PigletsDad
My intelligence test came back negative.
1uF/10K gives 10ms time constant, 3dB rolloff at 16Hz.
Audible loss of deep bass. 30K should fix it.
Audible loss of deep bass. 30K should fix it.
B4 Buffer PCB (and parts) new GB #3?
- Thread starter natzev_i
- Start date
istari_knight
pfm Member
Thanks for the confirmation.. At least I know I'm not going mad
I've made another change tonight, R5/105 is back to 10k but C5/105 have been replaced with jumpers which has really lifted a veil... The difference is such that I cant believe I thought it sounded alright with them in place.
I'll remove the output coupling caps next but I need to buy some more trimmers first.
istari_knight
pfm Member
Trimmers fitted @ R3/R103 and output caps removed.
Much more like it ! I would advise anyone that has coupling caps on the power amp input to remove them from the B4.
Much more like it ! I would advise anyone that has coupling caps on the power amp input to remove them from the B4.
jwb5463
pfm Member
C5=1uf/R5=10k is what's on the Mouser all-in-one link so I'd guess there's a few people not getting the best out of it yet.
I've just replaced the output caps with wire links, and re-used the 3.3uF MKS4s as input caps. Drops the rolloff from 16 to 4.8Hz
Hate to quote myself: but was my question completely stupid?
These must be some experiences with different transistors.
PigletsDad
My intelligence test came back negative.
I would need to check the spec sheets for the parts.
PigletsDad
My intelligence test came back negative.
Answer: would probably work, but not recommended - much slower transistor, with low gain.
The B4 Looks interesting only problem seems to be hard to get parts i.e. the 1N5287/5297 from UK suppliers
But if there is a common replacement I would be interested in getting the PCB if still available on Here and is there a link to an updated parts list and build manual and Schematic
Thanks
Col
But if there is a common replacement I would be interested in getting the PCB if still available on Here and is there a link to an updated parts list and build manual and Schematic
Thanks
Col
There's no readily available replacements for the above diodes as far as I am aware. The diodes do ramp up the price of a B4, but it's still a very cheap pre amp for what you get.
istari_knight had surplus of the 1N5287/J501 not so long ago at a very good price, so well worth PMing him. I found some 1N5297/J505 going cheap from a UK supplier fairly recently, but iirc they may have been duff...I'll look into it. I order from Mouser fairly regularly, so I could always add some diodes (£4.60 each last time I ordered, now £5.14) to my order and forward them to you, if that helped.
istari_knight had surplus of the 1N5287/J501 not so long ago at a very good price, so well worth PMing him. I found some 1N5297/J505 going cheap from a UK supplier fairly recently, but iirc they may have been duff...I'll look into it. I order from Mouser fairly regularly, so I could always add some diodes (£4.60 each last time I ordered, now £5.14) to my order and forward them to you, if that helped.
Hi grazie
Thank you for your reply
And Thanks for offering to forward them on I will see whats what then PM you later if need be litteldiode have J501/505 but pricey
Thanks
Col
martin clark
pinko bodger
Alternatives:
http://www.pinkfishmedia.net/forum/archive/index.php/t-149013.html
Another solution would be to use a jfet and a selected resistor to make a 2-pin current source yourself.
If you short teh gate and source pins of a jftet it limits teh current passing through it to Idss - this really is all that the J50x and similar parts are, inside: selected jfets with two pins shorted.
Since discrete jFets will have quite a large spread, you can set the drain current you want by interposing a resistor between source and gate, and drawing the output from the gate side of that resistor. the R value will depend on the jfet family you choose in the first place, mostly, and for these low currents (0.3 and 1.0mA) being in the range 1-3Kohms (guess) will likely swamp the Idss spread anyway.
Afterthought: Adding the resistor gives much better current regulation but the 'gotcha' here is that the B4 operates with very small voltage drops across the diodes -which isn't ideal for best performance of a jfet current source (which is best at least 2x vpinchoff across it). Likely much better than just using a resistor though (that works, too)
http://www.pinkfishmedia.net/forum/archive/index.php/t-149013.html
Another solution would be to use a jfet and a selected resistor to make a 2-pin current source yourself.
If you short teh gate and source pins of a jftet it limits teh current passing through it to Idss - this really is all that the J50x and similar parts are, inside: selected jfets with two pins shorted.
Since discrete jFets will have quite a large spread, you can set the drain current you want by interposing a resistor between source and gate, and drawing the output from the gate side of that resistor. the R value will depend on the jfet family you choose in the first place, mostly, and for these low currents (0.3 and 1.0mA) being in the range 1-3Kohms (guess) will likely swamp the Idss spread anyway.
Afterthought: Adding the resistor gives much better current regulation but the 'gotcha' here is that the B4 operates with very small voltage drops across the diodes -which isn't ideal for best performance of a jfet current source (which is best at least 2x vpinchoff across it). Likely much better than just using a resistor though (that works, too)
neiljadman
Senior Member
The 1N5297 and the IN5287 are both available from stock at Mouser.
They are going up in price - now at $6.45 each = Tax + Shipping
It might seem tempting to save buy buying from eBay, but reading the threads ~90% of the problems encountered have been dud diodes of t'Bay And given the overall cost of parts - this is still a very inexpensive preamp to build.
They are going up in price - now at $6.45 each = Tax + Shipping
It might seem tempting to save buy buying from eBay, but reading the threads ~90% of the problems encountered have been dud diodes of t'Bay And given the overall cost of parts - this is still a very inexpensive preamp to build.
martin clark
pinko bodger
Ouch.
I've just had a quick look at the jfet+resistor idea; based on teh datasheet for something available and cheap (the 2N5457, 60p at Rapid electronics) it looks like gate-source resistors of R=4K7 for 0.3mA out and R=820 for 1mA output is about right, and should maintain regulation down below 2V too, which is useful to the B4. Output impedance should be up around 500Kohms or more too - 'good enough' in other words.
I've just had a quick look at the jfet+resistor idea; based on teh datasheet for something available and cheap (the 2N5457, 60p at Rapid electronics) it looks like gate-source resistors of R=4K7 for 0.3mA out and R=820 for 1mA output is about right, and should maintain regulation down below 2V too, which is useful to the B4. Output impedance should be up around 500Kohms or more too - 'good enough' in other words.
PigletsDad
My intelligence test came back negative.
The low current diode (nominal 0.3mA) is the one that runs on about 4V; the other sees most of a voltage rail. So I think this should work out fairly well.
Much of the variation in JFETs is in the value of IDSS; the spread of currents at larger values of VGS tends to be much less, so you should get reasonable matching out of the box. There is also the option to hand select the resistor values for close current matching; if a particular JFET gives too little current, reduce the resistor, too much increase it.