Health

Latest Publications

JBAA - High Fidelity Tube Junk Box Audio Amplifier

All DIYers have garbage boxes. I speculate that mine is better than expected. It should be as I have been structuring and assembling gear for a truly prolonged stretch of time. Mine is considerably bigger on the grounds that I have all the left overs and winnows from Oddwatt Audio. Still the appeal of building something from either rescued or surplus parts is very high among most DIYers I know. So what better approach to utilize a portion of the parts than building a truly elevated quality cylinder sound intensifier. To make certain there are heaps of cylinder speaker extends out there. This one is distinctive as the structure, while like a portion of my different undertakings, quite the PoddWatt, it can utilize a colossal assortment of cylinders and different segments. I won't state it is a conventional plan, however it presumably approaches. The genuine speaker in the photographs is one utilizing 12AX7s as enhancer/drivers and 6005s (modern 6AQ5s) as the yields. This intensifier conveys a spotless 3 Watts RMS with around one progressively somewhat less perfect on top. Mutilation and commotion are beneath 1% at 1 Watt and reaction is inside 0.1dB from 20Hz to 50kHz. It is just somewhere near about 0.5dB at 10Hz and 60kHz. The upper - 3dB point is a shocking 100kHz. I did exclude a volume control, yet one could be included at the sources of info. Supplanting the 100K fixed resistor with a 100K control would be my decision. Presently back to the garbage box idea. You can utilize any of the cylinder blends recorded in the segment Suggested Tube Types beneath for both the yield and driver tubes. All function admirably and there are likely some others, especially on the off chance that you utilize the mechanical variants. I have tried it with the majority of them. The more dominant ones like the EL84s will convey around 5 Watts RMS yield. The less incredible ones like the 6GV8 will just convey about 2.5. The essential structure is a push pull ultra direct class "A" type. A genuine pentode rendition would convey somewhat more force yield, yet have about 0.5% more twisting. I didn't think about triode modes, yet they are a plausibility also. Anyway the yield tubes are required to give some pick up and low increase triodes (like 6AS7) won't work. The driver organize is a SRPP followed by a self-modifying yield arrange. The utilization of the consistent current source in the cathodes of the yield arrange takes into consideration single finished drive. It looks weird, yet trust me it works very well. I have utilized it in various DIY and business structures up to push pull KT120s and it is about projectile evidence. The yield transformer is utilized to upset the sign to keep up appropriate stage connections. That way the intensifier is non-transforming and can utilize a negligible measure of negative criticism to guarantee solidness over the sound band. The negative criticism is discretionary and isn't utilized to "tidy up" the sign as in numerous different plans. It has basically no impact on the sound. I do prescribe it as the speakers (contingent upon tube types) can without much of a stretch be affected by high recurrence EMI.



There are a couple of things that are significant in the structure and might wreck a generally decent form. The LM317s will create warmth and need to relax. I mount mine through an opening in the body and utilize a little warmth sink. Know that the tabs on them are not at ground potential. They are really at around 12-18 volts DC. Surely not unsafe, yet in the event that you ground them the amp will fall to pieces. I utilized strong state rectifiers and propose you do likewise for straightforwardness. A cylinder adaptation would work fine however you would need to build the auxiliary voltage of the force transformer to cover the drop in the cylinder rectifier. I utilized DC on the warmers, incompletely on the grounds that the force supply sheets had that arrangement and it is marginally calmer. Air conditioning radiators are fine yet recall in either case the warmer circuit can't be grounded. Doing so will cause the driver cylinder to fizzle. My involvement in all "totem" post plans is that one of the cylinder cathodes will be at around one a large portion of the B+ voltage. On the off chance that you ground the radiator circuit the differential between the warmers and that cathode will be high and my experience has been that anything over around one portion of the cylinder particular for that cylinder will bring about inevitable disappointment through inside arcing. To beat this issue a voltage divider from the B+ is connected to the coasting warmer circuit and raises it by around 60-70 volts DC. There is for all intents and purposes no present stream in the divider. Something else to know about is that I utilize a three wire power association with hot, impartial and earth ground for the AC mains association. The earth ground associates straightforwardly to the frame. This enables it to shield the client from any kind of inward gear disappointment and it can go about as an EMI shield. I suggest steel skeleton as they are the best for that. The enhancer signal ground isn't straightforwardly associated with the body. It interfaces by means of a kind X2 capacitor and parallel resistor. This game plan stays away from ground circles between different parts and the enhancer. A nose to tail parallel pair of rectifiers can likewise be utilized instead of the X2 capacitor and resistor. I for one have not seen that as great however.



The force transformer can be any one that can supply around 360 volts focus tapped for full wave correction or on the off chance that you utilize a scaffold rectifier around 180 volts. For tube rectifiers I would use around 400-430 focus tapped. The all out current required for the cylinders is about 200ma (DC) and to have a sensible edge 250-300 ought to be accessible. The one I utilized had an exceptional radiator optional of 10.9 VAC. It was a "pack" left over part. (Edcor conveys it and will offer it to people) When amended and sifted this gives a decent 12VDC to the radiators. Around 2 amperes are required for the 6005s as I utilized an arrangement course of action for them. Utilizing a real 12 volt auxiliary will require a dropping resistor that will fluctuate in an incentive with the decision of cylinder types. Something in the 0.5 to 2 ohm go is regular. It will disperse a goodly measure of warmth so arrangement is significant. Your capacity transformer ought to have the option to convey at any rate 1.5 occasions the required radiator current.

The yield transformers I utilized originated from Edcor and are type CXPP-MS-10K. They are somewhat expensive, yet like I said my garbage box is extremely enormous and very much supplied. Any yield transformers with 8-10K essential impedance that can deal with 100ma adjusted (50 for every side) or more will be fine. I utilized the ultra straight setup. The U/L taps can be anything from about 23% to 43% and not have a lot of effect. Notice that the plan utilizes the yield transformers to upset the sign. It brings about the general enhancer being "non-reversing". In the event that you check the stage shifts you will see this works. In the event that you utilize negative input and get it in reverse the amp will sway.

The nature of the coupling capacitors is imperative to the sound of the enhancers. You don't have to utilize "boutique" capacitors, however great ones from set up makers are prescribed. I would propose ones from, Panasonic, WIMA, Vishay, Jantzen Audio, Audyn, Sprague, Solen, and comparable ones. The Russian K40Y-9 paper in oil ones are somewhat more expensive yet well in this structure. The 200 volt size in them is adequate. Similarly the nature of the yield transformers is significant. The ones indicated are from Edcor (CXPP10-MS-10K) and somewhat pricy however IMO justified, despite all the trouble. The more affordable GXPP10-6-10K are entirely as acceptable and just diminish the top and base finishes marginally. Hammond ones are accessible too. Every single other part are conventional in nature. I favor one half watt metal film resistors (with the exception of as noted on the schematic) yet the decision is yours. The LM317s do need to have a humble warmth sink.

JBAA Amplifier utilizing 6005 and 12AX7 cylinders

Photo 2: JBAA Amplifier utilizing 6005 and 12AX7 cylinders with a portion of the cylinder types you can utilize

Building the Junk Box Audio Amplifier (JBAA)

The plan fits either PCB or point to point wiring. I utilized both in the enhancers appeared in the photographs. My capacity supply was on a PCB left over from a business pack, however the rest of the hardware was point to point. It was not especially rich, yet well into the soul of DIY. As usual, I prescribe utilizing a frame about 1.5 occasions the size you think you need. It makes for simpler forms, simpler difficulty shooting (stuff occurs every now and then) and better part cooling.

Cautioning: This venture utilizes conceivably deadly voltages and ought not be attempted by any individual who is curious about with working with such voltages or may not be OK with ventures that involve such voltages.

JBAA (Junk Box Audio Amplifier) Schematic

Figure 1: JBAA (Junk Box Audio Amplifier) Schematic 


The genuine form isn't especially basic and the design is entirely adaptable. You have to utilize great wiring practices and binding system. I locate that most form disappointments are a direct result of binding issues. A "chilly weld joint" will wreck a generally decent form and regularly be elusive. I am supportive of ensuring the earth, however I just use toxic bind. I have seen an excessive number of DIY develops that were messed by lead free bind. It surely will work, however takes more aptitude and more warmth to get right. I utilize a hot iron (900 F) to safeguard great associations. I have discovered that high warmth for a brief span works far superior than lower heat and a long term. Segments are more averse to be harmed that way and associations bound to be acceptable. A few interesting points in the format and manufacture are:

Shield all low level sign conveying conductors over around 5 cm long.

Utilize a significant sign ground buss or star course of action.

Get signal wires and segments far from different wires and segments that convey power, especially on the off chance that it is AC. Watch for touchy rounded sign capacitors. Some get murmur and commotion from outside sources.

Spot the driver tubes from the force transformer. The yield tubes for the most part don't make a difference.

Make certain to ground the transformer cases to the undercarriage by scratching ceaselessly

No comments