What determines the size of the output decoupling capacitor?
I'm looking at building a "beefed up" BA-3 preamp with a cascode for the JFETs and current mirrors between the JFET stage and the MOSFETs.
The HPA-1 is similar and appears it uses 100uF at the output (whereas the BA-3 uses 10uF). What are the factors that feed into the choice of values here? (Disregarding cost, space, etc. I'm just trying to understand the electrical side of it.)
Thanks,
Jeff.
I'm looking at building a "beefed up" BA-3 preamp with a cascode for the JFETs and current mirrors between the JFET stage and the MOSFETs.
The HPA-1 is similar and appears it uses 100uF at the output (whereas the BA-3 uses 10uF). What are the factors that feed into the choice of values here? (Disregarding cost, space, etc. I'm just trying to understand the electrical side of it.)
Thanks,
Jeff.
It depends of the load. E.g. if it is 10kohm or 8ohm load. It defines the lower cut off frequency of the "high pass" filter that is formed by the C (output cap) and the R (load) …..assumed it is almost an "ohmic" load.
You may use this calculator to see low end cut off frequency:
RC High Pass Filter Calculator
You may use this calculator to see low end cut off frequency:
RC High Pass Filter Calculator
I can only get a hold of 18-0-18 50VA or 25-0-25 50VA. I already have an 18-0-18 50VA would that be ok to run two channel as it should give 23.5v to the regs, or should I buy the 25-0-25?
I will be using this LM317-337 regulator board - LM317 / LM337 +/-1.5V~37V Adjustable Dual Voltage Regulator Power Supply PCB 699917672211 | eBay
thanks.
I will be using this LM317-337 regulator board - LM317 / LM337 +/-1.5V~37V Adjustable Dual Voltage Regulator Power Supply PCB 699917672211 | eBay
thanks.
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I bought 7020s for mine and they don’t fit great, rather go for these
551002B00000G Aavid, Thermal Division of Boyd Corporation | Fans, Thermal Management | DigiKey
551002B00000G Aavid, Thermal Division of Boyd Corporation | Fans, Thermal Management | DigiKey
Built my dual mono front end/pre and it sounds really good adding a little life into the chain.
Putting it between a passive volume control/source selector will give a flexible setup.
There is only one annoyance, it's adding hiss like an old tube preamp.
Based on others here, it should be dead quiet when input shorted and going into an F6 or M2 - here it is in neither.
The hiss is annoyingly loud at 1m from my 99db speakers. Not that much at the listening seat, but enough to kill the experience. My DCG3 pre does not make a sound in the same chain.
My build is standard parts after the BOM/schematics, board from the store and Fairchild mosfets with 1K pots in P1/P2. PSU is dual mono Salas SSLV1.3 shunts giving the BA3 front end dead on +-24V. Bias and offset seems fine.
Both channels produce exactly the same hiss.
Tried paralell 330ohms to R13 and 100ohms series to R5 after reading here, thinking it would be too much gain. That solved nothing.
Anyone clever?
Putting it between a passive volume control/source selector will give a flexible setup.
There is only one annoyance, it's adding hiss like an old tube preamp.
Based on others here, it should be dead quiet when input shorted and going into an F6 or M2 - here it is in neither.
The hiss is annoyingly loud at 1m from my 99db speakers. Not that much at the listening seat, but enough to kill the experience. My DCG3 pre does not make a sound in the same chain.
My build is standard parts after the BOM/schematics, board from the store and Fairchild mosfets with 1K pots in P1/P2. PSU is dual mono Salas SSLV1.3 shunts giving the BA3 front end dead on +-24V. Bias and offset seems fine.
Both channels produce exactly the same hiss.
Tried paralell 330ohms to R13 and 100ohms series to R5 after reading here, thinking it would be too much gain. That solved nothing.
Anyone clever?
Attachments
Thank you for your answer WalterW.
I haven't tried the volume control after the BA3, only in front. I will try mixing it up a little!
Im thinking supressing the noise/hiss into a potentiometer would not remove it, just mask it until you turn the knob? But it makes sense if it's just gain related. How about impedances placing a pot between?
Others is saying it's dead silent in similar setups, so that kinda had me worrying.
I hope to mainly use this gain stage in front of the BA complementary when done, so hopefully this hiss I'm chasing will not matter.
I haven't tried the volume control after the BA3, only in front. I will try mixing it up a little!
Im thinking supressing the noise/hiss into a potentiometer would not remove it, just mask it until you turn the knob? But it makes sense if it's just gain related. How about impedances placing a pot between?
Others is saying it's dead silent in similar setups, so that kinda had me worrying.
I hope to mainly use this gain stage in front of the BA complementary when done, so hopefully this hiss I'm chasing will not matter.
Thanks! I will give it a try!
Or maybe put up a standard CRC psu - as I have the parts without looking through every box. Should't be too noisy?
