Hi, im looking for a tube based tone control, pretty simple, perhaps a Baxandall 2 band type..
But by simple i mean using a smallish amount of components without sacrificing any sound quality..
Ive seen the one that uses 3(?) 12ax7's and although it looks really nice, im not sure if that the way to go as i need to build a couple of them..
Thanks!
But by simple i mean using a smallish amount of components without sacrificing any sound quality..
Ive seen the one that uses 3(?) 12ax7's and although it looks really nice, im not sure if that the way to go as i need to build a couple of them..
Thanks!
Do you want the EQ for listening or instrument use? For the former, try the classic tube amps/receivers of the 50's/60's and just copy them. Google for Dynaco, Quad, Fisher, Eico, Sherwood, Heathkit, Marantz (7C) and Harmon Kardon (Citation 1) shematics. They're all out there. Dunno which will sound best though.
If it's for MI, then use the Duncan Amps TSC
If it's for MI, then use the Duncan Amps TSC
Optical said:
You're going to need a tube before the TC's to get sme gain to make up for the TC's losses, and one after, to buffer the wildly varying impedances of the TC circuit.
Look at the links below for a ton of amps with TC's in them. All you need are the TC stages; ignore the rest.
One-Electron
Try the Dyna PAS, Fisher 400/500/800, amongst others there.
I built this VP10 and it sounded good.It uses Baxandall feedback arrangemnt with standard comp.
Computer poayaling up.......cannot attach link....typed instead:
Study the dubris in this web address.
http://www.geocities.com/mattijs1970/preamp/brpreamp.gif
www.Chelmervalve.com can assist with the ECC807 (if still on their cards). If they do it, then go for premium types. Otherwise a poorman's sub is ECC83. Personally I DON'T LIKE THE ECC83.
Somewhere out there must be the Brimar VA12 20Watt power amp using EL506's. Another cracker amp with a fine spec.
good luck
rich
Computer poayaling up.......cannot attach link....typed instead:
Study the dubris in this web address.
http://www.geocities.com/mattijs1970/preamp/brpreamp.gif
www.Chelmervalve.com can assist with the ECC807 (if still on their cards). If they do it, then go for premium types. Otherwise a poorman's sub is ECC83. Personally I DON'T LIKE THE ECC83.
Somewhere out there must be the Brimar VA12 20Watt power amp using EL506's. Another cracker amp with a fine spec.
good luck
rich
It's nice to see all those early triode designs come out, but in reality having worked many years a design eng in the studio equipment domain, I am somewhat more aligned towards using pentodes with g2 either strapped to Anode to get better bandwidth or as g2 as an intermodulation injection to get different type of sound.
I did like the ECC807, especially in the Brimar VP10. However, the real bogey from the ciorcuit is the poor hum & noise figure just scrapping -60dB below 130mV output i.e full 20 Watts from a Brimar VA12 amp. Like alot of these circuits, the output Z of 1Mohm is too high, a drawback.
The rest of the design is sound with alot of feedback with the Baxandall configuration, T & B controls giving approx +/- 18dB lift and cut @30hz & 15Khz.
With 56dB feedack in radio posit and an overload factor of 40dB.
My power amp produces -70dB below 150+150W pc for 0dBu in, so the preamp scores more noise at this colossal power. Connect the pair together and the figures are worse by -8dB. In fact they aren't compatible as the power amp has an input Z of 10Kohms. It's hard to get real performance from a tube preamp esp with fast digital, this is where I desert ranks to either go towards pentodes or SS design.
For some strange reason, alot of equipment users say my amp sounds far louder than SS mosfet amps with double the Pout.
Can anyone explain this ? (I know the bit about clipping is smoother etc).
rich
I did like the ECC807, especially in the Brimar VP10. However, the real bogey from the ciorcuit is the poor hum & noise figure just scrapping -60dB below 130mV output i.e full 20 Watts from a Brimar VA12 amp. Like alot of these circuits, the output Z of 1Mohm is too high, a drawback.
The rest of the design is sound with alot of feedback with the Baxandall configuration, T & B controls giving approx +/- 18dB lift and cut @30hz & 15Khz.
With 56dB feedack in radio posit and an overload factor of 40dB.
My power amp produces -70dB below 150+150W pc for 0dBu in, so the preamp scores more noise at this colossal power. Connect the pair together and the figures are worse by -8dB. In fact they aren't compatible as the power amp has an input Z of 10Kohms. It's hard to get real performance from a tube preamp esp with fast digital, this is where I desert ranks to either go towards pentodes or SS design.
For some strange reason, alot of equipment users say my amp sounds far louder than SS mosfet amps with double the Pout.
Can anyone explain this ? (I know the bit about clipping is smoother etc).
rich
Yes fdegrove
due to system problems I missed that bit about your E283CC tubes as ECC807 subs. This is a tempter and will investigate sources.
It appears for some reason I'm not able to read everyones mail.
Regarding the VP10 output ........I've looked into this..... I'm wrong you are right....misinterpreted....... .from a US brochure (a reprint) ; quote "output impedance approx equal to 0.05M without HF loss with 10' screened cable".?????.......... I'm still open minded about that 50kZ for the type of feedback circuit used). However is way more realistic.
rich
due to system problems I missed that bit about your E283CC tubes as ECC807 subs. This is a tempter and will investigate sources.
It appears for some reason I'm not able to read everyones mail.
Regarding the VP10 output ........I've looked into this..... I'm wrong you are right....misinterpreted....... .from a US brochure (a reprint) ; quote "output impedance approx equal to 0.05M without HF loss with 10' screened cable".?????.......... I'm still open minded about that 50kZ for the type of feedback circuit used). However is way more realistic.
rich
Yes.....fdegrove.... the website circuit of VP10 shows 100K as anode res with 1M out/ potty. My hardcopy circuit (dated 1961?) shows same anode resistor but 500K potty coupled to anode with 1uF. It seems there could have been another mod'd version of the same preamp. It clearly states that passive EQ/input selector switch be M.B.B type otherwise (obvious) the circuit will break into instability. however nowhere does my copy say
So there we have it.
Although I am very satisfied with the audio performance of the VP10, the S/N is the own side, as is of most tube preamps. Many times I've gone for IC designs simply to get the noise floor down to -90 to -100dB ref 0dBu and so be it. It is a constant area of looking at other designs and seeing what can be optimised to bring tube preamps more into line. I don't like the EF86 (sound wise) the 7199 is better as it has a med mu triode included, but I find both tubes from non-original vendors never performed up to origonal spec. On my VP10 with Brimar tubes I use an AC heater supply because these tubes were origonals, and from my experience of using 2nd vendors tubes, the hum performance becomes untolerable without resorting to DC supply. I can understand that the spiral heater design (which was the best for low noise performance) was uneconomic to produce and subsequent vendors went to the "up and over" type construction.
As I'm trying to keep with the original question of post#1, the preamp No2 recommended for the GEC KT88-50 design is also worth considering (and better documented) as it has a presence control and Baxandall network. On original combined spec of both No2 preamp and KT88-50 amp, it mentions, quote; "noise of KT88-50Watt amp is
-76dB relative to 50W with gain at min and controls set for level response. With gain at max, and inputs s/c to grnd, generalised S/N varies from -52dB for tape and -69dB for radio". For my standard it's a knapp nah.... esp for headphone use. Looking at this particular design it does have the merit that only 3 stages are used (ex tape inp) whereas the Brimar VP10 uses 4 with more feedback. Bit like comparing Stellar Artois with 1664.
Perhaps I ought to examine a tube preamp design based on cascode benefits., (I haven't researched this for a while)..........Meanwhile for excelsior performance I'm back to 5534's with input & output trannies until I have time to relook at some existing tube preamp designs to see what can be optimised. Long live Lo impedance!
Off-bier and bitter comments always welcome!
From the pit
rich
rich
So there we have it.
Although I am very satisfied with the audio performance of the VP10, the S/N is the own side, as is of most tube preamps. Many times I've gone for IC designs simply to get the noise floor down to -90 to -100dB ref 0dBu and so be it. It is a constant area of looking at other designs and seeing what can be optimised to bring tube preamps more into line. I don't like the EF86 (sound wise) the 7199 is better as it has a med mu triode included, but I find both tubes from non-original vendors never performed up to origonal spec. On my VP10 with Brimar tubes I use an AC heater supply because these tubes were origonals, and from my experience of using 2nd vendors tubes, the hum performance becomes untolerable without resorting to DC supply. I can understand that the spiral heater design (which was the best for low noise performance) was uneconomic to produce and subsequent vendors went to the "up and over" type construction.
As I'm trying to keep with the original question of post#1, the preamp No2 recommended for the GEC KT88-50 design is also worth considering (and better documented) as it has a presence control and Baxandall network. On original combined spec of both No2 preamp and KT88-50 amp, it mentions, quote; "noise of KT88-50Watt amp is
-76dB relative to 50W with gain at min and controls set for level response. With gain at max, and inputs s/c to grnd, generalised S/N varies from -52dB for tape and -69dB for radio". For my standard it's a knapp nah.... esp for headphone use. Looking at this particular design it does have the merit that only 3 stages are used (ex tape inp) whereas the Brimar VP10 uses 4 with more feedback. Bit like comparing Stellar Artois with 1664.
Perhaps I ought to examine a tube preamp design based on cascode benefits., (I haven't researched this for a while)..........Meanwhile for excelsior performance I'm back to 5534's with input & output trannies until I have time to relook at some existing tube preamp designs to see what can be optimised. Long live Lo impedance!
Off-bier and bitter comments always welcome!
From the pit
richrich
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