ok then increase only to 15K just for peace of mind
with one pair of output IRFPs what is the max impedance op preamp to drive it?
with one pair of output IRFPs what is the max impedance op preamp to drive it?
How could you keep your peace of mind by modifying the F4 for the worse? Your objective eludes me.
As Papa said, 1k source is ok, insert a better than 1k buffer if your source is higher and you refuse to use the j74/k170 jfets. What is your problem?
As Papa said, 1k source is ok, insert a better than 1k buffer if your source is higher and you refuse to use the j74/k170 jfets. What is your problem?
if preamp is having more than 1K Rout , it's simply sissy
if that's is output stage of some source , it's simply just half sissy
25 years ago , when Rin of power amps were a range higher , situation was different ...... thought pro range was always in 600R area , having far more jewels than common drek intended for home use
if that's is output stage of some source , it's simply just half sissy
25 years ago , when Rin of power amps were a range higher , situation was different ...... thought pro range was always in 600R area , having far more jewels than common drek intended for home use
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The issue is usually more about the capacitance of the Mosfets. A single
pair is easier to drive than 3 pair, so maybe we can relax the output
impedance requirement.
Best thing is to try it and see what you get. You won't break anything.
If it sounds good, then 🙂
I have 2 sources (DAC):
DAC1 is 5K output impedance and 2.8Vrms, don't need gain for good listening volume
DAC2 600 ohm output impedance and 1Vrms, volume is too low
I will try DAC1 to drive directly one pair of IRFP, no gain needed, hooping that capacitance of gates and bias resistors don't load too much the output of the DAC
If I use DAC2 volume is too low, I need some gain preamp
I would try to avoid LSK because with shipping costs and import tax (customs) in europe, it would cost a fortune compared to the rest of the sound chain.
Could you advise me on a schema of a good sounding buffer (if with 3 to 6 db gain even better) not using n and p fets, maybe just BF862 or other easy to find transistor?
If it has the possibility of symmetric input even better, my DAC2 has symmetric output.
DAC1 is 5K output impedance and 2.8Vrms, don't need gain for good listening volume
DAC2 600 ohm output impedance and 1Vrms, volume is too low
I will try DAC1 to drive directly one pair of IRFP, no gain needed, hooping that capacitance of gates and bias resistors don't load too much the output of the DAC
If I use DAC2 volume is too low, I need some gain preamp
I would try to avoid LSK because with shipping costs and import tax (customs) in europe, it would cost a fortune compared to the rest of the sound chain.
Could you advise me on a schema of a good sounding buffer (if with 3 to 6 db gain even better) not using n and p fets, maybe just BF862 or other easy to find transistor?
If it has the possibility of symmetric input even better, my DAC2 has symmetric output.
Try it first as is.
When it is certain that you only need a buffer with no gain, you can build the B1 Buffer. You should use the LSK170 B or A grade if you want plug and play solution. Other n jfets can be used only when you understand how to bias them properly.
If you want real simple solution, use regular buffer chip like the HA5002 or BUF634, needed lower supply voltage can easily be supplied through 7818 and 7918.
If you do need gain, the choice is enormous. I believe the simplest will be the BOZ Preamp.
Good sounding is very subjective. Reserve a more complex preamp for later when you have more budget and know how.
When it is certain that you only need a buffer with no gain, you can build the B1 Buffer. You should use the LSK170 B or A grade if you want plug and play solution. Other n jfets can be used only when you understand how to bias them properly.
If you want real simple solution, use regular buffer chip like the HA5002 or BUF634, needed lower supply voltage can easily be supplied through 7818 and 7918.
If you do need gain, the choice is enormous. I believe the simplest will be the BOZ Preamp.
Good sounding is very subjective. Reserve a more complex preamp for later when you have more budget and know how.
I know this is a risk most people wouldn't take, but do you think you could find NOS Toshiba 2SJ74/2SK170 on ebay available in Europe? Being a little careful about whom I bought from, I bought good Toshiba's in 2017 that are quiet and curve match perfectly (US source).
If you could find a local source, it would be way cheaper than building any kind of buffer or re-engineering the amp. Just a thought.
Good, learn how to match and bias the fets.
BF861A or BF861B will be easier.
861A could complement J270
861B with J271
861B with j309
861C with J310
Yes I know how to match Idss
if those smd jfets are 10cent each I can buy 100 and match them pair to pair
more difficult to measure transconductance without a tracer
861B with J271
861B with j309
861C with J310
Yes I know how to match Idss
if those smd jfets are 10cent each I can buy 100 and match them pair to pair
more difficult to measure transconductance without a tracer
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I think they go for $0.40-0.50 at Mouser. But read up Buffer for Pass' LXmini OX/EQ thread before you proceed.
It's your money and your system, you are free to do as you please.
It's your money and your system, you are free to do as you please.
A DAC with an output impedance of 5kohms sounds very abnormal. Are you misreading the specification?
Or could the specification have been written by a nicompoop. Ask the retailer if the spec is correct? Or measure it yourself.
This seems odd as well 600ohms is on the higher side. and 1Vac as a maximum output is unusually low. Download Pano's sound files and check your output at the set -9dB level.
PM me for a UK source of jFETs.
Maybe I am misreading the datasheets
Dac1 is AK4420
Dac2 is Ak4393 using only the positive out referenced to ground. So half the Vrms output.
Dac1 is AK4420
Dac2 is Ak4393 using only the positive out referenced to ground. So half the Vrms output.
I have nothing new to contribute other than I have been and am currently loving this amp.
Tomorrow I will have everything on hand to finish a second.
My capacitors have hemp in them, and that's all that counts at the moment.
-Cheers
Tomorrow I will have everything on hand to finish a second.
My capacitors have hemp in them, and that's all that counts at the moment.
-Cheers
