thanks for the info , is there a special value for the grid leak resistor when you go direct coupling to a 26?
i have some carbon pot, LDR, wire wound 10 turn pots to use as volume pot ..
don't you think it will be better to put it on the Amp side to attenuate the noise frome the 26 and drived by the line output transfo than put it between the dac output and 26 and having to deal with DC on the pot? 😕
don't you think it will be better to put it on the Amp side to attenuate the noise frome the 26 and drived by the line output transfo than put it between the dac output and 26 and having to deal with DC on the pot? 😕
Last edited:
Yes , but usually you would put the attenuator before the pre not the amp by DC coupling to the DAC you are making what I would call a powerful DAC with a #26 output. I would think you want a low grid leak so as to prevent the #26 grid from damaging your DAC maybe even protection zeners? Some DAC's are sensitive to a voltage other than thier own.
not mine , it"s a resistor base dac ( TOTALDAC) so i think i would have no ptoblem from this side . the only drawback of this dac is that it have an opamp as buffer, i have tried a B1 buffer, sounds better but i'm a tube guy , so i would think a DHT output could be smart enough😀.
the only problem is too much choice avalaible with the 26.
choose your flavor?🙂
1. DAC ...Cap.. battery bias CCS Cap
2. DAC ...Cap.. battery bias 10K/600ohm transfo
3. DAC... dc coupling, filament bias, CCS Cap
4. DAC... dc coupling, filament bias, 10K/600ohm transfo
choose your flavor?🙂
1. DAC ...Cap.. battery bias CCS Cap
2. DAC ...Cap.. battery bias 10K/600ohm transfo
3. DAC... dc coupling, filament bias, CCS Cap
4. DAC... dc coupling, filament bias, 10K/600ohm transfo
the only problem is too much choice avalaible with the 26.
choose your flavor?🙂
1. DAC ...Cap.. battery bias CCS Cap
2. DAC ...Cap.. battery bias 10K/600ohm transfo
3. DAC... dc coupling, filament bias, CCS Cap
4. DAC... dc coupling, filament bias, 10K/600ohm transfo
choose your flavor?🙂
1. DAC ...Cap.. battery bias CCS Cap
2. DAC ...Cap.. battery bias 10K/600ohm transfo
3. DAC... dc coupling, filament bias, CCS Cap
4. DAC... dc coupling, filament bias, 10K/600ohm transfo
Hi!
This will not work with a volume pot at the input of the pre. Depending on volume setting the DC offset would also be changed. And resistive pots tend to crackle when subjected to DC.
Best
Thionas
This will not work with a volume pot at the input of the pre. Depending on volume setting the DC offset would also be changed. And resistive pots tend to crackle when subjected to DC.
Best
Thionas
Last edited:
thanks thomas, so with DC coupling what about the grid leak resistor of the 26 ? put one or not? any value?
( the dac has 1V output level and 10K output impedance)
( the dac has 1V output level and 10K output impedance)
Last edited:
Maybe I've got something wrong, but at a certain point here there was a mention of a Tribute OPT for 26 with an option of attenuation. But I can't seem to find more any info (or my search abilities are limited).
Anyone knows about it?
Anyone knows about it?
Hi!
Pieter developed these on my request. So far I got some made for the 10Y. They can be made for 26 as well. The ones for 10Y are shown here:
VinylSavor: Cool Links: www.tribute-audio.nl
Best regards
Thomas
Pieter developed these on my request. So far I got some made for the 10Y. They can be made for 26 as well. The ones for 10Y are shown here:
VinylSavor: Cool Links: www.tribute-audio.nl
Best regards
Thomas
Or you could do what I did and use the Bent Audio autoformer volume controls in parafeed to function as both output transformers and volume controls. Works great, and you get 80% nickel laminations, remote control, left/right balance control and 61 1dB steps of volume control.
Attachments
John Chapman of Bent doesn't sell the assembled TAP-X units anymore, but he sells the parts for OEM (or DIY) use. Manufacturers such as Purity Audio use them (see the Purity Statement preamp as an example). I bought mine last year, and John was very helpful and always answered my questions promptly. Piece of cake to put together, too, just run the ribbon cable from subunit to subunit, in any order. The ribbon cable handles the power and control functions only; I made all signal connections with 23ga. silver in teflon. Not a cheap solution, but worth every penny for the features it provides.
Last edited:
Hello guys!
I tested the Rod Coleman regulators I am going to use in the 26 preamp and I have some questions if you do not mind.
I have the circuit for raw DC exactly the same as shown in the schematic above. I am using Hammond 166M18 (18 VCT vrms, 54 VA, 3A) and a Hammond 159ZC (60mH, 2A). On the 166M8, CT was not connected(not used).
Using a load of 1.5 ohms 20W, I can adjust the current on the regulator from 825 mA to 1.4 A no problem. My question is how come my raw DC voltage feeding the regulator was 28Vdc instead of the 18Vdc as per PSUD when my current is at 825mA up to 1.4A flowing to the load resistor?
What did I miss? Is that too large and I need to replaced the power transformer to a lower rms voltage output?
Thank you!
Abe
I tested the Rod Coleman regulators I am going to use in the 26 preamp and I have some questions if you do not mind.
An externally hosted image should be here but it was not working when we last tested it.
I have the circuit for raw DC exactly the same as shown in the schematic above. I am using Hammond 166M18 (18 VCT vrms, 54 VA, 3A) and a Hammond 159ZC (60mH, 2A). On the 166M8, CT was not connected(not used).
Using a load of 1.5 ohms 20W, I can adjust the current on the regulator from 825 mA to 1.4 A no problem. My question is how come my raw DC voltage feeding the regulator was 28Vdc instead of the 18Vdc as per PSUD when my current is at 825mA up to 1.4A flowing to the load resistor?
What did I miss? Is that too large and I need to replaced the power transformer to a lower rms voltage output?
Thank you!
Abe
Last edited:
The 166M18 is certainly 18v rms, so it will yield near to 18V dc for a circuit that acts as a choke-input filter. The 159ZC should work well enough for the choke.
I'd try it with the first capacitor reduced from 440uF to a lower value - maybe even 5-10uF polypropylene.
The regulators will run hotter with 28V dc input - please make sure the heatsink keeps to a reasonable temperature (<65 deg C).
I'd try it with the first capacitor reduced from 440uF to a lower value - maybe even 5-10uF polypropylene.
The regulators will run hotter with 28V dc input - please make sure the heatsink keeps to a reasonable temperature (<65 deg C).
That PSU looks fine to me. But to try it out you need to connect it to either the actual circuit or a bench construction of it. By that I mean connecting the + output of the regulator to one side of the 26 filament, the other side of the filament to the cathode resistor and the opposite end of the cathode resistor to the - output of the regulator. If you do this it should work. I suspect you are forgetting to insert the cathode resistor in the circuit.
Hi Rod, Andy!
Rod, post #2513 shows the heatsink I am using (4.5 inches long, 2 inches tall, and 1.5 of depth).
Andy, you are right. I connected the regulator with just 1.5 ohm load and did not add the 10 ohm (cathode) resistor.
I am contemplating on changing the power transformer to say 10Vrms. I can only work on the preamp during weekends, so I am very slow on my progress. Will keep you updated.
Abe
Rod, post #2513 shows the heatsink I am using (4.5 inches long, 2 inches tall, and 1.5 of depth).
Andy, you are right. I connected the regulator with just 1.5 ohm load and did not add the 10 ohm (cathode) resistor.
I am contemplating on changing the power transformer to say 10Vrms. I can only work on the preamp during weekends, so I am very slow on my progress. Will keep you updated.
Abe