No, oddly and annoyingly the ZED 10 does not have channel inserts. I have one and found that out! Good mixer otherwise mind.
I shall have a look round but if anyone else knows? Shout!
Dave.
What preamp for country-blues/folk music?
- Thread starter MIC83
- Start date
No, oddly and annoyingly the ZED 10 does not have channel inserts. I have one and found that out! Good mixer otherwise mind.
I shall have a look round but if anyone else knows? Shout!
Dave.
jamesperrett
Active member
Looks like you have to go up to the Zed 12 or the Mix Wizard series to get channel inserts.
Way back at the start of this topic Snow Lizard passed a comment about "starved plate tubes" and the sound quality of many of the lower ended valve pre amps. I could not agree more.
However having said that I would like to add that not only is the supplying the valves with a very low voltage a problem --- (most pre-amp type valves like a plate voltage of about 100volts + and not the very low voltage that they are being supplied in the modern valve pre-amp).
I have one such unit that is being fed by a 12volt supply (hardly enough to drive a condenser mic let alone a pre-amp unit), but the real problem is that the valves (eg 12AX7, 12AT7, 12AU7, etc) that are now being used are the incorrect valve for the purpose.
If you go back to the time when valves were all that was available, you would never use the above detailed "triad" valves in a high quality pre-amplifier (whether studio or a domestic Hi-Fi system or even a really good guitar amplifier), instead you would used an EF86 "pentode" valve running at a high voltage of about 100Volts, then that valve possibly fed into one of the above valves (also running at high voltage) to give extra gain. In the circuit for both valves they were designed to operate well below their maximum capacity to give extra head-room, less distortion and lower noise.
I remember very clearly one day about 15 years ago showing a modern valve pre-amp circuit to an old friend (he was responsible for designing/building the electronics for one of the country's biggest radio and television networks and a number of other stations and was an excellent radio engineer) and asking him what he thought of the circuit. His comment -- "they are using the wrong valve they should be using an EF86 not a 12AX7". I rested my case !!!!!!!
I am not sure if you can still buy the EF86 valve, but if so it is probably now made in either China or Russia where the quality is nothing compared to the old Mullard or Miniwatt/Phillips valves, this also goes for what I consider to be the incorrect valves that are currently being used today. RCA did not make EF86 valves, but did make their version of it -- 5879-- but it was not as good and was generally only used in equipment manufactured in the USA and why British equipment sound so much better !!!
Thankfully I still have a small supply of the original EF86 valves (probably threw out about 50 of them many years ago ---- bummer as they would be worth a fortune today) and have used some of these in a couple of VERY high quality pre-amps that I designed. By the way, the mic input transformers that I designed for these pre-amps almost required a fork lift truck to carry them ---- kidding but close !!!!!!!
I have also designed a couple of IC based pre-amps using the TL072/TL074 IC and have been able to obtain exceptional results, because I did not design to circuits so that they pushed the ICs to the limit to save money, as is unfortunately the case with many/most circuits today ---- squeeze out as much as is possible at the lowest possible manufacturing price, so that the sale price looks good to the prospective purchaser.
BUT when listeners to day are listening to music recorded in MP3 (often low res) and it is then often played back on cheap earphones or cheap "tinkle-tinkle-boom-boom" speakers, and so much of it is being streamed/downloaded in often lo-fi, what does it all really matter.
Just don't get me started on the actual music being recorded
Feel much better now after my rant for the day and will feel even better after I have a cup of cheap instant coffee, while listening to my latest illegally downloaded crap song being played back on my $50 MP3 player through my super cheap $10 ear buds, while sitting on my patio hearing the roar of trucks and hotted up cars screaming past !!!!!!!
David
However having said that I would like to add that not only is the supplying the valves with a very low voltage a problem --- (most pre-amp type valves like a plate voltage of about 100volts + and not the very low voltage that they are being supplied in the modern valve pre-amp).
I have one such unit that is being fed by a 12volt supply (hardly enough to drive a condenser mic let alone a pre-amp unit), but the real problem is that the valves (eg 12AX7, 12AT7, 12AU7, etc) that are now being used are the incorrect valve for the purpose.
If you go back to the time when valves were all that was available, you would never use the above detailed "triad" valves in a high quality pre-amplifier (whether studio or a domestic Hi-Fi system or even a really good guitar amplifier), instead you would used an EF86 "pentode" valve running at a high voltage of about 100Volts, then that valve possibly fed into one of the above valves (also running at high voltage) to give extra gain. In the circuit for both valves they were designed to operate well below their maximum capacity to give extra head-room, less distortion and lower noise.
I remember very clearly one day about 15 years ago showing a modern valve pre-amp circuit to an old friend (he was responsible for designing/building the electronics for one of the country's biggest radio and television networks and a number of other stations and was an excellent radio engineer) and asking him what he thought of the circuit. His comment -- "they are using the wrong valve they should be using an EF86 not a 12AX7". I rested my case !!!!!!!
I am not sure if you can still buy the EF86 valve, but if so it is probably now made in either China or Russia where the quality is nothing compared to the old Mullard or Miniwatt/Phillips valves, this also goes for what I consider to be the incorrect valves that are currently being used today. RCA did not make EF86 valves, but did make their version of it -- 5879-- but it was not as good and was generally only used in equipment manufactured in the USA and why British equipment sound so much better !!!
Thankfully I still have a small supply of the original EF86 valves (probably threw out about 50 of them many years ago ---- bummer as they would be worth a fortune today) and have used some of these in a couple of VERY high quality pre-amps that I designed. By the way, the mic input transformers that I designed for these pre-amps almost required a fork lift truck to carry them ---- kidding but close !!!!!!!
I have also designed a couple of IC based pre-amps using the TL072/TL074 IC and have been able to obtain exceptional results, because I did not design to circuits so that they pushed the ICs to the limit to save money, as is unfortunately the case with many/most circuits today ---- squeeze out as much as is possible at the lowest possible manufacturing price, so that the sale price looks good to the prospective purchaser.
BUT when listeners to day are listening to music recorded in MP3 (often low res) and it is then often played back on cheap earphones or cheap "tinkle-tinkle-boom-boom" speakers, and so much of it is being streamed/downloaded in often lo-fi, what does it all really matter.
Just don't get me started on the actual music being recorded
Feel much better now after my rant for the day and will feel even better after I have a cup of cheap instant coffee, while listening to my latest illegally downloaded crap song being played back on my $50 MP3 player through my super cheap $10 ear buds, while sitting on my patio hearing the roar of trucks and hotted up cars screaming past !!!!!!!
David
Hi David (great name!) I HOPE the EF86 is still being made! There are two guitar amplifier designs still in production that use one.
Not however as the front end valve. This had been done decades ago in the first Vox AC30s and the valve was too noisy and microphonic. The ECC83 triode is a much better choice. The pentode is used in the amplifier as a second stage with almost 100% feedback as a tone stack driver.
"Starvation" operation is a perfectly valid design technique* the most famous application perhaps (for people MY age!) is the Mullard '3-3' amplifier where the 86 anode is DC coupled to the grid of an EL84. The anode load of the EF86 is one meg Ohm! This give the stage massive gain and after feed back results in a 3 watt amplifier that has close to 'hi fi' distortion levels...By the standards of the day!
The valve can be used as a pre amp and is in some capacitor microphones but is always strapped as a triode because pentodes are always noisier due to the screen gid and 'partition noise'.
The use of a high ratio transformer and the 'cooking grade' TL072 seems an odd design choice? Not only is the 72 some 10dB noisier than better FET input op amps but also suffers lockup if driven too hard, something quite likely in a mic pre! There are of course design steps you can do to avoid it.
The NE5534 and a more modest transformer ratio will give better noise figures I am sure? See OEP Walter Transformers app' notes.
If you don't already have it, can I commend to you Douglas Self's 'Small Signal Audio Design' ? That has a wealth of information about IC circuits where very low noise amplifiers are needed.
*It is my great regret that I no longer have the time, energy or resources to investigate fully very low voltage valve operation. I am sure it could yield valuable results, at least in the guitar effects field?
Dave.
Not however as the front end valve. This had been done decades ago in the first Vox AC30s and the valve was too noisy and microphonic. The ECC83 triode is a much better choice. The pentode is used in the amplifier as a second stage with almost 100% feedback as a tone stack driver.
"Starvation" operation is a perfectly valid design technique* the most famous application perhaps (for people MY age!) is the Mullard '3-3' amplifier where the 86 anode is DC coupled to the grid of an EL84. The anode load of the EF86 is one meg Ohm! This give the stage massive gain and after feed back results in a 3 watt amplifier that has close to 'hi fi' distortion levels...By the standards of the day!
The valve can be used as a pre amp and is in some capacitor microphones but is always strapped as a triode because pentodes are always noisier due to the screen gid and 'partition noise'.
The use of a high ratio transformer and the 'cooking grade' TL072 seems an odd design choice? Not only is the 72 some 10dB noisier than better FET input op amps but also suffers lockup if driven too hard, something quite likely in a mic pre! There are of course design steps you can do to avoid it.
The NE5534 and a more modest transformer ratio will give better noise figures I am sure? See OEP Walter Transformers app' notes.
If you don't already have it, can I commend to you Douglas Self's 'Small Signal Audio Design' ? That has a wealth of information about IC circuits where very low noise amplifiers are needed.
*It is my great regret that I no longer have the time, energy or resources to investigate fully very low voltage valve operation. I am sure it could yield valuable results, at least in the guitar effects field?
Dave.