Another tube preamp/lineamp circuit

[NewYorkDave]

Why would you want to do that? You'll just be wasting power in the resistors.

If this is to power my circuit, just use the transformer with a full-wave centertap rectifier. With a capacitor-input filter, that'll give you approx. 380V B+, which can be dropped to the desired final value through a couple of stages of R-C filters.

http://www.atc-frost.com/products/design/va.htm#FWCT

 

[bovox]

A short reflection from the recording scene; I recorded for the national radio SR a concert at a local club KB in Malmoe, with Martha Wainwrright with band.She sang in to a Shure beta58 wich were their soundman´s requiest. We splitted the signal via a LL 1527. The direct signal went to the NY-Dave preamp via 50m Mogami-cable and the other to a BSS-split, wich came in to the van on another line.That cable was longer.
We put the signals, gained them equally, and feeded our SSL 4000 G+. And the differences was big,a little to big in our taste. The signal thrue the Tube-amp was warm and with a big breath on the top.
Of course you cant really make a fair A/B
test with this becouse there are to many different parameters on the way.
The split, different cable,the SSL preamp... but it was nice to get a blended character of her voice. So you guys, it pays off to DIY.
Thanks again to NY-Dave & PRR.
Cheers Bo

 

[NewYorkDave]

Bo: Which circuit did you build, the one with global feedback, or the one with the gain control between the stages? Were you using a different output tube type as you mentioned earlier in the thread? Any other modifications?

 

[bovox]

Hey I´ve used the E88CC on both places.
I´ts the "PREAMP/LINE AMP from sept. 04" the one without feedback.
Havent loaded the output down to 600 ohms, but nearby 2k ohms.
The R8 I changed to about 900 ohms, I actually put 500ohm pot. in series with 470ohms. R7 is also raised to 330 ohms. That gave me about 7 mA
flowing down the output tube. I also as you recommended biased the filament to about halfed (+53V) the voltage of the output.
At cathode V1A the dc is 3.0V ,that gives you +7dBu max input.
Input Tx 1:4 is Mr.Schou, this one is a favourite and sufficient enough to fill my noisespecs. It´s compensated with 24k+470pF. The output Tx is an Altec 15356 wired backwards. 2:1( no comp.)
I also put in 4M7ohm resistor from gate V1B to ground, it helped to get rid
off scratch from VR1. I cant give you any THD specs but there is level
enough at the output to feed any equipment,around me beyond +26dBu.
Cheers Bo

 

[bovox]

Hey Guy´s, I just want to put in some load results of my E88CC type
of NY-D amp. It actually got down to half of the output swing at 1kHz
(square)at 188 ohms load. At 600 ohms load it whent down under 1 dB, versus 10kohm load, at 100 , 1k & 10 kHz.
The maximum output is about +24dBu at 600 ohms load.
I have read that this tube is perhaps not the best one to choose
as WCF in loads of under 5 kohm (primary load).But lets say that those 10,000 of livinghours is cut down to half, then...
I bring you all a new report in 3 years time!! My calculation of 200 recording days, 8 hour a day ( Thats a lot of soundwaves).
Until then, A happy new DIY Year to You all.
Cheers Bo :grin:

 

[Sleeper]

I'm using the 12bh7A on the back end of a 12ax7 circuit (basically a fender twin preamp and tone circuit, which isn't much different than daves 12av7. where i'm connecting the 2 circuits, the output of the 12ax7 is identical.

its at the junction of the 100k from b+, pin 6.

I have a few oscillations when i crank up the volume pot (also between stages as in the NYDLA) , but some changes to the layout have helped.
I only had a 600-600 out trafo, so maybe that was a problem as well, changing this later today, I have a 2k to 600, which should be ideal.

it sounds great at the lower gains though, and is very quiet.


I have a question though,

I don't have a center tap on my heater trafo, but i do have a hum balance pot in place. so I sort of have a ground referenced heater supply, in this case would I need the heater bias circuit that was suggested?

Thanks
Kelly

 

[bovox]

Hi Sleeper, I´m not sure following your set up with the guitarr-amp. But..
When I look in my "Taschenbuch" from Telefunken 1968 it tells of the
ECC83 that it can handle 180V (f/k) in difference between filament/cathode.This is maximum rating. I cant tell about the 12BH7 but search at TDSL.
Cheers Bo

 

[Sleeper]

just to clarify that one.
it's not the whole amp, just the first tube in a fender,
like this

1 gain stage +tone and volume control +gain stage+daves 12bh7 stage.

sleeper