OldManMatt
Active Member
Hello to anyone that reads this, hope life is being good to you. I have a question that seems to have been asked a thousand times yet I still need a little clarification. I hope I posted this in the correct area, and all though I'm not a newbie or beginner to audio I felt maybe these are beginner questions.
The last year or so I've been dabbling in DIY type stuff, replacing old parts on old gear, tube preamp kits, a couple dynakit rebuilds. So my question comes from me working on a tube preamp, fixing a couple issues that the prior owner left for me. I do have to take out the output capacitors on this preamp and I've been told I need to raise the value to make sure my bass rolloff is high enough for the low input impedance of the power amp..so here's my questions.
If the builder of the preamp designed the preamp to send the full bandwidth with say a .22uf output cap and there is no impedance mismatch between the Pre and Power amp, why do I need to raise the value? The power amp has a low 10k ohm input impedance. The output Z of the pre is like 100 ohms. Should be a big enough gap to cause no issues, but that depends on who you ask. If I follow the normal guidelines I read everywhere I should up the value on the cap to at least 2.2uf I believe, I didn't check the capacitor calculator but this number is what was thrown in my ear.
I feel like I understand how that works or the theory behind it, but if a preamp was designed to work a certain way with certain values and there is no mismatch do I need to follow these Capacitor rules? I listened to the pre for a short bit before I pulled it out for repairs/mods and everything was quiet and the bass didn't seem rolled off to me. I have a mic and should have measured but I didn't think it was an issue at the time. It wasn't til after when others were saying I need to up the value on my capacitor.
It's not like everytime I've bought a new amp or pre in the past that I've had to switch up capacitors to make sure everything sounded right, it's just plug and play. But in the world of DIY or "modding" all of a sudden I need big capacitors or I will have high bass roll-off. So obviously I don't know what I'm missing here..or I wouldn't be asking this question. Should I always follow the output capacitor value rule of matching it according to the input impedance of the power amp? If a builder says his preamp design is linear to say 10hz, is this only true if you are using an amp similar to what he tested on?
Thanks for any insight on this..and for reading my long post. I appreciate it.
The last year or so I've been dabbling in DIY type stuff, replacing old parts on old gear, tube preamp kits, a couple dynakit rebuilds. So my question comes from me working on a tube preamp, fixing a couple issues that the prior owner left for me. I do have to take out the output capacitors on this preamp and I've been told I need to raise the value to make sure my bass rolloff is high enough for the low input impedance of the power amp..so here's my questions.
If the builder of the preamp designed the preamp to send the full bandwidth with say a .22uf output cap and there is no impedance mismatch between the Pre and Power amp, why do I need to raise the value? The power amp has a low 10k ohm input impedance. The output Z of the pre is like 100 ohms. Should be a big enough gap to cause no issues, but that depends on who you ask. If I follow the normal guidelines I read everywhere I should up the value on the cap to at least 2.2uf I believe, I didn't check the capacitor calculator but this number is what was thrown in my ear.
I feel like I understand how that works or the theory behind it, but if a preamp was designed to work a certain way with certain values and there is no mismatch do I need to follow these Capacitor rules? I listened to the pre for a short bit before I pulled it out for repairs/mods and everything was quiet and the bass didn't seem rolled off to me. I have a mic and should have measured but I didn't think it was an issue at the time. It wasn't til after when others were saying I need to up the value on my capacitor.
It's not like everytime I've bought a new amp or pre in the past that I've had to switch up capacitors to make sure everything sounded right, it's just plug and play. But in the world of DIY or "modding" all of a sudden I need big capacitors or I will have high bass roll-off. So obviously I don't know what I'm missing here..or I wouldn't be asking this question. Should I always follow the output capacitor value rule of matching it according to the input impedance of the power amp? If a builder says his preamp design is linear to say 10hz, is this only true if you are using an amp similar to what he tested on?
Thanks for any insight on this..and for reading my long post. I appreciate it.