Of course the output impedance of a TVC changes with volume setting, that is normal.
I specifically chose 1:1 in this case, to have the possibility to utilize the maximum gain of the linestage if needed. Normally I stick with low output impedances for my preamps, like 200-300 Ohms at max volume setting
This particular linestage is a demo unit which I use for all kinds of purposes, so this flexibility to get more gain at the cost of a higher output impedance was chosen.
These transformers can also be ordered for a specific max setting, say 4:1 at the loudest level. The next batch I'm getting has some pairs configured like that.
best regards
Thomas
What I'm doing with my output autoformers is feeding them from the mu output of the 26 plate CCS, which gives a MUCH lower output impedance than feeding from the plate itself (I'll measure it tomorrow and post results). With my gain structure I get response below 10Hz at outputs up to -6dB, and about 12-15Hz at 0dB, which is VERY loud, into the lowish 20kohm input impedance of my computer audio interface. And that's with only a 1uf parafeed cap; my simulations show I should get that down to 4-5Hz with a bigger cap or lossy parafeed cap plus resistor (trying that tomorrow as well). The bass response is excellent!
Tomorrow I'll post pictures, measurements, etc when I get home. Right now sitting on a beach in Florida...
Tomorrow I'll post pictures, measurements, etc when I get home. Right now sitting on a beach in Florida...
Ok, to use the max. gain of the linestage is an argument .... but I agree to use lower output impedances and would prefer this solution and, if gain is needed, to design a 2 stage linestage.
Thomas, there is no need for this advertisment - do think so?
No worry and keep smiling
Joao
I for one am not at all worried about Rod and Thomas making us aware of products that were developed specifically for users of 26 preamps on this thread. I think they need to tell us about these developments so we know what can build our preamps with. Both Rod and Thomas have been quite discreet about what they have available, and have spent a lot of time helping people with advice.
I don't know how others feel, but I think they are an essential part of this whole project, which could not have achieved its present stage of evolution otherwise. I'm not aware that either have discussed prices. Can't we just self-regulate on this?
Andy
I don't know how others feel, but I think they are an essential part of this whole project, which could not have achieved its present stage of evolution otherwise. I'm not aware that either have discussed prices. Can't we just self-regulate on this?
Andy
Hi Andy
I agree that Rod and Thomas are helpful and share experiences. Yes there is not discussion about prices, but the mention that you can order this parts by them, what do you call it if not advertisment.
For me, getting those reposts, I will leave such forums because I have no interest in such discussions. I stand to the rules and make no self-promoting, and therefore I await this from comercial colleagues as well. But I see the world is changing.
Joao
Hi All,
sorry if I crossed a line, I will refrain from mentioning my products. Anyways I only wrote about these since someone asked about them
Joao,
I find it a bit unfair that you critizise the high output impedance of the 1:1 version, then complain that I mentioned it can be made as 4:1 as well.
Best regards
Thomas
sorry if I crossed a line, I will refrain from mentioning my products. Anyways I only wrote about these since someone asked about them
Joao,
I find it a bit unfair that you critizise the high output impedance of the 1:1 version, then complain that I mentioned it can be made as 4:1 as well.
Best regards
Thomas
@Magz: I've built multiple preamps with Mu-follower cascoded gyrator loads (eg 01a, 30, 30sp, 46, 26 and of course 4p1L) with superb bass response given its low output impedance (circa 300 ohms). Without an expensive good OT, can make a cx301a preamp sound with a tight bass and magnificent tone. I've been playing this 01a preamp for over a year now on and off alternating it with transformer-based preamps and keep praising the good bass that can be achieved with it.
I have short cables to my 45SE, so 01a is not a problem. Haven't tried yet the addition of cathode/source follower as we discussed earlier in the thread but encouraged DHTRob to do so and he was very pleased with the sound improvement on his system
I'm a true "follower" of the Mu-follower gyrator!
Ale
I have short cables to my 45SE, so 01a is not a problem. Haven't tried yet the addition of cathode/source follower as we discussed earlier in the thread but encouraged DHTRob to do so and he was very pleased with the sound improvement on his system
I'm a true "follower" of the Mu-follower gyrator!
Ale
Thomas
Sorry, I would not hurt you, I like your heart and soul for amplifiers and your personality, and after your kind words you have to get an answer.
Look not that it's critism regarding the 1:1 version, I only want to point the high impedances when using tubes with high plate resistance - and the problems you can getr with long or high capacitance cables (mostly forgotten). Take one with low plate resistance and the world looks diferent
Hope you can agree ...So the next step to use step-down ratio to 4:1 is logic. Hope we are on the same point of view here.
Another point I see more critical with DHT in a line stage, like the 26 or 10Y, is the liability to microphonics. But that's another point of a discussion ...
Have a nice weekend
Joao
I'd just like to state again a different view here - Thomas went to the trouble of developing a new transformer for the 26 from Lundahl. This is important to know for people building a 26 preamp, so I really don't want a situation where this is kept secret from readers of this thread. Thomas has been so important in developing filament bias and solutions involving transformers that I can't imagine this thread without his contributions.
Andy
Andy,
thanks for your kind encouragement. I try to keep it at a level which does not cross the boundary of advertizing products. If someone feels I cross a line don't hesitate to say so.
Let's just not make too much a fuzz about this and lets get back to topic, technical aspects of 26 preamp implementations
Best regards
Thomas
thanks for your kind encouragement. I try to keep it at a level which does not cross the boundary of advertizing products. If someone feels I cross a line don't hesitate to say so.
Let's just not make too much a fuzz about this and lets get back to topic, technical aspects of 26 preamp implementations
Best regards
Thomas
tube 26 needs an OPT with high impedance of primary, at least 15K. A good quality pair is expensive. If I use 25K-600 ohms OPT, then I have no gain of ouput. Maybe I can add one stage, one tube or step up transformer to get suitable Vout. But the sound now is not only of 26.
How is to get the best sound of 26 without OPT ?
Does anyone build tube 26 input (plate choke maybe) Direct coupling to 27/ 56/ 76/ 6J5 in cathode follower ? I guess the sound is not bad
How is to get the best sound of 26 without OPT ?
Does anyone build tube 26 input (plate choke maybe) Direct coupling to 27/ 56/ 76/ 6J5 in cathode follower ? I guess the sound is not bad
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tube 26 needs an OPT with high impedance of primary, at least 15K. A good quality pair is expensive. If I use 25K-600 ohms OPT, then I have no gain of ouput. Maybe I can add one stage, one tube or step up transformer to get suitable Vout. But the sound now is not only of 26.
How is to get the best sound of 26 without OPT ?
Does anyone build tube 26 input (plate choke maybe) Direct coupling to 27/ 56/ 76/ 6J5 in cathode follower ? I guess the sound is not bad
You could do what I did and load with a CCS then take the mu output. Lower Rp means less stepdown needed. I'm going directly into an autoformer volume control, so only stepdown is in the VC.
Hi!
Normally not much gain is needed from a linestage. Most linelevel sources have an output level of up to 2V RMS. Typical input sensitivites of power amps is 0.5 - 0,75v RMS for full power output. So most of the time the level will even be reduced in the linestage.
For me the task of a linestage is:
- input selection
- volume control
- drive power amps through potentially long cable
The lienstage should have a high input impedance so it is an easy load for the sources and low output impedance to drive any power amp also through lobger cables.
If you need gain in your system I would rather add it in the sources or power amps
Best regards
Thomas
Normally not much gain is needed from a linestage. Most linelevel sources have an output level of up to 2V RMS. Typical input sensitivites of power amps is 0.5 - 0,75v RMS for full power output. So most of the time the level will even be reduced in the linestage.
For me the task of a linestage is:
- input selection
- volume control
- drive power amps through potentially long cable
The lienstage should have a high input impedance so it is an easy load for the sources and low output impedance to drive any power amp also through lobger cables.
If you need gain in your system I would rather add it in the sources or power amps
Best regards
Thomas
Is that 2.0 volt rms or pp for output voltages? Measurements I took several years ago (with a good dmm and eighties CDs recorded at -20dB level) gave no more than 0,5Vrms on peaks. So I was under the impression that it was 2.0/2.83= 0.7Vrms maximum.
Searching the web results in most curious answers to this simple question (who has a copy of the Red Book? ), among others this wiki on output levels: The impedance is around 100 Ω, the voltage can reach 2 volts peak-to-peak with levels referenced to -10 dBV (300 mV) at 10 kΩ,
Searching the web results in most curious answers to this simple question (who has a copy of the Red Book?
), among others this wiki on output levels: The impedance is around 100 Ω, the voltage can reach 2 volts peak-to-peak with levels referenced to -10 dBV (300 mV) at 10 kΩ,
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tube 26 needs an OPT with high impedance of primary, at least 15K. A good quality pair is expensive. If I use 25K-600 ohms OPT, then I have no gain of ouput. Maybe I can add one stage, one tube or step up transformer to get suitable Vout. But the sound now is not only of 26.
How is to get the best sound of 26 without OPT ?
Does anyone build tube 26 input (plate choke maybe) Direct coupling to 27/ 56/ 76/ 6J5 in cathode follower ? I guess the sound is not bad
In my case the "preamp" is actually part of the amplification chain, and I can't do without the gain. I have the preamp next to the amp and short cables. A more precise way to look at inductance isn't "15K" but the actual value in Henries if it's given. For the 26 I'd be wanting over 100H, and actually well over 100H like 200H or more. The sound really cleans up with the added inductance. It's also a question of the primary and secondary ratio, but when it's 1:1 I'm after around 200H.
I don't use the 26 anymore, but when I did I used two Hammond 156C chokes in series, bolted top to bottom and wired out of phase - all the details are in the thread somewhere. That was a good sound and cheap to achieve. This gives you all the gain of the 26 with a Russian teflon cap in my case. The issue with this setup is hum - the Hammonds are prone to hum pickup so you need to place magnetic components carefully, and well away from the chokes.
This whole question of inductance comes up with the 4P1L preamp I use (it's a lot easier to work with since the plate impedence is much lower at around 2K). Ale is adamant that the 4P1L sounds better at over 20mA, and I'd agree that you get big gains up to 15mA and a little bit more body and bass after that. But here you are in another trade-off with inductance. As the current goes up the inductance comes down, and I like the sound of the higher inductance options so I'm currently at 18mA with the LL1660. It's all swings and roundabouts.
I wouldn't add a stage if you need all the gain - I'd be looking for a 1:1 solution and if necessary put the preamp right next to the amp with short cables. If you don't need the gain Thomas' solution is standard practice. I have a 3 stage setup in total (4P1L>4P1L>300b) and you lose transparency when you add a stage. You can juggle around with transformers and higher mu tubes, and also solid state. We've had a few different solutions on the thread.
Andy
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@ Thomas
can agree here that's a good point. What gain do you use in your phono stages? I think of increasing it to ~ 60dB.
Advantage of a 2nd stage will be to lower the output impedance, easier way to drive long distance cables. Old German studio gear - Klangfilm etc. - used to have output impedances of 60Ω .
BR, Joao
can agree here that's a good point. What gain do you use in your phono stages? I think of increasing it to ~ 60dB.
Advantage of a 2nd stage will be to lower the output impedance, easier way to drive long distance cables. Old German studio gear - Klangfilm etc. - used to have output impedances of 60Ω .
BR, Joao
Hi!
There is no standardized line level output voltage for consumer electronics.
With the introduction of the CD in the eighties a 'quasi' standard got widely accepted which was 2V RMS. This is the maximum output voltage (at 0dB) most CD players still have.
This is rather high and if you have a linestage with 20dB gain, which is not uncommon, you end up with to much gain and the situation that the usable range on your volume control is very small, maybe up to the 9 o' Clock setting.
But this is not a mandatory standard it was adopted by many. There are exceptions. I have seen digital gear with even higher output level. less is possible too of course.
This is why it is important to understand the gain needs of the system when choosing the right line stage.
Best regards
Thomas
There is no standardized line level output voltage for consumer electronics.
With the introduction of the CD in the eighties a 'quasi' standard got widely accepted which was 2V RMS. This is the maximum output voltage (at 0dB) most CD players still have.
This is rather high and if you have a linestage with 20dB gain, which is not uncommon, you end up with to much gain and the situation that the usable range on your volume control is very small, maybe up to the 9 o' Clock setting.
But this is not a mandatory standard it was adopted by many. There are exceptions. I have seen digital gear with even higher output level. less is possible too of course.
This is why it is important to understand the gain needs of the system when choosing the right line stage.
Best regards
Thomas
Hi Thomas,
I want my preampli have 4-6V out, so I can build many tube ampli with only one amplified stage.
many tubes need gain of 50-70V (100-140Vpp) and more, eg. VT52, 300B, also 845, 211, 811A... so most of these ampli have to get 2 stage of amplification.
When you have plan of C3g triode strapped driver for 300B with IT 5k:5k, maybe you need more 2V input to get full fower. If I use C3g doing driver in power, so I don't need pot Volume at the input. Consequently, Miller effect maybe not present.
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