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Old 5th October 2012, 03:56 PM   #2061
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Quote:
Originally Posted by Joao@AltheaMusica View Post
The disadvantage is that you have no constant output impedance because it increases with increasing of the volume. In your configuration with ratio 1:1 you have the max. output impedance of tubes plate resistance - assume the source input from the next stage is large. So with high plate resistance of the 10Y you deal with high output imedances ...
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
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Old 5th October 2012, 04:14 PM   #2062
Magz is offline Magz  United States
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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...
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Old 5th October 2012, 04:36 PM   #2063
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Quote:
Originally Posted by Vinylsavor View Post
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
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.


Quote:
Originally Posted by Vinylsavor View Post
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.
Thomas
Thomas, there is no need for this advertisment - do think so?

No worry and keep smiling
Joao
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Old 5th October 2012, 04:54 PM   #2064
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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
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Old 5th October 2012, 05:12 PM   #2065
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Originally Posted by andyjevans View Post
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
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
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Old 5th October 2012, 05:21 PM   #2066
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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
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Old 5th October 2012, 05:35 PM   #2067
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@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
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Old 5th October 2012, 06:22 PM   #2068
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Quote:
Originally Posted by Vinylsavor View Post
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

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
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Old 5th October 2012, 06:44 PM   #2069
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Originally Posted by Vinylsavor View Post
Hi All,

sorry if I crossed a line, I will refrain from mentioning my products. Best regards

Thomas
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
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Old 5th October 2012, 06:47 PM   #2070
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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
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