Search found 106 matches

by Wolfgang
Fri Aug 23, 2019 4:14 pm
Forum: Speakers
Topic: Fane 12-250TC Retro Speaker.
Replies: 284
Views: 28934

Re: Fane 12-250TC Retro Speaker.

For full-range drivers like these, the cone(s) will be bending all over the place. Correcting for that by altering the signal at the voice coil would be immensely difficult. You are right. I was under the impression that Backes& Mueller active speakers would have used in the 90ies already some cont...
by Wolfgang
Thu Aug 22, 2019 1:46 am
Forum: Speakers
Topic: Fane 12-250TC Retro Speaker.
Replies: 284
Views: 28934

Re: Fane 12-250TC Retro Speaker.

To control mechanical cone breakup would need a tiny mic mounted on the cone which measures the velocity/acceleration and sends back data for controlling the amp. I have such a thing in my active Velodyne sub. But I was thinking rather along the lines of this discussing like taming some small freque...
by Wolfgang
Wed Aug 21, 2019 10:59 pm
Forum: Speakers
Topic: Fane 12-250TC Retro Speaker.
Replies: 284
Views: 28934

Re: Fane 12-250TC Retro Speaker.

As far as speakers are concerned there was pretty much nothing W.E., RCA, Stromberg & others didn't do, apart from digital, network synthesis design method and some of the material developments of the past 50 years. That's what happens when you get some of the best engineers in the world and give t...
by Wolfgang
Thu Aug 15, 2019 1:46 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

Yes, Ray. Standard build, heat sinks like in the picture (get warm after hrs but not hot).

This is the circuit:
SLB circuit.png
and this is how it's connected :

SLB circuit.png[/attachment]
by Wolfgang
Thu Aug 15, 2019 2:43 am
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

I knew that even a little bit of hum can already modulate the music signal with some negative effects but I didn’t expect such a dramatic change. The difference between the original CRC psu and using the SLB is like watching a movie on VHS tape on a 4:3 TV vs. a Blu-ray DVD on a 16:9 flat screen TV....
by Wolfgang
Sun Aug 11, 2019 11:39 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

Ray, there are these nice positive surprises like the Maida regulator or the SLB which are like an island in the middle of struggling with strange phenomena or resolving problems. It was fun to work with these high quality PCBs. The power transistors get hardly warm at 0,8A and there is only about 1...
by Wolfgang
Sun Aug 11, 2019 3:13 pm
Forum: Everyones Projects
Topic: 6C33C SE-OTL Project
Replies: 84
Views: 11550

Re: 6C33C SE-OTL Project

I don't think you will face any problems. The original circuit (6SN7/6C33)has enough input sensitivity and gain. It depends of course also on the amount of NFB you are planning to use.You can always adjust the 13E1 B+/idle current to your needs which should be easy as it has a lot of reserves to pla...
by Wolfgang
Tue Aug 06, 2019 3:34 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

Ray, I don't have any DC offset issues any more as I tried to explain already because of the better power resistors I use and how I use them. I also don't need the SLB because of any voltage drift or DC offset issues. I need it only for lowest ripple current which should result in the darkest possib...
by Wolfgang
Mon Aug 05, 2019 5:04 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

I forgot to mention that the next lower value (using Avel toroids) would be at 50VCT which would lower DC per rail for about 8V. Don't think that would make much difference regarding thermal issues but would probably throw off the balance I have achieved with DC offset,idle current and sound.
by Wolfgang
Mon Aug 05, 2019 4:54 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

On your Inverted OTL project, wouldn't it be good to minimise the thermal aspect of the DC offset by not having to burn off lots of volts? With a cap multiplier like the SLB you don't need to do that for ripple reduction. If you run separate 'right sized' transformers for each side of the output po...
by Wolfgang
Sat Aug 03, 2019 6:20 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

The SLB is really the best input for me at this moment and I have to study more details now in order to figure everything out. On your Inverted OTL project, wouldn't it be good to minimise the thermal aspect of the DC offset by not having to burn off lots of volts? With a cap multiplier like the SLB...
by Wolfgang
Sat Aug 03, 2019 1:35 am
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

I will try this, Ray. Thanks! It looks to be ideal for this job considering amps,voltages, heat if I can make it work with the resistors/(smaller value) cap/chokes. Do you know the max input voltage for these boards? I simply couldn't find this information. The thermal issues/DC offset fluctuations ...
by Wolfgang
Fri Aug 02, 2019 7:33 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

Because I started this thread I feel kind of responsible and didn't want to miss my chance to post the updated and final schematics. I also found the cause for the slight down slope of the frequency response. It's the missing bypass cap parallel to the first cathode resistor. I didn't want the input...
by Wolfgang
Mon Jul 08, 2019 3:40 pm
Forum: Everyones Projects
Topic: Inverted OTL with 6SN7/6AS7
Replies: 93
Views: 4645

Re: Inverted OTL with 6SN7/6AS7

While I was getting ready for putting everything into the amp housing I realized that there is a mistake in the schematics of the output power supply. The two 20ohm/20W resistors between the two caps have to be in series (40ohm) and NOT parallel as the schematics show. It must have happened when I c...
by Wolfgang
Sun Jul 07, 2019 12:57 am
Forum: Everyones Projects
Topic: Remember These?
Replies: 667
Views: 36699

Re: Remember These?

The biggest advantage of tubes like the 5687 for the InvOTL is that the heaters need a less powerful transformer. Considering the output impedance the 6AS7 is relatively close to the 5687: 3,4ohm for ten 5687 and 5,6 ohm for 10 6AS7. If one measures the CDF for a single driver speaker one will end u...