Gunter,
Actually it will probably be about 40uA through first transistor. Lets call the B-E voltage of 2nd BJT 0.68V so 0.68/22000= 30.9uA but there will also be some small
amount of additional current coming from base of 2nd BJT, maybe 10uA max depnding on its Beta. So total will be around 40uA max.
TCD
Joe, that discussion was quite some time ago and centered around your application (why doesn't that surprise meHi Terry
I hear you, but...
I seem to recall having this discussion before.
The stage I posted in #803 and here is the part where the Darlington pair sits:
View attachment 1079565
As we both know, I do not use 2SC2547 pair. They are different, as per our dicussion.
) so my recollection of it is minimal.There are thousands of IP devices that you can use and from memory the part I was advising you on was the use of mixed property BJT's in the Darlington pair
to obtain some of the benefits of each different BJT.
The 22k resistor looks very much like a current source to the first BJT's emitter. I'm not sure how this will limit maximum voltage swing. Can you clarify this.
Yep, it's a cascode... V -> I -> V
How so?
I have a spice model of this stage up and running, give me some R values, supplies etc etc and I'll pump them through, see what the results are.
Cheers
Terry
Hi Joe and Terry,
Thank you both for plenty of information.
As I said already earlier I might give this circuit a try in the RTP3 phono stage replacing the MAT02's.
I would suppose that getting lowest possible noise there is definitely important and limiting voltage swing is not important considering the low output
of a MC cartridge.
So for a phono amp I think using 22k makes no sense at all. 1K could be ok and maybe using no resistor at all in that particular position is best in order to get low noise and maximum gain, right?
Would be keen to hear your opinions.
Thanks
Günter
Thank you both for plenty of information.
As I said already earlier I might give this circuit a try in the RTP3 phono stage replacing the MAT02's.
I would suppose that getting lowest possible noise there is definitely important and limiting voltage swing is not important considering the low output
of a MC cartridge.
So for a phono amp I think using 22k makes no sense at all. 1K could be ok and maybe using no resistor at all in that particular position is best in order to get low noise and maximum gain, right?
Would be keen to hear your opinions.
Thanks
Günter
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Spot on Günter. Something like 1K should be a good choice and the input transistor will be set at around 0.6mA constant current (as Terry said, it acts virtually as a current source). I think Terry would approve as well, but I will leave that to him. MAT02's as well.
As it turns out, in Ltspice the size of the B-E resistor on IP BJT, (22k) actually doesn't make much difference to the distortion numbers. I thought it might but that is not the case.Spot on Günter. Something like 1K should be a good choice and the input transistor will be set at around 0.6mA constant current (as Terry said, it acts virtually as a current source). I think Terry would approve as well, but I will leave that to him. MAT02's as well.
Probably because it does act much like a CCS and there is very little current modulation through the IP BJT.
So for a Phono IP stage probably best approach would be looking at optimizing noise. A single non darlington IP pair will be superior noise wise.
I'm not sure what major advantage the darlington brings to the table here except slightly higher IP Z and lower IP bias current.
Joe?
TCD
Are there folks working on builds of this preamp? There hasn’t been a lot of activity on this thread in a while.
I started working on a build a couple of months ago. I am building a line-stage only preamp that will use Allen’s RTP3C line-stage design, but I’m not trying to build a clone of his preamp. My build will use custom PCBs for everything. I’m mostly still in the planning/design phase, but I have fabricated a few of the power supply boards to do some testing.
I am building a two-chassis implementation, but the power supply chassis will include all the front-panel controls. I am using a custom-programmed Arduino to control a 256 level relay stepped attenuator with 0.25db steps (to provide enough precision for balance adjustment). I’m also using relays for input selection, output muting, and power supply control. A color TFT display will show input selection, volume level and other information.
The power supply is completely separate for each chassis from the transformers forward. I’m using separate transformers for the heaters and the B+, etc., so that they can be turned on separately. These will also have an Arduino-controlled soft-start.
The B+ supply will use a cLCLC filter into a Salas HV shunt regulator. The first “c” is a small (1-2uF) cap to adjust the shunt regulator input voltage. The first choke is a 17H Lundahl choke. The second is a Tent Labs mini-electronic choke mounted on the shunt regulator board. All caps are film caps. The larger ones are ClarityCap TC4s.
The heater supplies use two-stage regulation, with three regulated supplies (elevated to different voltages) in the power supply chassis, and individual current regulators for each tube close to the tubes in the line stage. The current regulators are adjustable from 260mA to 380mA to support a variety of tubes.
I also have an op-amp (OPA1612, OPA1611) based single-ended output for my subwoofers. This is also powered by a two-stage regulator using 1085s in the power supply chassis and Sparkos regulators near the op-amps.
Below are images showing the PCB layouts in the two chassis. Two DC umbilical cables between the two chassis will provide power to the two channels. A 9-pin D-Shell cable will be used for serial communication to control the attenuators, input selectors, and output muting relay.
I started working on a build a couple of months ago. I am building a line-stage only preamp that will use Allen’s RTP3C line-stage design, but I’m not trying to build a clone of his preamp. My build will use custom PCBs for everything. I’m mostly still in the planning/design phase, but I have fabricated a few of the power supply boards to do some testing.
I am building a two-chassis implementation, but the power supply chassis will include all the front-panel controls. I am using a custom-programmed Arduino to control a 256 level relay stepped attenuator with 0.25db steps (to provide enough precision for balance adjustment). I’m also using relays for input selection, output muting, and power supply control. A color TFT display will show input selection, volume level and other information.
The power supply is completely separate for each chassis from the transformers forward. I’m using separate transformers for the heaters and the B+, etc., so that they can be turned on separately. These will also have an Arduino-controlled soft-start.
The B+ supply will use a cLCLC filter into a Salas HV shunt regulator. The first “c” is a small (1-2uF) cap to adjust the shunt regulator input voltage. The first choke is a 17H Lundahl choke. The second is a Tent Labs mini-electronic choke mounted on the shunt regulator board. All caps are film caps. The larger ones are ClarityCap TC4s.
The heater supplies use two-stage regulation, with three regulated supplies (elevated to different voltages) in the power supply chassis, and individual current regulators for each tube close to the tubes in the line stage. The current regulators are adjustable from 260mA to 380mA to support a variety of tubes.
I also have an op-amp (OPA1612, OPA1611) based single-ended output for my subwoofers. This is also powered by a two-stage regulator using 1085s in the power supply chassis and Sparkos regulators near the op-amps.
Below are images showing the PCB layouts in the two chassis. Two DC umbilical cables between the two chassis will provide power to the two channels. A 9-pin D-Shell cable will be used for serial communication to control the attenuators, input selectors, and output muting relay.
Attachments
Hi,
I actually have 2 separate boards (line channels only) of this preamp lying on my bench. They are build and tested, And some Toroidy special made transformers.
I am very much in doubt that I will find the energy to finish the project.
The amp is still being sold as a new product, am I allowed to sell it?
Best regards
Arthur.
I actually have 2 separate boards (line channels only) of this preamp lying on my bench. They are build and tested, And some Toroidy special made transformers.
I am very much in doubt that I will find the energy to finish the project.
The amp is still being sold as a new product, am I allowed to sell it?
Best regards
Arthur.
I've made some slow progress with my build. It's been a very busy several months with work so I haven't had much chance to work on this. I've finished building the power supply chassis (at least the power supply part), and am close to finishing the front panel circuitry which uses an Arduino DUE for control with a front-panel TFT display. I'm going to route the ribbon cable under the HV power supply board and transformers. This connects to a custom Arduino Shield PCB mounted to the front panel, which will sit in front of the transformers.
I've done some redesign of the PCBs for the second chassis to move the regulated op-amp supply to the input/output board (which has the input relays, stepped attenuator, and op-amp buffer for the subwoofer output). This tightens up the layout of both boards. I haven't fabricated these boards yet and am still fine tuning the layout. But I hope to start work on these in the next month.
I've done some redesign of the PCBs for the second chassis to move the regulated op-amp supply to the input/output board (which has the input relays, stepped attenuator, and op-amp buffer for the subwoofer output). This tightens up the layout of both boards. I haven't fabricated these boards yet and am still fine tuning the layout. But I hope to start work on these in the next month.
I use my RTP3 with 300 monblocs too (Kevin Kennedy's design), and love the result.
Given that the RTP3 preamp is fully differential, I think it would be ideal to match it with a differential power amplifier. I see you have an input transformer on your amplifier, so I would recommend a balanced connection from the RTP3 outputs.
Alex
Given that the RTP3 preamp is fully differential, I think it would be ideal to match it with a differential power amplifier. I see you have an input transformer on your amplifier, so I would recommend a balanced connection from the RTP3 outputs.
Alex
@poseidonsvoice - Thanks Anand. I'm that as well
@Alex M - yes, that's the plan. I'm running balanced cables from my current DIY SS preamp to my amps. The Kevin Kennedy design looks like a nice amp. I'm glad you are liking your RTP3!
@Alex M - yes, that's the plan. I'm running balanced cables from my current DIY SS preamp to my amps. The Kevin Kennedy design looks like a nice amp. I'm glad you are liking your RTP3!
Does anyone have the details of this test circuit? The circuit in both my copies of Allen's Tube Pre-Amp Cookbook (pdf and actual book) is illegible.
Thanks,
Karl
I am thinking about designing a cut-down version of the RTP line stage.
Instead of tubes I will be using all Darlingtons. I have already worked out the circuit and have the schematic done in CAD. The calculations have also been done, but there are always adjustments when building. It should work with -/+ 24V. Both sides will have 6 discrete Darlingtons (12 Bipolars) plus 5 non-discrete Darlingtons, a total of 17 active components. So for both channels we have 34 active bipolar components. This being about the RTP preamp, no doubt some of you have heard of Rowan McCombe. The use of an all Darlington circuit is influenced by him. He was very enamoured by this device and taught it to us. In my circuits it sneaks in quite a lot. Make it work in constant voltage and use it to convert voltage to current, so the product is current, same as the bottom part of the cascode circuit in the RTP. BTW, I remember working on the first RTP and just realised the RTP is now 40 years old. The original RTP has been rebuilt several times and is till in use by Chris Pritchard in Grafton, NSW, Oz-stralia.
I have bought a March Audio P262 and I saw Alan March at the Sydney Audio Show this past weekend. It's a power amp and I have a phono stage that goes into my hybrid tube amp (unusual that it is solid-state front and EL34 tube out), but I now need a preamp to connect up to my phono stage. I need a preamp or I can't listen to records. The P262 is of course fully balanced. It is the best solid-state amplifier I have heard. That is saying something.
Instead of tubes I will be using all Darlingtons. I have already worked out the circuit and have the schematic done in CAD. The calculations have also been done, but there are always adjustments when building. It should work with -/+ 24V. Both sides will have 6 discrete Darlingtons (12 Bipolars) plus 5 non-discrete Darlingtons, a total of 17 active components. So for both channels we have 34 active bipolar components. This being about the RTP preamp, no doubt some of you have heard of Rowan McCombe. The use of an all Darlington circuit is influenced by him. He was very enamoured by this device and taught it to us. In my circuits it sneaks in quite a lot. Make it work in constant voltage and use it to convert voltage to current, so the product is current, same as the bottom part of the cascode circuit in the RTP. BTW, I remember working on the first RTP and just realised the RTP is now 40 years old. The original RTP has been rebuilt several times and is till in use by Chris Pritchard in Grafton, NSW, Oz-stralia.
I have bought a March Audio P262 and I saw Alan March at the Sydney Audio Show this past weekend. It's a power amp and I have a phono stage that goes into my hybrid tube amp (unusual that it is solid-state front and EL34 tube out), but I now need a preamp to connect up to my phono stage. I need a preamp or I can't listen to records. The P262 is of course fully balanced. It is the best solid-state amplifier I have heard. That is saying something.
Alert!
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Some of you may have noticed that www.vacuumstate.com is offline at the moment. It will soon be back but with a different server to host it. Hopefully it won't be long, but it will definitely be back.
.
The circuit is scalable and fets could be used, by I want to do an all Darlington version, my tribute to Rowan I suppose. Trust me, Darlingtons are great and they are high input impedance. Small Fets sounds a bit lose or light in comparison. When gravitating away from tubes I have come to prefer bipolar over Fets, but it just depends. If you want to swing a lot of volts, I would use bipolar Darlington on the bottom and a high voltage HexFET that behaves a bit like a Pentode and get as little possible voltage swing as possible seen by the Darling pair. It just sounds great, can have a gain above 500 and swing 1000V p/p with the right Fet. No voltage on the gate, the Fet is current driven via Source. Like this:
PLEASE NOTE: (c) 2020 Copyright Joe Rasmussen
PLEASE NOTE: (c) 2020 Copyright Joe Rasmussen