Hi Thomas,
Im using PCC88 and 12BH7 in my preamplifier. Till now heathing was AC i would like to try DC heathing using LM317T.
Any suggestion will be welcomed.
A very usefull information. I should look for a proper circuit for DC heathing.
Any impressions about difference in sound between DHT and NDHT?
Hi!
Depends on the level your preamp needs to amplify. If it is linelevel or above, don't bother with DC. AC, possibly biased slightly positive is fine.
Otherwise the sound impact with IDHT is insignificant. There are 100 other things which are way more important
Best regards
Thomas
Depends on the level your preamp needs to amplify. If it is linelevel or above, don't bother with DC. AC, possibly biased slightly positive is fine.
Otherwise the sound impact with IDHT is insignificant. There are 100 other things which are way more important
Best regards
Thomas
Not a problem at all with these particular types using an LM317 in my experience.
I don't think IMLE with an IDHT there is any difference at all except in terms of potential hum and noise pick up. With DHTs I use AC with 2.5V tubes in output stages, but based on George's (tubelab) recent comments about IMD on AC may not continue the practice. I'm using some of Rod Colemans DHT CCS in new projects and that will probably be the case going forward. Historically I've used monolithic based CCS, combined with VREGs in some cases and VREGS with chokes to heat DHTs. All seem to work well and sound good if properly implemented. YMMV
Like a "power amp" im using single ended topology without gain. A mosfet power follower in A class. The only gain stage is the PCC88 in the preamp. For this setup i think i need more gain.
I don't believe you have limited experience
.It is probably the reduction in hum that people hear!
Regards
M. Gregg
The preamp is perfectly quiet with AC heathing. I just wanted to hear from others about experience with DC heathing, and if that have some noticable influence of sound in general.
I have compared AC vs. DC supplies on IDHTs in several linestages. In each case, there was no noise with either type of supply. Also in each case, the AC supply was significantly better sounding. The AC supply had more body in the midrange and a fuller, richer midbass. The DC supply sounded brighter, leaner, somewhat recessed in the midrange. As a result, I only use DC when I absolutely have to, such as with a phono stage. By the way, component quality in the heater supply has a major impact on sound quality too. Different types of capacitors affect the sound just like with the B+ power supply. I found this out rather accidentally, but it is true.
Hello GoranB,
$0.02 worth.
I have used several versions of all the above.
First with any AC, DC or regulated DC I would use a GE Sensing inrush limiter. I do not recall the part number it starts out cold at 120 or so ohms cold and reduces to 8 or 9 ohms hot. This goes in series with the transformer primary. I have never had any issues with the LM 317 or 1085 type devices, by the time the heaters are hot the heat sinks attached to the adjustable regulators are still cold. Fixed regulators 7812 or 7806 work as well. Non-regulated power supplies also work, the voltage is adjusted under test by adding series resistors.
Take it apart and play with it.
DT
All just for fun!
AC heating cannot be considered a quiet enough solution for high rez systems. In many cases, it can sound better than DC. Certainly, many people can live with the "colourations" of AC heating (namely a veiled, fuzzy presentation with soft deep bass) over the unmusical nature of improperly executed DC heating which results in particularly annoying grungy, edgy mids and highs that is hard to live with.
One very wise person once told me that the following are some of the reasons why DC heating can and often does sound bad: RF hash injected from filament to cathode; induced electromagnetic energy from diodes and adjacent chokes and transformers; often ignored Common Mode noise transfer, common mode filament unbalancing and; noisy regulators that must track the load.
If you can control the above, the tube will sound way better than with AC or with any of the usual 317 DC heating topologies.
His (the wise person) solution was to use switch-mode power. But wait, you cannot use any old off the shelf wall wart type supply or cheap commercial SMPS. You need custom built units designed specifically to power tube heaters. There are guys who make such supplies but they tend to lie low, are too modest of their abilities and are not commercially minded. Besides, these SMPS supplies are not cheap and this will rule out its use by budget minded DIY enthusiasts.
Cheers
David
One very wise person once told me that the following are some of the reasons why DC heating can and often does sound bad: RF hash injected from filament to cathode; induced electromagnetic energy from diodes and adjacent chokes and transformers; often ignored Common Mode noise transfer, common mode filament unbalancing and; noisy regulators that must track the load.
If you can control the above, the tube will sound way better than with AC or with any of the usual 317 DC heating topologies.
His (the wise person) solution was to use switch-mode power. But wait, you cannot use any old off the shelf wall wart type supply or cheap commercial SMPS. You need custom built units designed specifically to power tube heaters. There are guys who make such supplies but they tend to lie low, are too modest of their abilities and are not commercially minded. Besides, these SMPS supplies are not cheap and this will rule out its use by budget minded DIY enthusiasts.
Cheers
David
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