I have seen these zero zone board before. Also a Chinese creation. What capacity are the big PSU Nichicon caps? They seem a bit small to me.. 4700uf 35V is normally 30x30 if I remember well.
Yes it´s a Zero Zone, but basically is the same kit. I have not received yet.
This kit has a "Precision paired genuine Toshiba A1358 C3421" (probably fake) but I want to compare between Toshibas and DB139/140 (original and matched).
Then, I would like do the typical mod:
. Replacement 1k1 for zener (I read something on HF)
. Mach pair of 550/560
. Replacement LM317/337
. Mundorf Mcap 2.2uF on Input.
. Replacement A1358/c3421 for a matched pair 139/140 if it´s necessary.
. Change Out put Resistors
. Change some OPA´s
Yes, the Nichicon are 3300uF but I think that it's not critic (is easy and cheap buy a pair of Nichi KW 4700uF/50 volt).
This kit has a "Precision paired genuine Toshiba A1358 C3421" (probably fake) but I want to compare between Toshibas and DB139/140 (original and matched).
Then, I would like do the typical mod:
. Replacement 1k1 for zener (I read something on HF)
. Mach pair of 550/560
. Replacement LM317/337
. Mundorf Mcap 2.2uF on Input.
. Replacement A1358/c3421 for a matched pair 139/140 if it´s necessary.
. Change Out put Resistors
. Change some OPA´s
Yes, the Nichicon are 3300uF but I think that it's not critic (is easy and cheap buy a pair of Nichi KW 4700uF/50 volt).
The KW series.. is it higher ranked than the KG type II?
I would advise everyone to just buy an empty board and cherry pick your own components.. because these Chinese boards are loaded with who knows what.. soldering voltage regs and transistors out is doing more harm to the board than you will gain by it.. The Zero Zone board was not the most high quality board considering the thin contacts used to solder on. Doens't really respond well to heat. So be careful. If you get an empty board of good quality, you can control the whole populating process from beginning to end.. I would trust that way more than what these Chinese shops do for you to make a profit.
I am going to do some other mods. I am going to experiment a bit with the impedance circuit around the opamp like suggested by abraxolito in one of the first posts.
Will replace the 4.7K, 2.2K and 680R resistors with some higher impedance ones. I have ordered two sets to try. 47K, 22K and 6.8K and 1M, 470K and 150K. I will solder in some sockets to do quick comparisons between the sets. I will keep the ratio the same but lower current. The goal is to enhance dynamics. Will keep the originals so no harm done if it doesn't work out.
H
I would advise everyone to just buy an empty board and cherry pick your own components.. because these Chinese boards are loaded with who knows what.. soldering voltage regs and transistors out is doing more harm to the board than you will gain by it.. The Zero Zone board was not the most high quality board considering the thin contacts used to solder on. Doens't really respond well to heat. So be careful. If you get an empty board of good quality, you can control the whole populating process from beginning to end.. I would trust that way more than what these Chinese shops do for you to make a profit.
I am going to do some other mods. I am going to experiment a bit with the impedance circuit around the opamp like suggested by abraxolito in one of the first posts.
Will replace the 4.7K, 2.2K and 680R resistors with some higher impedance ones. I have ordered two sets to try. 47K, 22K and 6.8K and 1M, 470K and 150K. I will solder in some sockets to do quick comparisons between the sets. I will keep the ratio the same but lower current. The goal is to enhance dynamics. Will keep the originals so no harm done if it doesn't work out.
H
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No, but I know the KW and i like it. I use this series cap on others PSU and work fine. If I like the amp, this could be a future Mod; replacing PSU cap.
Thanks for advice, you're right. 🙂 But I think that if you don´t know the amp, how it sounds, (as in my case), the best option is buy a complete amp. Then you can mod, replacing, and finally, If you like, you can buy a good quality PCB and pick components
It sounds very interesting. Do you think that will change the sound or performance?
I did almost that mod on my Lehmann clone and I would almost say the difference was 'night and day'. But I won't go that far 🙂 I actually moved the feedback R to the output of the diamond so its not quite the same.
My Lehmann variant had a TL072 as the opamp and that's known to have poor drive capability. With a beefier opamp there I suspect the difference will be more subtle. Let's see what Cidious reports.
I had some time to tinker some more with the headamp today.
I noticed that the first heatsink to heat up is the LM337.
That and that I get about 13mV one channel and 15mV on the other (nothing plugged in) tells me something is off.
I'll start with measuring parts around the vregs, then if they all measure ok, I'll swap the LM337 (the one fitted is ON, not by choice but that is what the supplier sent so the rest are the same brand).
I've made sure heatsinks are not toughing surrounding parts both visually and by putting transformer tape (mylar or capton, I don't remember which is which now) on the PCB under the heatsinks for the voltage regulators.
*sorry about poor quality cell phone pic*
I noticed that the first heatsink to heat up is the LM337.
That and that I get about 13mV one channel and 15mV on the other (nothing plugged in) tells me something is off.
I'll start with measuring parts around the vregs, then if they all measure ok, I'll swap the LM337 (the one fitted is ON, not by choice but that is what the supplier sent so the rest are the same brand).
I've made sure heatsinks are not toughing surrounding parts both visually and by putting transformer tape (mylar or capton, I don't remember which is which now) on the PCB under the heatsinks for the voltage regulators.
*sorry about poor quality cell phone pic*
Attachments
Did you isolate the lm337 from the heatsink also ? It should make good contact with the heatsink and isolate heatsink from the board.
You could just swap it for another sample, but have you paired all resistors ?
You could just swap it for another sample, but have you paired all resistors ?
Yes I know, I tried both with TIM only (Phobya Nano-Grease Extreme) and with a pad between heatsink and vreg.
Still, as they heat up fast there should be good enough contact between IC and heatsink (thermal transfer, not electrical contact).
All resistors are tested with LCR-meter/transistor tester and all have the same value.
About 7 or 8 years ago, before I became a DIYer, I bought a (orig.) Lehmann BCL hp amp. (for good money) . Last year I disassembled it, did some measurements and experiments on a breadboard, the plan was to build a redesigned improved version. But as offten happens, I shiftet this project to an indefinite point in time.
After reading this thread I got some inspirations and motivation to move on with it. Thanks
Mayday:
Runs the LM337 significant hoter then the 317 ?
Have you measured the output voltage of the regs. and as well the input voltages? They should be symmetrical (with slight variation of course). Also the BIAS current of the outputstage would be of interest (Sorry if you already posted it and I missed it).
The 15mV DC at the output seems to me not very dramatically.When I remember right, I was not pleased with the DC accuracy of my Lehmann, but can´t remember the values.
If you want me to do, I will measure it in the evening and tell you.
After reading this thread I got some inspirations and motivation to move on with it. Thanks
Mayday:
Runs the LM337 significant hoter then the 317 ?
Have you measured the output voltage of the regs. and as well the input voltages? They should be symmetrical (with slight variation of course). Also the BIAS current of the outputstage would be of interest (Sorry if you already posted it and I missed it).
The 15mV DC at the output seems to me not very dramatically.When I remember right, I was not pleased with the DC accuracy of my Lehmann, but can´t remember the values.
If you want me to do, I will measure it in the evening and tell you.
You can replace it just to be sure.
I have another question. The 2 3R 1W resistors in between the Mundorf caps are getting quite hot and they might be producing noise. I am going to replace them with some 2W dales. I have some black DALE CW-28 Wirewound and some light brown DALE CMF65 metal film resistors. Which should be the better choice for the PSU ?
I have another question. The 2 3R 1W resistors in between the Mundorf caps are getting quite hot and they might be producing noise. I am going to replace them with some 2W dales. I have some black DALE CW-28 Wirewound and some light brown DALE CMF65 metal film resistors. Which should be the better choice for the PSU ?
Hi,
I don't know if it is significantly hotter, I can only estimated the difference since I simply put a finger on the heatsink.
It does get hotter, and does so faster.
After a while the other heatsinks get very hot as well.
I have not measured regulated voltage yet.
I don't think the circuit runs that high in class A, I don't remember the values now and the values I do have are from simulations in ltspice.
I'm writing from my phone, so I don't have any info in front of me. Just what I remember.
Transformer is a 2x15vac toroidal transformer.
Please do measure DC offset, would be nice to have the values of the original 🙂
I'll remove the PCB from the enclosure and go over the board one more time with the DMM.
I'll swap the lm337 while I'm at it just in case as I have plenty.
Hi Cidious,
These 3R resistors in this position are not critical at all.
I did some thermal noise calculation: 3R at 25 °C gives 0,031µV noise voltage (in audioband). 3R at 75 °C gives 0,034µV. The voltage noise produced from LM317 (with bypass cap. at the adj. pin) at output is in the best case about 25µV. Lowering the temp. of the resistors will bring you a really negligible improvement.
These 3R resistors in this position are not critical at all.
I did some thermal noise calculation: 3R at 25 °C gives 0,031µV noise voltage (in audioband). 3R at 75 °C gives 0,034µV. The voltage noise produced from LM317 (with bypass cap. at the adj. pin) at output is in the best case about 25µV. Lowering the temp. of the resistors will bring you a really negligible improvement.
Hi Mayday,
it measures better than I thought.
2mV at left ch., -5mV at right ch. ( gain switch 0dB, 10 min. warm up time)
The values are of course drifting with temperature.
it measures better than I thought.
2mV at left ch., -5mV at right ch. ( gain switch 0dB, 10 min. warm up time)
The values are of course drifting with temperature.
I didn't have time to tinker with the headamp after all.
We went to the club and my fiance did some training with our dog.
I did manage to put together a shunt reg, got it as the pcb was very cheap and I had all parts at home already.
If it's good, then it was a find, if not...only about $5 lost not including parts but those can be removed and used for other things.
We went to the club and my fiance did some training with our dog.
I did manage to put together a shunt reg, got it as the pcb was very cheap and I had all parts at home already.
If it's good, then it was a find, if not...only about $5 lost not including parts but those can be removed and used for other things.
The reg in the pic is not meant for this headamp.
I've used LT1083 vregs for my previous BCL clone though.
I did the resistor experiment around the opamps by raising impedance. Failed experiment.
The idea came from Abraxalito that had some good experience with the mod with his Lehmann and some other amps. But what happens is that it sounds nice with my active loudspeakers since they have seperate amps.. but after the mod the amp is not able to drive my Mad Dog cans anymore. Everything sounds flat and dull.
I would not advise this mod to anyone driving serious cans like the Mad Dog planars I have not tried my low impedance M50X because I use the Mad Dogs mostly.
The idea came from Abraxalito that had some good experience with the mod with his Lehmann and some other amps. But what happens is that it sounds nice with my active loudspeakers since they have seperate amps.. but after the mod the amp is not able to drive my Mad Dog cans anymore. Everything sounds flat and dull.
I would not advise this mod to anyone driving serious cans like the Mad Dog planars I have not tried my low impedance M50X because I use the Mad Dogs mostly.