Search found 28 matches

by westernelectric300b
Thu Mar 31, 2022 10:51 pm
Forum: Attenuators
Topic: TVC Driving a 600 Ohm Input Transformer
Replies: 3
Views: 728

Re: TVC Driving a 600 Ohm Input Transformer

Hi Dave, Sorry for the late reply here. I should check this site more often for responses! At first glance, that 10hy of primary inductance and 12dB of TVC attenuation puts 160hy in parallel with the primary inductance of the TVC, looks to be a good thing, yes? I understand these TVC units are desig...
by westernelectric300b
Tue Mar 08, 2022 2:02 am
Forum: Attenuators
Topic: TVC Driving a 600 Ohm Input Transformer
Replies: 3
Views: 728

TVC Driving a 600 Ohm Input Transformer

I have a pair of TVCs (not AVCs), and I would like to now use them in a different application. Note that their input and output will be used in a true balanced configuration. They will be driven by various sources, each having a very low source impedance (600 ohms or less, and all sources provide a ...
by westernelectric300b
Sun Oct 10, 2021 5:13 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi Dave, In the immortal words of the classic film, "Cool Hand Luke", I think what we have here is a failure to communicate! Per your summation in your last post: "So to qualify the original statement taken out of context I would change it to: For a correct filter response when termin...
by westernelectric300b
Fri Oct 08, 2021 2:30 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

What you state here is mathematically not correct. For a correct filter response both sides of the t-network must be "terminated" with 600 ohms. I showed the effect of different driving impedance in my wp. Everything else than a driving impedance of 600 ohms is less correct. Then we come ...
by westernelectric300b
Fri Oct 01, 2021 10:53 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Looking at the schematic diagram of the 2-stage transformer-coupled LCR phono preamp posted here earlier, I see a potential issue. The LCR network is a T-network, and it's input and output impedances are identical. We also know that the network must either be terminated (as in the case of this circu...
by westernelectric300b
Fri Sep 17, 2021 1:24 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi Walter, Thanks very much for posting actual test data of an LCR preamp with two tubes and three audio transformers in the signal path. That is indeed very encouraging. Can you clarify your comment about, "you must have a proper test setup"? I understand that you are using an Audio Preci...
by westernelectric300b
Wed Sep 15, 2021 1:25 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Dave, I agree with that. I think any amplitude anomalies, particularly premature roll-off, would occur in the low (<100 Hz) and high (>10 Khz) portions of the audio band, due in large part to the cascaded complex impedances such a circuit would probably exhibit. But we are just speculating here. As ...
by westernelectric300b
Wed Sep 15, 2021 2:52 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

I have read all of the comments and reviewed the theoretical and actual measured data here. I believe all of this data is based upon a simulated/modeled analysis of the predicted amplitude and phase response of strictly the LCR network itself, as well as a possible circuit using a 600 ohm LCR networ...
by westernelectric300b
Thu Sep 09, 2021 5:02 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi Dave, Thanks very much for your comments and guidance, and for taking and posting this data. It is very helpful! I finished wiring up my new LCR phono preamp last night. Today, I'll start wiring up the power supply for it. I'm looking forward to putting it on the bench and taking data. Should be ...
by westernelectric300b
Mon Aug 23, 2021 7:59 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

I did some calculations today with regard to the Miller Effect and the D3A input tube (the first gain stage in this circuit). The Miller C that I calculated for the D3A in triode connection is about 468 pf, based upon a u+1 of 78. The load impedance that my moving coil cartridge (EMT TSD-15) likes t...
by westernelectric300b
Thu Jul 08, 2021 5:36 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hello Walter! I know this is off topic in this thread, but those are very beautiful 300B amplifiers! Here is a photo of my homebrew 2-stage WE-300B amplifier, driven by a transformer-coupled 245. The power supply for each amplifier has two separate HV supplies, one for the 245 driver, and one for th...
by westernelectric300b
Sat Jul 03, 2021 4:30 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi regarding bias personally I don't like to mix sand with vacuum :) So I used a cathode resistor and cap with around 20-25 mA of bias and around 200-220 Vdc perfectly stabilized with ss ( sand!), this because I got a very good s/n that is one of most important goal, in my opinion. Also the Thd was...
by westernelectric300b
Fri Jul 02, 2021 12:01 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

to WE First of all do you have a proper test set? Only following the results of a test lab you can reach the right results. If you check the pdf from Docali : Practical Considerations on Designing and Measering LCR RIAA Filters Dr. Bernd Ahlswede (May 2018) it gives you the right direction, with a ...
by westernelectric300b
Wed Jun 30, 2021 7:05 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

WE300B, I think the important factor here is to either drive the LCR with its characteristic impedance OR load it with its characteristic impedance and not both. If you choose to drive it with its characteristic Z then the output can (should) be left unterminated and if you load it with its interna...
by westernelectric300b
Wed Jun 30, 2021 6:56 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi WE300 In attach another test with only the LCR stage The previous one ws with Zsource 600 ohm and Zload = 600 ohm, 10k. 47k and 100k This one is with Zs = 20 ohm, 100, 200 and 60 ohm and Zload = 600 ohm, as Tango specs lcr risp Zs_20_100_200_600_zload_600.jpgTango These are real test and not sim...
by westernelectric300b
Mon Jun 28, 2021 1:50 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re:

Hello WE300B, I attach schematic of Thorsten LCR. You can find their full description of that preamp on Jogis Roehrenbunde site, but in German only. Please note SUT on input side missing in schematic and Thorsten use S&B TX103. Additionally, I add one schematic from Neumann, just for illustrati...
by westernelectric300b
Mon Jun 28, 2021 1:45 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hello Pecci! Please excuse my very late reply; today was the first day that I have visited this site since the very early part of June, and I completely missed your post! Thank you for posting the information concerning the fixed biasing arrangement. That is very interesting. I think for these very ...
by westernelectric300b
Sun Jun 27, 2021 9:13 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Dave Slagle, That makes perfect sense. In my case, the output of the 600 ohm LCR network is driving a transformer (Sowter type 9063) with a 600 ohm primary, and the secondary Z of the transformer is 10K ohms. Terminating the secondary of this transformer in a 10K load resistance (which is actually t...
by westernelectric300b
Sun Jun 27, 2021 5:21 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Re: Step-up after LCR

Hi Dave Slagle, So to cut to the chase, are you suggesting that the terminating Z at the output of the 600 ohm LCR network is essentially irrelevant to the accuracy of the RIAA curve provided by the network, and a terminating value of (example) 600 ohms only serves to attenuate the output of the net...
by westernelectric300b
Tue Jun 01, 2021 4:49 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Hi, led biasing is fine, and very probably better than cathode bias with resistor and cap, but even better solution is to go with some kind of semi fixed bias, like Thorsten use in Toccata MK3 preamp with E810F tubes. Actually that way of biasing has a long history and many versions are in Neumann ...
by westernelectric300b
Sat May 08, 2021 9:02 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

V! and V2 are just generic voltages and van be replaced by any biasing method that will give that voltage. I have used LED's in that position and like it. you will have to try a bunch of different types since they all sound and bias up differently. I think an unbypassed Rk is going to seriously eff...
by westernelectric300b
Sat May 08, 2021 8:47 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

After finished a LCR with pcb I will prepare soon another LCR but full trafo. If you want youn can see something interesting in nexth one moth Walter Hi Walter, Yes, I would very much like to see your other LCR phono preamp next month. The design I plan on building is largely modeled around the sch...
by westernelectric300b
Fri May 07, 2021 11:10 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Step-Up After LCR

Hi Dave, Thanks very much for the reply! I was beginning to wonder if anyone had seen any of the posts I had made on this topic. Perhaps you can answer a question ....reference designations V1 and V2 on the schematic are a little confusing to me. Here in the U.S., these designations of course refer ...
by westernelectric300b
Fri May 07, 2021 5:00 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Step-Up After LCR

Gee, I'm really surprised that after a week, I have not received any replies to my inquiries here!
by westernelectric300b
Mon May 03, 2021 8:14 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Step-Up After LCR

Further to my earlier postings; I plan on building this unit, but with a few possible changes to the schematic that was posted here. I assume that symbols V1 and V2 are LEDs for biasing of the tubes. I may try this approach, but I also plan on trying to use a cathode resistor with the so-called Ultr...
by westernelectric300b
Mon May 03, 2021 7:57 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

LCR Phono Preamp

I think I answered my own question about the purpose of schematic symbol E1; it is obviously the MC-SUT and it adds 20 dB of voltage gain. But schematic symbols V1 and V2 are still intriguing. Are these LEDs for cathode biasing of the tubes? Perhaps schematic symbol V is a European designation for a...
by westernelectric300b
Mon May 03, 2021 7:53 pm
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

LCR Phono Preamp

Has anyone built this unit to the schematic diagram that was posted here?

If so, I'd be curious as to the actual measured data, and the sonic performance.
by westernelectric300b
Fri Apr 30, 2021 1:41 am
Forum: Phono
Topic: Step-up after LCR
Replies: 85
Views: 8647

Step-Up After LCR

With regard to the two-stage LCR phono preamp schematic posted here with the two D3a tubes; please advise what symbols V1 and V2 are. Are these 1.3 volt LEDs, diodes, batteries, etc.? Also, what is symbol E1? Is this the RCA phono input connector, or the MC-SUT, etc.? And lastly, what is the gain of...