I am thinking about building a pre amp but don't really need that much gain. I thought about a DHT pre amp but then started thinking about going OTL pre amp. I've never heard of one.....any help?
Generally, preamps don't use output transformers. They use output coupling capacitors.
You could design a preamp without output coupling capacitors if you used bipolar voltages on the preamp. I'd be afraid of too much residual d.c. voltage on the output of the preamp as the tubes reach operating temperature and as they age. Readjustment of the bias would be necessary on a regular basis.
In general ... not a good idea. A tube failure could put a huge amount of d.c. on the output.
You could design a preamp without output coupling capacitors if you used bipolar voltages on the preamp. I'd be afraid of too much residual d.c. voltage on the output of the preamp as the tubes reach operating temperature and as they age. Readjustment of the bias would be necessary on a regular basis.
In general ... not a good idea. A tube failure could put a huge amount of d.c. on the output.
You have never heard of an OTL preamp because almost all preamps are OTL, so it doesn't need to be said.
OK, here is where I am coming from knowledge wise. The last and only pre amp I had was a John Hogan Line Stage. "line stage" might be different than pre amp....I don't know. But the Hogan line stage has OTs so I assumed all pre amps had OTs.
Thanks for the clarification.
Thanks for the clarification.
So- do you want to know how to set up a tube preamp with a direct-coupled output?
Why, yes I do. I was thinking OTL just to keep the signal path simple. Derect coupled sounds even cleaner.
Why, yes I do. I was thinking OTL just to keep the signal path simple. Derect coupled sounds even cleaner.
Try this: SYclotron Audio The Heretical Preamp
Did you have anything in mind besides a direct-coupled output?
Well, to be honest, I've been running my system (which I just sold off) with only a passive volume pot going into a Behringer 3400 then to three amps, each with a volume pot to balance the volume between drivers.
So, this whole preamp is new to me. Just before I got ride of everything, I put the Hogan line stage right in front of the 3400 and the system really came alive.
So in the new system I wanted to include a preamp/line stage.....if there is a difference.
I am building three amps at the moment. A 12HL7/GM70, a PP E-linar 807, and a Tim Mellow OTL.
I am also building a three way tube crossover.
My speakers are the big Heil on top, a large Tractrix horn with the TAD 4001 for mid, and a vented box with TD15M for midbass, and a pair of subs with Martin Logan Sub drivers.
I am using a passive volume pot/selector switch before the pre.
SO, I could use some advice as to what to include in the preamp.
Interesting read. I think I need to print that one out and do some studing.
Just a thought. If you are building a crossover then just slap a volume control on it and you have a preamp. Well I guess you would want to put a low gain VAS before the crossover but this approach would save you an entire power supply. If you need a phono preamp I think it probably better to do that as a separate piece though.
Hi Mike, the thing is, I am a large metal sculptor and my system is one have audio and the other half art. The volume pot and selector switch are going into a Lionel transformer (see pic). the left lever is volume and the right lever is selection. I've already build the phono pre on a piece of blue marble. I used the Hagerman Octal Cornet scheem.
Attachments
Cool idea. I never thought of using an old train xformer. Would want to be sure it wasn't a collectible though. Was there anything in the guts of the train transformer that was useful for the PS?
Well if you are planning to use a tube crossover, my inclination is that the thing to do is build that crossover with slightly more gain than you were planning, and then put a master control in front of the whole thing. Sort of build the line section into the crossover...Well, to be honest, I've been running my system (which I just sold off) with only a passive volume pot going into a Behringer 3400 then to three amps, each with a volume pot to balance the volume between drivers.
So, this whole preamp is new to me. Just before I got ride of everything, I put the Hogan line stage right in front of the 3400 and the system really came alive.
So in the new system I wanted to include a preamp/line stage.....if there is a difference.
I am building three amps at the moment. A 12HL7/GM70, a PP E-linar 807, and a Tim Mellow OTL.
I am also building a three way tube crossover.
My speakers are the big Heil on top, a large Tractrix horn with the TAD 4001 for mid, and a vented box with TD15M for midbass, and a pair of subs with Martin Logan Sub drivers.
I am using a passive volume pot/selector switch before the pre.
SO, I could use some advice as to what to include in the preamp.
The more building blocks you put between you and the speaker, the easier it is to screw things up. But since you are bi or tri-amplifying, doing it this way will keep things simple.
Good idea AT. I'll have to read up on the xover and see if that is easily done. I am using the Steve Bench's 6DJ8 tube crossover boards. Since I am still collecting parts for the SteamPunk chassis, I've not delved into the manual.
Hello djn,
Tubes are cool. The idea of a tube crossover is interesting. I think that in the bi-amped system you are speaking of the tube pre-amp is the easy part. Pick one. I like the Aikido Cathode Follower; it has the grunt to push the line level XO. The output capacitor can be part of the following XO network, no need for that Op-Amp servo.
You look in on the speaker threads there are recommendations of steep XO slopes. I have not read happy stories of tube XO’s doing the job. Lots of tubes, power supplies and related noise, I think. A 2SK170 JFET XO has my eye.
Most important Your creation should have a sculpted chassis.
DT
All Just for fun!
Tubes are cool. The idea of a tube crossover is interesting. I think that in the bi-amped system you are speaking of the tube pre-amp is the easy part. Pick one. I like the Aikido Cathode Follower; it has the grunt to push the line level XO. The output capacitor can be part of the following XO network, no need for that Op-Amp servo.
You look in on the speaker threads there are recommendations of steep XO slopes. I have not read happy stories of tube XO’s doing the job. Lots of tubes, power supplies and related noise, I think. A 2SK170 JFET XO has my eye.
Most important Your creation should have a sculpted chassis.
DT
All Just for fun!
HI DT, If you asked me last year, I would have agreed with you about tube crossovers, but a couple guys around here built the Steve Bench using The Planet PCB and REALLY good PS and they sounded better than the other actives I've had. They are 12db sloops.
The chassis is very steam punk and I am looking forward to starting the build on that.
The chassis is very steam punk and I am looking forward to starting the build on that.
I am glad to hear your report about the tube crossover, please let us know how yours turns out.HI DT, If you asked me last year, I would have agreed with you about tube crossovers, but a couple guys around here built the Steve Bench using The Planet PCB and REALLY good PS and they sounded better than the other actives I've had. They are 12db sloops.
The chassis is very steam punk and I am looking forward to starting the build on that.
Your chassis sounds like it should be front and center on your rack.
For years I made my living with a TIG torch in one hand and 316L wire in the other. One of my fellows does really nice welded art frogs, turtles and flowers out of pipe.
Your welded and painted creations with humps keep amplifiers fun looking.
DT
All Just For Fun!
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