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Post by Scotocaster on May 21, 2009 2:48:16 GMT
Hi Charlie, like others, i've been listening to Robbos demos on the Copycat Gold and some of the opinions on the sound. So far... i personally don't hear much difference from other digitals, but as Dave states, he has not had a great amount of time to play around with it. I myself have had a few moments to play with my own gear and this is the latest thing i've been toying around with. Rather than my strat into the Q20 then into my 64' super-twin, i tried putting my strat first through a 12ax7 pre-amp , into the Q20 then into the Vox , was quite surprised at the amount of change in the sound (for the better), it takes away quite a bit of the digital (tinny/metallic) sound, and sounds much softer/smoother. LOL I never did get around to removing the caps on the Q20, but this certainly sounds nicer, Any comments?. Have a great day. Scott
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Post by Charlie Hall on May 21, 2009 14:05:51 GMT
Hi Scott,
I think the addition of the 12AX7 is similar to what TVS have done with their Meazzi tone switch. It would change the sound for the better as it is getting closer to what the real Meazzi did.
The preamp would also remove the effect of the capacitors on the guitar pickups, but they could still soften the sound but in a different way, if the output impedance of the valve preamp is fairly high, which is usually the case with a valve stage unless it is a cathode follower output.
Regards,
Charlie
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Post by Scotocaster on May 21, 2009 16:25:15 GMT
Tnx Charlie, your correct on the sound.... all the folks on the site enjoy having your expert advise, I will be trying a few more ideas and will let you know how they turn out. Have a great day. Scott
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Post by didier on May 22, 2009 7:42:41 GMT
i tried putting my strat first through a 12ax7 pre-amp , into the Q20 then into the Vox , was quite surprised at the amount of change in the sound (for the better) Patrice Bastien's PB Box created in 2000 has been improved in 2004 with the addition of an ECC83 (12AX7) preamp for a closer emulation of the Meazzi sound (in addition of some EQ and other tone processing). I have heard it with a Q20 in direct comparison with a TVS3, and the results were very good and quite similar. Didier |
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Post by rogercook on May 22, 2009 10:49:28 GMT
There are some circuit diagrams here www.vintagehofner.co.uk/selmer/schematic/wire.html for valve tape echo units. Part of the sound we attribute to the Meazzi must come from the valves in the signal path. All of these circuits will add some colouration/EQ etc to the signal. If you drive a modern processor (eg a Quadraverb or Magicstomp) with a valve preamp I would imagine you would need to tweak any eq that is included in the echo patches Roger |
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Post by Charlie Hall on May 22, 2009 14:18:54 GMT
Hi Roger,
The EQ for the echo in the Q2 and Q20 EFTP patches is very accurately predefined to match closely the EQ of the real echo units as far as can be known without access to those original drum Meazzis. I have used accurate EQ curves for the tape Meazzi and Long Tom becauyse I had access to those units.
The EQ of the direct signal is flat in the Q2 and Q20. Applying the Meazzi curves (which I suspect don't change things that much, apart from probably removing a little low end and high end) and the addition of a 12AX7 running at a similar voltage to a Meazzi preamp first stage should give the right kind of result without having to change the echo EQ further. The EFTP EQ curves apply to the main echo signal and the feedback separately in many cases, and altering one could upset the other.
Regards,
Charlie
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Post by Deleted on May 23, 2009 2:26:32 GMT
HI CHARLIE & ALL ,,,THIS is a very interesting topic indeed ,& its a bit like my orange-squeezer ''fet'' project used prior to the Q2 ,which I have found in my opinion to be a good move .. just having the squeezer circuit in line with the compressor turned off so to speak definatly does enhance the sound [suttle but it's there] & the squeezer is actually a fet preamp with quite a lot of gain if needed without using the comp funtion as on my unit I have control of the comp funtion with a dedicated pot[actually 2 pot's] ... Saying this ''WOULD you have a go at describing a diagram of a 1x12ax7 preamp that you feel would be similar to say the meazzi ,I have schematic's of the meazzi's & am intiqued by the cathodes being grounded on the 1st triode & appears to go to a cathode follower next stage [other 1/2 of 12ax7?  ?? does this make sense to you & could you explain the cathode grounding aspect as I have not seen this before as usually it's a res&cap? .. CHEERS ....barry.. |
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Post by Charlie Hall on May 23, 2009 3:09:07 GMT
Hi Barry,
The FET preamp produces second harmonic distortion and will make the sound a little grittier and seem to add high end, but when measuring the frequency response it appears to still be flat.
If I remember rightly the FETs in the Orange Squeezer circuit are only there for gain control and don't amplify anything, that is done by the IC. It is possible that the FETs could add some distortion though but this is minimised by having half of the control voltage AC signal applied to the gate. This is why you will see two equal resistors in the circuit with a cap going to the gate.
I don't remember seeing the grounded cathode in a Meazzi circuit but I was intending to put some Meazzi preamp circuits in a simulation program to find out how much effect the coupling caps have on the sound. Can you let me know which diagram you have seen this on?
A grid attracts some electrons from the cathode. This appears as a negative voltage in the accepted sense and can be enough to bias an input stage if the input impedance is high, say between 4.7Meg and 10Meg. A coupling cap is used so that the input device cannot reduce the bias voltage or the bias voltage cause DC at the input. In this situation there is no need for a cathode resistor so the cathode can be grounded. It will work with small signals but I don't think the bias voltage would be high enough for large signals.
Regards,
Charlie
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Post by Deleted on May 23, 2009 5:36:15 GMT
HI CHARLIE ,, and thankyou for that explanation even if I don't quite understand the actual theory ,but do get the idea of your explanation & you are quite right on the input stage of the meazzi 1st triode ,as it has 4 meg grid to ground resistor & a coupling cap of .01 & a 500k prior to the coupling cap to ground one diagram has a 500k pot in this position & another has just a fixed res,, I guess to be able to contol the input level [the pot i mean]quite a good idea.. THE drum meazzi circuit has a similar 1st stage with the grid to ground res at 4.7 meg & the same input coupling as the ''echomatic''-loop -tape as above!!,this then goes to a 500k pot via a .oo42 cap....and then to the 2nd triode via a 220k res,the cathode fowlower has a 4.7k res cathode res to ground & an electo-10uf-from cathode to a1.5k to out....,, the path of the amplified play-back signals is also fed into that cathode-follower stage as you will see from the diagrams ..my diagram's came from schematic-heaven... It seems to me all 3 circuit,s I have are very much the same but with some cap value's changed & res value's , but otherwise the princable appears to be the same just the drum mech against the loop tape mechanism,, ? CHEERS charlie I feel this will a very interesting project & may well be worth pursuing futher ,especially after ''didier's above comments!!!!!..cheers..........barry..   [ps] remember I said no more project's & more guitar practice well I ''lied'' ha.haar.. ;D ;D |
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Post by didier on May 23, 2009 7:38:37 GMT
THE drum meazzi circuit has a similar 1st stage with the grid to ground res at 4.7 meg & the same input coupling as the ''echomatic''-loop -tape as above!!, I don't have myself enough knowledge in electronics to discuss about circuits design, but Patrice told me that the Meazzi drum units didn't have the recording pre-emphasis and corresponding playback de-emphasis as usual in tape recorders. Recording and playback circuits are linear, with obvious consequences on the echo sound. I don't know if it can be easily emulated... Didier |
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Post by rogercook on May 23, 2009 8:52:57 GMT
I'm quite keen to try a valve circuit to drive my echo units. I have a Quadraverb+ and a Magicstomp, both with Charlie's patches. Problem is at the moment I don't have time to experiment - and I still have my AC30 project to finish! So I'll be interested to follow any design ideas and practical developments. Keep 'em coming!
Roger
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Post by Charlie Hall on May 23, 2009 14:34:31 GMT
Hi Didier,
It is correct that most echo unit circuits do not work in the same way as tape recorder circuits.
Because the tape itself has a peaking frequency response (which varies depending on the tape speed), tape recorders have a treble boost in the record amp and bass boost in the playback amp. Different EQ circuits come into play when different tape speeds are selected, to get the flattest possible response at each speed.
With most echo units, there is no treble boost (but there might be some bass cut) in the record amp, and there is no bass boost in the playback amp, but there is a treble cut which is designed to flatten out the peak of the tape response. The end result is a very sharp fall in the treble range at and above around 2-3KHz in the case of Meazzi units.
Most of my echo programs mimic these responses.
Regards,
Charlie
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[ps] remember I said no more project's & more guitar practice well I ''lied'' ha.haar.. ;D ;D