Hi Kissabout2002,
I'd like to also build a tube based EQ however I'm a bit confused about your journey building one in this post. On the first page you mention that you're building the Rickard Berglund design. In the second page you mention that you're building the Blonder-Tongue design. Did you end up building both or was just a typo? If yes, does one sound better than the other? Which one would you recommend to build?
Thanks
I'd like to also build a tube based EQ however I'm a bit confused about your journey building one in this post. On the first page you mention that you're building the Rickard Berglund design. In the second page you mention that you're building the Blonder-Tongue design. Did you end up building both or was just a typo? If yes, does one sound better than the other? Which one would you recommend to build?
Thanks
Hi Dromichet,
I build both EQ, currently using both of them, I must say musically speaking are quite different, the Rickard Berglund design give a gentle equalisation, despite in the original project declared to give a 12dB boost or cut for every frequency in fact give just 6dB boost or cut while the Blonder-Tongue is more punching and can really give life to a flat record....all the best and fell free to ask anything......thanks
I build both EQ, currently using both of them, I must say musically speaking are quite different, the Rickard Berglund design give a gentle equalisation, despite in the original project declared to give a 12dB boost or cut for every frequency in fact give just 6dB boost or cut while the Blonder-Tongue is more punching and can really give life to a flat record....all the best and fell free to ask anything......thanks
Thanks for the quick response, much appreciated. I will probably tackle the Blonder schematic in the near future. I’ll have to sell some gear first to come up with the funds as building this will be quite pricey.
Thanks again for all your work on this and sharing with us your findings.
Thanks again for all your work on this and sharing with us your findings.
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The frequency-determining components for each octave seems to be doubling the capacitance as the frequency steps down,
52nF 52nF and 12nF -80hz
27nF 27nF and 6.8nF -160Hz
15nF 15nF and 3.3nF -320Hz
... as frequency goes up octave by octave...
820pF 910pF and 220pF -5120Hz
so a 40Hz and 20Hz discrete pots should also be possible
210nF and 49nF -20Hz
104nF and 24nF -40Hz
... and also10KHz and 20KHz..
410pF 460pF and110pF -10240Hz
205pF 230pF and 55pF -20480Hz
though the smaller C values bring their own issues in the wiring/parasitic scheme..
So more bands instead of the last two controls of bass (40Hz and below) and treble (10Khz and above) placed after the bottom-of-page vacuum tube. - though it's nit-picking. It is not a criticism of the project in any way.
At some point, could an EQ me made for just the sub.. 1/3 octave (pain of precision componentry) but copying the basic tenet of the Rolls REQ-131, which also incidentally has a HPF tunable from 15-500Hz so might be of use cutting off the sub at too-low-a frequency for it. More importantly, a 1/3 octave eq should have narrower bands. I have not examined the schematic of the Rolls very much and make no claims as to how simple to tubularize the idea may be.
schematic/parts https://rolls.com/doc/infosheets/infosheet_1_REQ131.pdf
data-sheet https://rolls.com/doc/datasheets/datasheet_REQ131.pdf
52nF 52nF and 12nF -80hz
27nF 27nF and 6.8nF -160Hz
15nF 15nF and 3.3nF -320Hz
... as frequency goes up octave by octave...
820pF 910pF and 220pF -5120Hz
so a 40Hz and 20Hz discrete pots should also be possible
210nF and 49nF -20Hz
104nF and 24nF -40Hz
... and also10KHz and 20KHz..
410pF 460pF and110pF -10240Hz
205pF 230pF and 55pF -20480Hz
though the smaller C values bring their own issues in the wiring/parasitic scheme..
So more bands instead of the last two controls of bass (40Hz and below) and treble (10Khz and above) placed after the bottom-of-page vacuum tube. - though it's nit-picking. It is not a criticism of the project in any way.
At some point, could an EQ me made for just the sub.. 1/3 octave (pain of precision componentry) but copying the basic tenet of the Rolls REQ-131, which also incidentally has a HPF tunable from 15-500Hz so might be of use cutting off the sub at too-low-a frequency for it. More importantly, a 1/3 octave eq should have narrower bands. I have not examined the schematic of the Rolls very much and make no claims as to how simple to tubularize the idea may be.
schematic/parts https://rolls.com/doc/infosheets/infosheet_1_REQ131.pdf
data-sheet https://rolls.com/doc/datasheets/datasheet_REQ131.pdf
All you've posted is very interesting. Very nice build projects. I wonder how did you make the led bar circuit (what IC is used) and how did you connect those led bar circuits to the tube circuits? Hope you will share your solution/ schematic. It looks very very nice. Thanks in advance for reply, best regards Eric21
Hi Eric21, no problem here the schematic, how you can see the led bar is not connected to the tube circuit but using a dual gang 500k potentiometer (RV8/RV14) allowed to synchronise the two circuit then RV13,15 and 16 for get the exactly center of the bar graph ( yellow led ) corresponding with the center of the 500k potentiometer, I hope is clear if you have more question I am always available.......all the best
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Hi Guys,
It has been 4 months since my last post. The Tube eq was completed in about a month but had to wait for the tubes to come in which took 3 months.
In my build, I have used the Blonder circuit and followed it value for value except that I've added an Input volume, Output balance and volume, Tube EQ on/off. I find that bypassing function still goes through the tubes and it affects the FR...see below FR graphs. Also I've used 6N2P's instead of 12AX7's and adjusted B+ to be 250v as Kissabout2002.
Everything is great except for some ground noise which I have to solve and the frequency response going through this circuit, namely the 40hz and 10Khz (half of tube) and 5.2Khz the other half of the triode tube. You can see in the graph that it dips at these frequencies. I first thought that it might be the tube so I rolled them with no effect. Then I checked the circuit work and there are no mistakes, especially both channels exhibit the same dip.
Kissabout2002 and others that build this, do you experience the same response on your build? Did I do something wrong or is there some flaw with the design? Does the response look right to you?
When I adjust the pots for the dipped freq it looks better but it's still waive....not sure if that matters. I labeled each FR curve.
Any response will be appreciated.
Thanks
It has been 4 months since my last post. The Tube eq was completed in about a month but had to wait for the tubes to come in which took 3 months.
In my build, I have used the Blonder circuit and followed it value for value except that I've added an Input volume, Output balance and volume, Tube EQ on/off. I find that bypassing function still goes through the tubes and it affects the FR...see below FR graphs. Also I've used 6N2P's instead of 12AX7's and adjusted B+ to be 250v as Kissabout2002.
Everything is great except for some ground noise which I have to solve and the frequency response going through this circuit, namely the 40hz and 10Khz (half of tube) and 5.2Khz the other half of the triode tube. You can see in the graph that it dips at these frequencies. I first thought that it might be the tube so I rolled them with no effect. Then I checked the circuit work and there are no mistakes, especially both channels exhibit the same dip.
Kissabout2002 and others that build this, do you experience the same response on your build? Did I do something wrong or is there some flaw with the design? Does the response look right to you?
When I adjust the pots for the dipped freq it looks better but it's still waive....not sure if that matters. I labeled each FR curve.
Any response will be appreciated.
Thanks
Attachments
Congrats Dromichet, looks fantastic, wow I like your approach using slide pot, less space and no need to get mad as myself with a led graph, brilliant idea. Regarding the frequency response I attach response of my EQ ( EQ bypassed violet line - EQ pot 0dB purple line ) and as you can see my problem from day 1 is at 2.8KHz, this dips of around -11dB, me too I check and recheck but all correspond to the original design so I thought was a flaw of the original schematic but now that I see the response of your EQ I really do not know what to say, I start thinking that this circuit could be influenced by the layout of the component? The wiring? I really do not know but I will make different attempt as soon as I have time for understand the problem and of course I will share the result. I also suggest to rewire your EQ using more shielded cables especially on the signal path. All the best
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Kissabout2002, thanks for the quick reply and sharing your experience. I agree, I should have used more shielded cable and that’s what i plan to do as my next step. My hum is 120hz and i’m assuming it comes from these unshielded cables. If I would do it again I would use a different design approach.
Regarding your graph, it is indeed weird. I studied your circuit and did notice that at times throughout your circuit you’re using different component values as the ones in the original schematic. I wasn’t sure if it was by design or if it was a mistake. That would have been my next question to you. I’ll check and point these discrepancies to you, maybe it’s related to the dip you’re experiencing.
My problem itks in the 4th tube circuit which drags the entire fr down. If I remove that tube the rest of the freq align with each other.
I’ll continue to poke around as seeing your FR gives me hope that I’ve made a mistake along the way.
Regarding your graph, it is indeed weird. I studied your circuit and did notice that at times throughout your circuit you’re using different component values as the ones in the original schematic. I wasn’t sure if it was by design or if it was a mistake. That would have been my next question to you. I’ll check and point these discrepancies to you, maybe it’s related to the dip you’re experiencing.
My problem itks in the 4th tube circuit which drags the entire fr down. If I remove that tube the rest of the freq align with each other.
I’ll continue to poke around as seeing your FR gives me hope that I’ve made a mistake along the way.
Dromichet, can you kindly, when you have time, point out what are the component you found I changed the value from the original schematic?
For your problem of the 4th tube, did you notice the shielded wire to be used? Interesting in the original Baton was not show but in the BBC AM1/11 yes as you can see, maybe doesn't do anything but at least worth try......all the best
For your problem of the 4th tube, did you notice the shielded wire to be used? Interesting in the original Baton was not show but in the BBC AM1/11 yes as you can see, maybe doesn't do anything but at least worth try......all the best
Attachments
Kissabout2002, just looking at your schematic, I see several discrepancies with the original schematic in the 2.5khz circuit. That might be the reason of your dip.
Your schematic Original
C14 = 16.1n C22 = 1.8n
C21 = 16.1n C21 = 1.6n
R45 = 560k R39 = 680k
R54 = 4.7M R79 = 2.7M
I'm not sure which schematic you followed, yours or the original, but these discrepancies might be the reason of you dip. There are other discrepancies as well.
Your schematic Original
C14 = 16.1n C22 = 1.8n
C21 = 16.1n C21 = 1.6n
R45 = 560k R39 = 680k
R54 = 4.7M R79 = 2.7M
I'm not sure which schematic you followed, yours or the original, but these discrepancies might be the reason of you dip. There are other discrepancies as well.