2nd harmonics, causing undue generation of higher order harmonics.

Such high harmonic distortion may be fed into the secondary winding & then into the loading loudspeaker by capacitive coupling unless there is an effective static shield between the primary & 2nd windings.

Ideally, lower plate resistance of the driving tubes, less will be such distortion at high frequencies. That's why triodes are always preferred to pentode/tetrodes which all get much much high plate resistance than a triode.

That's one of the reasons I always go for single-ended Class A power topology using triodes only - more output transformers friendly + better sound !

Listening is believing

Jack L

tonykaz's picture
Submitted by tonykaz on April 17, 2021 - 8:52pm

Nice literature here, hell of a review, applause +++!

I look to have one of these designs, one day.

Nice Work,

Tony in Venice Florida

a.wayne's picture
Submitted by a.wayne on April 18, 2021 - 1:10pm

This Doshi does measure well for a modern tooby amp ,, interestingly prices are clearly for limited sales numbers , 40K plus is a bit much for an unknown Brand, especially when considering its 3times that of the last VAC integrated tested ..

Regards

Jack L's picture
Submitted by Jack L on April 19, 2021 - 9:41am

Hi

Agreed. In fact, some $200/output watt per JA's test report for 8ohm loudspeaker load is very expensive. 8-ohm load s the standard specified load impedance of any loudspeakers, right ?

The bias adjustment of the power tubes: It looks so similar to Dynaco ST-70. I did the same bias adjustment upgrade to my ST-70 by reducing the cathode to signal ground resistor (used to monitor the "bias voltage") from original 15.6R to 2.3R. Such reduction allows me to set the optimum voltage from original 1.56V to 107mV.
Yes, it pretty sensitive to adjust as JA pointed out in his test report. But I found it so helpful to improve the sound quality.

Why? The best sounding bias topology, IMO, is ground cathode. So by reducing the "bias monitoring" cathode resistor to practically MINIMUM would help to improve the sound.

$21,000 for 106Wrms/8-ohm is pretty expensive, my friend.

Jack L

Ortofan's picture
Submitted by Ortofan on April 19, 2021 - 3:21am

... (and sound quality) of this Doshi amp compare to those of the $11K McIntosh MC1502?
https://www.mcintoshlabs.com/products/amplifiers/MC1502

The MC1502 is the regular production replacement for the limited edition MC2152 - minus the fancier chassis with carbon fiber panels - but with identical specifications and sound quality.
Hi-Fi World tested the MC2152 and found that it could deliver 220W at the onset of clipping and 240W at 1% distortion.
https://www.mcintoshlabs.com/-/media/Files/mcintoshlabs/ReviewAwardDocuments/MC2152-and-C70-Hi-Fi-World-July-2019.ashx

The Part-time Audiophile reviewed the MC1502 and concluded that it provided "true high-end audiophile sound in all its refined glory, without any rare tube types, finicky setup, or usage idiosyncrasies."
https://parttimeaudiophile.com/2021/01/24/mcintosh-labs-mc1502-power-amplifier-review/

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