Pioneer SX-34 modification and about other author’s audio stuff 07-2015

Dream System worked out by me.

Dream system worked out by me


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The loudspeaker project is unique in mechanical and electrical way. Two amplifiers cover every day use with semiconductor Luxman 210L and full delivery with Pioneer tube amplituner SX-34 serviced and upgraded for real sound by me. . Bang& Olufsen for sound source and remote control. Electrical  power of Luman L201 is 2 x 60W and for Pioneer app 2x 7W  but no lack of loudness for both of them


1. Pioneer SX-34 Amplituner Modification Description + Schematic

2. RLC Cooperation in Amplifier

3. Acoustic Construction of Used Speaker System – sketch with dimensions

4. Example of Tube/Solid Vintage Audio Center

5.Tesla  B 116 – a „new baby” on board

6. Visual tuning of „Pioneer SX-34″

Here You will find details of upgrading of Pioneer SX-34 amplifier

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Pioneer SX-34 is one of vintage wonders from japan producer. Produced in the end of sixties years of last century was example of fashion after were gone those days of. treating radio reception as source of vital information at first place  Cinema and TV made their strongholds in cultural entertainment and 60tees generation fall in love with pop and BIG Beat music.



Producers of home electronic like PIONEER from Japan answered with extension of music abilities to radios – they were no more radios but „Amplituners”. Change is not semantic only. Radio before was device with purpose  to get best long distance reception – selectivity was in high agenda. With the development of frequency modulation radios achieved new quality of transmission.  Simultaneous development of radio stations network made selectivity and sensitivity a second choice. Days of world  II prewar philosophy of radio reception were counted and this philosophy became shifted to narrow shortwave amateur communication where exists until today.


In 60-tees most important became FM reception, stereo, and wide acoustic range of amplifiers and speakers. This at first forced removal of internal .speakers from radios. Separate dedicated enclosures gave more room to acoustic quality. In their place and in place of devices for sensitive AM reception (which had been spared with simple tuners for local reception) appeared powerful amplifiers and FM tuners with stereo decoders . And that was it – AMPLITUNER.



Amplituners were just like wing American cruisers in this days – the area for fantasy in design. And the same as for cars the technical perfection of amplituners was limited to real demand of mass customer. But in 70-tees the new customer was born – an Audiophile. For him amplituners had to be disregarded and new philosophy of totally separated elements appeared as era of semiconductors in amplifiers started..  Power delivered by amplifiers raised few times.



Engineers and audiophiles put many years of efforts to get perfection from solid state amplification. And still they share opinion that the reality is impossible. Authors idea is to get the best of both. He believes that having many years of experience with quality of semiconductors and having tubes as only true analogue amplification there may be the better way.



Looking for tube amplifier he set his requirements:


1. The construction should incorporate long years of past developments by serious producers.


2. Typical and long time produced types of tubes.


3. Power enough to living room excluded type A tube amplifier so it should be push-pull



Pioneer SX-34 is like that. But as mentioned technical perfection was limited in 60-tees years by average customer demands. Moreover at first  author had to  solve main problems with age degradation. Between them arose most difficult – position of volume potentiometer affects frequency characteristic. Probably for average quality of speaker sets it was little noticeable and no reason for complaints. But with used by author originally developed by him speaker sets this change of characteristic unveiled in no acceptable degree. On other hand problem is not the potentiometer itself, but triode input tubes and it is almost not removable. Only possible solution he found in keeping potentiometers in highest position and pass the volume adjustment to semiconductor preamp with low output resistance – just as Bang & Olufsen allow.


First  problem was found in grids circuits of input triodes. Connecting wires in neighbor to second stage anodes  were receiving voltage by bilateral capacity. This was effecting in small negative feedback for soprano tones . To rectify that wires and coupling capacitors wrapped with foil and grounded

After all was done and no problem was expected the testing with own construction speaker sets had shown that sound had proper frequency range but for some „soft” analogue magnetic tape recordings amplifier seemed lacking reality and energy comparing to standard tube class A . What was interesting that „good” energy was observed the same: with small wide-range driven by original recorder tube class A amplifier and also with constructed speaker set connected to that class A. Direct comparison was evident. It was the proof that Pioneer SX-34 had been making unwanted change. The main difference between two amplifiers is that first is single end type and second a push-pull type . It is generally known that push-pull class  has sonic disadvantage in compare to class A and author knowing this explanation, but also having much better experience with other push-pull tube amplifier  in past, started his research from last stage of Pioneer. The only possible problem found was  lack of widely applauded by many (and by author   between them) ultra-linear circuitry which he used to have in old days. . Unfortunately this circuitry could be installed only accompanied with replacement of two output transformers. In author’s opinion unwanted changes to sound quality could happen in such case as no data of original transformers windings is available. In order to preserve original transformers he applied his own circuitry adopting it to original transformers output experimentally in a way similar to which ultra-linear circuitry works. After many hours of experimenting presented modification was elaborated. RC correction was unavoidable. It provides more acoustic frequency feedback to third grid and this feedback is the  main target.    Author couldn’t proof how exactly it is happening but next tests of compare between class A and Pioneer did not show noticeable difference.


See update!

It is worthy to mention that also Pioneer Company in few other their tube amplifiers applied a bit mystery modifications to last stage of amplification affecting also preamp. Exactly in standard feedback they included connection to last penthode 1st grid. Could it be another way of upgrade?.

Update on 14 April 2015 to schema of modification: . 

    With last  constructed by me speaker sets based on wide range Stern speaker L4055/P554 I found that amplifier together with them sounds best with capacity applied in 2 grid of push pull value 0,0145uF. there is no calculation to that capacity and for me best results I obtained by  judging the sound with used speakers. .

Update on 02 May 2015 to schema of modification:

   Modification of volume potentiometer marked in red has been redesigned in a way to bring back the „loudness correction”. New potentiometer circuitry is presented in part „Pioneer SX-34 loudness correction in perception…”








The traditional crossover filters when returning the wattless/reactive power to amplifiers output provides the difference to the balance of feedback . Originally feedback balance is intended to send to a preamplifier signal being result of simple compare between output signal and preamp input. No phase shift depending on frequency between input and output is expected and allowed and that is of course secured by amplifier construction. When multiband speaker with crossover is connected to output it is right to expect phase shifted reactive power to be created in bands of electrical LC resonances. This power is a multiplication of phase shifted return voltage and actual current. Does not load amplifier but reactive voltage appear on terminals from where is seen in preamp by feedback. This voltages does not input to transmission but change the reactance of load. and may affect signal on feedback input point. In author’s opinion this created voltage signal affects the frequency characteristic of amplifier but due to passive character they are not active in speakers. In that way correction is false and provides weakening of crossover bands in performance. Author compared headphones and multiway speaker and observed that for headphone the difference of sound between solid state Luxman 210 and tube Pioneer was not noticeable while even with his invented cross-filtering system slight difference of sound between amplifiers is observed. It may be the proof that the multi-band filtering is the source of more than transmission only faults

  There are four solutions to get rid of that faults -

- one is to use amplifier with lowered feedback – it means popular using of tube amplifier.with acceptance of lower electrical damping factor for speaker Fr and that is to be eventually corrected by mechanical damping.,


- second is to decrease only feedback coming from output terminals and increase those covering only the particular amplification stages in the way author modified his Pioneer SX-34,


- third is not to use LC circuitry in speaker systems at all – using of wide range speakers, headphones.


- fourth is to modify LC circuitry in way Crossfrequency management is done.


Actually author applied solutions no 1, 2, 4 with unusual result to reality and non fatiguing naturalism of sound.

                      Acoustic construction of used speaker systems




Example of Audio System

Objective for building this original design vintage audio system was to arrange all connections to operate in simplest way with no need to disconnect/connect cables in so many possible modes of operation .

By testing all combinations of solid/tube phono inputs with solid/tube amplifiers was found that mixing of techniques was not reasonable – Solid amplifier is matched by Luxman with it’s solid phono input and tube Pioneer amplifier with it’s tube phono input. By my decision I had chosen tube technique as leading.

Other objectives :

-Remote Control: Volume& pan & tone control for : gramophone, PC, tape recorder, Casio, CD, Cassette tape recorder, radio receiver and TV sound.

-Turntable : phono input type :Tube ECC 83 incorporated in Pioneer.

-Power amplifier type : tube – 17 Watts max per channel 35Hz – 25 kHz incorporated in Pioneer.

-Volume potentiometer in tube amplifier in maximum position to avoid impact of ECC 83 anode-grid capacity to sound – volume control is provided by remote in B&O .

-Low level of noise from phono input of SX-34 in maximum manual position of volume potentiometer obtained with division of voltage by recording output from Pioneer. Input back to Pioneer connected to tape monitoring sockets.

-Easy and quick switching turntable source from tube amplifier to solid state amplifier for comparison..

Stuff :

Pioneer SX-34 paid for damaged 130 USD 7 years ago.  All tubes replaced, upgraded circuitry, general overhaul with RC replacements, contact cleaning, potentiometers cleaning ..

Luxman 210L – no pay -a gift 4 years ago. Damaged -  – channel output end pair replaced, on-timer repair, contacts cleaning, front lighting done.

Speakers – Done by myself 18 years ago, tunned now to tube amplifier and analogue sound.

B&O Ouverture – internet auction in good condition – 350 USD in 2013

B&O Beogram 1700 – internet auction in good condition 100 USD in 2013

Remote Beo4 – internet auction 100 USD in 2013

Speaker cables – 2 USD / 1 Meter

Chinch and Din Interconnections cabling – self done..

Total paid 680 USD plus used time.

Sound value – hard to believe.


As presented above the Sound Center may be controlled and tested in few ways. The objective was to compare MATCH speaker sets behavior in maximum number of different conditions. This conditions vary due to differences of preamplifiers and amplifiers input impedance, mentioned above impact of different feedbacks, transformers and different tube and transistors capacities. Target was to check how Crossmanagement can handle different conditions of system and vice verse – systems cooperate with Crossmanagement. Diagram presents all of them with main features of each


Last time hunting trophy to author’s vintage audio system is Reel to Reel tape recorder TESLA B116. It is widely appreciated economy but top model from Tchechoslowak producer delivered in 1980 – 1986 and is designated by author to work in system and save very hard efforts from owned since 1971 tube/transistor model Tesla SONET B3.


SONET B3 was two speed (4,75/9,6 cm/s)  mono, 4 tracker with tube ECL 82 output and internal speaker. Produced 1963 – 1965 Preamp with two transistors and ECC 83. It’s data were : frequency range 50 – 14 kHz, granted dynamic 40dB, max reel size 15 cm.. Purchased also as second hand had undergone major improvements in 1971 by author – the only two transistors 105NU70 from TESLA were spared with polish  low noise BC109 on Japan license. Having also higher h21 allowed  change of  circuitry to obtain lower currents in both stages. Frequency characteristic modified in way to increase higher frequencies during recording mode and complementary lowering their level in reading. That allowed improvement of dynamic. Weary universal head replaced then with new one. After this modifications recorder working frequency range was covering even stereo key frequency at 19 kHz.and maximum dynamic had reached 65 dB. With good tube mono radio SONET B3  in  7-ties and 80-ties  served more than satisfactory. Now, still working in play mode became memorable. Anyway author’s best greetings to TESLA for this  so durable construction.

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TESLA B116 is stereo deck, 4 tracker,  3 heads: recording, reading, wiping, two speeds -9,5/s and 19 cm/s. Factory data 40-15 kHz at 19 cm. After „obligatory” author’s overhaul and adjustments factory data looks by ear still fulfilled, even copying from SONET B3 to B116 had shown copying  stereo key signal from first to second at 9,5 cm/s. (!?) . Granted dynamic 52 dB seems to be underestimated – in standard recording from turntable deck noise does not prevail in black LP level of noise. Author shares rather unusual opinion that recordings get some positive character after written in magnetic tape.


In photos can be seen author’s tuning:

- added lighting to the tape counter in two colours

- channels volume indicators covered with green filters.

- masking blends on switches have red track to enforce visibility of position.

- original sliders handles for recording are not available – another types were adopted.

It is worthy to point out the unusually ergonomic construction of unit for servicing, cleaning an adjustments.

Added on 30 August 2013


My new audio garden :) . See page „What’s new in my audio garden”

panorama C


Update on 14 April 2015

Visual Tuning for Pioneer SX-34

Original enclosure of receiver stands of silver alloy front panel, plated steel chassis with cooling grid, and steel top with cooling grid.

I had experienced some bad conductivity of push pull tubes pins and I blamed for it the high temperatures of upper construction. Bad conductivity is danger of damage for tube. So my idea was to open top cover as much as possible. That is why I replaced U shaped steel plate with wider and higher wooden sides with 5 wooden bars instead small relatively grid. . Usually when listening I take it complete also for nice impression.

Originally scale of receiver is lighted by two small 6,3V radio scale bulbs. Light is beaming from sides of scale, travels in glass by so called „complete reflection” and nicely glows printing on glass at night . Pointer is bronze attached to linkage. My complaint to that solution was that with full light of day often it was forgotten  by me that receiver is still switched on stand by and glows it’s 22 tubes.

Looking for any stronger „sign of life” and to avoid damages I removed original bronze pointer and applied one which I had removed from my another HiFi receiver produced about 1970 by  VIDEOTON from Hungary . It’s made of red transparent plastic and was intended with special reflective cuts  for bulb attachment to make reflected light. Producer resigned to make it working in Chopin but I did in my Chopin also in past. So I transferred that pointer to SX-34, assembled sub miniature 9V bulb and connected by soft elastic wires to side bulbs. Now no forgetting..

    Still I was missing lovely impression of classic tube radios at night. With very low room light they were capable to shine whole their place with big bright scales in center. Just nostalgia. Pioneer SX-34 scale is too small and only two bulbs does not beam light outside scale. In darkness it is not shining around  and front plate id dark.

     Again – to prevent permanent alterations I made cover plastic glass with all needed wholes to  cover whole front plate, designed black frames and assembled six sub miniature 9V bulbs in material of plastic glass. That installation is connected to separate 220V/6V small transformer fixed to main plate. To avoid more  load of tube heaters supply.   The target of lighting is also to make visible the knobs positions according to original printings on front. Now you may see how it looks

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05 June 2015

Step ahead in lighting/tuning modification

 Lighting for  Rotating Control Knobs arranged

To original Pioneer’s rotating knobs fixed round plates with  green transparent windows. That windows are lighted by front plate light dispersed at fixed  to plate round disperse self stick tape. The same tape was used to make  loudness range glowing  marks  for  volume knob. Between the 1-2 and 3-4 knobs visible is loudness activation switch.

Pioneer SX-034 rotating knobs

Front view after modification

Improved front panel of Pioneer SX-34

The original lighting view before modification . Visible is active lighting pointer arranged by author

Pioneer SX-34 scale  lightingPioneer SX-34 front panel

Side view of receiver. and rotating knobs after tuning details.

Modified Pioneer SX-34 side viewPioneer SX-34 Modified knobs

310 myśli nt. „Pioneer SX-34 modification and about other author’s audio stuff 07-2015

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