Delta Studio                 The Wonderful Sound of Music

Delta Studio Amplifier KT88

"Hi-Fi i muzyka" 6/2002

    The beginnings of Delta Studio aren't hiden in a darkness of a garage on suburbs of Cambridge. The firm arised in 1991 as ... an advertising agency and that's still the main profile of its work. The amplifiers appeared much later, only three years ago.

Fortunately, at this time history of the Wrocław company starts to fit to an audiophile archetype. Witold Jaskułowski's passion of good sound isn't satisfied by products offered in shops, so he decides to create a construction of his dreams by himself. Maybe not exactly, because he asks for help an appropriately educated engineer (Marek Kochański). As the effect first amplifiers named Delta Studio are being created. After three years of activity the company can boast with several products - starting from integrated constructions to corrective preamplifiers for turntables. Their prices and construction details are different but they have one thing in common - they all have been made on the basis of a tube technique. The reason is simple - both proprietor of Delta Studio and engaged constructor are unanimous that a really musical and charming sound can be offered only by a red-hot electron tube. Semiconductor technologies are surely more modern, but glass bulb in a role of a time machine speeding along a space of musical subtleties can't be replaced by even the best transistor.

Construction

Round casing finished with wood is very pleasuring to eye, and simultaneously unique and showy. Form of the amplifier can be described as a repeated invention of circle. It would appear that there is nothing simpler under the sun. But so far none of producers hit on an idea to give the beautiful gentle shape to their devices. Wrocław Delta is a sensation in this respect and its amplifiers will be a real decoration of even the most beautiful interiors. Rounded front perfectly harmonizes with ovals of tubes making the unique combination. We should take a note, that the front wooden panel has been made with care that Franco Serblina's carpenters (Sonus Faber) wouldn't feel ashamed of. Nut-brown wood has been ideally polished and coated with few coats of colorless varnish. Glossy finish has nothing to cheap trinket. Its class leaves no doubts - we deal with a luxury product, designed for a wealthy buyer.

First impression is confirmed by a price list. More wealthy buyers may order version with separated power supplier, but the price smoothly exceeds 10000 zł and not only because of a cost of an additional box. Construction of the power supply changes, and the most visible determinant, but not only one, is a transformer. Instead of an applied in integrated amplifier toroid, in version called "Special" there is a traditional transformer based on EI shapes installed. In constructor's opinion this solution gives the optimal sound quality, although a production of the right class transformer drastically rises the price of this device. So it's an option for buyers which can afford additional charge. For listeners whose requirements always were beyond their financial capabilities Delta Studio designed KT88 "SE" with power supply placed in a shared casing.

A view of a rear side makes a good impression again. At this time designer abandoned the idea of rounded shapes, increasing functionality of the device. Unfortunately sockets' placing is awful. It brings discredit onto elementary logic. Speakers' terminals have been placed in a direct neighbourhood of a power socket and a power switch, and because of that connecting speaker wires requires a big dexterity. Not to mention a possible signal modulation with an electromagnetic field of a power cable, because in this case this issue is second-rate. A proper connection of Delta to rest of a system is so difficult, that we stop to take a note of tone consequences. It's necessary to do something about this, because users of expensive power and speaker wires, especially those equipped with "fork plugs" won't be satisfied.

It's good that at least access to line input is not difficult. Installation of even thick wires is quick, and solid, Teflon isolated, sockets guarantee a good contact and many years of operation. Near the standard connectors on the rear side we will find also a measurement connector which enables checking a quiescent current, and a very interesting for an audiophile switch: "triode/pentode". Depending on a repertoire and demand for decibels user can choose amplifier's work mode. In pentode mode the power will be high (from technical data 2 x 63 W), thanks to that the device will manage with an entertaining music and hard rock. In triode mode (g2 connected to anode) power is half of that in a pentode mode, but tone should be smoother, richer in harmonic components and sweeter. Choice of an option should result from user's individual preferences, or a nature of speakers' tone.

By the way of them - from the bulletin follows that the amplifier has been adapted to work with 8 ohms speakers. Used for test Antals XS were nominally 6 Ohms, but the producer ensured us that the amplifier will work correctly with them. Futhermore in case of Triangle in compensation for lower resistance is high efficiency reaching 91 dB. The amplifier won't have to work on the efficiency limit, what should appear in free and clear sound transmission.

From side of power supply the interior is constructed in quasi dual-mono system. Both channels use a shared transformer, but later each one has its own PCB's with rectifiers and filters. The only contact is in the ground point, what is very advantageous as regards of reduction of interferences. KT88 SE is equipped with an active delay system, counteracting using up of the tubes. After turning on the amplifier goes into two minutes long stand-by mode, what is indicated by red color of a LED. At this time tubes reach the right work temperature and then in the end the anodes are connected. Anode voltage is filtrated by Samsung's electrolytes. Although they are designed to work in temperature up to 85 °C, the constructor - just in case - mounted them far from heat sources. Signal capacitors are very high class Wima's polypropylenes. They are not cheap, and especially those high capacity, but their tone virtues can not be questionated. Resistors also leave no room to criticism - they are metalized, and where necessary wire. We pay attention to precise description of PCB. The constructor gives both numerical description of elements and their values, what is very helpful for service.

Speaker transformers - one of the most important elements in tube amplifier - are own study of Delta Studio. Producer is convinced of technical and sound primacy of traditional construction based on EI shapes. Transformers arise from annealed silicon sheets and after winding they are sunken in electroinsulating lacquer. Well thought out is their location - they are located in a save distance, and on other level than the mains transformer, and every one is additionally hidden in a separate metal casing which is painted in mat black color.

Everything has its matter. Electromagnetic field generated by mains transformer shouldn't affect into output transformer's work, and especially shouldn't cause the troublesome hum in speakers. Moving away and isolating the output transformers from each other decreases inter-channel crosstalk, what should be noticed in form of a more transparent and precise sound scene. Metal shields are as an electromagnetic insulation reducing influence of external fields onto transformer and vice versa. Mat black surface transfers heat, what improves work and longevity of these very important for tone elements. The only thing, to which we can have reservations about is using steel screws to twist up the transformers. Using brass made screws would be better (non magnetic material), but even though the quality of workmanship deserves the respect.

Care of details is visible also in internal wiring. Wires are thick and in many places additional insulation jackets are applied. Thanks to that the system is safer for user, and risk of failure is minimized. Potentiometers used to set quiescent current are inside the device. They are a very high class ceramic regulators, characterizing with high stability of parameters in time and they guarantee constancy of settings. This means that the amplifier will not change its settings by itself, and once made settings will be remembered to next correction. We have to stress that adjustment requires strong pressure to screw. Unskilled user can damage the potentiometer by pressing to hard. Better don't turn these screws by yourself - but if it's necessary you should ask somebody who knows what is doing.

As regards power tubes, Delta Studio used experience of Slovaks and used KT88 produced by JJ Electronic. These are high quality components with guaranteed work time up to 1000 hours, but practically 3000 to 5000 hours of use. In case of KT88 "SE" we may have a hope to reach the upper limit (5000 hours) for the sake of "anode connection delay system". Bulbs from Jan Jurco's factory have two rings of geter, what guarantees effective absorbing leftovers of gas and helps to keep a perfect vacuum inside the bulb.

First state is based on 6N2P tubes - which are Russian equivalent of ECC83. This is a special version, made for military needs, and it's displayed by longer vitality. In this case it's over 5000 hours of use, and this shows good about producer's attitude to customer. In the driver state work double triodes ECC88, just like these in first state - made for military needs.

The amplifier isn't equipped with system which secures before disconnecting load (speakers). It was an entirely conscious decision, thanks to it the signal route is as simple as possible, but we must remember that we can't disconnect speakers when an amplifier is working and don't turn a device on when the speakers aren't connected. It will allow us to avoid unpleasant surprises and unplanned visits in service. Although on other side, such visit would have its advantages. Wrocław as Wrocław, but its inhabitants (girls) are just lovely.

Sound

Delta's amplifier surprised me very pleasantly. Not only by the appearance, although it's hard to ignore such a showy look, but first of all by sound. I wasn't expecting miracles. The company is very young, little-known and aims at a high segment of market straight away. It's rather brave action, because from constructions for 10000 zł we could require almost everything. Yet concerns of constructor's skills vanished along with first moments of listening. KT88 "SE" started very good and later it was just prooving first impression.

Great advantages are here undoubtedly balancing of registers and transparency of sound. Even sceptics must admit that Delta's sound has nothing in common with heavy playing, lacking edges of frequency band. Wrocław amplifier has treble, middle tones and bass, thanks to what it saves us unpleasant feeling that sound comes from behind a curtain, or that the bass speakers aren't working. After selecting right speakers, the best effective, just like Antals XS, we will receive a full spectrum of frequencies, further more pretty composed together. The constructor avoided basic tube systems' problems, what is more admirable as he made output transformers by himself. We can see and hear that it's a very well thought-out device, but also made with big dose of feeling. The designer without an intuition wouldn't be able to make such an amplifier in so short time. Three years on the market is not much, but as we see, long enough to learn a lot.

Associating with KT88 "SE" we can't be surprised why so many demanding music lovers still remain faithful to traditional recipes. We may make fun of tube amplifiers and stick them a plate of Desa's exhibits, but when hundreds of ignored by cheaper transistor amplifiers details start coming to our ears, then stupid laughs stop in a throat. The vocals felt very well, although it's them on what we usually catch that a play is out of tune and inaccurate. Here they sound pleasantly, and it's not a result of radical warming or smoothing penetrating tones. It's even contrary - they are reproduced with such a precision and it's just what gives us so much pleasure. There are so many details and every next authenticates the presentation more and more. Delta isn't reaching yet standards of the best SE [Single-End] systems, which can cast us and move to the world of completely new experiences, but nevertheless Delta joined precision with pleasure. Such a combination is a feature of good devices, and I have no doubt that KT88 SE is one of them.

Not to be too sweet - for contrast two spoons of birch-tar to a cask of honey. First one is a limitation of selectivity on high volumes. In spite of listening on effective speakers and in a room of 16,5 m2 I drove Delta to extremes. Loud hip-hop isn't certainly its element, but to make sure I checked orchestras tutti. Effect was the same - at dense textures reproduced with high, but not exaggerated, volume final state starts to choke, what is shown by disorder of sound definition and sounding of stereophonic scene. Pity, especially the last one, because when listening in low and middle volume Delta showed the best space of all three. Delta didn't play by spots but described instrument's positions very precisely and even their relations resulted from building the scene deep. It was very good although Antal XS will not seduce us by holographic effects. One shudders to think what would happen if we put together KT88 "SE" with Audio Phisics Virgo 3. But it had to be about disadvantages.

The second thing is in principle a little scarcity which I couldn't have noticed if I hadn't listened to JJ828. It's bass. In KT88 SE it's a complete to entirely, in JJ828 - rightful (maybe sometimes even excessively dominant) participant of musical events. In my taste Delta gives prominence of speed and hardness to much, treating their mass and density a little neglect. I don't want to say that there is a lack of bass but I wouldn't be offended if it has, we could call it: stronger personality. And this seductive softness, which I heard from JJ828. But these are excessive demands. And without it the sound is so pleasant, that you can listen for hours and the next day can't wait till next audio monitoring session. And this is much. Very much.

Summary

Delta Studio KT88 "SE" is almost only advantages. Reliable and precise sounding construction offered in a reasonable price. And amazing appearance. I wouldn't like to be in competitors' shoes.


Delta Studio KT88
Technical data
Output power 63 W (30 W in triode mode)
Speakers' impedancy 4 - 8 Ohms
Band width 2,7 Hz - 120 kHz (-3dB)
Distortions 0,03% (1W/1kHz)
Signal/noise ratio > 90 dB
Line inputs 1
Phono input -
Tone control -
Remote control -

Rating
Neutrality * * * * *
Dynamic * * * *
Stereophony * * * * *
Clarity * * * * *
Musicality * * * * *
Bass * * *
Sound * * * * *
Quality/price * * * *
Delta Studio Amplifiers - High End audio tube amplifiers