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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

E180F Preamp

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#41
Euro,

if you look at my schematic you will see several spice directives (Black text) like ".lib "C:\LTC Spice\Models\E180F.inc"

This tells Spice where to look for the model you are using. I use a library in C:\LTC Spice\Models\.. for my tube models. You can put it anywhere but the C:\Program Files\LTC\LTspiceIV\lib is the traditional location. I use several computers to do simulations and find it easier to synchronize my personal libraries if I keep them seperate from the LT spice ones.

Comments are in blue.

DF96,
And, that is why I changed the 4.7M output resistor to a lower value to more accuratly reflect how the stage would behave driving an amp.

In reality, this preamp needs an additional stage with a gain of 10 to get it up to line level. The gain of 25 is just not going to do it so unless you are driving a preamp with gain, so one might as well add another stage and finish the design.
 
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#42
TheGimp said:
Euro,

if you look at my schematic you will see several spice directives (Black text) like ".lib "C:\LTC Spice\Models\E180F.inc"

This tells Spice where to look for the model you are using. I use a library in C:\LTC Spice\Models\.. for my tube models. You can put it anywhere but the C:\Program Files\LTC\LTspiceIV\lib is the traditional location. I use several computers to do simulations and find it easier to synchronize my personal libraries if I keep them seperate from the LT spice ones.

Comments are in blue.

DF96,
And, that is why I changed the 4.7M output resistor to a lower value to more accuratly reflect how the stage would behave driving an amp.

In reality, this preamp needs an additional stage with a gain of 10 to get it up to line level. The gain of 25 is just not going to do it so unless you are driving a preamp with gain, so one might as well add another stage and finish the design.
Click to expand...

If the extra stage is put before this design it could solve nearly all the issues in one go 😉 Put a low noise stage first, reduce the hiss generating 51k resistor with 5k1 or lower, change the rest of the feedback loop to reverse the extra x10 gain you just got, halve it again with more NFB to get lower distortion and lower output impedance. Sorted. Probably will need to change values of RIAA network to maintain accuracy though.
 
#44
DF96 said:
You might get away with that, but the pentode won't drive a low impedance RIAA network and it still has too little loop gain for comfort. There isn't a simple fix for this design, apart from finding a better design. There is a reason why single-valve phono preamps are quite rare!
Click to expand...

Yes I agree... Just didn't want to complicate matters with too many "ifs and buts" in my previous post!
The Audio Research SP8 phono section is both fairly simple, well engineered, sounds good and measures good. Reckon that would be a good one for the OP to build. I made one myself many years ago with excellent results. It uses an ECC83 and half an ECC88 per channel. I seem to recall it uses a high HT of about 390 V though...
 
#45
Dagwood said:
First off, thanks guys for having a good look at this.

I was planning on using the preamp for various sources, Is this design specifically for RIAA stages or could I use it for CD as well?

Could some explain to me how I should measure the resistance from the source (CD player) output and the input on the power amp (Pete Millett’s DCPP)?

Sorry for the school boy questions
Click to expand...

Sort of ironic that in all of this discussion your question does not appear to have been answered. 😀

This stage is very specifically a phono stage, and is not suitable for use with a CD player or any line level sources. The fact is that it is not a very good phono stage either..

Maybe we can recommend something more suitable..
 
#46
Hi Kevin

Question not answered but hey I'm learning loads from you guys! 🙂

That would be great, I have a load of tubes but most are not much use. I had heard the E180F's were fairly good for preamps? If they are not suitable I could PM you my stock list of tubes,you may see something better???

Originally I was going to run a passive preamp with a stepped attenuator. I guess I wanted to see as much glowing glass as possible.....🙂
 
#47
One other possibility might be to take Sy's Phono Pre-Amp that he designed for MC cartridge and switch the first stage from D3a to E180F (*1). The transformer on the front could be changed to a lower ratio (maybe Edcor) to help offset the higher output of the MM vs MC cartridge and hold down the cost.

http://www.diyaudio.com/forums/diyaudio-com-articles/163570-his-masters-noise-thoroughly-modern-tube-phono-preamp.html?garpg=4

*1 -The E180F has an ra of 100K vs 120K for the D3a. This is at the 20% limit of tube tolerances. It would be possible to leave the RIAA network as is since the Ra is as close as it is.

Ia would have to be reduced since the Pa for the E180F is only 3W vs the 4.2W of the D3a. Changing the bias diode from IR to cheap red led would accomplish this.

Some additional tweaking would be necessary, but it certainly would be better than the single tube amp.
 
#50
I have found that sometimes a post does not appear until some time after it should have. I suspect that something strange is going on with caches, but which sort of caches (internet, ISP, DIYaudio server?) I don't know. I have replied to a post, then found that new posts appeared which were not visible before even though their timestamp means they should have been - perhaps an hour or two earlier! Maybe stuck in a queue somewhere?
 
#51
DF96 said:
I have found that sometimes a post does not appear until some time after it should have. I suspect that something strange is going on with caches, but which sort of caches (internet, ISP, DIYaudio server?) I don't know. I have replied to a post, then found that new posts appeared which were not visible before even though their timestamp means they should have been - perhaps an hour or two earlier! Maybe stuck in a queue somewhere?
Click to expand...

This actually makes a lot of sense to me, because I swear I actually looked quite carefully for once.. I do tend to miss obvious things from time to time so that was my concern 😀
 
#53
Is it possible that the underlying software maintains multiple copies of the forum (e.g. north america, europe, far east), and our postings go first to our local copy before being propagated elsewhere? Something like that would explain it. When things get busy the copies get temporarily out of sync. I would expect a few seconds; minutes or hours suggest a problem somewhere.
 
#54
See my post #40?
Click to expand...

Hi, yeah not sure how that was missed???

I spent most of the weekend finishing of my DCPP and testing it!!! Will post a pic once the end cheeks are on.

Ok, measuring the source and load impedance..... Has anyone see or used this site??
Measuring input impedance and calculating output impedance calculation calculate amplifier amp total loudspeaker speaker microphone resistance resistor bridging matching test load loudspeaker source resistance - Why input impedance is in parallel and

Thanks again for all the help.
 
#57
The stuff on that page about making the measurements looked OK. You use the unknown impedance as part of a potential divider (just like a volume pot), then working from the known resistance and measured signal voltages you can calculate the unknown impedance.

As I said, normally much quicker to look at the circuit diagram. You don't need exact figures. 'High enough' and 'low enough' are good enough.
 
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