# My Ultima DB-01 Dual JFET+DB Head-Amp



## mtlin12

Introducing my new Cascode JFET+Diamond Buffer Pre-& Head-amp, Ultima DB-01.






 Using DIYZONE's shunt regulator +/-24V for DB-01 with Relay PCB






 stereo Ultima DB-01 Pre-& Headphone-Amp Module






 Circuit Topology: All discrete JFET,BJT except LM334Z for C.S with no zener diode and aluminum Capacitors on the module.

 The input stage is Linear Systems LS844 low noise Dual JFET.
 This module was modified from my 150W MOSFET drive module.

http://myweb.hinet.net/home3/mtlin12/audio/articles.htm


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## guzzler

wow! that is a seriously professional looking job! and a very nice looking setup overall; good stuff!

 g


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## mtlin12

Thank you, guzzler.

 Actually Ultima DB-01 not only LS844 Dual JFET, but also use other
 7*JFET, 2*CRD, 13*BJT, many 0.1% Philips resistors and Wima caps, 
 it cost a lot, but it is worth for DB-01's high speed, low noise and 
 high current drive capability (>200mA). It is the same
 as my Ultima DT-01 MOSFET 150W Amp, all designed for SACD.

 I've test them with my Marantz SACD DV8300, my headphone AKG
 K-501 and my speaker B&W P6, it's better than my new tube Pre-Amp 
 and my old Perreaux 3350 300W MOSFET Power Amp.






 DB-01 at 10K Hz Square wave input vs ouput






 DB-01 at 100K Hz Square wave input vs ouput






 DB-01 at 50K Hz 100 Ohm loading output 11.3Vrms






 DB-01 at 50K Hz 100 Ohm loading nearly no phase shift






 Very low noise about 10uV rms when input shorted .
 DB-01 original bread board with DZ STAX-like shunt regulator.


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## JohnFerrier

Nice 1st and 2nd posts. What output transistors did you use? What VCC?


 JF


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## mtlin12

I use normal MJE340/350 as output stage, it maybe not the best choice , but just the same as my second cascode stage, 
 when in DT-01 power amp mode I drive them at +/-68V, of course MJE340/350 can sustain much higher voltage.

 When use in the DB-01 headphone-amp, the DZ STAX-like Shunt
 regulator's voltages are +/-30V , and their currents are set at 280mA for both channels.

 The other DZ's shunt regulator use OPamp instead the STAX-like 
 differential BJT, it is set at only +/-24V.

 All pictures above are tested with STAX-like +/-30V shunt regulator. Because AKG K-1000 needs more power!


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## ppl

A Real nice design, there is nothing wrong with using an Op amp circuit topology as the basis for a discrete component design. I know of at least one well respected Amplifier designer that learned Amplifier design from Playing with discrete versions of Circuits found in Op Amp data Sheet simplified Schematics.

 You might give some consideration to the Following Changes I would do to your circuit. (1) Add resistors to the base of Output and driver transistors to Kill the "Q" formed by Wire inductance and the transistors input capacitance. (2) using the lower current source to balance the Differing gain of the NPN and PNP Voltage gain stages. is a great idea and i have done this allot myself, However you could also leave that fixed and adjust the current source between the Bases of the transistors as an alternative. 

 Cascoding a Jfet to a BJT is or shall i say can be made into an Ideal Cascode. I would be interested in why you used a Jfet + BJT Cascode rather than an BJT+BJT or JFET+JFET Cascode?

 Is that phase lead cap across the feedback there by default or did you have instability problems without it? if unstable with out the cap the circuit should be made stable without it and then if you still like use the cap to trim the Sq wave Response. IMHO phase lead compensation should not be relied upon to stop oscillation as this then is just a band-Aid used to fix an inherently unstable circuit. I do not like the use phase compensation cap's as they seriously affect the sound through out the audio range even though the effect of the capacitor is well up in to the MHz. range. Since it is your design the choice is yours as to the use of this cap or not just as long as the circuit is stable without it.

 Good luck and happy listening to your Amp and please do share any further Designs you come up with on this Site.


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## JohnFerrier

Thanks for the pictures and information.

 Is this a finished project, or do you have other ideas that you want to try?


 JF


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## mtlin12

Thank you, ppl. Your suggestions are very good.

 Let me explain why I use JFET+BJT, it simply wants to have some different designs with Erno Boberly's JFET+MOS , the BJT actually
 should be a darlington pair, I use 2N5551/5401 with MJE340/350,
 to get higher hfe.

 2. I do not like cap in signal pass also, it is not because of unstable, I use 22pF to filter 200KhZ above, I think maybe can lower some noise, I use 2 other 22pF ceramic caps , one is for phase lead.

 3.The CRD is choosed about 2mA, and I use High hfe BJT 2SC2240/2SA970 in the front that will lower the current from JFET.

 4.The first stage current source, I even add a zero temp-compensate diode between the JFET and LM334, it is also set at 2mA.

 5.Between the two Voltage source , I also design a stand-by circuit , that can stop the current source's working, but it must
 be co-work with my relay board, it is not very useful at the Pre-amp, but very useful at the power amp. It also can be controlled by microprocessor.


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## mtlin12

Quote:


 Is this a finished project, or do you have other ideas that you want to try? 
 

I have finished two projects on Ultima-1 series, DT-01 and DB-01.

 Now in Taiwan, they have been licenced to DIYZONE.

http://www.diyzone.net 

 I'm still plaining other products using this same structure module.
 Like this:




 using SANKEN BJT 2SC2922/2SA1216 Pc200W to have about 70W.







 It is very easy to changed from 70W Class AB to 25W Class A design.


 But first I just want to ensure the DT-01 and DB-01 to be 
 excellent products for DIYer.


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## mtlin12

It is time I should go to bed, see you tomorrow.


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## erix

Nice work!

 You stole my fire with the stacked PCB's though! I have a couple of amps in the works using that idea. 
	

	
	
		
		

		
		
	


	




 Keep it up!

 ok,
 erix


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## Superkiwi

Bravo!


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## steel

That's a great job....


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## jeffreyj

Quote:


 _Originally posted by ppl _
*...
 You might give some consideration to the Following Changes I would do to your circuit. (1) Add resistors to the base of Output and driver transistors to Kill the "Q" formed by Wire inductance and the transistors input capacitance. 
* 
 




 Mtlin, this is an excellent suggestion; alternatively, you can try slipping a ferrite bead over the Base leg; sometimes this works just as well and has the added benefit of counteracting some of the inevitable phase shift.


  Quote:


 *...IMHO phase lead compensation should not be relied upon to stop oscillation as this then is just a band-Aid used to fix an inherently unstable circuit. * 
 

Ppl and I don't quite agree on the use of pole compensation (aka - phase lead, from when your only choice of amplifying device was a vacuum tube), but the point he makes above is a good one. If your circuit is oscillating, then it needs some help. Despite my evil love of pole compensation - 
	

	
	
		
		

		
		
	


	




 - I would ditch the cap in this case because the output buffer topology looks to be extremely well behaved. If there is any hint of misbehavior (as is, there is just the barest hint of underdamping in the first square wave response photo), such as leading edge ringing, then I'd try swamping the Miller capacitance of the voltage gain stage with 47-100pF. This is usually much less offensive to the most sensitive ears among us (which I *don't* claim to have, mind you...)


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## mtlin12

I watched closely at my Metrix OX 800 scope, and I found there
 exist about 1.5MHZ oscillation in the first few minutes when powered on. 
 I doubt it was caused by the shunt regulator, so I
 use the pole compensation cap to minimized this oscillation, I
 think if there is no harm for the power Amp, user can take this 22pF off.

 In my "paintbrush" layout PCB, there are many options for DIYer
 to change the circuit, including the resistor to the base of the BJT.
 Also different pin functions like 2SK214/2SJ77 and IRF610/9610
 MOSFET can be handled, I want users to decide which component
 will be the best.

 In original design, DT-01 used MOSFET to be the source follower.
 But in DB-01, I found that Diamond Buffer structure's speed is much higher 
 than the MOSFET, because of the Ciss, Crss of the MOS is much higher arround 
 100pF, so I decided to use Diamond output Buffer, very similar with the META42?!

 Sorry, I must go to the church right now, see you.


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## JohnFerrier

I was having some trouble with the term "Diamond Buffer". I found a short write up and figure 22 that helped a bit.

http://web.engr.oregonstate.edu/~bat...tes/AB-183.pdf

 Others here are probably familiar with the diamond structure.



 JF


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## mtlin12

You can also see on the Burr-Brown BUF634 datasheet:

http://focus.ti.com/lit/ds/symlink/buf634.pdf 

 Several Headphone-amp use this 250mA high-speed buffer.

 I just changed it to discrete components.


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## JohnFerrier

Quote:


 _Originally posted by mtlin12 _
*You can also see on the Burr-Brown BUF634 datasheet:

http://focus.ti.com/lit/ds/symlink/buf634.pdf 

 Several Headphone-amp use this 250mA high-speed buffer.

 I just changed it to discrete components. * 
 


 The text in the BUF634 mentions nothing about diamond structure and the simplified diagram does not resemble your schematic. Are you sure you mean BUF634? Maybe OPA633?


 JF


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## mtlin12

As you mention on the Burr-Brown Application Bulletin of OPA660
 page 2 schematic, between pin5 and pin6 it is called Diamond 
 Buffer (DB), it construced by the same base NPN & PNP and two
 push-pull emitter follower, other 2 BJTs function like current source
 which I use 2 CRD instead.

 So if you check the BUF634 structure page 7, it will be the same,
 only BUF634 built-in input output protect circuits.

 My DB-01 built one BJT bias at 0.6V ~ it will give the output R 10£[
 to have 0.3V each, it means 30mA static current, quite a lot for
 headphone amp.


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## J.Y.

Great work!!
 Impressive layout. Although I know little about the circuit, the transformer and the enclosure always looked amazing to me..


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## mtlin12

This is the DB-01 full circuit diagram, it should be made as a tiny
 module as several SMD produucts do. But it is quite small now.






 Sorry, I have no tool about circuit drawing, I just can use paintbrush only.

 The two resistors R* are suggested by ppl, DIYers can add them on the original PCB, 
 don't have to cut any copper side.


  Quote:


 You might give some consideration to the Following Changes I would do to your circuit. (1) Add resistors to the base of Output and driver transistors to Kill the "Q" formed by Wire inductance and the transistors input capacitance.


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## ppl

Looks good, although the driver transistors need Base resistors and since you have them pluged in to the main board with probaly some lenght of wire you should use a resistor at the base or the alternate method sugested by jefferyj by sliping a ferrite bead over the base lead. BTW put these parts as close to the atual base lead of the Driver transistors as possible.


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## mtlin12

Quote:


 _Originally posted by ppl _
*Looks good, although the driver transistors need Base resistors and since you have them pluged in to the main board with probaly some lenght of wire you should use a resistor at the base or the alternate method sugested by jefferyj by sliping a ferrite bead over the base lead. BTW put these parts as close to the atual base lead of the Driver transistors as possible. * 
 

Thank you, you are very kind.






 The DB-01 is all on this tiny PCB, the Diamond Buffer BJTs are on the top of the photo,
 when use as a pre & Head-amp ,it is no need to be pluged in to the main board.

 The main board is called DT-02, there are some holes for power MOS like 2SK1529/2SJ200 or 
 power transistors like Sanken 2SC2922/2SA1216.






 150W MOSFET module using Toshiba 2SK1529/2SJ200 
 DT-01 is a little different from the DB-01, the drive voltage is +/-68V, 
 and it does not have diamond buffer but IRF610/IRF9610 or 
 Hitachi 2SK214/2SJ77 instead.








 Ultima-1 DT-01+DT-02 and power transformer.

 Ultima-1 also included a special stand-by circuit, that can stop
 Q16 constant current, and cease the two voltage sources at the
 same time, and shut-down the output stage, so it need relay
 board. The two LEDs are designed for showing power-down or not,
 DB-01 doesn't have this function, so the LEDs can be shorted to
 get more higher output voltages.


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## ppl

good trick on the shutdown circuit. Also note that mosfets tend to be more unstable than BJT's so quite large resistors should be in series with the Gate of these and right on the Gate leed 220-1K should work ok. slipping a ferrite beed over the gate leed in addition to the resistor is also helpful. you might give some thought to playing around with the value of C9 typicay 0.1UF is used hear by default however some circuits sound better with higher value capacitors and Some high End Amps use a Non polar electrolytic and bypass that with a film cap. a polar Electrolytic is not a good idea at this point although i have seen them used at this location.

 You also might give a try to driving the Base of Q25 right off the colector of Q5 and Q6 and not making the signal go through the LED. do the same with Q26 and Q18 & Q19.


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## mtlin12

As above I said,
  Quote:


 DB-01 doesn't have this function, so the LEDs can be shorted to 
 

C9 I use 2.2uF/100V WIMA MKS4, yes I think it is important to use
 film cap. here, it is at the top on the PCB two big red ones. 

 C9 can also mentain some current when shutdown stared, I have to 
 make sure that the relay is off first.


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## mtlin12

ppl said,
  Quote:


 Is that phase lead cap across the feedback there by default or did you have instability problems without it? if unstable with out the cap the circuit should be made stable without it and then if you still like use the cap to trim the Sq wave Response. IMHO phase lead compensation should not be relied upon to stop oscillation as this then is just a band-Aid used to fix an inherently unstable circuit. I do not like the use phase compensation cap's as they seriously affect the sound through out the audio range even though the effect of the capacitor is well up in to the MHz. range. Since it is your design the choice is yours as to the use of this cap or not just as long as the circuit is stable without it. 
 

I have double checked again that the C7 22pF across the feedback can be removed no problem now, I have fixed the problem of the start-up 1.5 MHz oscillation caused by the shunt regulator.

 Thanks, ppl.


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## mtlin12

This is one pre-amp made by my friend cjr84, he used shunt regulator and hand-made stepped attenuator by himself.

 Very low noise! And pure DC amp without DC servo or output capacitor.


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## JohnFerrier

Nice. I like that work. Nice metal enclosure. JFETs and low noise--kind of like the project I'm finishing soon.

 I wonder what gain you are using. As low as 10uV rms noise is it seems higher than I would expect (maybe more like 2uV). It's difficult though to measure such low level signals. You may be using high gain too--like 20+???.


 JF


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## mtlin12

The gain is 20dB, i don't have professional test equipment to
 measure how low noise it will be, next time I should try to borrow
 an AP2 again.


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## mtlin12

I've spent 4 days to build up this Full Balanced pre & headphone 
 amp, I used 4 DB-01 amp-module and a large hand-made stepped attenuator by 
 my friend cjr84, with shunt regulator and speaker (headphone) protector. 
 I also used a copper shielding tolimit noise from the transformer.


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## JohnFerrier

FWIW Steel is better at shielding low frequency tranformer noise than copper. Copper certainly will not hurt... See figure 16 here: http://www.analog.com/UploadedFiles/...6254AN-347.pdf


 JF


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## mtlin12

why not use
*sziklai-darlington diamond buffer (SDDB) for power output stages ? * 

 from http://www.diyaudio.com/forums/showt...threadid=54247 

 I changed a little circuit of my own DB-01 headphone Amp recently,
 to test the SDDB power output stages, and find it works very
 good with my AKG-501.

 I think it can be changed with only few components to
 be a small Class-A power Amp.

 here are the two circuits' pdf.files and pictures about the head
 phone amp, please note the first output stage with only 4 bjts
 , and the second with 6 transistors.

 M.T. 

ULTIMA-SDDB CLASS-A AMP CIRCUIT PDF FILE 







 DB-01 with normal 4-transistor DB






 DB-01 with 6-transistor sziklai diamond output buffer


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## individual6891

Wow cool, the stacked PCBS remind me of my old GCSE project..












 AM Transmitter for a remote control car. Acts like a transponder, sending a high logic output via AM encoder/decoder (HT12 series) to a seperate receiver linked to a PIC counter. Times lap times for RC cars, everytime they pass the white start/stop line 
	

	
	
		
		

		
		
	


	




 (yes that's a lot of dust)


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