Hi, I'm new to this site. I am looking into building a simple tube preamp with an active crossover at 400Hz. The idea is to drive and Adcom 555 for lows, and a Luxman MQ68 Custom for mids and highs. They would drive a set of ADS L1290/II. I would only need an AUX input on the preamp.
Problem is that I have no idea what to look for..... I could marry pieces of existing schematics, that part is not that hard, but which brands/models of preamps and crossovers are worth looking into? Any pointers?
Problem is that I have no idea what to look for..... I could marry pieces of existing schematics, that part is not that hard, but which brands/models of preamps and crossovers are worth looking into? Any pointers?
Hi, an easy one that I built 10 years ago ( just a buffer with passive filtering )
Go to : Audiocostruzioni - Il Portale dell'alta fedeltà amatoriale
then "autocostruzione/DIY" >then Elettroniche> then Altro ( other) > scroll down the page and you'll find " Crossover elettronico a valvole..."
Power transformer is 180 V -5mA ( !!!) and 12 V 1 A but you can go for 6,3 V as the heaters are wired in series
Go to : Audiocostruzioni - Il Portale dell'alta fedeltà amatoriale
then "autocostruzione/DIY" >then Elettroniche> then Altro ( other) > scroll down the page and you'll find " Crossover elettronico a valvole..."
Power transformer is 180 V -5mA ( !!!) and 12 V 1 A but you can go for 6,3 V as the heaters are wired in series
Thanks! I also found this other one:
http://www.jacmusic.com/techcorner/SBENCH-PAGES/sbench101/Crossover/xover.gif
It has the same tube count, but has the filter before the buffer, instead of after. Since there will be cathode follower from the preamp driving the crossover, I wonder if it is better to use the second one. This way the signal flow is Preamp CF out, buffer passive filter into CF buffer, into solid state and tube power amp.
Am I on the right track?
http://www.jacmusic.com/techcorner/SBENCH-PAGES/sbench101/Crossover/xover.gif
It has the same tube count, but has the filter before the buffer, instead of after. Since there will be cathode follower from the preamp driving the crossover, I wonder if it is better to use the second one. This way the signal flow is Preamp CF out, buffer passive filter into CF buffer, into solid state and tube power amp.
Am I on the right track?
I fixed the links just before i posted. If the date on the page isn't 05-august-2016 you have an old page cached.
dave
dave
Thank you. Also, this was brought to my attention. Looks interesting too. http://akdatabase.org/AKview/albums/userpics/10007/Heathkit%20XO-1%20Assembly%20Manual.pdf
They didn't work when I first tried the links you posted . They do now. I guess the redo takes time to take effect.
I've found high transconductance types work much better in follower based VCVS (Sallen-Key) type filters than the usual suspects**, but the fact that available gain is always less than unity and output impedance is not close to zero means some compromise is required.
**
12AX7
12AU7
**
12AX7
12AU7
Thanks guys for all the information. In the mean time, I have been studying a few well regarded vintage preamps with tone controls. I noticed the Audio Research SP3A-1, Marantz 7c, and the Luxman CL34/35 preamps have a gain stage fed into a Baxandall tone stack/gain stage. I like that concept and am considering that topology.
Is there another preamp I should look into?
I am planning on designing something along the lines of:
- Balance control, volume control, 6DJ7/ECC88/6922 voltage amp,
- Bax active tone stack with either a 6DJ7 direct coupled into another 6DJ7 cathode follower (like CJ PV10), taking the signal from the cathode, or using a EF86 pentode into a 12AU7 cathode follower.
- Then the signal would go to my Luxman tube power amp, or there would be an passive 6DJ7 tube buffered crossover for biamping. The woofer output would get a phase inversion switch (plate or cathode output) into an Adcom GFA 555.
The L1290 crossover is 500Hz and in Biamping mode, the L1290 crossover remains intact for the mids and tweets, the lows go straight into the woofer drivers. I Multisim modeled a stripped down (single pole) version of the Steve Bench buffered crossover to have the low pass -3dB point at 500Hz. The high pass filter I set at about 300Hz, so it would not overlap with the 500Hz crossover of the L1290, and cause accumulative phase aberrations. The idea is that in Biamp mode, the speaker crossover is still engaged and filters out the lows below 500Hz.
Would this overall idea work?
I will draw up a proposed schematic once I have a better idea if the preamps I am working off are a good idea. BTW, I understand that combining sub sections of old designs will require tweaking, that is part of the fun. 🙂
Is there another preamp I should look into?
I am planning on designing something along the lines of:
- Balance control, volume control, 6DJ7/ECC88/6922 voltage amp,
- Bax active tone stack with either a 6DJ7 direct coupled into another 6DJ7 cathode follower (like CJ PV10), taking the signal from the cathode, or using a EF86 pentode into a 12AU7 cathode follower.
- Then the signal would go to my Luxman tube power amp, or there would be an passive 6DJ7 tube buffered crossover for biamping. The woofer output would get a phase inversion switch (plate or cathode output) into an Adcom GFA 555.
The L1290 crossover is 500Hz and in Biamping mode, the L1290 crossover remains intact for the mids and tweets, the lows go straight into the woofer drivers. I Multisim modeled a stripped down (single pole) version of the Steve Bench buffered crossover to have the low pass -3dB point at 500Hz. The high pass filter I set at about 300Hz, so it would not overlap with the 500Hz crossover of the L1290, and cause accumulative phase aberrations. The idea is that in Biamp mode, the speaker crossover is still engaged and filters out the lows below 500Hz.
Would this overall idea work?
I will draw up a proposed schematic once I have a better idea if the preamps I am working off are a good idea. BTW, I understand that combining sub sections of old designs will require tweaking, that is part of the fun. 🙂
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